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The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the opposite wingtip. For example, the Boeing 777–200 has a wingspan of 60.93 metres (199 ft 11 in), and a wandering albatross (Diomedea exulans) caught in 1965 had a wingspan of 3.63 metres (11 ft 11 in), the official record for a living bird.
The term wingspan, more technically 'extent', is also used for other winged animals such as pterosaurs, bats, insects, etc., and other aircraft such as ornithopters.
In humans, the term wingspan also refers to the arm span, which is the distance between the length from the end of an individual's arm (measured at the fingertips) to the individual's fingertips on the other arm when raised parallel to the ground at shoulder height.
== Wingspan of aircraft ==
The wingspan of an aircraft is always measured in a straight line, from wingtip to wingtip, regardless of wing shape or sweep.
=== Implications for aircraft design and animal evolution ===
The lift from wings is proportional to their area, so the heavier the animal or aircraft the bigger that area must be. The area is the product of the span times the width (mean chord) of the wing, so either a long, narrow wing or a shorter, broader wing will support the same mass. For efficient steady flight, the ratio of span to chord, the aspect ratio, should be as high as possible (the constraints are usually structural) because this lowers the lift-induced drag associated with the inevitable wingtip vortices. Long-ranging birds, like albatrosses, and most commercial aircraft maximize aspect ratio. Alternatively, animals and aircraft which depend on maneuverability (fighters, predators and prey, as well as those who live amongst trees and bushes, insect catchers, etc.) need to be able to roll fast to turn, and the high moment of inertia of long narrow wings, as well as the high angular drag and quick balancing of aileron lift with wing lift at a low rotation rate, produce lower roll rates. For them, short-span, broad wings are preferred. Additionally, ground handling in aircraft is a significant problem for very high aspect ratios and flying animals may encounter similar issues.
The highest aspect ratio of man-made wings are aircraft propellers, in their most extreme form as helicopter rotors.
== Wingspan of flying animals ==
To measure the wingspan of a bird, a live or freshly-dead specimen is placed flat on its back, the wings are grasped at the wrist joints and the distance is measured between the tips of the longest primary feathers on each wing.
The wingspan of an insect refers to the wingspan of pinned specimens, and may refer to the distance between the centre of the thorax and the apex of the wing doubled or to the width between the apices with the wings set with the trailing wing edge perpendicular to the body.
== Wingspan in sports ==
In basketball and gridiron football, a fingertip-to-fingertip measurement is used to determine the player's wingspan, also called armspan. This is called reach in boxing terminology. The wingspan of 16-year-old BeeJay Anya, a top basketball Junior Class of 2013 prospect who played for the NC State Wolfpack, was officially measured at 7 feet 9 inches (2.36 m) across, one of the longest of all National Basketball Association draft prospects, and the longest ever for a non-7-foot player, though Anya went undrafted in 2017. The wingspan of Manute Bol, at 8 feet 6 inches (2.59 m), is (as of 2013) the longest in NBA history, and his vertical reach was 10 feet 5 inches (3.18 m).
== Wingspan records ==
=== Largest wingspan ===
Aircraft: Scaled Composites Stratolaunch — 117 m (383 ft 10 in)
Bat: Large flying fox – 1.5 m (4 ft 11 in)
Bird
Extant: Wandering albatross – 3.63 m (11 ft 11 in)
Extinct: Pelagornis – Approximately 6.06–7.38 m (19 ft 11 in – 24 ft 3 in)
Insect
Extant: White witch moth – 28.6 cm (11.3 in)
Extinct: Meganeuropsis (Griffinfly, relative of dragonflies) – Approximately 71 cm (2 ft 4 in)
Reptile: Hatzegopteryx (Azhdarchid pterosaur) – Approximately 10–12 m (32 ft 10 in – 39 ft 4 in)
=== Smallest wingspan ===
Aircraft
Biplane: Starr Bumble Bee II – 1.68 m (5 ft
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in)
Jet: Bede BD-5 – 4.27 m (14 ft 0 in)
Twin engine: Colomban Cri-cri – 4.9 m (16 ft 1 in)
Bat: Bumblebee bat – 16 cm (6.3 in)
Bird: Bee hummingbird – 6.5 cm (2.6 in)
Insect: Tanzanian parasitic wasp (Fairyfly) – 0.2 mm (0.0079 in)
Reptile: Nemicolopterus (Tapejaromorph pterosaur) – Approximately 25 cm (10 in)
== See also ==
List of large aircraft
List of largest birds
Largest living flying birds by wingspan
List of largest insects
Pterosaur size
== References ==
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Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula CH3NO2. It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent. As an intermediate in organic synthesis, it is used widely in the manufacture of pesticides, explosives, fibers, and coatings. Nitromethane is used as a fuel additive in various motorsports and hobbies, e.g. Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft.
== Preparation ==
Nitromethane is produced industrially by combining propane and nitric acid in the gas phase at 350–450 °C (662–842 °F). This exothermic reaction produces the four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The reaction involves free radicals, including the alkoxyl radicals of the type CH3CH2CH2O, which arise via homolysis of the corresponding nitrite ester. These alkoxy radicals are susceptible to C—C fragmentation reactions, which explains the formation of a mixture of products.
=== Laboratory methods ===
It can also be prepared by other methods that are of instructional value. The reaction of sodium chloroacetate with sodium nitrite in aqueous solution produces this compound, along with sodium chloride and sodium bicarbonate:
ClCH2COONa + NaNO2 + H2O → CH3NO2 + NaCl + NaHCO3
== Uses ==
The dominant use of the nitromethane is as a precursor reagent. A major derivative is chloropicrin (CCl3NO2), a widely used pesticide. It condenses with formaldehyde (Henry reaction) to eventually give tris(hydroxymethyl)aminomethane ("tris"), a widely used buffer and ingredient in alkyd resins.
=== Solvent and stabilizer ===
The major application is as a stabilizer in chlorinated solvents. As an organic solvent, nitromethane has an unusual combination of properties: highly polar (εr = 36 at 20 °C and μ = 3.5 Debye) but aprotic and weakly basic. This combination makes it useful for dissolving positively charged, strongly electrophilic species. It is a solvent for acrylate monomers, such as cyanoacrylates (more commonly known as "super-glues").
=== Fuel ===
Although a minor application in terms of volume, nitromethane also is used as a fuel or fuel additive for sports and hobby. For some applications, it is mixed with methanol in racing cars, boats, and model engines.
Nitromethane is used as a fuel in motor racing, particularly drag racing, as well as for radio-controlled model power boats, cars, planes and helicopters. In this context, nitromethane is commonly referred to as "nitro fuel" or simply "nitro", and is the principal ingredient for fuel used in the "Top Fuel" category of drag racing.
The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen than conventional fuels. During nitromethane combustion, nitric oxide (NO) is one of the major emission products along with CO2 and H2O. Nitric oxide contributes to air pollution, acid rain, and ozone layer depletion. Recent (2020) studies suggest the correct stoichiometric equation for the burning of nitromethane is:
4 CH3NO2 + 5 O2 → 4 CO2 + 6 H2O + 4 NO
The amount of air required to burn 1 kg (2.2 lb) of gasoline is 14.7 kg (32 lb), but only 1.7 kg (3.7 lb) of air is required for 1 kg of nitromethane. Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.6 times as much nitromethane as gasoline can be burned in one stroke. Nitromethane, however, has a lower specific energy: gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen.
Nitromethane can also be used as a monopropellant, i.e., a propellant that decomposes to release energy without added oxygen. It was first tested as rocket monopropellant in 1930s by Luigi Crocco fom Italian Rocket Society. There is
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renewed interest in nitromethane as safer replacement of hydrazine monopropellant. The following equation describes this process:
2 CH3NO2 → 2 CO + 2 H2O + H2 + N2
Nitromethane has a laminar combustion velocity of approximately 0.5 m/s, somewhat higher than gasoline, thus making it suitable for high-speed engines. It also has a somewhat higher flame temperature of about 2,400 °C (4,350 °F). The high heat of vaporization of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge (about twice that of methanol), resulting in reasonably low temperatures.
Nitromethane is usually used with rich air–fuel mixtures because it provides power even in the absence of atmospheric oxygen. When rich air–fuel mixtures are used, hydrogen and carbon monoxide are two of the combustion products. These gases often ignite, sometimes spectacularly, as the normally very rich mixtures of the still burning fuel exits the exhaust ports. Very rich mixtures are necessary to reduce the temperature of combustion chamber hot parts in order to control pre-ignition and subsequent detonation. Operational details depend on the particular mixture and engine characteristics.
A small amount of hydrazine blended in nitromethane can increase the power output even further. With nitromethane, hydrazine forms an explosive salt that is again a monopropellant. This unstable mixture poses a severe safety hazard. The National Hot Rod Association and Academy of Model Aeronautics do not permit its use in competitions.
In model aircraft and car glow fuel, the primary ingredient is generally methanol with some nitromethane (0% to 65%, but rarely over 30%, and 10–20% lubricants (usually castor oil and/or synthetic oil)). Even moderate amounts of nitromethane tend to increase the power created by the engine (as the limiting factor is often the air intake), making the engine easier to tune (adjust for the proper air/fuel ratio).
=== Former uses ===
It formerly was used in the explosives industry as a component in a binary explosive formulation with ammonium nitrate and in shaped charges, and it was used as a chemical stabilizer to prevent decomposition of various halogenated hydrocarbons.
=== Other ===
It can be used as an explosive, when gelled with several percent of gelling agent. This type of mixture is called PLX. Other mixtures include ANNM and ANNMAl – explosive mixtures of ammonium nitrate, nitromethane and aluminium powder.
A YouTuber posted a video that demonstrated that burning nitromethane will give off a very unusually colored flame. The flame actually appears to be black and white. He has used methanol to start the fire in the mentioned video.
== Reactions ==
=== Acid-base properties ===
Nitromethane is a relatively acidic carbon acid. It has a pKa of 17.2 in DMSO solution. This value indicates an aqueous pKa of about 11. It is so acidic because the anion admits an alternate, stabilizing resonance structure:
The acid deprotonates only slowly. Protonation of the conjugate base O2NCH−2, which is nearly isosteric with nitrate, occurs initially at oxygen.
=== Organic reactions ===
In organic synthesis nitromethane is employed as a one carbon building block. Its acidity allows it to undergo deprotonation, enabling condensation reactions analogous to those of carbonyl compounds. Thus, under base catalysis, nitromethane adds to aldehydes in 1,2-addition in the nitroaldol reaction. Some important derivatives include the pesticides chloropicrin Cl3CNO2, beta-nitrostyrene, and tris(hydroxymethyl)nitromethane (HOCH2)3CNO2. Reduction of the latter gives tris(hydroxymethyl)aminomethane, (HOCH2)3CNH2, better known as tris, a widely used buffer. In more specialized organic synthesis, nitromethane serves as a Michael donor, adding to α,β-unsaturated carbonyl compounds via 1,4-addition in the Michael reaction.
== Purification ==
Nitromethane is a popular solvent in organic and electroanalytical chemistry. It can be purified by cooling below its freezing point, washing the solid with cold diethyl ether, followed by distillation.
== Safety ==
Nitromethane has a modest acute toxicity. LD50 (oral, rats) is 1210±322 mg/kg.
Nitromethane is "reasonably anticipated to be a human carcinogen" according to a U.
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. government report.
=== Explosive properties ===
Nitromethane was not known to be a high explosive until a railroad tank car loaded with it exploded on June 1, 1958. After much testing, it was realized that nitromethane was a more energetic high explosive than TNT, although TNT has a higher velocity of detonation (VoD) and brisance. Both of these explosives are oxygen-poor, and some benefits are gained from mixing with an oxidizer, such as ammonium nitrate. Pure nitromethane is an insensitive explosive with a VoD of approximately 6,400 m/s (21,000 ft/s), but even so inhibitors may be used to reduce the hazards. The tank car explosion was speculated to be due to adiabatic compression, a hazard common to all liquid explosives. This is when small entrained air bubbles compress and superheat with rapid rises in pressure. It was thought that an operator rapidly snapped shut a valve creating a "hammer-lock" pressure surge.
If mixed with ammonium nitrate, which is used as an oxidizer, it forms an explosive mixture known as ANNM.
Nitromethane is used as a model explosive, along with TNT. It has several advantages as a model explosive over TNT, namely its uniform density and lack of solid post-detonation species that complicate the determination of equation of state and further calculations.
Nitromethane reacts with solutions of sodium hydroxide or methoxide in alcohol to produce an insoluble salt of nitromethane. This substance is a sensitive explosive which reverts to nitromethane under acidic conditions and decomposes in water to form another explosive compound, sodium methazonate, which has a reddish-brown color:
2 CH3NO2 + NaOH → HON=CHCH=NO2Na + 2 H2O
Nitromethane's reaction with solid sodium hydroxide is hypergolic.
== See also ==
Top Fuel
Adiabatic flame temperature, a thermodynamic calculation of the flame temperature of nitromethane
Dinitromethane
Model engine
Trinitromethane
Tetranitromethane
RE factor
== References ==
== Cited sources ==
Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.
== Further reading ==
Makovky, A.; Lenji, L. (August 1958). "Nitromethane - Physical Properties, Thermodynamics, Kinetics Of Decomposition, And Utilization As Fuel". Chemical Reviews. 58 (4): 627–644. doi:10.1021/cr50022a002. ISSN 0009-2665.
Boyer, Eric; Kuo, Kenneth (January 2006). Characteristics of Nitromethane for Propulsion Applications. 44th AIAA Aerospace Sciences Meeting and Exhibit. AIAA. doi:10.2514/6.2006-361. ISBN 978-1-62410-039-0. AIAA 2006-361.
Schmidt, Eckart W. (2022). "Nitromethane". Nitromethanes. Encyclopedia of Oxidizers. De Gruyter. pp. 2731–2817. doi:10.1515/9783110750294-022. ISBN 978-3-11-075029-4.
Schmidt, Eckart W. (2023). "Nitromethane as a Monopropellant". Organic Monopropellants. Encyclopedia of Monopropellants. De Gruyter. pp. 1439–1480. doi:10.1515/9783110751390-010. ISBN 978-3-11-075139-0.
== External links ==
WebBook page for nitromethane
History of Nitromethane
CDC – NIOSH Pocket Guide to Chemical Hazards
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Konstantin Eduardovich Tsiolkovsky (; Russian: Константин Эдуардович Циолковский, IPA: [kənstɐnʲˈtʲin ɪdʊˈardəvʲɪtɕ tsɨɐlˈkofskʲɪj] ; 17 September [O.S. 5 September] 1857 – 19 September 1935) was a Russian rocket scientist who pioneered astronautics. Along with Hermann Oberth and Robert H. Goddard, he is one of the pioneers of space flight and the founding father of modern rocketry and astronautics.
His works later inspired Wernher von Braun and leading Soviet rocket engineers Sergei Korolev and Valentin Glushko, who contributed to the success of the Soviet space program.
Tsiolkovsky spent most of his life in a log house on the outskirts of Kaluga, about 200 km (120 mi) southwest of Moscow. A recluse by nature, his unusual habits made him seem bizarre to his fellow townsfolk.
== Early life ==
Tsiolkovsky was born in Izhevskoye (now in Spassky District, Ryazan Oblast), in the Russian Empire, to a middle-class family. His father, Makary Edward Erazm Ciołkowski, was a Polish forester of Roman Catholic faith who relocated to Russia. His Russian Orthodox mother Maria Ivanovna Yumasheva was of mixed Volga Tatar and Russian origin. According to family tradition, Tsiolkovsky family is of the Zaporozhian Cossack descent, related to Cossack Hetman Nalyvaiko. His father was successively a forester, teacher, and minor government official. At the age of 9, Konstantin caught scarlet fever and lost his hearing.
When he was 13, his mother died. He was not admitted to elementary schools because of his hearing problem, so he was self-taught. As a reclusive home-schooled child, he passed much of his time by reading books and became interested in mathematics and physics. As a teenager, he began to contemplate the possibility of space travel.
Tsiolkovsky spent three years attending a Moscow library, where Russian cosmism proponent Nikolai Fyodorov worked. He later came to believe that colonizing space would lead to the perfection of the human species, with immortality and a carefree existence.
Inspired by the fiction of Jules Verne, Tsiolkovsky theorized many aspects of space travel and rocket propulsion. He is considered the father of spaceflight and the first person to conceive the space elevator, becoming inspired in 1895 by the newly constructed Eiffel Tower in Paris.
Despite the youth's growing knowledge of physics, his father was concerned that he would not be able to provide for himself financially as an adult and brought him back home at the age of 19 after learning that he was overworking himself and going hungry. Afterwards, Tsiolkovsky passed the teacher's exam and went to work at a school in Borovsk near Moscow. He met and married his wife Varvara Sokolova during this time. Despite being stuck in Kaluga, a small town far from major learning centers, Tsiolkovsky managed to make scientific discoveries on his own.
The first two decades of the 20th century were marred by personal tragedy. In 1902, Tsiolkovsky's son Ignaty committed suicide. In 1908, many of his accumulated papers were lost in a flood. In 1911, his daughter Lyubov was arrested for engaging in revolutionary activities.
== Scientific achievements ==
Tsiolkovsky stated that he developed the theory of rocketry only as a supplement to philosophical research on the subject. He wrote more than 400 works including approximately 90 published pieces on space travel and related subjects. Among his works are designs for rockets with steering thrusters, multistage boosters, space stations, airlocks for exiting a spaceship into the vacuum of space, and closed-cycle biological systems to provide food and oxygen for space colonies.
Tsiolkovsky's first scientific study dates back to 1880–1881. He wrote a paper called "Theory of Gases," in which he outlined the basis of the kinetic theory of gases, but after submitting it to the Russian Physico-Chemical Society (RPCS), he was informed that his discoveries had already been made 25 years earlier. Undaunted, he pressed ahead with his second work, "The Mechanics of the Animal Organism". It received favorable feedback, and Tsiolkovsky was made a member of the Society. Tsiolkovsky's main works after 1884 dealt with four major areas: the scientific rationale for the
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-metal balloon (airship), streamlined airplanes and trains, hovercraft, and rockets for interplanetary travel.
In 1892, he was transferred to a new teaching post in Kaluga where he continued to experiment. During this period, Tsiolkovsky began working on a problem that would occupy much of his time during the coming years: an attempt to build an all-metal dirigible that could be expanded or shrunk in size.
Tsiolkovsky developed the first aerodynamics laboratory in Russia in his apartment. In 1897, he built the first Russian wind tunnel with an open test section and developed a method of experimentation using it. In 1900, with a grant from the Academy of Sciences, he made a survey using models of the simplest shapes and determined the drag coefficients of the sphere, flat plates, cylinders, cones, and other bodies.
Tsiolkovsky's work in the field of aerodynamics was a source of ideas for Russian scientist Nikolay Zhukovsky, the father of modern aerodynamics and hydrodynamics. Tsiolkovsky described the airflow around bodies of different geometric shapes. Because the RPCS did not provide any financial support for this project, he was forced to pay for it largely out of his own pocket.
Tsiolkovsky studied the mechanics of lighter-than-air powered flying machines. He first proposed the idea of an all-metal dirigible and built a model of it. The first printed work on the airship was "A Controllable Metallic Balloon" (1892), in which he gave the scientific and technical rationale for the design of an airship with a metal sheath. Tsiolkovsky was not supported on the airship project, and the author was refused a grant to build the model. An appeal to the General Aviation Staff of the Russian army also had no success.
