Jet aircraft

"Jet plane" redirects here. For the Rumania Montevideo album, seeJet Plane.

McDonnell Douglas DC-10ofContinental Airlinesis an example of aTrijetconfiguration

Ajet aircraft(or simplyjet) is anaircraft(nearly always afixed-wing aircraft) propelled by one or morejet engines.

Whereas the engines inpropeller-powered aircraftgenerally achieve their maximum efficiency at much lower speeds and altitudes, jet engines achieve maximum efficiency at speeds close to or even well above thespeed of sound.Jet aircraft generally cruise most efficiently at aboutMach0.8 (981 km/h (610 mph)) and at altitudes around 10,000–15,000 m (33,000–49,000 ft) or more.

The idea of the jet engine was not new, but the technical problems involved could not begin to be solved until the 1930s. Frank Whittle,anEnglishinventor andRAFofficer, began development of a viable jet engine in 1928,andHans von Ohainin Germany began work independently in the early 1930s. In August 1939 theturbojetpoweredHeinkel He 178,the world's first jet aircraft, made its first flight. A wide range of different types of jet aircraft exist, both for civilian and military purposes.

History

TheHeinkel He 178was the first aircraft to fly on turbojet power, in August 1939

After the first instance of powered flight, a large number of jet engine designs were suggested.René Lorin,Morize, Harris proposed systems for creating a jet efflux.

After other jet engines had been run, Romanian inventorHenri Coandăclaimed to have built a jet-powered aircraft in 1910, theCoandă-1910.However, to support this claim, he had to make substantial alterations to the drawings which he used to support his subsequently debunked claims.In fact the ducted-fan engine backfired, setting the aircraft on fire before any flights were ever made, and it lacked nearly all of the features necessary for a jet engine - including a lack of fuel injection, and any concern about hot jet efflux being directed at a highly flammable fabric surface.

During the 1920s and 1930s a number of approaches were tried. A variety ofmotorjet,turboprop,pulsejetandrocket poweredaircraft were designed. Rocket-engine research was being carried out in Germany and the first aircraft to fly under rocket power was theLippisch Ente,in 1928.The Ente had previously been flown as a glider. The next year, in 1929, theOpel RAK.1became the first purpose-built rocket aircraft to fly.

Theturbojetwas invented in the 1930s, independently byFrank Whittleand laterHans von Ohain.The first turbojet aircraft to fly was theHeinkel He 178,on August 27, 1939 inRostock(Germany), powered by von Ohain's design.This was largely a proof of concept, as the problem of "creep"(metal fatigue caused by the high temperatures within the engine) had not been solved, and the engine quickly burned out. 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.

The first flight of a jet-propelled aircraft to come to public attention was theItalianCaproni Campini N.1motorjetprototype which flew on August 27, 1940.It was the first jet aircraft recognised by theFédération Aéronautique Internationale(at the time the German He 178 program was still kept secret). Campini began development of the motorjet in 1932; it differed from a true turbojet in that the turbine was driven by a piston engine, rather than combustion of the turbine gases - which was a much more complex solution.

Boeing 707

The British experimentalGloster E.28/39first flew on May 15, 1941, powered bySir Frank Whittle's turbojet.The United StatesBell XP-59Aflew on October 1, 1942, using two examples of a version of the Whittle engine built byGeneral Electric.The Meteor was the first production jet, with the first orders for production examples being made on 8 August 1941,the prototype first flying on 5 March 1943 and the first production aircraft flying on 12 January 1944,while the first orders for production Me 262 aircraft were not issued until 25 May 1943,and the first production Me 262 did not fly until 28 March 1944despite the Me 262 program having started earlier than that of the Meteor, as Projekt 1065, with initial plans drawn up by Waldemar Voigt's design team in April 1939.

TheMesserschmitt Me 262was the first operational jetfighter,manufactured by Germany during World War II and entering service on 19