In 1892, he turned to the new and unexplored field of heavier-than-air aircraft. Tsiolkovsky's idea was to build an airplane with a metal frame. In the article "An Airplane or a Birdlike (Aircraft) Flying Machine" (1894) are descriptions and drawings of a monoplane, which in its appearance and aerodynamics anticipated the design of aircraft that would be constructed 15 to 18 years later. In an Aviation Airplane, the wings have a thick profile with a rounded front edge and the fuselage is faired.
Work on the airplane, as well as on the airship, did not receive recognition from the official representatives of Russian science, and Tsiolkovsky's further research had neither monetary nor moral support. In 1914, he displayed his models of all-metal dirigibles at the Aeronautics Congress in St. Petersburg, but was met with a lukewarm response.
Disappointed at this, Tsiolkovsky gave up on space and aeronautical problems with the onset of World War I and turned his attention to the problem of alleviating poverty. This occupied his time during the war years until the Russian Revolution in 1917.
Starting in 1896, Tsiolkovsky systematically studied the theory of motion of rocket apparatus. Thoughts on the use of the rocket principle in the cosmos were expressed by him as early as 1883, and a rigorous theory of rocket propulsion was developed in 1896. Tsiolkovsky derived the formula, which he called the "formula of aviation", now known as Tsiolkovsky rocket equation, establishing the relationship between:
change in the rocket's speed (
Δ
v
{\displaystyle \Delta v}
)
exhaust velocity of the engine (
v
e
{\displaystyle v_{e}}
)
initial (
m
0
{\displaystyle m_{0}}
) and final (
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m
f
{\displaystyle m_{f}}
) mass of the rocket
Δ
v
=
v
e
ln
m
0
m
f
{\displaystyle \Delta v=v_{e}\ln {\frac {m_{0}}{m_{f}}}}
After writing out this equation, Tsiolkovsky recorded the date: 10 May 1897. In the same year, the formula for the motion of a body of variable mass was published in the thesis of the Russian mathematician I. V. Meshchersky ("Dynamics of a Point of Variable Mass," I. V. Meshchersky, St. Petersburg, 1897).
His most important work, published in May 1903, was Exploration of Outer Space by Means of Rocket Devices (Russian: Исследование мировых пространств реактивными приборами). Tsiolkovsky calculated, using the Tsiolkovsky equation, that the horizontal speed required for a minimal orbit around the Earth is 8,000 m/s (5 miles per second) and that this could be achieved by means of a multistage rocket fueled by liquid oxygen and liquid hydrogen. In the article "Exploration of Outer Space by Means of Rocket Devices", it was suggested for the first time that a rocket could perform space flight. In this article and its sequels (1911 and 1914), he developed some ideas of missiles and considered the use of liquid rocket engines.
The outward appearance of Tsiolkovsky's spacecraft design, published in 1903, was a basis for modern spaceship design. The design had a hull divided into three main sections. The pilot and copilot would occupy the first section, while the second and third sections held the liquid oxygen and liquid hydrogen needed to fuel the spacecraft.
The result of the first publication was not what Tsiolkovsky expected. No foreign scientists appreciated his research, which today is a major scientific discipline. In 1911, he published the second part of the work "Exploration of Outer Space by Means of Rocket Devices". Here Tsiolkovsky evaluated the work needed to overcome the force of gravity, determined the speed needed to propel the device into the Solar System ("escape velocity"), and examined calculation of flight time. The publication of this article made a splash in the scientific world, and Tsiolkovsky found many friends among his fellow scientists.
In 1926–1929, Tsiolkovsky solved the practical problem regarding the role played by rocket fuel in getting to escape velocity and leaving the Earth. He showed that the final speed of the rocket depends on the rate of gas flowing from it and on how the weight of the fuel relates to the weight of the empty rocket.
Tsiolkovsky conceived a number of ideas that
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been later used in rockets. They include: gas rudders (graphite) for controlling a rocket's flight and changing the trajectory of its center of mass, the use of components of the fuel to cool the outer shell of the spacecraft (during re-entry to Earth) and the walls of the combustion chamber and nozzle, a pump system for feeding the fuel components, the optimal descent trajectory of the spacecraft while returning from space, etc.
In the field of rocket propellants, Tsiolkovsky studied a large number of different oxidizers and combustible fuels and recommended specific pairings: liquid oxygen and hydrogen, and oxygen with hydrocarbons. Tsiolkovsky did much fruitful work on the creation of the theory of jet aircraft, and invented his chart Gas Turbine Engine. In 1927, he published the theory and design of a train on an air cushion. He first proposed a "bottom of the retractable body" chassis.
Space flight and the airship were the main problems to which he devoted his life. Tsiolkovsky had been developing the idea of the hovercraft since 1921, publishing a fundamental paper on it in 1927, entitled "Air Resistance and the Express Train" (Russian: Сопротивление воздуха и скорый по́езд). In 1929, Tsiolkovsky proposed the construction of multistage rockets in his book Space Rocket Trains (Russian: Космические ракетные поезда).
Tsiolkovsky championed the idea of the diversity of life in the universe and was the first theorist and advocate of human spaceflight.
Hearing problems did not prevent the scientist from having a good understanding of music, as outlined in his work "The Origin of Music and Its Essence."
== Later life ==
After the October Revolution, the Cheka jailed him in the Lubyanka prison for several weeks.
Still, Tsiolkovsky supported the Bolshevik revolution, and eager to promote science and technology, the new Soviet government elected him a member of the Socialist Academy in 1918.
He worked as a high school mathematics teacher until retiring in 1920 at the age of 63. In 1921, he received a lifetime pension.
In his late lifetime, from the mid-1920s onwards, Tsiolkovsky was honored for his pioneering work, and the Soviet state provided financial backing for his research. He was initially popularized in Soviet Russia in 1931–1932 mainly by two writers: Yakov Perelman and Nikolai Rynin. Tsiolkovsky died in Kaluga on 19 September 1935 after undergoing an operation for stomach cancer. He bequeathed his life's work to the Soviet state.
== Legacy ==
Tsiolkovsky influenced later rocket scientists throughout Europe, including Wernher von Braun. Soviet search teams at Peenemünde found a German translation of a book by Tsiolkovsky of which "almost every page...was embellished by von Braun's comments and notes." Leading Soviet rocket-engine designer Valentin Glushko and rocket designer Sergey Korolev studied Tsiolkovsky's works as youths, and both sought to turn Tsiolkovsky's theories into reality. In particular, Korolev saw traveling to Mars as the more important priority, until in 1964 he decided to compete with the American Project Apollo for the Moon.
In 1989, Tsiolkovsky was inducted into the International Air & Space Hall of Fame at the San Diego Air & Space Museum.
== Philosophical work ==
In 1928, Tsiolkovsky wrote a book called The Will of the Universe: The Unknown Intelligence, in which he propounded a philosophy of panpsychism. He believed humans would eventually colonize the Milky Way galaxy. His thought preceded the Space Age by several decades, and some of what he foresaw in his imagination has come into being since his death.
Tsiolkovsky did not believe in traditional religious cosmology, but instead, and to the chagrin of the Soviet authorities, he believed in a cosmic being that governed humans as "marionettes, mechanical puppets, machines, movie characters". He adhered to a mechanical view of the universe, which he believed would be controlled in the millennia to come through the power of human science and industry. In a short article in 1933, he explicitly formulated what was later to be known as the Fermi paradox.
He wrote a few works on ethics, espousing negative utilitarianism.
== Tributes ==
In 1964, The Monument to the Conquerors of Space was erected to celebrate the achievements of the Soviet people in space exploration. Located in Moscow, the monument is 107 meters (350 feet) tall and covered with titanium cladding
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The main part of the monument is a giant obelisk topped by a rocket and resembling in shape the exhaust plume of the rocket. A statue of Konstantin Tsiolkovsky, the precursor of astronautics, is located in front of the obelisk.
The State Museum of the History of Cosmonautics in Kaluga now bears his name. His residence during the final months of his life (also in Kaluga) was converted into a memorial museum a year after his death.
The town Uglegorsk in Amur Oblast was renamed Tsiolkovsky by President of Russia Vladimir Putin in 2015.
The crater Tsiolkovskiy, the most prominent crater on the far side of the Moon, was named after him. Asteroid 1590 Tsiolkovskaja was named after his wife. The Soviet Union obtained naming rights by operating Luna 3, the first space device to successfully transmit images of the side of the Moon not seen from Earth.
The Tsiolkovsky Memorial Apartment. A museum created in Borovsk where he lived and had started his career as a teacher.
There is a statue of Konstantin Tsiolkovsky directly outside the Sir Thomas Brisbane Planetarium in Brisbane, Queensland, Australia.
There is a Google Doodle honoring the famous pioneer.
There is a Tsiolkovsky exhibit on display at the Museum of Jurassic Technology in Los Angeles, California.
There is a 1 ruble 1987 coin commemorating the 130th anniversary of Konstantin Tsiolkovsky's birth.
=== Awards and decorations dedicated to Tsiolkovsky ===
The USSR Academy of Sciences issued the golden table-top Tsiolkovsky Medal "For outstanding work in the field of interplanetary communications". It was awarded to Sergey Korolev, V.P. Glushko, N.A. Pilyugin, M.V. Keldysh, K.D. Bushuev, Yuri Gagarin, German Titov, A.G. Nikolaev and many other cosmonauts.
The USSR Cosmonautics Federation issued its own Tsiolkovsky Medal
The Russian Federal Space Agency («Федеральное космическое агентство») instituted the Tsiolkovsky badge
After the Federal Space Agency was reformed into the Roscosmos State Corporation for Space Activities, it replaced the Tsiolkovsky badge with the K.E.Tsiolkovsky badge
== In popular culture ==
Tsiolkovsky was consulted for the script to the 1936 Soviet science-fiction film, Kosmicheskiy reys.
Science-fiction writer Alexander Belyaev's novel KETs Star features a city and space station named with Tsiolkovsky's initials.
The Mars-based space elevators in the Horus Heresy novel Mechanicum by Graham McNeill, set in the Warhammer 40k universe, are called "Tsiolkovsky Towers".
Episode eight of Denpa Onna to Seishun Otoko is called "Tsiolkovsky's Prayer".
"Tsiolkovski" is the name given to an underground facility in a huge Farside crater on the Moon in Arthur C. Clarke and Stephen Baxter’s science-fiction Sunstorm: A Time Odyssey (2005). In the same book the Russian astrophysicist Mikhail Martynov, says: “we Russians have always been drawn to the sun. Tsiolkovski himself, our great space visionary, drew on sun worship in some of his thinking, so it’s said.” Martynov refers to him as „father of Russian astronautics“, and at one time speculates „ No wonder that Tsiolkovski’s vision of humanity’s future in space had been full of sunlight; indeed, he had dreamed that ultimately humankind in space would evolve into a closed, photosynthesizing metabolic unit, needing nothing but sunlight to live. Some philosophers even regarded the whole of the Russian space program as nothing but a modern version of a solar-worshiping ritual.“ (Chap. 42, pp.293-4.)
In a 2015 episode of Murdoch Mysteries, set in about 1905, James Pendrick works with Tsiolkovsky's daughter to build a suborbital rocket based on his ideas and be the first man in space; a second rocket built to the same design is adapted as a ballistic missile for purposes of extortion.
== Works ==
Tsiolkovsky, Konstantin E., “Citizens of the Universe” (1933), (PDF), English.
Tsiolkovsky, Konstantin E., “Creatures of Higher Levels of Development than Humans” (1933), (PDF), English.
Tsiol
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sky, Konstantin E., “Beings of Different Evolutionary Stages of the Universe” (1902), (PDF), English.
Tsiolkovsky, Konstantin E., “Is There a God?” (1932), (PDF), English.
Tsiolkovsky, Konstantin E., “Are There Spirits?” (1932), (PDF), English.
Tsiolkovsky, Konstantin E., “Planets are Inhabited by Living Creatures” (1933), (PDF), English.
Tsiolkovsky, Konstantin E., “The Cosmic Philosophy” (1935), (PDF), English.
Tsiolkovsky, Konstantin E., “Conditional Truth” (1933), (PDF), English.
Tsiolkovsky, Konstantin E., “Evaluation of People” (1934), (PDF), English.
Tsiolkovsky, Konstantin E., “Non-Resistance or Struggle” (1935), (PDF), English.
Tsiolkovsky, Konstantin E., “Living Beings in the Cosmos” (1895), (PDF), English.
Tsiolkovsky, Konstantin E., “The Animal of Space” (1929), (PDF), English.
Tsiolkovsky, Konstantin E., “The Will of the Universe” (1928), (PDF), English.
Tsiolkovsky, Konstantin E., “On the Moon (На Луне)” (1893).
Tsiolkovsky, Konstantin E., “The Exploration of Cosmic Space by Means of Reaction Devices (Исследование мировых пространств реактивными приборами)” (1903). (PDF), Russian.
Tsiolkovsky, Konstantin E., “The Exploration of Cosmic Space by Means of Reaction Devices (Исследование мировых пространств реактивными приборами)” (1914). (PDF), Russian.
Tsiolkovsky, Konstantin E., “The Exploration of Cosmic Space by Means of Reaction Devices (Исследование мировых пространств реактивными приборами)” (1926). (PDF), Russian.
Tsiolkovsky, Konstantin E., “The Path to the Stars (Путь к звездам)” (1966), Collection of Science Fiction Works, (PDF), English.
Tsiolkovsky, Konstantin E., “The Call of the Cosmos (Зов Космоса)” (1960), The monograph was first published by the U.S.S.R. Academy of Science Publishing House in 1954 in the second volume of Tsiolkovsky`s Collected Works, (PDF), English.
== See also ==
Cosmonauts Alley, a Russian monument park where Tsiolkovsky is honored
History of the internal combustion engine
Robert Esnault-Pelterie, a Frenchman who independently arrived at Tsiolkovsky's rocket equation
Russian cosmism
Russian philosophy
Soviet space program
Timeline of hydrogen technologies
== Citations ==
== General and cited sources ==
Miller, Ron (1993). The Dream Machines. Krieger Publishing Company. ISBN 0-89464-039-9.
== Further reading ==
Andrews, James T. (2009), Red Cosmos: K.E. Tsiolkovskii, Grandfather of Soviet Rocketry, Texas A&M University Press, ISBN 978-1-60344-168-1 Review
Georgiy Stepanovich Vetrov (1994). S. P. Korolyov and Space: First steps. M. Nauka. ISBN 5-02-000214-3.
Львов, Владимир Евгеньевич (1963). Страницы жи
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�ни Циолковского (in Russian). Ленинград: Лениздат. p. 8.
== External links ==
Konstantin Tsiolkovsky. The collection of philosophical works. Biography, books, audiobooks, articles, photographs, video. Russian, English.
“The Theory of Cosmic Eras” The text is an interview between Alexander Leonidovich Chizhevsky and Konstantin Eduardovich Tsiolkovsky, English.
Tsiolkovsky's house The house museum of Tsiolkovsky
Virtual Matchbox Labels Museum – Russian labels – Space – Page 2 – Konstantin Tsiolkovsky Historic images
Tsiolkovsky from Russianspaceweb.com
Spaceflight or Extinction: Konstantin Tsiolkovsky Excerpts from "The Aims of Astronautics", The Call of the Cosmos
The Foundations of the Space Age: The Life and Work of Tsiolkovskiy, by Vladimir V. Lytkin, Tsiolkovskiy Museum, Kaluga.
Tsiolkovski: The Cosmic Scientist and His Cosmic Philosophy by Daniel H. Shubin. ISBN 978-1365259814
The Path to the Stars: Collection of Science Fiction Works
The Call of the Cosmos
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The Boeing 767 is an American wide-body airliner developed and manufactured by Boeing Commercial Airplanes.
The aircraft was launched as the 7X7 program on July 14, 1978, the prototype first flew on September 26, 1981, and it was certified on July 30, 1982. The initial 767-200 variant entered service on September 8, 1982, with United Airlines, and the extended-range 767-200ER in 1984. It was stretched into the 767-300 in October 1986, followed by the extended-range 767-300ER in 1988, the most popular variant. The 767-300F, a production freighter version, debuted in October 1995. It was stretched again into the 767-400ER from September 2000.
Designed to complement the larger 747, it has a seven-abreast cross-section accommodating smaller LD2 ULD cargo containers.
The 767 is Boeing's first wide-body twinjet, powered by General Electric CF6, Rolls-Royce RB211, or Pratt & Whitney JT9D turbofans. JT9D engines were eventually replaced by PW4000 engines.
The aircraft has a conventional tail and a supercritical wing for reduced aerodynamic drag.
Its two-crew glass cockpit, a first for a Boeing airliner, was developed jointly for the 757 − a narrow-body aircraft, allowing a common pilot type rating. Studies for a higher-capacity 767 in 1986 led Boeing to develop the larger 777 twinjet, introduced in June 1995.
The 159-foot-long (48.5 m) 767-200 typically seats 216 passengers over 3,900 nautical miles [nmi] (7,200 km; 4,500 mi), while the 767-200ER seats 181 over a 6,590 nmi (12,200 km; 7,580 mi) range.
The 180-foot-long (54.9 m) 767-300 typically seats 269 passengers over 3,900 nmi (7,200 km; 4,500 mi), while the 767-300ER seats 218 over 5,980 nmi (11,070 km; 6,880 mi).
The 767-300F can haul 116,000 lb (52.7 t) over 3,225 nmi (6,025 km; 3,711 mi), and the 201.3-foot-long (61.37 m) 767-400ER typically seats 245 passengers over 5,625 nmi (10,415 km; 6,473 mi). Military derivatives include the E-767 for surveillance and the KC-767 and KC-46 aerial tankers.
Initially marketed for transcontinental routes, a loosening of ETOPS rules starting in 1985 allowed the aircraft to operate transatlantic flights.
A total of 742 of these aircraft were in service in July 2018, with Delta Air Lines being the largest operator with 77 aircraft in its fleet.
As of July 2025, Boeing has received 1,430 orders from 74 customers, of which 1,336 airplanes have been delivered, while the remaining orders are for cargo or tanker variants. Competitors have included the Airbus A300, A310, and A330-200. Its successor, the 787 Dreamliner, entered service in 2011.
== Development ==
=== Background ===
In 1970, the 747 entered service as the first wide-body jetliner with a fuselage wide enough to feature a twin-aisle cabin. Two years later, the manufacturer began a development study, code-named 7X7, for a new wide-body jetliner intended to replace the 707 and other early generation narrow-body airliners. The aircraft would also provide twin-aisle seating, but in a smaller fuselage than the existing 747, McDonnell Douglas DC-10, and Lockheed L-1011 TriStar wide-bodies. To defray the high cost of development, Boeing signed risk-sharing agreements with Italian corporation Aeritalia and the Civil Transport Development Corporation (CTDC), a consortium of Japanese aerospace companies. This marked the manufacturer's first major international joint venture, and both Aeritalia and the CTDC received supply contracts in return for their early participation. The initial 7X7 was conceived as a short take-off and landing airliner intended for short-distance flights, but customers were unenthusiastic about the concept, leading to its redefinition as a mid-size, transcontinental-range airliner. At this stage the proposed aircraft featured two or three engines, with possible configurations including over-wing engines and a T-tail.
By 1976, a twinjet layout, similar to the one which had debuted on the Airbus A300, became the baseline configuration. The decision to use two engines reflected increased industry confidence in the reliability and economics of new-generation jet powerplants. While airline requirements for new wide-body aircraft remained ambiguous, the 7X7 was generally focused on mid-size
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high-density markets. As such, it was intended to transport large numbers of passengers between major cities. Advancements in civil aerospace technology, including high-bypass-ratio turbofan engines, new flight deck systems, aerodynamic improvements, and more efficient lightweight designs were to be applied to the 7X7. Many of these features were also included in a parallel development effort for a new mid-size narrow-body airliner, code-named 7N7, which would become the 757. Work on both proposals proceeded through the airline industry upturn in the late 1970s.
In January 1978, Boeing announced a major extension of its Everett factory—which was then dedicated to manufacturing the 747—to accommodate its new wide-body family. In February 1978, the new jetliner received the 767 model designation, and three variants were planned: a 767-100 with 190 seats, a 767-200 with 210 seats, and a trijet 767MR/LR version with 200 seats intended for intercontinental routes. The 767MR/LR was subsequently renamed 777 for differentiation purposes. The 767 was officially launched on July 14, 1978, when United Airlines ordered 30 of the 767-200 variant, followed by 50 more 767-200 orders from American Airlines and Delta Air Lines later that year. The 767-100 was ultimately not offered for sale, as its capacity was too close to the 757's seating, while the 777 trijet was eventually dropped in favor of standardizing the twinjet configuration.
=== Design effort ===
In the late 1970s, operating cost replaced capacity as the primary factor in airliner purchases. As a result, the 767's design process emphasized fuel efficiency from the outset. Boeing targeted a 20 to 30 percent cost saving over earlier aircraft, mainly through new engine and wing technology. As development progressed, engineers used computer-aided design for over a third of the 767's design drawings, and performed 26,000 hours of wind tunnel tests. Design work occurred concurrently with the 757 twinjet, leading Boeing to treat both as almost one program to reduce risk and cost. Both aircraft would ultimately receive shared design features, including avionics, flight management systems, instruments, and handling characteristics. Combined development costs were estimated at $3.5 to $4 billion.
Early 767 customers were given the choice of Pratt & Whitney JT9D or General Electric CF6 turbofans, marking the first time that Boeing had offered more than one engine option at the launch of a new airliner. Both jet engine models had a maximum output of 48,000 pounds-force (210 kN) of thrust. The engines were mounted approximately one-third the length of the wing from the fuselage, similar to previous wide-body trijets. The larger wings were designed using an aft-loaded shape which reduced aerodynamic drag and distributed lift more evenly across their surface span than any of the manufacturer's previous aircraft. The wings provided higher-altitude cruise performance, added fuel capacity, and expansion room for future stretched variants. The initial 767-200 was designed for sufficient range to fly across North America or across the northern Atlantic, and would be capable of operating routes up to 3,850 nautical miles (7,130 km; 4,430 mi).
The 767's fuselage width was set midway between that of the 707 and the 747 at 16.5 feet (5.03 m). While it was narrower than previous wide-body designs, seven abreast seating with two aisles could be fitted, and the reduced width produced less aerodynamic drag. The fuselage was not wide enough to accommodate two standard LD3 wide-body unit load devices side-by-side, so a smaller container, the LD2, was created specifically for the 767. Using a conventional tail design also allowed the rear fuselage to be tapered over a shorter section, providing for parallel aisles along the full length of the passenger cabin, and eliminating irregular seat rows toward the rear of the aircraft.
The 767 was the first Boeing wide-body to be designed with a two-crew digital glass cockpit. Cathode-ray tube (CRT) color displays and new electronics replaced the role of the flight engineer by enabling the pilot and co-pilot to monitor aircraft systems directly. Despite the promise of reduced crew costs, United Airlines initially demanded a conventional three-person cockpit, citing concerns about the risks associated with introducing a new aircraft. The carrier maintained this position until July 1981, when a US presidential task force determined that a crew of two was safe for operating wide-body jets. A three-crew cockpit remained as an option and was fitted to the first production models. Ansett Australia ordered 767s with three-crew cockpits due to union demands; it was the only airline to operate 767s so configured. The 767's two-crew cockpit was also applied to the 757, allowing pilots to operate both
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after a short conversion course, and adding incentive for airlines to purchase both types.
=== Production and testing ===
To produce the 767, Boeing formed a network of subcontractors which included domestic suppliers and international contributions from Italy's Aeritalia and Japan's CTDC. The wings and cabin floor were produced in-house, while Aeritalia provided control surfaces, Boeing Vertol made the leading edge for the wings, and Boeing Wichita produced the forward fuselage. The CTDC provided multiple assemblies through its constituent companies, namely Fuji Heavy Industries (wing fairings and gear doors), Kawasaki Heavy Industries (center fuselage), and Mitsubishi Heavy Industries (rear fuselage, doors, and tail). Components were integrated during final assembly at the Everett factory. For expedited production of wing spars, the main structural member of aircraft wings, the Everett factory received robotic machinery to automate the process of drilling holes and inserting fasteners. This method of wing construction expanded on techniques developed for the 747. Final assembly of the first aircraft began in July 1979.
The prototype aircraft, registered as N767BA and equipped with Pratt & Whitney JT9D turbofans, was rolled out on August 4, 1981. By this time, the 767 program had accumulated 173 firm orders from 17 customers, including Air Canada, All Nippon Airways, Britannia Airways, Transbrasil, and Trans World Airlines (TWA). On September 26, 1981, the prototype took its maiden flight under the command of company test pilots Tommy Edmonds, Lew Wallick, and John Brit. The maiden flight was largely uneventful, save for the inability to retract the landing gear because of a hydraulic fluid leak. The prototype was used for subsequent flight tests.
The 10-month 767 flight test program utilized the first six aircraft built. The first four aircraft were equipped with JT9D engines, while the fifth and sixth were fitted with CF6 engines. The test fleet was largely used to evaluate avionics, flight systems, handling, and performance, while the sixth aircraft was used for route-proving flights. During testing, pilots described the 767 as generally easy to fly, with its maneuverability unencumbered by the bulkiness associated with larger wide-body jets. Following 1,600 hours of flight tests, the JT9D-powered 767-200 received certification from the US Federal Aviation Administration (FAA) and the UK Civil Aviation Authority (CAA) in July 1982. The first delivery occurred on August 19, 1982, to United Airlines. The CF6-powered 767-200 received certification in September 1982, followed by the first delivery to Delta Air Lines on October 25, 1982.
=== Entry into service ===
The 767 entered service with United Airlines on September 8, 1982. The aircraft's first commercial flight used a JT9D-powered 767-200 on the Chicago-to-Denver route. The CF6-powered 767-200 commenced service three months later with Delta Air Lines. Upon delivery, early 767s were mainly deployed on domestic routes, including US transcontinental services. American Airlines and TWA began flying the 767-200 in late 1982, while Air Canada, China Airlines, El Al, and Pacific Western began operating the aircraft in 1983. The aircraft's introduction was relatively smooth, with few operational glitches and greater dispatch reliability than prior jetliners.
=== Exemptions from major certification rule changes ===
Following the 1996 in-flight explosion of TWA Flight 800, the FAA introduced new rules about flammability reduction in 2008. In 2012, Boeing requested an exemption for the 767 from new wiring separation rules that would prevent ignition sources, because design improvements it introduced fell short of meeting such rules. One of the justification by Boeing: changes to the fuel quantity indication system would require a halt of delivery by three years as production of the 767 model was expected to end shortly. FAA gave the manufacturer three years to have a compliant system while deliveries continued. In 2014, Boeing, without a new design available, asked for and received another time-limited exemption for just the 767-300 and 767-300ER until 2019 when commercial production was expected to cease. But in 2017, with continual demand for the 767-300F, Boeing asked for another exemption up to the end of 2027, well past the revised production end date. It is noted that while Boeing requested extension of the original exemption from 2016 to 2019 based upon the cost of upgrading the design and their low production rate and ending production in 2019, Boeing developed the KC-46 tanker (based on the 767) which fully compliant with the new rulings and is assembled on the same production line as the 767. Since the 2019 exemption went into effect, Boeing has increased production of the freighter to satisfy demand.
=== Stretched derivatives ===
==== First stretch: -300/-300ER/F ====
Forecasting airline interest in larger-capacity
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, Boeing announced the stretched 767-300 in 1983 and the extended-range 767-300ER in 1984. Both models offered a 20 percent passenger capacity increase, while the extended-range version was capable of operating flights up to 5,990 nautical miles (11,090 km; 6,890 mi). Japan Airlines placed the first order for the -300 in September 1983. Following its first flight on January 30, 1986, the type entered service with Japan Airlines on October 20, 1986. The 767-300ER completed its first flight on December 9, 1986, but it was not until March 1987 that the first firm order, from American Airlines, was placed. The type entered service with American Airlines on March 3, 1988. The 767-300 and 767-300ER gained popularity after entering service, and came to account for approximately two-thirds of all 767s sold. Until the 777's 1995 debut, the 767-300 and 767-300ER remained Boeing's second-largest wide-bodies behind the 747.
Buoyed by a recovering global economy and ETOPS approval, 767 sales accelerated in the mid-to-late 1980s; 1989 was the most prolific year with 132 firm orders. By the early 1990s, the wide-body twinjet had become its manufacturer's annual best-selling aircraft, despite a slight decrease due to economic recession. During this period, the 767 became the most common airliner for transatlantic flights between North America and Europe. By the end of the decade, 767s crossed the Atlantic more frequently than all other aircraft types combined. The 767 also propelled the growth of point-to-point flights which bypassed major airline hubs in favor of direct routes. Taking advantage of the aircraft's lower operating costs and smaller capacity, operators added non-stop flights to secondary population centers, thereby eliminating the need for connecting flights. The increased number of cities receiving non-stop services caused a paradigm shift in the airline industry as point-to-point travel gained prominence at the expense of the traditional hub-and-spoke model.
In February 1990, the first 767 equipped with Rolls-Royce RB211 turbofans, a 767-300, was delivered to British Airways. Six months later, the carrier temporarily grounded its entire 767 fleet after discovering cracks in the engine pylons of several aircraft. The cracks were related to the extra weight of the RB211 engines, which are 2,205 pounds (1,000 kg) heavier than other 767 engines. During the grounding, interim repairs were conducted to alleviate stress on engine pylon components, and a parts redesign in 1991 prevented further cracks. Boeing also performed a structural reassessment, resulting in production changes and modifications to the engine pylons of all 767s in service.
In January 1993, following an order from UPS Airlines, Boeing launched a freighter variant, the 767-300F, which entered service with UPS on October 16, 1995. The 767-300F featured a main deck cargo hold, upgraded landing gear, and strengthened wing structure. In November 1993, the Japanese government launched the first 767 military derivative when it placed orders for the E-767, an Airborne Early Warning and Control (AWACS) variant based on the 767-200ER. The first two E-767s, featuring extensive modifications to accommodate surveillance radar and other monitoring equipment, were delivered in 1998 to the Japan Self-Defense Forces.
==== Second stretch:-400ER ====
In November 1995, after abandoning development of a smaller version of the 777, Boeing announced that it was revisiting studies for a larger 767. The proposed 767-400X, a second stretch of the aircraft, offered a 12 percent capacity increase versus the 767-300, and featured an upgraded flight deck, enhanced interior, and greater wingspan. The variant was specifically aimed at Delta Air Lines' pending replacement of its aging Lockheed L-1011 TriStars, and faced competition from the A330-200, a shortened derivative of the Airbus A330. In March 1997, Delta Air Lines launched the 767-400ER when it ordered the type to replace its L-1011 fleet. In October 1997, Continental Airlines also ordered the 767-400ER to replace its McDonnell Douglas DC-10 fleet. The type completed its first flight on October 9, 1999, and entered service with Continental Airlines on September 14, 2000.
=== Dreamliner introduction ===
In the early 2000s, cumulative 767 deliveries approached 900, but new sales declined during an airline industry downturn. In 2001, Boeing dropped plans for a longer-range model, the 767-400ERX, in favor of the proposed Sonic Cruiser, a new jetliner which aimed to fly 15 percent faster while having comparable fuel costs to the 767. The following year, Boeing announced the KC-767 Tanker Transport, a second military derivative of the 767-200
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. Launched with an order in October 2002 from the Italian Air Force, the KC-767 was intended for the dual role of refueling other aircraft and carrying cargo. The Japanese government became the second customer for the type in March 2003. In May 2003, the United States Air Force (USAF) announced its intent to lease KC-767s to replace its aging KC-135 tankers. The plan was suspended in March 2004 amid a conflict of interest scandal, resulting in multiple US government investigations and the departure of several Boeing officials, including Philip Condit, the company's chief executive officer, and chief financial officer Michael Sears. The first KC-767s were delivered in 2008 to the Japan Self-Defense Forces.
In late 2002, after airlines expressed reservations about its emphasis on speed over cost reduction, Boeing halted development of the Sonic Cruiser. The following year, the manufacturer announced the 7E7, a mid-size 767 successor made from composite materials which promised to be 20 percent more fuel efficient. The new jetliner was the first stage of a replacement aircraft initiative called the Boeing Yellowstone Project. Customers embraced the 7E7, later renamed 787 Dreamliner, and within two years it had become the fastest-selling airliner in the company's history. In 2005, Boeing opted to continue 767 production despite record Dreamliner sales, citing a need to provide customers waiting for the 787 with a more readily available option. Subsequently, the 767-300ER was offered to customers affected by 787 delays, including All Nippon Airways and Japan Airlines. Some aging 767s, exceeding 20 years in age, were also kept in service past planned retirement dates due to the delays. To extend the operational lives of older aircraft, airlines increased heavy maintenance procedures, including D-check teardowns and inspections for corrosion, a recurring issue on aging 767s. The first 787s entered service with All Nippon Airways in October 2011, 42 months behind schedule.
=== Continued production ===
In 2007, the 767 received a production boost when UPS and DHL Aviation placed a combined 33 orders for the 767-300F. Renewed freighter interest led Boeing to consider enhanced versions of the 767-200 and 767-300F with increased gross weights, 767-400ER wing extensions, and 777 avionics. Net orders for the 767 declined from 24 in 2008 to just three in 2010. During the same period, operators upgraded aircraft already in service; in 2008, the first 767-300ER retrofitted with blended winglets from Aviation Partners Incorporated debuted with American Airlines. The manufacturer-sanctioned winglets, at 11 feet (3.35 m) in height, improved fuel efficiency by an estimated 6.5 percent. Other carriers including All Nippon Airways and Delta Air Lines also ordered winglet kits.
On February 2, 2011, the 1,000th 767 rolled out, destined for All Nippon Airways. The aircraft was the 91st 767-300ER ordered by the Japanese carrier, and with its completion the 767 became the second wide-body airliner to reach the thousand-unit milestone after the 747. The 1,000th aircraft also marked the last model produced on the original 767 assembly line. Beginning with the 1,001st aircraft, production moved to another area in the Everett factory which occupied about half of the previous floor space. The new assembly line made room for 787 production and aimed to boost manufacturing efficiency by over twenty percent.
At the inauguration of its new assembly line, the 767's order backlog numbered approximately 50, only enough for production to last until 2013. Despite the reduced backlog, Boeing officials expressed optimism that additional orders would be forthcoming. On February 24, 2011, the USAF announced its selection of the KC-767 Advanced Tanker, an upgraded variant of the KC-767, for its KC-X fleet renewal program. The selection followed two rounds of tanker competition between Boeing and Airbus parent EADS, and came eight years after the USAF's original 2003 announcement of its plan to lease KC-767s. The tanker order encompassed 179 aircraft and was expected to sustain 767 production past 2013.
In December 2011, FedEx Express announced a 767-300F order for 27 aircraft to replace its DC-10 freighters, citing the USAF tanker order and Boeing's decision to continue production as contributing factors. FedEx Express agreed to buy 19 more of the −300F variant in June 2012. In June 2015, FedEx said it was accelerating retirements of planes both to reflect demand and to modernize its fleet, recording charges of $276 million (~$347 million in 2023). On July 21, 2015, FedEx announced an order for 50 767-300F with options on another 50, the largest order for the type. With the announcement FedEx confirmed that it has firm orders for 106 of the freighters for delivery between 2018 and 2023. In February 2018, UPS announced an order for 4 more
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67-300Fs to increase the total on order to 63.
With its successor, the Boeing New Midsize Airplane, that was planned for introduction in 2025 or later, and the 787 being much larger, Boeing could restart a passenger 767-300ER production to bridge the gap. A demand for 50 to 60 aircraft could have to be satisfied. Having to replace its 40 767s, United Airlines requested a price quote for other widebodies. In November 2017, Boeing CEO Dennis Muilenburg cited interest beyond military and freighter uses. However, in early 2018 Boeing Commercial Airplanes VP of marketing Randy Tinseth stated that the company did not intend to resume production of the passenger variant.
In its first quarter of 2018 earnings report, Boeing plans to increase its production from 2.5 to 3 monthly beginning in January 2020 due to increased demand in the cargo market, as FedEx had 56 on order, UPS has four, and an unidentified customer has three on order. This rate could rise to 3.5 per month in July 2020 and 4 per month in January 2021, before decreasing to 3 per month in January 2025 and then 2 per month in July 2025.
In 2019, unit cost was US$217.9 million for a -300ER, and US$220.3 million for a -300F.
Production of the 767 was expected to cease by the end of 2027 due to more stringent emissions and noise limits that will go into effect in 2028. However, as of May 2024, the US Congress is considering giving Boeing a waiver to continue to produce the 767 freighter for an additional five years. If granted, these aircraft would be restricted to domestic use within the US only. Boeing is widely expected to begin production of 787 Freighter during that extension period.
=== Continued development ===
==== 767-X (partial double-deck) ====
After the debut of the first stretched 767s, Boeing sought to address airline requests for greater capacity by proposing larger models, including a partial double-deck version informally named the "Hunchback of Mukilteo" (from a town near Boeing's Everett factory) with a 757 body section mounted over the aft main fuselage. In 1986, Boeing proposed the 767-X, a revised model with extended wings and a wider cabin, but received little interest. The 767-X did not get enough interest from airlines to launch and the model was shelved in 1988 in favor of the Boeing 777.
==== 767-400ERX ====
In March 2000, Boeing was to launch the 259-seat 767-400ERX with an initial order for three from Kenya Airways with deliveries planned for 2004, as it was proposed to Lauda Air.
Increased gross weight and a tailplane fuel tank would have boosted its range by 5,990 to 6,490 nautical miles (11,100 to 12,025 km), and GE could offer its 65,000–68,000 lbf (290–300 kN) CF6-80C2/G2. Rolls-Royce offered its 68,000–72,000 lbf (300–320 kN) Trent 600 for the 767-400ERX and the Boeing 747X.
Offered in July, the longer-range -400ERX would have a strengthened wing, fuselage and landing gear for a 15,000 lb (6.8 t) higher MTOW, up to 465,000 lb (210.92 t).
Thrust would rise to 72,000 lbf (320 kN) for better takeoff performance, with the Trent 600 or the General Electric/Pratt & Whitney Engine Alliance GP7172, also offered on the 747X.
Range would increase by 525 nmi (604 mi; 972 km) to 6,150 nmi (7,080 mi; 11,390 km), with an additional fuel tank of 2,145 US gal (8,120 L) in the horizontal tail.
The 767-400ERX would offer the capacity of the Airbus A330-200 with 3% lower fuel burn and costs.
Boeing cancelled the variant development in 2001. Kenya Airways then switched its order to the 777-200ER.
==== 767-XF (re-engine) ====
In October 2019, Boeing was reportedly studying a re-engined 767-XF for entry into service around 2025, based on the 767-400ER with an extended landing gear to accommodate larger General Electric GEnx turbofan engines.
The cargo market is the main target, but a passenger version could be a cheaper alternative to the proposed New Midsize Airplane.
== Design ==
=== Overview ===
The 767 is a low-wing cantilever monoplane with a conventional tail unit featuring a single fin and rudder. The wings are swept
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31.5 degrees and optimized for a cruising speed of Mach 0.8 (533 mph or 858 km/h). Each wing features a supercritical airfoil cross-section and is equipped with six-panel leading edge slats, single- and double-slotted flaps, inboard and outboard ailerons, and six spoilers. The airframe further incorporates Carbon-fiber-reinforced polymer composite material wing surfaces, Kevlar fairings and access panels, plus improved aluminum alloys, which together reduce overall weight by 1,900 pounds (860 kg) versus preceding aircraft.
To distribute the aircraft's weight on the ground, the 767 has a retractable tricycle landing gear with four wheels on each main gear and two for the nose gear. The original wing and gear design accommodated the stretched 767-300 without major changes. The 767-400ER features a larger, more widely spaced main gear with 777 wheels, tires, and brakes. To prevent damage if the tail section contacts the runway surface during takeoff, 767-300 and 767-400ER models are fitted with a retractable tailskid.
All passenger Boeing 767 models have full-sized doors at the front and rear of the aircraft. Most -200 and -200ER models feature a single overwing exit, though an optional second overwing exit increases maximum capacity from 255 to 290. The 767-300 and 767-300ER typically have either two overwing exits or an additional full-sized mid-cabin door along with a single overwing exit. A higher-capacity configuration includes the full-sized mid-cabin door a smaller exit door aft the wing, raising the maximum capacity from 290 to 351. The 767-400ER is configured with the full-sized mid-cabin door a smaller exit door aft the wing. The 767-300F cargo model has a single exit door on the forward left side of the aircraft.
In addition to shared avionics and computer technology, the 767 uses the same auxiliary power unit, electric power systems, and hydraulic parts as the 757. A raised cockpit floor and the same forward cockpit windows result in similar pilot viewing angles. Related design and functionality allows 767 pilots to obtain a common type rating to operate the 757 and share the same seniority roster with pilots of either aircraft.
=== Flight systems ===
The original Boeing 767 flight deck features a two-crew glass cockpit, the first of its kind on a Boeing airliner, developed jointly with the narrow-body 757. This design allows for a common pilot type rating between the two aircraft. The cockpit includes six Rockwell Collins CRT screens that display electronic flight instrument system (EFIS) and engine indication and crew alerting system (EICAS) information, eliminating the need for a flight engineer by enabling pilots to manage monitoring tasks. These CRT screens replace the traditional electromechanical instruments used in earlier aircraft. The aircraft's enhanced flight management system, an improvement over early Boeing 747 versions, automates navigation and other functions. Additionally, an automatic landing system supports CAT IIIb instrument landings in low-visibility conditions. In 1984, the 767 became the first aircraft to receive FAA certification for CAT IIIb landings, permitting operations with a minimum visibility of 980 feet (300 m). The 767-400ER further simplifies the cockpit layout with six Rockwell Collins LCD screens, designed for operational similarity with the 777 and 737NG. To maintain commonality, these LCD screens can be configured to present information in the same format as earlier 767 models. In 2012, Rockwell Collins introduced a 787-inspired cockpit upgrade for the 767, featuring three landscape-format LCD screens capable of displaying two windows each.
=== Interior ===
The 767 features a twin-aisle cabin with a typical configuration of six abreast in business class and seven across in economy. The standard seven abreast, 2–3–2 economy class layout places approximately 87 percent of all seats at a window or aisle. As a result, the aircraft can be largely occupied before center seats need to be filled, and each passenger is no more than one seat from the aisle. It is possible to configure the aircraft with extra seats for up to an eight abreast configuration, but this is less common.
The 767 interior introduced larger overhead bins and more lavatories per passenger than previous aircraft. The bins are wider to accommodate garment bags without folding, and strengthened for heavier carry-on items. A single, large galley is installed near the aft doors, allowing for more efficient meal service and simpler ground resupply. Passenger and service doors are an overhead plug type, which retract upwards, and commonly used doors can be equipped with an electric-assist system.
In 2000, a 777-style interior, known as the Boeing Signature Interior, debuted on the 767-400ER. Subsequently, adopted for all new-
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767s, the Signature Interior features even larger overhead bins, indirect lighting, and sculpted, curved panels. The 767-400ER also received larger windows derived from the 777. Older 767s can be retrofitted with the Signature Interior. Some operators have adopted a simpler modification known as the Enhanced Interior, featuring curved ceiling panels and indirect lighting with minimal modification of cabin architecture, as well as aftermarket modifications such as the NuLook 767 package by Heath Tecna.
== Operational history ==
In its first year, the 767 logged a 96.1 percent dispatch rate, which exceeded the industry average for all-new aircraft. Operators reported generally favorable ratings for the twinjet's sound levels, interior comfort, and economic performance. Resolved issues were minor and included the recalibration of a leading edge sensor to prevent false readings, the replacement of an evacuation slide latch, and the repair of a tailplane pivot to match production specifications.
Seeking to capitalize on its new wide-body's potential for growth, Boeing offered an extended-range model, the 767-200ER, in its first year of service. Ethiopian Airlines placed the first order for the type in December 1982. Featuring increased gross weight and greater fuel capacity, the extended-range model could carry heavier payloads at distances up to 6,385 nautical miles (11,825 km; 7,348 mi), and was targeted at overseas customers. The 767-200ER entered service with El Al Airline on March 27, 1984. The type was mainly ordered by international airlines operating medium-traffic, long-distance flights. In May 1984, an Ethiopian Airlines 767-200ER set a non-stop record for a commercial twinjet of 12,082 km (6,524 nmi; 7,507 mi) from Washington, D.C. to Addis Ababa.
In the mid-1980s, the 767 and its European rivals, the Airbus A300 and A310, spearheaded the growth of twinjet flights across the northern Atlantic under extended-range twin-engine operational performance standards (ETOPS) regulations, the FAA's safety rules governing transoceanic flights by aircraft with two engines. In 1976, the A300 was the first twinjet to secure permission to fly 90 minutes away from diversion airports, up from 60 minutes. In May 1985, the FAA granted its first approval for 120-minute ETOPS flights to the 767, on an individual airline basis starting with TWA, provided that the operator met flight safety criteria. This allowed the aircraft to fly overseas routes at up to two hours' distance from land. The 767 burned 7,000 lb (3.2 t) less fuel per hour than a Lockheed L-1011 TriStar on the route between Boston and Paris, a huge savings. The Airbus A310 secured approval for 120-minute ETOPS flights one month later in June. The larger safety margins were permitted because of the improved reliability demonstrated by twinjets and their turbofan engines. The FAA lengthened the ETOPS time to 180 minutes for CF6-powered 767s in 1989, making the type the first to be certified under the longer duration, and all available engines received approval by 1993. Regulatory approval spurred the expansion of transoceanic flights with twinjet aircraft and boosted the sales of both the 767 and its rivals.
== Variants ==
The 767 has been produced in three fuselage lengths. These debuted in progressively larger form as the 767-200, 767-300, and 767-400ER. Longer-range variants include the 767-200ER and 767-300ER, while cargo models include the 767-300F, a production freighter, and conversions of passenger 767-200 and 767-300 models.
When referring to different variants, Boeing and airlines often collapse the model number (767) and the variant designator, e.g. –200 or –300, into a truncated form, e.g. "762" or "763". Subsequent to the capacity number, designations may append the range identifier, though -200ER and -300ER are company marketing designations and not certificated as such. The International Civil Aviation Organization (ICAO) aircraft type designator system uses a similar numbering scheme, but adds a preceding manufacturer letter; all variants based on the 767-200 and 767-300 are classified under the codes "B762" and "B763"; the 767-400ER receives the designation of "B764".
=== 767-200 ===
The 767-200 was the original model and entered service with United Airlines in 1982. The type has been used primarily by mainline U.S. carriers for domestic routes between major hub centers such as Los Angeles to Washington. The 767-200 was the first aircraft to be used on transatlantic ETOPS flights, beginning with
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WA on February 1, 1985, under 90-minute diversion rules. Deliveries for the variant totaled 128 aircraft. There were 52 examples of the model in commercial service as of July 2018, almost entirely as freighter conversions. The type's competitors included the Airbus A300 and A310.
The 767-200 was produced until 1987 when production switched to the extended-range 767-200ER. Some early 767-200s were subsequently upgraded to extended-range specification. In 1998, Boeing began offering 767-200 conversions to 767-200SF (Special Freighter) specification for cargo use, and Israel Aerospace Industries has been licensed to perform cargo conversions since 2005. The conversion process entails the installation of a side cargo door, strengthened main deck floor, and added freight monitoring and safety equipment. The 767-200SF was positioned as a replacement for Douglas DC-8 freighters.
=== 767-2C ===
A commercial freighter version of the Boeing 767-200 with wings from the -300 series and an updated flightdeck was first flown on December 29, 2014. A military tanker variant of the Boeing 767-2C is developed for the USAF as the KC-46. Boeing is building two aircraft as commercial freighters which will be used to obtain Federal Aviation Administration certification, a further two Boeing 767-2Cs will be modified as military tankers. As of 2014, Boeing does not have customers for the freighter.
=== 767-200ER ===
The 767-200ER was the first extended-range model and entered service with El Al in 1984. The type's increased range is due to extra fuel capacity and higher maximum takeoff weight (MTOW) of up to 395,000 lb (179,000 kg). The additional fuel capacity is accomplished by using the center tank's dry dock to carry fuel. The non-ER variant's center tank is what is called cheek tanks; two interconnected halves in each wing root with a dry dock in between. The center tank is also used on the -300ER and -400ER variants.
This version was originally offered with the same engines as the 767-200, while more powerful Pratt & Whitney PW4000 and General Electric CF6 engines later became available. The 767-200ER was the first 767 to complete a non-stop transatlantic journey, and broke the flying distance record for a twinjet airliner on April 17, 1988, with an Air Mauritius flight from Halifax, Nova Scotia to Port Louis, Mauritius, covering 8,727 nmi (16,200 km; 10,000 mi). The 767-200ER has been acquired by international operators seeking smaller wide-body aircraft for long-haul routes such as New York to Beijing. Deliveries of the type totaled 121 with no unfilled orders. As of July 2018, 21 examples of passenger and freighter conversion versions were in airline service. The type's main competitors of the time included the Airbus A300-600R and the A310-300.
=== 767-300 ===
The 767-300, the first stretched version of the aircraft, entered service with Japan Airlines in 1986. The type features a 21.1-foot (6.43 m) fuselage extension over the 767-200, achieved by additional sections inserted before and after the wings, for an overall length of 180.25 ft (54.9 m). Reflecting the growth potential built into the original 767 design, the wings, engines, and most systems were largely unchanged on the 767-300. An optional mid-cabin exit door is positioned ahead of the wings on the left, while more powerful Pratt & Whitney PW4000 and Rolls-Royce RB211 engines later became available. The 767-300's increased capacity has been used on high-density routes within Asia and Europe. The 767-300 was produced from 1986 until 2000. Deliveries for the type totaled 104 aircraft with no unfilled orders remaining. The type's main competitor was the Airbus A300.
=== 767-300ER ===
The 767-300ER, the extended-range version of the 767-300, entered service with American Airlines in 1988. The type's increased range was made possible by greater fuel tankage and a higher MTOW of 407,000 lb (185,000 kg). Design improvements allowed the available MTOW to increase to 412,000 lb (187,000 kg) by 1993. Power is provided by Pratt & Whitney PW4000, General Electric CF6, or Rolls-Royce RB211 engines. The 767-300ER comes in three exit configurations: the baseline configuration has four main cabin doors and four over-wing window exits, the second configuration has six main cabin doors and two over-wing window exits; and the third configuration has six main cabin doors, as well as two smaller doors that are located behind the wings. Typical routes for the type include New York
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Frankfurt.
The combination of increased capacity and range for the -300ER has been particularly attractive to both new and existing 767 operators. It is the most successful 767 version, with more orders placed than all other variants combined. As of November 2017, 767-300ER deliveries stand at 583 with no unfilled orders. There were 376 examples in service as of July 2018. The type's main competitor is the Airbus A330-200. At its 1990s peak, a new 767-300ER was valued at $85 million, dipping to around $12 million in 2018 for a 1996 build.
=== 767-300F ===
The 767-300F, the production freighter version of the 767-300ER, entered service with UPS Airlines in 1995. The 767-300F can hold up to 24 standard 88-by-125-inch (220 by 320 cm) pallets on its main deck and up to 30 LD2 unit load devices on the lower deck, with a total cargo volume of 15,469 cubic feet (438 m3). The freighter has a main deck cargo door and crew exit, while the lower deck features two starboard-side cargo doors and one port-side cargo door. A general market version with onboard freight-handling systems, refrigeration capability, and crew facilities was delivered to Asiana Airlines on August 23, 1996. As of August 2019, 767-300F deliveries stand at 161 with 61 unfilled orders. Airlines operated 222 examples of the freighter variant and freighter conversions in July 2018.
==== Converted freighters ====
In June 2008, All Nippon Airways took delivery of the first 767-300BCF (Boeing Converted Freighter), a modified passenger-to-freighter model. The conversion work was performed in Singapore by ST Aerospace Services, the first supplier to offer a 767-300BCF program, and involved the addition of a main deck cargo door, strengthened main deck floor, and additional freight monitoring and safety equipment.
Israel Aerospace Industries offers a passenger-to-freighter conversion program called the 767-300BDSF (BEDEK Special Freighter). Wagner Aeronautical also offers a passenger-to-freighter conversion program for 767-300 series aircraft.
=== 767-400ER ===
The 767-400ER, the first Boeing wide-body jet resulting from two fuselage stretches, entered service with Continental Airlines in 2000. The type features a 21.1-foot (6.43-metre) stretch over the 767-300, for a total length of 205.11 feet (62.5 m). The wingspan is also increased by 14.3 feet (4.36 m) through the addition of raked wingtips. The exit configuration uses six main cabin doors and two smaller exit doors behind the wings, similar to certain 767-300ERs. Other differences include an updated cockpit, redesigned landing gear, and 777-style Signature Interior. Power is provided by uprated General Electric CF6 engines.
The FAA granted approval for the 767-400ER to operate 180-minute ETOPS flights before it entered service. Because its fuel capacity was not increased over preceding models, the 767-400ER has a range of 5,625 nautical miles (10,418 km; 6,473 mi), less than previous extended-range 767s. No 767-400 (non-extended range) version was developed.
The longer-range 767-400ERX was offered in July 2000 before being cancelled a year later, leaving the 767-400ER as the sole version of the largest 767. Boeing dropped the 767-400ER and the -200ER from its pricing list in 2014.
A total of 37 767-400ERs were delivered to the variant's two airline customers, Continental Airlines (now merged with United Airlines as of 2010) and Delta Air Lines, with no unfilled orders. All 37 examples of the -400ER were in service in July 2018. One additional example was produced as a military testbed for cancelled E-10, and later sold to Bahrain as a VIP transport. The type's closest competitor is the Airbus A330-200.
=== Military and government ===
Versions of the 767 serve in a number of military and government applications, with responsibilities ranging from airborne surveillance and refueling to cargo and VIP transport. Several military 767s have been derived from the 767-200ER, the longest-range version of the aircraft.
Airborne Surveillance Testbed – the Airborne Optical Adjunct (AOA) was modified from the prototype 767-200 for a United States Army program, under a contract signed with the Strategic Air Command in July 1984. Intended to evaluate the feasibility of using airborne optical sensors to detect and track hostile intercontinental ballistic missiles, the modified aircraft
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flew on August 21, 1987. Alterations included a large "cupola" or hump on the top of the aircraft from above the cockpit to just behind the trailing edge of the wings, and a pair of ventral fins below the rear fuselage. Inside the cupola was a suite of infrared seekers used for tracking theater ballistic missile launches. The aircraft was later renamed as the Airborne Surveillance Testbed (AST). Following the end of the AST program in 2002, the aircraft was retired for scrapping.
E-767 – the Airborne Early Warning and Control (AWACS) platform for the Japan Self-Defense Forces; it is essentially the Boeing E-3 Sentry mission package on a 767-200ER platform. E-767 modifications, completed on 767-200ERs flown from the Everett factory to Boeing Integrated Defense Systems in Wichita, Kansas, include strengthening to accommodate a dorsal surveillance radar system, engine nacelle alterations, as well as electrical and interior changes. Japan operates four E-767s. The first E-767s were delivered in March 1998.
KC-767 Tanker Transport – the 767-200ER-based aerial refueling platform operated by the Italian Air Force (Aeronautica Militare), and the Japan Self-Defense Forces. Modifications conducted by Boeing Integrated Defense Systems include the addition of a fly-by-wire refueling boom, strengthened flaps, and optional auxiliary fuel tanks, as well as structural reinforcement and modified avionics. The four KC-767Js ordered by Japan have been delivered. The Aeronautica Militare received the first of its four KC-767As in January 2011.
KC-767 Advanced Tanker – the 767-200ER-based aerial tanker developed for the USAF KC-X tanker competition. It is an updated version of the KC-767, originally selected as the USAF's new tanker aircraft in 2003, designated KC-767A, and then dropped amid conflict of interest allegations. The KC-767 Advanced Tanker is derived from studies for a longer-range cargo version of the 767-200ER, and features a fly-by-wire refueling boom, a remote vision refueling system, and a 767-400ER-based flight deck with LCD screens and head-up displays.
KC-46 Pegasus – a 767-based tanker, not derived from the KC-767, awarded as part of the KC-X contract for the USAF.
Tanker conversions – the 767 MMTT or Multi-Mission Tanker Transport is a 767-200ER-based aircraft operated by the Colombian Air Force (Fuerza Aérea Colombiana) and modified by Israel Aerospace Industries. In 2013, the Brazilian Air Force ordered two 767-300ER tanker conversions from IAI for its KC-X2 program.
E-10 MC2A – the Northrop Grumman E-10 was to be a 767-400ER-based replacement for the USAF's 707-based E-3 Sentry AWACS, Northrop Grumman E-8 Joint STARS, and RC-135 SIGINT aircraft. The E-10 would have included an all-new AWACS system, with a powerful active electronically scanned array (AESA) that was also capable of jamming enemy aircraft or missiles. One 767-400ER aircraft was built as a testbed for systems integration, but the program was terminated in January 2009 and the prototype was later sold to Bahrain as a VIP transport.
== Operators ==
In July 2018, 742 aircraft were in airline service: 73 -200s, 632 -300, and 37 -400ER with 65 -300F on order; the largest operators are Delta Air Lines (77), FedEx (60; largest cargo operator), UPS Airlines (59), United Airlines (51), Japan Airlines (35), All Nippon Airways (34).
The largest 767 customers by orders placed are FedEx Express (150), Delta Air Lines (117), All Nippon Airways (96), American Airlines (88), and United Airlines (82). Delta and United are the only customers of all -200, -300, and -400ER passenger variants. In July 2015, FedEx placed a firm order for 50 Boeing 767 freighters with deliveries from 2018 to 2023. The type's competitors included the Airbus A300 and A310.
=== Orders and deliveries ===
Boeing 767 orders and deliveries (cumulative, by year):
Orders Deliveries — as of July 2025
=== Model summary ===
Data as of July 2025.
== Accidents and incidents ==
As of February 2025, the Boeing 767 has been in 67 aviation occurrences, including 19 hull-loss accidents. Eleven fatal crashes, including seven hijackings, have resulted in a total of 854 occupant fatalities.
=== Accidents
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The airliner's first fatal crash, Lauda Air Flight 004, occurred near Bangkok on May 26, 1991, following the in-flight deployment of the left engine thrust reverser on a 767-300ER. None of the 223 onboard survived. As a result of this accident, all 767 thrust reversers were deactivated until a redesign was implemented. Investigators determined that an electronically controlled valve, common to late-model Boeing aircraft, was to blame. A new locking device was installed on all affected jetliners, including 767s.
On October 31, 1999, EgyptAir Flight 990, a 767-300ER, crashed off Nantucket, Massachusetts, in international waters killing all 217 people on board. The United States National Transportation Safety Board (NTSB) concluded "not determined", but determined the probable cause to be a deliberate action by the first officer; the Egyptian government disputed this conclusion.
On April 15, 2002, Air China Flight 129, a 767-200ER, crashed into a hill amid inclement weather while trying to land at Gimhae International Airport in Busan, South Korea. The crash resulted in the death of 129 of the 166 people on board, and the cause was attributed to pilot error. This was the deadliest plane crash in South Korea at the time.
On February 23, 2019, Atlas Air Flight 3591, a Boeing 767-300ERF air freighter operating for Amazon Air, crashed into Trinity Bay near Houston, Texas, while on descent into George Bush Intercontinental Airport; both pilots and the single passenger were killed. The cause was attributed to pilot error and spatial disorientation.
Hull losses
On November 1, 2011, LOT Polish Airlines Flight 16, a 767-300ER, safely landed at Warsaw Chopin Airport in Warsaw, Poland, after a mechanical failure of the landing gear forced an emergency landing with the landing gear retracted. There were no injuries, but the aircraft involved was damaged and written off. At the time aviation analysts speculated that it may have been the first instance of a complete landing gear failure in the 767's service history. Subsequent investigation determined that while a damaged hose had disabled the aircraft's primary landing gear extension system, an otherwise functional backup system was inoperative due to an accidentally deactivated circuit breaker.
On October 29, 2015, Dynamic Airways Flight 405, a 767-200ER, caught fire while taxiing to the runway at Hollywood International Airport. There were no fatalities, but 22 people were injured, 1 of them seriously. The aircraft was written off.
On October 28, 2016, American Airlines Flight 383, a 767-300ER with 161 passengers and 9 crew members, aborted takeoff at Chicago O'Hare Airport following an uncontained failure of the right GE CF6-80C2 engine. The engine failure, which hurled fragments over a considerable distance, caused a fuel leak, resulting in a fire under the right wing. Fire and smoke entered the cabin. All passengers and crew evacuated the aircraft, with 20 passengers and one flight attendant sustaining minor injuries using the evacuation slides.
Hijackings
The 767 has been involved in six hijackings, three resulting in loss of life, for a combined total of 282 occupant fatalities. On November 23, 1996, Ethiopian Airlines Flight 961, a 767-200ER, was hijacked and crash-landed in the Indian Ocean near the Comoro Islands after running out of fuel, killing 125 out of the 175 persons on board; this was a rare example of occupants surviving a land-based aircraft ditching on water. Two 767s were involved in the September 11 attacks on the World Trade Center in 2001, resulting in the collapse of its two main towers. American Airlines Flight 11, a 767-200ER, crashed into the North Tower, killing all 92 people on board, and United Airlines Flight 175, a 767-200, crashed into the South Tower, with the death of all 65 on board. In addition, more than 2,600 people were killed in the towers or on the ground. A failed shoe bomb attempt in December 2001 involved an American Airlines 767-300ER.
=== Incidents ===
The 767's first incident was Air Canada Flight 143, a 767-200, on July 23, 1983. The airplane ran out of fuel at an altitude of about 41,000 feet. Eventually, the pilots had to glide with both engines out for almost 43 nautical miles (80 km; 49 mi) to an emergency landing at Gimli, Manitoba, Canada. The pilots used the aircraft's ram air turbine to power the hydraulic systems for aerodynamic control. There were no fatalities and only minor injuries. This aircraft was nicknamed "Gimli Glider" after its landing site. The aircraft, registered as C-GAUN, continued flying for Air Canada until its retirement in January 2008.
In January 2014, the U.S. Federal Aviation Administration issued a
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that ordered inspections of the elevators on more than 400 767s beginning in March 2014; the focus was on fasteners and other parts that can fail and cause the elevators to jam. The issue was first identified in 2000 and has been the subject of several Boeing service bulletins. The inspections and repairs are required to be completed within six years. The aircraft has also had multiple occurrences of "uncommanded escape slide inflation" during maintenance or operations, and during flight. In late 2015, the FAA issued a preliminary directive to address the issue.
== Aircraft on display ==
As new 767 variants roll off the assembly line, older series models have been retired and converted to cargo use, stored, or scrapped. One complete aircraft, N102DA, is the first 767-200 to operate for Delta Air Lines and the twelfth example built. It was retired from airline service in February 2006 after being repainted back to its original 1982 Delta widget livery and given a farewell tour. It was then put on display at the Delta Flight Museum in the Delta corporate campus at the edge of Hartsfield–Jackson Atlanta International Airport. "The Spirit of Delta" is on public display as of 2022.
In 2013 a Brazilian entrepreneur purchased a 767-200 that had operated for the now-defunct carrier Transbrasil under the registration PT-TAC. The aircraft, which was sold at a bankruptcy auction, was placed on outdoor display in Taguatinga as part of a proposed commercial development. As of 2019, however, the development has not come to fruition. The aircraft is devoid of engines or landing gear and has deteriorated due to weather exposure and acts of vandalism but remains publicly accessible to view.
== Specifications ==
Below is an organized chart composed of the variants of the 767 and their specifications.
== See also ==
Competition between Airbus and Boeing
Related development
Boeing 757
Boeing E-767
Boeing KC-46 Pegasus
Boeing KC-767
Northrop Grumman E-10 MC2A
Aircraft of comparable role, configuration, and era
Airbus A300
Airbus A310
Related lists
List of jet airliners
List of civil aircraft
== Notes ==
== References ==
== Sources ==
== External links ==
Media related to Boeing 767 at Wikimedia Commons
Official website
"Introducing the 767-400ER". Aero Magazine. Boeing. July 1998.
"Strategic stretch". Flight International. August 25, 1999.
"767-300BCF converted freighter" (PDF). Boeing. 2007. Archived from the original (PDF) on July 5, 2016.
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Apparent retrograde motion is the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point. Direct motion or prograde motion is motion in the same direction as other bodies.
While the terms direct and prograde are equivalent in this context, the former is the traditional term in astronomy. The earliest recorded use of prograde was in the early 18th century, although the term is now less common.
== Etymology and history ==
The term retrograde is from the Latin word retrogradus – "backward-step", the affix retro- meaning "backwards" and gradus "step". Retrograde is most commonly an adjective used to describe the path of a planet as it travels through the night sky, with respect to the zodiac, stars, and other bodies of the celestial canopy. In this context, the term refers to planets, as they appear from Earth, stopping briefly and reversing direction at certain times, though in reality, of course, we now understand that they perpetually orbit in the same uniform direction.
Although planets can sometimes be mistaken for stars as one observes the night sky, the planets actually change position from night to night in relation to the stars. Retrograde (backward) and prograde (forward) are observed as though the stars revolve around the Earth. Ancient Greek astronomer Ptolemy in 150 AD believed that the Earth was the center of the Solar System and therefore used the terms retrograde and prograde to describe the movement of the planets in relation to the stars. Although it is known today that the planets revolve around the Sun, the same terms continue to be used in order to describe the movement of the planets in relation to the stars as they are observed from Earth. Like the Sun, the planets appear to rise in the East and set in the West. When a planet travels eastward in relation to the stars, it is called prograde. When the planet travels westward in relation to the stars (opposite path) it is called retrograde.
This apparent retrogradation puzzled ancient astronomers, and was one reason they named these bodies 'planets' in the first place: 'Planet' comes from the Greek word for 'wanderer'. In the geocentric model of the Solar System proposed by Apollonius in the third century BCE, retrograde motion was explained by having the planets travel in deferents and epicycles. It was not understood to be an illusion until the time of Copernicus, although the Greek astronomer Aristarchus in 240 BCE proposed a heliocentric model for the Solar System.
Galileo's drawings show that he first observed Neptune on December 28, 1612, and again on January 27, 1613. On both occasions, Galileo mistook Neptune for a fixed star when it appeared very close—in conjunction—to Jupiter in the night sky, hence, he is not credited with Neptune's discovery. During the period of his first observation in December 1612, Neptune was stationary in the sky because it had just turned retrograde that very day. Since Neptune was only beginning its yearly retrograde cycle, the motion of the planet was far too slight to be detected with Galileo's small telescope.
== Apparent motion ==
=== From Earth ===
When standing on the Earth looking up at the sky, it would appear that the Moon travels from east to west, just as the Sun and the stars do. Day after day however, the Moon appears to move to the east with respect to the stars. In fact, the Moon orbits the Earth from west to east, as do the vast majority of manmade satellites such as the International Space Station. The apparent westward motion of the Moon from the Earth's surface is actually an artifact of its being in a supersynchronous orbit. This means that the Earth completes one sidereal rotation before the Moon is able to complete one orbit. As a result, it looks like the Moon is travelling in the opposite direction, otherwise known as apparent retrograde motion. A person standing on Earth "catches up" to the Moon and passes it because the Earth completes one rotation before the Moon completes one orbit.
This phenomenon also occurs on Mars, which has two natural satellites, Phobos and Deimos. Both moons orbit Mars in an eastward (prograde) direction; however, Deimos has an orbital period of 1.23 Martian sidereal days, making it supersynchronous, whereas Phobos has an orbital period of 0.31 Martian sidereal days, making it subsynchronous. Consequently, although both moons are traveling in an eastward (prograde) direction, they appear to be traveling in opposite directions when viewed from the surface of Mars due to their orbital periods in relation to the rotational period of the planet.
All other planetary bodies in the Solar System also appear to periodically switch direction as they cross Earth's sky. Though all stars and planets
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to move from east to west on a nightly basis in response to the rotation of Earth, the outer planets generally drift slowly eastward relative to the stars. Asteroids and Kuiper Belt objects (including Pluto) exhibit apparent retrograde motion. This motion is normal for the planets, and so is considered direct motion. However, since Earth completes its orbit in a shorter period of time than the planets outside its orbit, it periodically overtakes them, like a faster car on a multi-lane highway. When this occurs, the planet being passed will first appear to stop its eastward drift, and then drift back toward the west. Then, as Earth swings past the planet in its orbit, it appears to resume its normal motion west to east.Inner planets Venus and Mercury appear to move in retrograde in a similar mechanism, but as they can never be in opposition to the Sun as seen from Earth, their retrograde cycles are tied to their inferior conjunctions with the Sun. They are unobservable in the Sun's glare and in their "new" phase, with mostly their dark sides toward Earth; they occur in the transition from evening star to morning star.
The more distant planets retrograde more frequently, as they do not move as much in their orbits while Earth completes an orbit itself. The retrograde motion of a hypothetical extremely distant (and nearly non-moving) planet would take place during a half-year, with the planet's apparent yearly motion being reduced to a parallax ellipse.
The center of the retrograde motion occurs at the planet's opposition which is when the planet is exactly opposite the Sun. This position is halfway, or 6 months, around the ecliptic from the Sun. The planet's height in the sky is opposite that of the Sun's height. The planet is at its highest at the winter solstice, and at its lowest at the summer solstice, on those (rare) occasions when it passes through the center of its retrograde motion near a solstice. Note particularly that the hemisphere the observer is in is critical to what they observe. The December Solstice will place the planet high in the northern hemisphere sky where it is winter and place it low in the southern hemisphere sky where it is summer. The opposite is true if this happens at the June Solstice.
Since the planet's opposition retrograde motion is when the Earth passes closest, the planet appears at its brightest for the year.
The period between the center of such retrogradations is the synodic period of the planet.
=== From Mercury ===
From any point on the daytime surface of Mercury when the planet is near perihelion (closest approach to the Sun), the Sun undergoes apparent retrograde motion. This occurs because, from approximately four Earth days before perihelion until approximately four Earth days after it, Mercury's angular orbital speed exceeds its angular rotational velocity. Mercury's elliptical orbit is farther from circular than that of any other planet in the Solar System, resulting in a substantially higher orbital speed near perihelion. As a result, at specific points on Mercury's surface an observer would be able to see the Sun rise part way, then reverse and set before rising again, all within the same Mercurian day.
== See also ==
Deferent and epicycle
Retrograde and prograde motion
Hipparchus
Ptolemy
Shen Kuo
Spherical astronomy
Wei Pu
== References ==
== External links ==
NASA Astronomy Picture of the Day: Composite photograph of the 2009/2010 retrograde motion of Mars (13 June 2010)
Animated explanation of the mechanics of a retrograde orbit of a planet Archived 2013-10-05 at the Wayback Machine, University of South Wales
NASA: Mars retrograde motion
Double sunrises, 3DS Max Animation – illustrating the case of Mercury (the animation of an imaginary apparent retrograde motion of the Sun as seen from Earth begins at 1:35)
Mars Looping – The Retrograde Motion of Mars – 2018
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A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
Air-breathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle—this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high-speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.
The thrust of a typical jetliner engine went from 5,000 lbf (22 kN) (de Havilland Ghost turbojet) in the 1950s to 115,000 lbf (510 kN) (General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops.
== History ==
The principle of the jet engine is not new; however, the technical advances necessary to make the idea work did not come to fruition until the 20th century.
A rudimentary demonstration of jet power dates back to the aeolipile, a device described by Hero of Alexandria in 1st-century Egypt. This device directed steam power through two nozzles to cause a sphere to spin rapidly on its axis. It was seen as a curiosity. Meanwhile, practical applications of the turbine can be seen in the water wheel and the windmill.
Historians have further traced the theoretical origin of the principles of jet engines to traditional Chinese firework and rocket propulsion systems. Such devices' use for flight is documented in the story of Ottoman soldier Lagâri Hasan Çelebi, who reportedly achieved flight using a cone-shaped rocket in 1633.
The earliest attempts at airbreathing jet engines were hybrid designs in which an external power source first compressed air, which was then mixed with fuel and burned for jet thrust. The Italian Caproni Campini N.1, and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II were unsuccessful.
Even before the start of World War II, engineers were beginning to realize that engines driving propellers were approaching limits due to issues related to propeller efficiency, which declined as blade tips approached the speed of sound. If aircraft performance were to increase beyond such a barrier, a different propulsion mechanism was necessary. This was the motivation behind the development of the gas turbine engine, the most common form of jet engine.
The key to a practical jet engine was the gas turbine, extracting power from the engine itself to drive the compressor. The gas turbine was not a new idea: the patent for a stationary turbine was granted to John Barber in England in 1791. The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer Ægidius Elling. Such engines did not reach manufacture due to issues of safety, reliability, weight and, especially, sustained operation.
The first patent for using a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume. His engine was an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. Alan Arnold Griffith published An Aerodynamic Theory of Turbine Design in 1926 leading to experimental work at the RAE.
In 1928, RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929, he developed his ideas further. On 16 January 1930, in England, Whittle submitted his first patent (granted in 1932). The patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Practical axial compressors were made possible by ideas from A.A.Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). Whittle would later concentrate on the simpler centrifugal compressor only. Whittle was unable to
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the government in his invention, and development continued at a slow pace.
In Spain, pilot and engineer Virgilio Leret Ruiz was granted a patent for a jet engine design in March 1935. Republican president Manuel Azaña arranged for initial construction at the Hispano-Suiza aircraft factory in Madrid in 1936, but Leret was executed months later by Francoist Moroccan troops after unsuccessfully defending his seaplane base on the first days of the Spanish Civil War. His plans, hidden from Francoists, were secretly given to the British embassy in Madrid a few years later by his wife, Carlota O'Neill, upon her release from prison.
In 1935, Hans von Ohain started work on a similar design to Whittle's in Germany, both compressor and turbine being radial, on opposite sides of the same disc, initially unaware of Whittle's work. Von Ohain's first device was strictly experimental and could run only under external power, but he was able to demonstrate the basic concept. Ohain was then introduced to Ernst Heinkel, one of the larger aircraft industrialists of the day, who immediately saw the promise of the design. Heinkel had recently purchased the Hirth engine company, and Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure. Their subsequent designs culminated in the gasoline-fuelled HeS 3 of 5 kN (1,100 lbf), which was fitted to Heinkel's simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939, from Rostock-Marienehe aerodrome, an impressively short time for development. The He 178 was the world's first jet plane. Heinkel applied for a US patent covering the Aircraft Power Plant by Hans Joachim Pabst von Ohain on May 31, 1939; patent number US2256198, with M Hahn referenced as inventor. Von Ohain's design, an axial-flow engine, as opposed to Whittle's centrifugal flow engine, was eventually adopted by most manufacturers by the 1950s.
Austrian Anselm Franz of Junkers' engine division (Junkers Motoren or "Jumo") introduced the axial-flow compressor in their jet engine. Jumo was assigned the next engine number in the RLM 109-0xx numbering sequence for gas turbine aircraft powerplants, "004", and the result was the Jumo 004 engine. After many lesser technical difficulties were solved, mass production of this engine started in 1944 as a powerplant for the world's first jet-fighter aircraft, the Messerschmitt Me 262 (and later the world's first jet-bomber aircraft, the Arado Ar 234). A variety of reasons conspired to delay the engine's availability, causing the fighter to arrive too late to improve Germany's position in World War II, however this was the first jet engine to be used in service.
Meanwhile, in Britain the Gloster E28/39 had its maiden flight on 15 May 1941 and the Gloster Meteor finally entered service with the RAF in July 1944. These were powered by turbojet engines from Power Jets Ltd., set up by Frank Whittle. The first two operational turbojet aircraft, the Messerschmitt Me 262 and then the Gloster Meteor entered service within three months of each other in 1944; the Me 262 in April and the Gloster Meteor in July. The Meteor only saw around 15 aircraft enter World War II action, while up to 1400 Me 262 were produced, with 300 entering combat, delivering the first ground attacks and air combat victories of jet planes.
Following the end of the war the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed-wing aircraft have had some inspiration from this design.
By the 1950s, the jet engine was almost universal in combat aircraft, with the exception of cargo, liaison and other specialty types. By this point, some of the British designs were already cleared for civilian use, and had appeared on early models like the de Havilland Comet and Avro Canada Jetliner. By the 1960s, all large civilian aircraft were also jet powered, leaving the piston engine in low-cost niche roles such as cargo flights.
The efficiency of turbojet engines was still rather worse than piston engines, but by the 1970s, with the advent of high-bypass turbofan jet engines (an innovation not foreseen by the early commentators such as Edgar Buckingham, at high speeds and high altitudes that seemed absurd to them), fuel efficiency was about the same as the best piston and propeller engines.
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== Uses ==
Jet engines power jet aircraft, cruise missiles and unmanned aerial vehicles. In the form of rocket engines they power model rocketry, spaceflight, and military missiles.
Jet engines have propelled high speed cars, particularly drag racers, with the all-time record held by a rocket car. A turbofan powered car, ThrustSSC, currently holds the land speed record.
Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines or marine powerplants. These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower. Many of these engines are derived from older military turbojets such as the Pratt & Whitney J57 and J75 models. There is also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 horsepower (HP)
.
Jet engines are also sometimes developed into, or share certain components such as engine cores, with turboshaft and turboprop engines, which are forms of gas turbine engines that are typically used to power helicopters and some propeller-driven aircraft.
== Types of jet engine ==
There are a large number of different types of jet engines, all of which achieve forward thrust from the principle of jet propulsion.
=== Airbreathing ===
Commonly aircraft are propelled by airbreathing jet engines. Most airbreathing jet engines that are in use are turbofan jet engines, which give good efficiency at speeds just below the speed of sound.
==== Turbojet ====
A turbojet engine is a gas turbine engine that works by compressing air with an inlet and a compressor (axial, centrifugal, or both), mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure air through a turbine and a nozzle. The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to increased momentum of the gas flowing through the engine, producing thrust. All the air entering the compressor is passed through the combustor, and turbine, unlike the turbofan engine described below.
==== Turbofan ====
Turbofans differ from turbojets in that they have an additional fan at the front of the engine, which accelerates air in a duct bypassing the core gas turbine engine. Turbofans are the dominant engine type for medium and long-range airliners.
Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more drag. Therefore, in supersonic flight, and in military and other aircraft where other considerations have a higher priority than fuel efficiency, fans tend to be smaller or absent.
Because of these distinctions, turbofan engine designs are often categorized as low-bypass or high-bypass, depending upon the amount of air which bypasses the core of the engine. Low-bypass turbofans have a bypass ratio of around 2:1 or less.
==== Propfan ====
A propfan engine is a type of airbreathing jet engine which combines aspects of turboprop and turbofan. Its design consists of a central gas turbine which drives open-air contra-rotating propellers. Unlike turboprop engines, in which the propeller and the engine are considered two separate products, the propfan’s gas generator and its unshrouded propeller module are heavily integrated and are considered to be a single product. Additionally, the propfan’s short, heavily twisted variable pitch blades closely remember the ducted fan blades of turbofan engines.
Propfans are designed to offer the speed and performance of turbofan engines with fuel efficiency of turboprops. However, due to low fuel costs and high cabin noise, early propfan projects were abandoned. Very few aircraft have flown with propfans, with the Antonov An-70 being the first and only aircraft to fly while being powered solely by propfan engines.
==== Advanced technology engine ====
The term Advanced technology engine refers to the modern generation of jet engines. The principle is that a turbine engine will function more efficiently if the various sets of turbines can revolve at their individual optimum speeds, instead of at the same speed. The true advanced technology engine has a triple spool, meaning that instead of having a single drive shaft, there are three, in order that the three sets of blades may revolve at different speeds. An interim state is a twin-spool engine, allowing only two different speeds for the turbines.
==== Ram compression ====
Ram compression jet engines are airbreathing
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similar to gas turbine engines in so far as they both use the Brayton cycle. Gas turbine and ram compression engines differ, however, in how they compress the incoming airflow. Whereas gas turbine engines use axial or centrifugal compressors to compress incoming air, ram engines rely only on air compressed in the inlet or diffuser. A ram engine thus requires a substantial initial forward airspeed before it can function. Ramjets are considered the simplest type of air breathing jet engine because they have no moving parts in the engine proper, only in the accessories.
Scramjets differ mainly in the fact that the air does not slow to subsonic speeds. Rather, they use supersonic combustion. They are efficient at even higher speed. Very few have been built or flown.
==== Non-continuous combustion ====
== Other types of jet propulsion ==
=== Rocket ===
The rocket engine uses the same basic physical principles of thrust as a form of reaction engine, but is distinct from the jet engine in that it does not require atmospheric air to provide oxygen; the rocket carries all components of the reaction mass. However some definitions treat it as a form of jet propulsion.
Because rockets do not breathe air, this allows them to operate at arbitrary altitudes and in space.
This type of engine is used for launching satellites, space exploration and crewed access, and permitted landing on the Moon in 1969.
Rocket engines are used for high altitude flights, or anywhere where very high accelerations are needed since rocket engines themselves have a very high thrust-to-weight ratio.
However, the high exhaust speed and the heavier, oxidizer-rich propellant results in far more propellant use than turbofans. Even so, at extremely high speeds they become energy-efficient.
An approximate equation for the net thrust of a rocket engine is:
F
N
=
m
˙
g
0
I
sp,vac
−
A
e
p
{\displaystyle F_{N}={\dot {m}}\,g_{0}\,I_{\text{sp,vac}}-A_{e}\,p\;}
Where
F
N
{\displaystyle F_{N}}
is the net thrust,
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I
sp,vac
{\displaystyle I_{\text{sp,vac}}}
is the specific impulse,
g
0
{\displaystyle g_{0}}
is a standard gravity,
m
˙
{\displaystyle {\dot {m}}}
is the propellant flow in kg/s,
A
e
{\displaystyle A_{e}}
is the cross-sectional area at the exit of the exhaust nozzle, and
p
{\displaystyle p}
is the atmospheric pressure.
=== Hybrid ===
Combined-cycle engines simultaneously use two or more different principles of jet propulsion.
=== Water jet ===
A water jet, or pump-jet, is a marine propulsion system that uses a jet of water. The mechanical arrangement may be a ducted propeller with nozzle, or a centrifugal compressor and nozzle. The pump-jet must be driven by a separate engine such as a Diesel or gas turbine.
== General physical principles ==
All jet engines are reaction engines that generate thrust by emitting a jet of fluid rearwards at relatively high speed. The forces on the inside of the engine needed to create this jet give a strong thrust on the engine which pushes the craft forwards.
Jet engines make their jet from propellant stored in tanks that are attached to the engine (as in a 'rocket') as well as in duct engines (those commonly used on aircraft) by ingesting an external fluid (very typically air) and expelling it at higher speed.
=== Propelling nozzle ===
A propelling nozzle produces a high velocity exhaust jet. Propelling nozzles turn internal and pressure energy into high velocity kinetic energy. The total pressure and temperature don't change through the nozzle but their static values drop as the gas speeds up.
The velocity of the air entering the nozzle is low, about Mach 0.4, a prerequisite for minimizing pressure losses in the duct leading to the nozzle. The temperature entering the nozzle may be as low as sea level ambient for a fan nozzle in the cold air at cruise altitudes. It may be as high as the 1000 Kelvin exhaust gas temperature for a supersonic afterburning engine or 2200 K with afterburner lit. The pressure entering the nozzle may vary from 1.5 times the pressure outside the nozzle, for a single stage fan, to 30 times for the fastest manned aircraft at Mach 3+.
Convergent nozzles are only able to accelerate the gas up to local sonic (Mach 1) conditions. To reach high flight speeds, even greater exhaust velocities are required, and so a convergent-divergent nozzle is needed on high-speed aircraft.
The engine thrust is highest if the static pressure of the gas reaches the ambient value as it leaves the nozzle. This only happens if the nozzle exit area is the correct value for the nozzle pressure ratio (npr). Since the npr changes with engine thrust
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and flight speed this is seldom the case. Also at supersonic speeds the divergent area is less than required to give complete internal expansion to ambient pressure as a trade-off with external body drag. Whitford gives the F-16 as an example. Other underexpanded examples were the XB-70 and SR-71.
The nozzle size, together with the area of the turbine nozzles, determines the operating pressure of the compressor.
=== Thrust ===
=== Energy efficiency relating to aircraft jet engines ===
This overview highlights where energy losses occur in complete jet aircraft powerplants or engine installations.
A jet engine at rest, as on a test stand, sucks in fuel and generates thrust. How well it does this is judged by how much fuel it uses and what force is required to restrain it. This is a measure of its efficiency. If something deteriorates inside the engine (known as performance deterioration) it will be less efficient and this will show when the fuel produces less thrust. If a change is made to an internal part which allows the air/combustion gases to flow more smoothly the engine will be more efficient and use less fuel. A standard definition is used to assess how different things change engine efficiency and also to allow comparisons to be made between different engines. This definition is called specific fuel consumption, or how much fuel is needed to produce one unit of thrust. For example, it will be known for a particular engine design that if some bumps in a bypass duct are smoothed out the air will flow more smoothly giving a pressure loss reduction of x% and y% less fuel will be needed to get the take-off thrust, for example. This understanding comes under the engineering discipline Jet engine performance. How efficiency is affected by forward speed and by supplying energy to aircraft systems is mentioned later.
The efficiency of the engine is controlled primarily by the operating conditions inside the engine which are the pressure produced by the compressor and the temperature of the combustion gases at the first set of rotating turbine blades. The pressure is the highest air pressure in the engine. The turbine rotor temperature is not the highest in the engine but is the highest at which energy transfer takes place ( higher temperatures occur in the combustor). The above pressure and temperature are shown on a Thermodynamic cycle diagram.
The efficiency is further modified by how smoothly the air and the combustion gases flow through the engine, how well the flow is aligned (known as incidence angle) with the moving and stationary passages in the compressors and turbines. Non-optimum angles, as well as non-optimum passage and blade shapes can cause thickening and separation of Boundary layers and formation of Shock waves. It is important to slow the flow (lower speed means less pressure losses or Pressure drop) when it travels through ducts connecting the different parts. How well the individual components contribute to turning fuel into thrust is quantified by measures like efficiencies for the compressors, turbines and combustor and pressure losses for the ducts. These are shown as lines on a Thermodynamic cycle diagram.
The engine efficiency, or thermal efficiency, known as
η
t
h
{\displaystyle \eta _{th}}
. is dependent on the Thermodynamic cycle parameters, maximum pressure and temperature, and on component efficiencies,
η
c
o
m
p
r
e
s
s
o
r
{\displaystyle \eta _{compressor}}
,
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η
c
o
m
b
u
s
t
i
o
n
{\displaystyle \eta _{combustion}}
and
η
t
u
r
b
i
n
e
{\displaystyle \eta _{turbine}}
and duct pressure losses.
The engine needs compressed air for itself just to run successfully. This air comes from its own compressor and is called secondary air. It does not contribute to making thrust so makes the engine less efficient. It is used to preserve the mechanical integrity of the engine, to stop parts overheating and to prevent oil escaping from bearings for example. Only some of this air taken from the compressors returns to the turbine flow to contribute to thrust production. Any reduction in the amount needed improves the engine efficiency. Again, it will be known for a particular engine design that a reduced requirement for cooling flow of x% will reduce the specific fuel consumption by y%. In other words, less fuel will be required to give take-off thrust, for example. The engine is more efficient.
All of the above considerations are basic to the engine running on its own and, at the same time, doing nothing useful, i.e. it is not moving an aircraft or supplying energy for the aircraft's electrical, hydraulic and air systems. In the aircraft the engine gives away some of its thrust-producing potential, or fuel, to power these systems. These requirements, which cause installation losses, reduce its efficiency. It is using some fuel that does not contribute to the engine's thrust.
Finally, when the aircraft is flying the propelling jet itself contains wasted kinetic energy after it has left the engine. This is quantified by the term propulsive, or Froude, efficiency
η
p
{\displaystyle \eta _{p}}
and may be reduced by redesigning the engine to give it bypass flow and a lower speed for the propelling jet, for example as a turboprop or turbofan engine. At the same time forward speed increases the
η
t
h
{\displaystyle \eta _{th}}
by increasing the Overall pressure ratio.
The overall efficiency of the engine at flight speed is defined as
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η
o
=
η
p
η
t
h
{\displaystyle \eta _{o}=\eta _{p}\eta _{th}}
.
The
η
o
{\displaystyle \eta _{o}}
at flight speed depends on how well the intake compresses the air before it is handed over to the engine compressors. The intake compression ratio, which can be as high as 32:1 at Mach 3, adds to that of the engine compressor to give the Overall pressure ratio and
η
t
h
{\displaystyle \eta _{th}}
for the Thermodynamic cycle. How well it does this is defined by its pressure recovery or measure of the losses in the intake. Mach 3 manned flight has provided an interesting illustration of how these losses can increase dramatically in an instant. The North American XB-70 Valkyrie and Lockheed SR-71 Blackbird at Mach 3 each had pressure recoveries of about 0.8, due to relatively low losses during the compression process, i.e. through systems of multiple shocks. During an 'unstart' the efficient shock system would be replaced by a very inefficient single shock beyond the inlet and an intake pressure recovery of about 0.3 and a correspondingly low pressure ratio.
The propelling nozzle at speeds above about Mach 2 usually has extra internal thrust losses because the exit area is not big enough as a trade-off with external afterbody drag.
Although a bypass engine improves propulsive efficiency it incurs losses of its own inside the engine itself. Machinery has to be added to transfer energy from the gas generator to a bypass airflow. The low loss from the propelling nozzle of a turbojet is added to with extra losses due to inefficiencies in the added turbine and fan. These may be included in a transmission, or transfer, efficiency
η
T
{\displaystyle \eta _{T}}
. However, these losses are more than made up by the improvement in propulsive efficiency. There are also extra pressure losses in the bypass duct and an extra propelling nozzle.
With the advent of turbofans with their loss-making machinery what goes on inside the engine has been separated by Bennett, for example, between gas generator and transfer machinery giving
η
|
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|
o
=
η
p
η
t
h
η
T
{\displaystyle \eta _{o}=\eta _{p}\eta _{th}\eta _{T}}
.
The energy efficiency (
η
o
{\displaystyle \eta _{o}}
) of jet engines installed in vehicles has two main components:
propulsive efficiency (
η
p
{\displaystyle \eta _{p}}
): how much of the energy of the jet ends up in the vehicle body rather than being carried away as kinetic energy of the jet.
cycle efficiency (
η
t
h
{\displaystyle \eta _{th}}
): how efficiently the engine can accelerate the jet
Even though overall energy efficiency
η
o
{\displaystyle \eta _{o}}
is:
η
o
=
η
p
η
t
|
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|
h
{\displaystyle \eta _{o}=\eta _{p}\eta _{th}}
for all jet engines the propulsive efficiency is highest as the exhaust jet velocity gets closer to the vehicle speed as this gives the smallest residual kinetic energy. For an airbreathing engine an exhaust velocity equal to the vehicle velocity, or a
η
p
{\displaystyle \eta _{p}}
equal to one, gives zero thrust with no net momentum change. The formula for air-breathing engines moving at speed
v
{\displaystyle v}
with an exhaust velocity
v
e
{\displaystyle v_{e}}
, and neglecting fuel flow, is:
η
p
=
2
1
+
v
e
v
{\displaystyle \eta _{p}={\frac {2}{1+{\frac {v_{e}}{v}}}}}
And for a rocket:
η
p
=
2
|
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|
(
v
v
e
)
1
+
(
v
v
e
)
2
{\displaystyle \eta _{p}={\frac {2\,({\frac {v}{v_{e}}})}{1+({\frac {v}{v_{e}}})^{2}}}}
In addition to propulsive efficiency, another factor is cycle efficiency; a jet engine is a form of heat engine. Heat engine efficiency is determined by the ratio of temperatures reached in the engine to that exhausted at the nozzle. This has improved constantly over time as new materials have been introduced to allow higher maximum cycle temperatures. For example, composite materials, combining metals with ceramics, have been developed for HP turbine blades, which run at the maximum cycle temperature. The efficiency is also limited by the overall pressure ratio that can be achieved. Cycle efficiency is highest in rocket engines (~60+%), as they can achieve extremely high combustion temperatures. Cycle efficiency in turbojet and similar is nearer to 30%, due to much lower peak cycle temperatures.
The combustion efficiency of most aircraft gas turbine engines at sea level takeoff conditions
is almost 100%. It decreases nonlinearly to 98% at altitude cruise conditions. Air-fuel ratio ranges from 50:1 to 130:1. For any type of combustion chamber there is a rich and weak limit to the air-fuel ratio, beyond which the flame is extinguished. The range of air-fuel ratio between the rich and weak limits is reduced with an increase of air velocity. If the
increasing air mass flow reduces the fuel ratio below certain value, flame extinction occurs.
=== Consumption of fuel or propellant ===
A closely related (but different) concept to energy efficiency is the rate of consumption of propellant mass. Pro
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ant consumption in jet engines is measured by specific fuel consumption, specific impulse, or effective exhaust velocity. They all measure the same thing. Specific impulse and effective exhaust velocity are strictly proportional, whereas specific fuel consumption is inversely proportional to the others.
For air-breathing engines such as turbojets, energy efficiency and propellant (fuel) efficiency are much the same thing, since the propellant is a fuel and the source of energy. In rocketry, the propellant is also the exhaust, and this means that a high energy propellant gives better propellant efficiency but can in some cases actually give lower energy efficiency.
It can be seen in the table (just below) that the subsonic turbofans such as General Electric's CF6 turbofan use a lot less fuel to generate thrust for a second than did the Concorde's Rolls-Royce/Snecma Olympus 593 turbojet. However, since energy is force times distance and the distance per second was greater for the Concorde, the actual power generated by the engine for the same amount of fuel was higher for the Concorde at Mach 2 than the CF6. Thus, the Concorde's engines were more efficient in terms of energy per distance traveled.
=== Thrust-to-weight ratio ===
The thrust-to-weight ratio of jet engines with similar configurations varies with scale, but is mostly a function of engine construction technology. For a given engine, the lighter the engine, the better the thrust-to-weight is, the less fuel is used to compensate for drag due to the lift needed to carry the engine weight, or to accelerate the mass of the engine.
As can be seen in the following table, rocket engines generally achieve much higher thrust-to-weight ratios than duct engines such as turbojet and turbofan engines. This is primarily because rockets almost universally use dense liquid or solid reaction mass which gives a much smaller volume and hence the pressurization system that supplies the nozzle is much smaller and lighter for the same performance. Duct engines have to deal with air which is two to three orders of magnitude less dense and this gives pressures over much larger areas, which in turn results in more engineering materials being needed to hold the engine together and for the air compressor.
=== Comparison of types ===
Propeller engines handle larger air mass flows, and give them smaller acceleration, than jet engines. Since the increase in air speed is small, at high flight speeds the thrust available to propeller-driven aeroplanes is small. However, at low speeds, these engines benefit from relatively high propulsive efficiency.
On the other hand, turbojets accelerate a much smaller mass flow of intake air and burned fuel, but they then reject it at very high speed. When a de Laval nozzle is used to accelerate a hot engine exhaust, the outlet velocity may be locally supersonic. Turbojets are particularly suitable for aircraft travelling at very high speeds.
Turbofans have a mixed exhaust consisting of the bypass air and the hot combustion product gas from the core engine. The amount of air that bypasses the core engine compared to the amount flowing into the engine determines what is called a turbofan's bypass ratio (BPR).
While a turbojet engine uses all of the engine's output to produce thrust in the form of a hot high-velocity exhaust gas jet, a turbofan's cool low-velocity bypass air yields between 30% and 70% of the total thrust produced by a turbofan system.
The net thrust (FN) generated by a turbofan can also be expanded as:
F
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{\displaystyle F_{N}={\dot {m}}_{e}v_{he}-{\dot {m}}_{o}v_{o}+BPR\,({\dot {m}}_{c}v_{f})}
where:
Rocket engines have extremely high exhaust velocity and thus are best suited for high speeds (hypersonic) and great altitudes. At any given throttle, the thrust and efficiency of a rocket motor improves slightly with increasing altitude (because the back-pressure falls thus increasing net thrust at the nozzle exit plane), whereas with a turbojet (or turbofan) the falling density of the air entering the intake (and the hot gases leaving the nozzle) causes the net thrust to decrease with increasing altitude. Rocket engines are more efficient than even scramjets above roughly Mach 15.
=== Altitude and speed ===
With the exception of scramjets, jet engines, deprived of their inlet systems can only accept air at around half the speed of sound. The inlet system's job for transonic and supersonic aircraft is to slow the air and perform some of the compression.
The limit on maximum altitude for engines is set by flammability – at very high altitudes the air becomes too thin to burn, or after compression, too hot. For turbojet engines altitudes of about 40 km appear to be possible, whereas for ramjet engines 55 km may be achievable. Scramjets may theoretically manage 75 km. Rocket engines of course have no upper limit.
At more modest altitudes, flying faster compresses the air at the front of the engine, and this greatly heats the air. The upper limit is usually thought to be about Mach 5–8, as above about Mach 5.5, the atmospheric nitrogen tends to react due to the high temperatures at the inlet and this consumes significant energy. The exception to this is scramjets which may be able to achieve about Mach 15 or more, as they avoid slowing the air, and rockets
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have no particular speed limit.
=== Noise ===
The noise emitted by a jet engine has many sources. These include, in the case of gas turbine engines, the fan, compressor, combustor, turbine and propelling jet/s.
The propelling jet produces jet noise which is caused by the violent mixing action of the high speed jet with the surrounding air. In the subsonic case the noise is produced by eddies and in the supersonic case by Mach waves. The sound power radiated from a jet varies with the jet velocity raised to the eighth power for velocities up to 600 m/s (2,000 ft/s) and varies with the velocity cubed above 600 m/s (2,000 ft/s). Thus, the lower speed exhaust jets emitted from engines such as high bypass turbofans are the quietest, whereas the fastest jets, such as rockets, turbojets, and ramjets, are the loudest. For commercial jet aircraft the jet noise has reduced from the turbojet through bypass engines to turbofans as a result of a progressive reduction in propelling jet velocities. For example, the JT8D, a bypass engine, has a jet velocity of 400 m/s (1,450 ft/s) whereas the JT9D, a turbofan, has jet velocities of 300 m/s (885 ft/s) (cold) and 400 m/s (1,190 ft/s)(hot).
The advent of the turbofan replaced the very distinctive jet noise with another sound known as "buzz saw" noise. The origin is the shockwaves originating at the supersonic fan blade tip at takeoff thrust.
=== Cooling ===
Adequate heat transfer away from the working parts of the jet engine is critical to maintaining strength of engine materials and ensuring long life for the engine.
After 2016, research is ongoing in the development of transpiration cooling techniques to jet engine components.
== Operation ==
In a jet engine, each major rotating section usually has a separate gauge devoted to monitoring its speed of rotation.
Depending on the make and model, a jet engine may have an N1 gauge that monitors the low-pressure compressor section and/or fan speed in turbofan engines. The gas generator section may be monitored by an N2 gauge, while triple spool engines may have an N3 gauge as well. Each engine section rotates at many thousands RPM. Their gauges therefore are calibrated in percent of a nominal speed rather than actual RPM, for ease of display and interpretation.
== See also ==
Air turboramjet
Balancing machine
Components of jet engines
Intake momentum drag
Rocket engine nozzle
Rocket turbine engine
Spacecraft propulsion
Thrust reversal
Turbojet development at the RAE
Variable cycle engine
Water injection (engine)
== Notes ==
== References ==
=== Bibliography ===
== External links ==
Media related to Jet engines at Wikimedia Commons
The dictionary definition of jet engine at Wiktionary
Media about jet engines from Rolls-Royce
How Stuff Works article on how a Gas Turbine Engine works
Influence of the Jet Engine on the Aerospace Industry
An Overview of Military Jet Engine History, Appendix B, pp. 97–120, in Military Jet Engine Acquisition (Rand Corp., 24 pp, PDF)
Basic jet engine tutorial (QuickTime Video)
An article on how reaction engine works
The Aircraft Gas Turbine Engine and Its Operation: Installation Engineering. East Hartford, Connecticut: United Aircraft Corporation. February 1958. Retrieved 29 September 2021.
Fusion Powered Jet Engine and Airplane
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The RQ-3 DarkStar (known as Tier III- or "Tier three minus" during development) is an unmanned aerial vehicle (UAV). Its first flight was on March 29, 1996. The Department of Defense terminated DarkStar in January 1999, after determining the UAV was not aerodynamically stable and was not meeting cost and performance objectives.
== Design and development ==
The RQ-3 DarkStar was designed as a "high-altitude endurance UAV", and incorporated stealth aircraft technology to make it difficult to detect, which allowed it to operate within heavily defended airspace, unlike the Northrop Grumman RQ-4 Global Hawk, which is unable to operate except under conditions of air supremacy. The DarkStar was fully autonomous: it could take off, fly to its target, operate its sensors, transmit information, return and land without human intervention. Human operators, however, could change the DarkStar's flight plan and sensor orientation through radio or satellite relay. The RQ-3 carried either an optical sensor or radar, and could send digital information to a satellite while still in flight. It used a single airbreathing jet engine of unknown type for propulsion. One source claims it used a Williams-Rolls-Royce FJ44-1A turbofan engine.
The first prototype made its first flight on March 29, 1996, but its second flight, on April 22, 1996, ended in a crash shortly after takeoff. A modified, more stable design (the RQ-3A) first flew on June 29, 1998, and made a total of five flights before the program was canceled just prior to the sixth and final flight planned for the airworthiness test phase. Two additional RQ-3As were built, but never made any flights before program cancellation.
The "R" is the Department of Defense designation for reconnaissance; "Q" means unmanned aircraft system. The "3" refers to it being the third of a series of purpose-built unmanned reconnaissance aircraft systems.
Although the RQ-3 was terminated on January 28, 1999, a July 2003 Aviation Week and Space Technology article reported in April 2003 that a derivative of the RQ-3 had been used in the 2003 invasion of Iraq. There has been no independent confirmation.
== Survivors ==
The second RQ-3A (A/V #2) is at the National Museum of the United States Air Force at Wright-Patterson AFB in Dayton, Ohio. Although part of the Museum's Research & Development Gallery, it is displayed hanging over the C-130E in Building 4's Global Reach Gallery.
The third RQ-3A (A/V #3) is on display in the Great Gallery of the Museum of Flight in Seattle, Washington.
The fourth RQ-3A (which never flew before the program ended) is held by the Smithsonian National Air and Space Museum in Washington, D.C., but is not on display.
== Specifications ==
General characteristics
Length: 15 ft 0 in (4.6 m)
Wingspan: 69 ft 0 in (21.3 m)
Height: 3 ft 6 in (1.1 m)
Empty weight: 4,360 lb (1,980 kg)
Gross weight: 8,500 lb (3,860 kg)
Powerplant: 1 × Williams-Rolls-Royce FJ44-1A turbofan, 1,900 lbf (8.5 kN) thrust
Performance
Cruise speed: 288 mph (464 km/h, 250 kn)
Range: 575 mi (925 km, 500 nmi)
Service ceiling: 45,000 ft (13,500 m)
== See also ==
Unmanned combat aerial vehicle
Aircraft of comparable role, configuration, and era
General Atomics MQ-9 Reaper (also known as the Predator B)
Lockheed Martin RQ-170 Sentinel
BAE Systems Corax
Dassault nEUROn
EADS Barracuda
Related lists
List of unmanned aerial vehicles
List of military aircraft of the United States
== References ==
== External links ==
DarkStar Tier III- from NASA Dryden Flight Center
DarkStar Tier III Minus
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Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking over long distances. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable.
The technology is useful where the physical connections are impractical due to high costs or other considerations.
== History ==
Optical communications, in various forms, have been used for thousands of years. The ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients.
In 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter created the photophone, at Bell's newly established Volta Laboratory in Washington, DC. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light. On June 3, 1880, Bell conducted the world's first wireless telephone transmission between two buildings, some 213 meters (699 feet) apart.
Its first practical use came in military communication systems many decades later, first for optical telegraphy. German colonial troops used heliograph telegraphy transmitters during the Herero Wars starting in 1904, in German South-West Africa (today's Namibia) as did British, French, US or Ottoman signals.
During the trench warfare of World War I when wire communications were often cut, German signals used three types of optical Morse transmitters called Blinkgerät, the intermediate type for distances of up to 4 km (2.5 mi) at daylight and of up to 8 km (5.0 mi) at night, using red filters for undetected communications. Optical telephone communications were tested at the end of the war, but not introduced at troop level. In addition, special blinkgeräts were used for communication with airplanes, balloons, and tanks, with varying success.
A major technological step was to replace the Morse code by modulating optical waves in speech transmission. Carl Zeiss, Jena developed the Lichtsprechgerät 80/80 (literal translation: optical speaking device) that the German army used in their World War II anti-aircraft defense units, or in bunkers at the Atlantic Wall.
The invention of lasers in the 1960s revolutionized free-space optics. Military organizations were particularly interested and boosted their development. In 1973, while prototyping the first laser printers at PARC, Gary Starkweather and others made a duplex 30 Mbit/s CAN optical link using astronomical telescopes and HeNe lasers to send data between offices; they chose the method due partly to less strict regulations (at the time) on free-space optical communication by the FCC. However, laser-based free-space optics lost market momentum when the installation of optical fiber networks for civilian uses was at its peak.
Many simple and inexpensive consumer remote controls use low-speed communication using infrared (IR) light. This is known as consumer IR technologies.
== Usage and technologies ==
Free-space point-to-point optical links can be implemented using infrared laser light, although low-data-rate communication over short distances is possible using LEDs. Infrared Data Association (IrDA) technology is a very simple form of free-space optical communications. On the communications side the FSO technology is considered as a part of the optical wireless communications applications. Free-space optics can be used for communications between spacecraft.
=== Useful distances ===
The reliability of FSO units has always been a problem for commercial telecommunications. Consistently, studies find too many dropped packets and signal errors over small ranges (400 to 500 meters (1,300 to 1,600 ft)). This is from both independent studies, such as in the Czech Republic, as well as internal studies, such as one conducted by MRV FSO staff.
Military based studies consistently produce longer estimates for reliability, projecting the maximum range for terrestrial links is of the order of 2 to 3 km (1.2 to 1.9 mi). All studies agree the stability and quality of the link is highly dependent on atmospheric factors such as rain, fog, dust and heat. Relays may be employed to extend the range for FSO communications.
TMEX USA ran two eight-mile links between Laredo, Texas and Nuevo Laredo, Mexico from 1998 to 2002. The links operated at 155 Mbit/s and reliably carried phone calls and internet service.
=== Extending the useful distance ===
The main reason terrestrial communications have been limited to non-commercial telecommunications functions is fog. Fog often prevents FSO laser links over 500 meters (1,600 ft) from achieving a year-round availability sufficient for commercial services. Several entities are continually attempting to overcome these key
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to FSO communications and field a system with a better quality of service. DARPA has sponsored over US$130 million in research toward this effort, with the ORCA and ORCLE programs.
Other non-government groups are fielding tests to evaluate different technologies that some claim have the ability to address key FSO adoption challenges. As of October 2014, none have fielded a working system that addresses the most common atmospheric events.
FSO research from 1998 to 2006 in the private sector totaled $407.1 million, divided primarily among four start-up companies. All four failed to deliver products that would meet telecommunications quality and distance standards:
Terabeam received approximately $575 million in funding from investors such as Softbank, Mobius Venture Capital and Oakhill Venture Partners. AT&T and Lucent backed this attempt. The work ultimately failed, and the company was purchased in 2004 for $52 million (excluding warrants and options) by Falls Church, Virginia-based YDI, effective June 22, 2004, and used the name Terabeam for the new entity. On September 4, 2007, Terabeam (then headquartered in San Jose, California) announced it would change its name to Proxim Wireless Corporation, and change its NASDAQ stock symbol from TRBM to PRXM.
AirFiber received $96.1 million in funding, and never solved the weather issue. They sold out to MRV communications in 2003, and MRV sold their FSO units until 2012 when the end-of-life was abruptly announced for the Terescope series.
LightPointe Communications received $76 million in start-up funds, and eventually reorganized to sell hybrid FSO-RF units to overcome the weather-based challenges.
The Maxima Corporation published its operating theory in Science, and received $9 million in funding before permanently shutting down. No known spin-off or purchase followed this effort.
Wireless Excellence developed and launched CableFree UNITY solutions that combine FSO with millimeter wave and radio technologies to extend distance, capacity and availability, with a goal of making FSO a more useful and practical technology.
One private company published a paper on November 20, 2014, claiming they had achieved commercial reliability (99.999% availability) in extreme fog. There is no indication this product is currently commercially available.
=== Extraterrestrial ===
The massive advantages of laser communication in space have multiple space agencies racing to develop a stable space communication platform, with many significant demonstrations and achievements.
==== Operational systems ====
The first gigabit laser-based communication was achieved by the European Space Agency and called the European Data Relay System (EDRS) on November 28, 2014. The system is operational and is being used on a daily basis.
In December 2023, the Australian National University (ANU) demonstrated its Quantum Optical Ground Station at its Mount Stromlo Observatory. QOGS uses adaptive optics and lasers as part of a telescope, to create a bi-directional communications system capable of supporting the NASA Artemis program to the Moon.
==== Demonstrations ====
A two-way distance record for communication was set by the Mercury laser altimeter instrument aboard the MESSENGER spacecraft. It was able to communicate across a distance of 24 million km (15 million mi), as the craft neared Earth on a fly-by in May 2005. The previous record had been set with a one-way detection of laser light from Earth by the Galileo probe, of 6 million km (3.7 million mi) in 1992.
In January 2013, NASA used lasers to beam an image of the Mona Lisa to the Lunar Reconnaissance Orbiter roughly 390,000 km (240,000 mi) away. To compensate for atmospheric interference, an error correction code algorithm similar to that used in CDs was implemented.
In the early morning hours of October 18, 2013, NASA's Lunar Laser Communication Demonstration (LLCD) transmitted data from lunar orbit to Earth at a rate of 622 megabits per second (Mbit/s). LLCD was flown aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, whose primary science mission was to investigate the tenuous and exotic atmosphere that exists around the Moon.
Between April and July 2014 NASA's OPALS instrument successfully uploaded 175 megabytes in 3.5 seconds and downloaded 200–300 MB in 20 s. Their system was also able to re-acquire tracking after the signal was lost due to cloud cover.
On December 7, 2021 NASA launched the Laser Communications Relay Demonstration (LCRD), which aims to relay data between spacecraft in geosynchronous orbit and ground stations. LCRD is NASA's first two-way, end-to-end optical relay. LCRD uses two ground stations, Optical Ground Station (OGS)-1 and -2, at Table Mountain Observatory in California, and Haleakalā, Hawaii. One of LCRD's
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operational users is the Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T), on the International Space Station. The terminal will receive high-resolution science data from experiments and instruments on board the space station and then transfer this data to LCRD, which will then transmit it to a ground station. After the data arrives on Earth, it will be delivered to mission operation centers and mission scientists. The ILLUMA-T payload was sent to the ISS in late 2023 on SpaceX CRS-29, and achieved first light on December 5, 2023.
On April 28, 2023, NASA and its partners achieved 200 gigabit per second (Gbit/s) throughput on a space-to-ground optical link between a satellite in orbit and Earth. This was achieved by the TeraByte InfraRed Delivery (TBIRD) system, mounted on NASA's Pathfinder Technology Demonstrator 3 (PTD-3) satellite.
==== Commercial use ====
Various satellite constellations that are intended to provide global broadband coverage, such as SpaceX Starlink, employ laser communication for inter-satellite links. This effectively creates a space-based optical mesh network between the satellites.
== LEDs ==
In 2001, Twibright Labs released RONJA Metropolis, an open-source DIY 10 Mbit/s full-duplex LED FSO system that can span 1.4 km (0.87 mi).
In 2004, a visible light communication consortium was formed in Japan. This was based on work from researchers that used a white LED-based space lighting system for indoor local area network (LAN) communications. These systems present advantages over traditional UHF RF-based systems from improved isolation between systems, the size and cost of receivers/transmitters, RF licensing laws and by combining space lighting and communication into the same system. In January 2009, a task force for visible light communication was formed by the Institute of Electrical and Electronics Engineers working group for wireless personal area network standards known as IEEE 802.15.7. A trial was announced in 2010, in St. Cloud, Minnesota.
Amateur radio operators have achieved significantly farther distances using incoherent sources of light from high-intensity LEDs. One reported 278 km (173 mi) in 2007. However, physical limitations of the equipment used limited bandwidths to about 4 kHz. The high sensitivities required of the detector to cover such distances made the internal capacitance of the photodiode used a dominant factor in the high-impedance amplifier which followed it, thus naturally forming a low-pass filter with a cut-off frequency in the 4 kHz range. Lasers can reach very high data rates which are comparable to fiber communications.
Projected data rates and future data rate claims vary. A low-cost white LED (GaN-phosphor) which could be used for space lighting can typically be modulated up to 20 MHz. Data rates of over 100 Mbit/s can be achieved using efficient modulation schemes and Siemens claimed to have achieved over 500 Mbit/s in 2010. Research published in 2009, used a similar system for traffic control of automated vehicles with LED traffic lights.
In September 2013, pureLiFi, the Edinburgh start-up working on Li-Fi, also demonstrated high speed point-to-point connectivity using any off-the-shelf LED light bulb. In previous work, high bandwidth specialist LEDs have been used to achieve the high data rates. The new system, the Li-1st, maximizes the available optical bandwidth for any LED device, thereby reducing the cost and improving the performance of deploying indoor FSO systems.
== Engineering details ==
Typically, the best scenarios for using this technology are:
LAN-to-LAN connections on campuses at Fast Ethernet or Gigabit Ethernet speeds
LAN-to-LAN connections in a city, a metropolitan area network
To cross a public road or other barriers which the sender and receiver do not own
Speedy service delivery of high-bandwidth access to optical fiber networks
Converged voice-data connection
Temporary network installation (for events or other purposes)
Reestablish high-speed connection quickly (disaster recovery)
As an alternative or add-on to existing wireless technologies
Especially powerful in combination with automatic aiming systems, in moving vehicles
As a safety add-on for important fiber connections (redundancy)
For communications between spacecraft, including elements of a satellite constellation
For inter- and intra-chip communication
The light beam can be very narrow, which makes FSO hard to intercept, improving security. Encryption can secure the data traversing the link. FSO provides vastly improved electromagnetic interference (EMI) behavior compared to using microwaves.
=== Technical advantages ===
Ease of deployment
Can be used to power devices
License-free long-range operation (in contrast with radio communication)
High bit rates
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bit error rates
Immunity to electromagnetic interference
Full-duplex operation
Protocol transparency
Increased security when working with narrow beam(s)
No Fresnel zone necessary
Reference open source implementation
Reduced size, weight, and power consumption compared to RF antennas
=== Range-limiting factors ===
For terrestrial applications, the principal limiting factors are:
Fog (10 to ~100 dB/km attenuation)
Beam dispersion
Atmospheric absorption
Rain
Snow
Terrestrial scintillation
Interference from background light sources (including the sun)
Shadowing
Pointing stability in wind
Pollution, such as smog
These factors cause an attenuated receiver signal and lead to higher bit error ratio (BER). To overcome these issues, vendors found some solutions, like multi-beam or multi-path architectures, which use more than one sender and more than one receiver. Some state-of-the-art devices also have larger fade margin (extra power, reserved for rain, smog, fog). To keep an eye-safe environment, good FSO systems have a limited laser power density and support laser classes 1 or 1M. Atmospheric and fog attenuation, which are exponential in nature, limit practical range of FSO devices to several kilometers. However, free-space optics based on 1550 nm wavelength, have considerably lower optical loss than free-space optics using 830 nm wavelength, in dense fog conditions. FSO using wavelength 1550 nm system are capable of transmitting several times higher power than systems with 850 nm and are safe to the human eye (1M class). Additionally, some free-space optics, such as EC SYSTEM, ensure higher connection reliability in bad weather conditions by constantly monitoring link quality to regulate laser diode transmission power with built-in automatic gain control.
== See also ==
Atomic line filter#Laser tracking and communication
Extremely high frequency
KORUZA
Laser safety
Mie scattering
Modulating retro-reflector
N-slit interferometer
Optical window
Radio window
Rayleigh scattering
Free-space path loss
== References ==
== Further reading ==
Christos Kontogeorgakis (May 1997). Millimeter Through Visible Frequency Waves Through Aerosols-Particle Modeling, Reflectivity and Attenuation (Thesis). Virginia Polytechnic Institute and State University. hdl:10919/37049. Master's Thesis
Heinz Willebrand & Baksheesh Ghuman (December 2001). Free Space Optics: Enabling Optical Connectivity in Today's Networks. SAMS. Archived from the original on 2012-06-22.
Moll, Florian (December 2013). "Free-space laser system for secure air-to-ground quantum communications". SPIE Newsroom. doi:10.1117/2.1201311.005189.
David G. Aviv (2006). Laser Space Communications. ARTECH HOUSE. ISBN 978-1-59693-028-5.
== External links ==
Free Space Optics on COST297 for HAPs
Explanation of Fresnel zones in microwave and optical links
video showing Lichtsprechgerät 80 in use on YouTube
International Space Station to Beam Video Via Laser Back to Earth, March 2014 NASA's Optical Payload for Lasercomm Science demonstration mission to the ISS
Wireless Optical Link Budget (with python examples)
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A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.
Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path. The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft. Any gain or loss of kinetic energy and linear momentum by a passing spacecraft is correspondingly lost or gained by the gravitational body, in accordance with Newton's Third Law. The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of Earth's Moon, and it was used by interplanetary probes from Mariner 10 onward, including the two Voyager probes' notable flybys of Jupiter and Saturn.
== Explanation ==
A gravity assist around a planet changes a spacecraft's velocity (relative to the Sun) by entering and leaving the gravitational sphere of influence of a planet. The sum of the kinetic energies of both bodies remains constant (see elastic collision). A slingshot maneuver can therefore be used to change the spaceship's trajectory and speed relative to the Sun.
A close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a train platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees the ball approaching at 80 km/h and then departing at 80 km/h after the ball bounces elastically off the front of the train. Because of the train's motion, however, that departure is at 130 km/h relative to the train platform; the ball has added twice the train's velocity to its own.
Translating this analogy into space: in the planet reference frame, the spaceship has a vertical velocity of v relative to the planet. After the slingshot occurs the spaceship is leaving on a course 90 degrees to that which it arrived on. It will still have a velocity of v, but in the horizontal direction. In the Sun reference frame, the planet has a horizontal velocity of v, and by using the Pythagorean Theorem, the spaceship initially has a total velocity of √2v. After the spaceship leaves the planet, it will have a velocity of v + v = 2v, gaining approximately 0.6v.
This oversimplified example cannot be refined without additional details regarding the orbit, but if the spaceship travels in a path which forms a hyperbola, it can leave the planet in the opposite direction without firing its engine. This example is one of many trajectories and gains of speed the spaceship can experience.
This explanation might seem to violate the conservation of energy and momentum, apparently adding velocity to the spacecraft out of nothing, but the spacecraft's effects on the planet must also be taken into consideration to provide a complete picture of the mechanics involved. The linear momentum gained by the spaceship is equal in magnitude to that lost by the planet, so the spacecraft gains velocity and the planet loses velocity. However, the planet's enormous mass compared to the spacecraft makes the resulting change in its speed negligibly small even when compared to the orbital perturbations planets undergo due to interactions with other celestial bodies on astronomically short timescales. For example, one metric ton is a typical mass for an interplanetary space probe whereas Jupiter has a mass of almost 2 x 1024 metric tons. Therefore, a one-ton spacecraft passing Jupiter will theoretically cause the planet to lose approximately 5 x 10−25 km/s of orbital velocity for every km/s of velocity relative to the Sun gained by the spacecraft. For all practical purposes the effects on the planet can be ignored in the calculation.
Realistic portrayals of encounters in space require the consideration of three dimensions. The same principles apply as above except adding the planet's velocity to that of the spacecraft requires vector addition as shown below.
Due to the reversibility of orbits, gravitational slingshots can also be used to reduce the speed of a spacecraft. Both Mariner 10 and MESSENGER performed this maneuver to reach Mercury.
If more speed is needed than available from gravity assist alone, a rocket burn near the periapsis (closest planetary approach) uses the least fuel. A given rocket burn always provides the same change in velocity (Δv), but the change in kinetic energy is proportional to the vehicle's velocity at the time of the burn. Therefore the maximum kinetic energy is obtained when the burn occurs at the vehicle's maximum velocity (periapsis). The Oberth effect describes this technique in more detail.
== Historical origins ==
In his paper "To Those Who Will Be Reading in Order to Build" ("�
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ем, кто будет читать, чтобы строить"), published in 1938 but dated 1918–1919, Yuri Kondratyuk suggested that a spacecraft traveling between two planets could be accelerated at the beginning and end of its trajectory by using the gravity of the two planets' moons. The portion of his manuscript considering gravity-assists received no later development and was not published until the 1960s. In his 1925 paper "Problems of Flight by Jet Propulsion: Interplanetary Flights" ("Проблема полета при помощи реактивных аппаратов: межпланетные полеты"), Friedrich Zander showed a deep understanding of the physics behind the concept of gravity assist and its potential for the interplanetary exploration of the Solar System.
Italian engineer Gaetano Crocco was first to calculate an interplanetary journey considering multiple gravity-assists in 1956.
The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of the Moon. The maneuver relied on research performed under the direction of Mstislav Keldysh at the Keldysh Institute of Applied Mathematics.
In 1961, Michael Minovitch, UCLA graduate student who worked at NASA's Jet Propulsion Laboratory (JPL), developed a gravity assist technique, that would later be used for the Gary Flandro's Planetary Grand Tour idea.
During the summer of 1964 at the NASA JPL, Gary Flandro was assigned the task of studying techniques for exploring the outer planets of the Solar System. In this study he discovered the rare alignment of the outer planets (Jupiter, Saturn, Uranus, and Neptune) and conceived the Planetary Grand Tour multi-planet mission utilizing gravity assist to reduce mission duration from forty years to less than ten.
== Purpose ==
A spacecraft traveling from Earth to an inner planet will increase its relative speed because it is falling toward the Sun, and a spacecraft traveling from Earth to an outer planet will decrease its speed because it is leaving the vicinity of the Sun.
Rocket engines can certainly be used to increase and decrease the speed of the spacecraft. However, rocket thrust takes propellant, propellant has mass, and even a small change in velocity (known as Δv, or "delta-v", the delta symbol being used to represent a change and "v" signifying velocity) translates to a far larger requirement for propellant needed to escape Earth's gravity well. This is because not only must the primary-stage engines lift the extra propellant, they must also lift the extra propellant beyond that which is needed to lift that additional propellant. The liftoff mass requirement increases exponentially with an increase in the required delta-v of the spacecraft.
Because additional fuel is needed to lift fuel into space, space missions are designed with a tight propellant "budget", known as the "delta-v budget". The delta-v budget is in effect the total propellant that will be available after leaving the earth, for speeding up, slowing down, stabilization against external buffeting (by particles or other external effects), or direction changes, if it cannot acquire more propellant. The entire mission must be planned within that capability. Therefore, methods of speed and direction change that do not require fuel to be burned are advantageous, because they allow extra maneuvering capability and course enhancement, without spending fuel from the limited amount which has been carried into space. Gravity assist maneuvers can greatly change the speed of a spacecraft without expending propellant, and can save significant amounts of propellant, so they are a useful technique to save fuel.
== Limits ==
The main practical limit to the use of a gravity assist maneuver is that planets and other large masses are seldom in the right places to enable a voyage to a particular destination. For example, the Voyager missions which started in the late 1970s were made possible by the "Grand Tour" alignment of Jupiter, Saturn, Uranus and Neptune. A similar alignment will not occur again until the middle of the 22nd century. That is an extreme case, but even for less ambitious missions there are years when the planets are scattered in unsuitable parts of their orbits.
Another limitation is the distance of closest approach to the planet. The magnitude of the change in velocity depends on the spacecraft's approach velocity and the planet's escape velocity at the point of closest approach. The closer to the center of the planet that approach is, the greater the achievable change in velocity. The atmosphere, if any, of the available planet will set a limit to the approach distance; for bodies with no atmosphere, like the moon
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the closest approach is set by the constraint that the trajectory must not intersect the surface. For planets with atmosphere, as a spacecraft gets deep into the atmosphere, the energy lost to drag can exceed that gained from the planet's velocity. (On the other hand, this drag can be used to accomplish a different delta-V maneuver, aerobraking). There have also been theoretical proposals to use aerodynamic lift as the spacecraft flies through the atmosphere. This maneuver, called an aerogravity assist, could bend the trajectory through a larger angle than gravity alone, and hence increase the gain in energy.
Interplanetary slingshots using the Sun itself are not possible because the Sun is at rest relative to the Solar System as a whole. However, thrusting when near the Sun has a related effect, the Oberth effect. This has the potential to magnify a spacecraft's thrusting power enormously, but is limited by the spacecraft's ability to resist the heat. For planetary gravity assists, a thrust applied near the closest approach (a "powered periapsis maneuver") can add the Oberth effect to the gravity slingshot effect, producing a larger change in orbital velocity than either effect by itself.
A rotating black hole might provide additional assistance, if its spin axis is aligned the right way. General relativity predicts that a large spinning mass produces frame-dragging—close to the object, space itself is dragged around in the direction of the spin. Any ordinary rotating object produces this effect. Although attempts to measure frame dragging about the Sun have produced no clear evidence, experiments performed by Gravity Probe B have detected frame-dragging effects caused by Earth. General relativity predicts that a spinning black hole is surrounded by a region of space, called the ergosphere, within which standing still (with respect to the black hole's spin) is impossible, because space itself is dragged at the speed of light in the same direction as the black hole's spin. The Penrose process may offer a way to gain energy from the ergosphere, although it would require the spaceship to dump some "ballast" into the black hole, and the spaceship would have had to expend energy to carry the "ballast" to the black hole.
== Notable examples of use ==
Luna 3
The gravity assist maneuver was first attempted in 1959 for Luna 3, to photograph the far side of the Moon. The satellite did not gain speed, but its orbit was changed in a way that allowed successful transmission of the photos.
Pioneer 10
NASA's Pioneer 10 is a space probe launched in 1972 that completed the first mission to the planet Jupiter. Thereafter, Pioneer 10 became the first of five artificial objects to achieve the escape velocity needed to leave the Solar System. In December 1973, Pioneer 10 spacecraft was the first one to use the gravitational slingshot effect to reach escape velocity to leave Solar System.
Pioneer 11
Pioneer 11 was launched by NASA in 1973, to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays. It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter (3 December 1974). To get to Saturn, the spacecraft got a gravity assist on Jupiter.
Mariner 10
The Mariner 10 probe was the first spacecraft to use the gravitational slingshot effect to reach another planet, passing by Venus on 5 February 1974 on its way to becoming the first spacecraft to explore Mercury.
Voyager 1
Voyager 1 was launched by NASA on September 5, 1977. It gained the energy to escape the Sun's gravity by performing slingshot maneuvers around Jupiter and Saturn. Having operated for 48 years and 2 days as of September 7, 2025 UTC [refresh], the spacecraft still communicates with the Deep Space Network to receive routine commands and to transmit data to Earth. Real-time distance and velocity data is provided by NASA and JPL. At a distance of 152.2 AU (22.8 billion km; 14.1 billion mi) from Earth as of January 12, 2020, it is the most distant human-made object from Earth.
Voyager 2
Voyager 2 was launched by NASA on August 20, 1977, to study the outer planets. Its trajectory took longer to reach Jupiter and Saturn than its twin spacecraft but enabled further encounters with Uranus and Neptune.
Galileo
The Galileo spacecraft was launched by NASA in 1989 and on its route to Jupiter got three gravity assists, one from Venus (February 10, 1990), and two from Earth (December 8, 1990 and December 8, 1992). Spacecraft reached Jupiter in December 1995. Gravity assists also allowed Galileo to flyby two asteroids, 243 Ida and 951 Gaspra.
Ulysses
In 1990, NASA launched the ESA spacecraft Ulysses to study the polar regions of the Sun. All the planets orbit approximately in a plane aligned with the equ
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of the Sun. Thus, to enter an orbit passing over the poles of the Sun, the spacecraft would have to eliminate the speed it inherited from the Earth's orbit around the Sun and gain the speed needed to orbit the Sun in the pole-to-pole plane. It was achieved by a gravity assist from Jupiter on February 8, 1992.
MESSENGER
The MESSENGER mission (launched in August 2004) made extensive use of gravity assists to slow its speed before orbiting Mercury. The MESSENGER mission included one flyby of Earth, two flybys of Venus, and three flybys of Mercury before finally arriving at Mercury in March 2011 with a velocity low enough to permit orbit insertion with available fuel. Although the flybys were primarily orbital maneuvers, each provided an opportunity for significant scientific observations.
Cassini
The Cassini–Huygens spacecraft was launched from Earth on 15 October 1997, followed by gravity assist flybys of Venus (26 April 1998 and 21 June 1999), Earth (18 August 1999), and Jupiter (30 December 2000). Transit to Saturn took 6.7 years, the spacecraft arrived at 1 July 2004. Its trajectory was called "the Most Complex Gravity-Assist Trajectory Flown to Date" in 2019.
After entering orbit around Saturn, the Cassini spacecraft used multiple Titan gravity assists to achieve significant changes in the inclination of its orbit as well so that instead of staying nearly in the equatorial plane, the spacecraft's flight path was inclined well out of the plane of the rings. A typical Titan encounter changed the spacecraft's velocity by 0.75 km/s, and the spacecraft made 127 Titan encounters. These encounters enabled an orbital tour with a wide range of periapsis and apoapsis distances, various alignments of the orbit with respect to the Sun, and orbital inclinations from 0° to 74°. The multiple flybys of Titan also allowed Cassini to flyby other moons, such as Rhea and Enceladus.
Rosetta
The Rosetta probe, launched in March 2004, used four gravity assist maneuvers (including one just 250 km from the surface of Mars, and three assists from Earth) to accelerate throughout the inner Solar System. That enabled it to flyby the asteroids 21 Lutetia and 2867 Šteins as well as eventually match the velocity of the 67P/Churyumov–Gerasimenko comet at the rendezvous point in August 2014.
New Horizons
New Horizons was launched by NASA in 2006, and reached Pluto in 2015. In 2007 it performed a gravity assist on Jupiter.
Juno
The Juno spacecraft was launched on August 5, 2011 (UTC). The trajectory used a gravity assist speed boost from Earth, accomplished by an Earth flyby in October 2013, two years after its launch on August 5, 2011. In that way Juno changed its orbit (and speed) toward its final goal, Jupiter, after only five years.
Parker Solar Probe
The Parker Solar Probe, launched by NASA in 2018, has seven planned Venus gravity assists. Each gravity assist brings the Parker Solar Probe progressively closer to the Sun. As of 2022, the spacecraft has performed five of its seven assists. The Parker Solar Probe's mission will make the closest approach to the Sun by any space mission. The mission's final planned gravity assist maneuver, completed on November 6, 2024, prepared it for three final solar flybys reaching just 3.8 million miles of the surface of the sun on December 24, 2024 (see figure).
Solar Orbiter
Solar Orbiter was launched by ESA in 2020. In its initial cruise phase, which lasts until November 2021, Solar Orbiter performed two gravity-assist manoeuvres around Venus and one around Earth to alter the spacecraft's trajectory, guiding it towards the innermost regions of the Solar System. The first close solar pass took place on 26 March 2022 at around a third of Earth's distance from the Sun.
BepiColombo
BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. It was launched on 20 October 2018. It will use the gravity assist technique with Earth once, with Venus twice, and six times with Mercury. It will arrive in 2026. BepiColombo is named after Giuseppe (Bepi) Colombo who was a pioneer thinker with this way of maneuvers.
Lucy
Lucy was launched by NASA on 16 October 2021. It gained one gravity assist from Earth on the 16th of October, 2022, and after a flyby of the main-belt asteroid 152830 Dinkinesh it will gain another in 2024. In 2025, it will fly by the inner main-belt asteroid 52246 Donaldjohanson. In 2027, it will arrive at the L4 Trojan cloud (the Greek camp of asteroids
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orbits about 60° ahead of Jupiter), where it will fly by four Trojans, 3548 Eurybates (with its satellite), 15094 Polymele, 11351 Leucus, and 21900 Orus. After these flybys, Lucy will return to Earth in 2031 for another gravity assist toward the L5 Trojan cloud (the Trojan camp which trails about 60° behind Jupiter), where it will visit the binary Trojan 617 Patroclus with its satellite Menoetius in 2033.
In fiction
In the 1968 novel 2001: A Space Odyssey – but not the movie – the spaceship Discovery performs such a maneuver to gain speed as it goes around Jupiter. As Arthur C. Clarke made clear at various times, the location of TMA-2 was switched from near Saturn (in the novel) to near Jupiter (in the movie).
A gravity assist maneuver appears on the climax of the 2014 film Interstellar — without fuel the protagonists slingshot their spaceship around a black hole. The maneuver costs them 51 years due to time dilation.
== See also ==
3753 Cruithne, an asteroid which periodically has gravitational slingshot encounters with Earth
Delta-v budget
Low-energy transfer, a type of gravitational assist where a spacecraft is gravitationally snagged into orbit by a celestial body. This method is usually executed in the Earth-Moon system.
Dynamical friction
Flyby anomaly, an anomalous delta-v increase during gravity assists
Gravitational keyhole
Interplanetary Transport Network
n-body problem
Oberth effect, applying thrust near closest approach in a gravity well
Pioneer H, first Out-Of-The-Ecliptic mission (OOE) proposed, for Jupiter and solar (Sun) observations
STEREO, a gravity-assisted mission which used Earth's Moon to eject two spacecraft from Earth's orbit into heliocentric orbit
== Notes ==
== References ==
== External links ==
Basics of Space Flight: A Gravity Assist Primer at NASA.gov
Spaceflight and Spacecraft: Gravity Assist, discussion at Phy6.org
"Gravitational Slingshot". MathPages.com.
Double-ball drop experiment
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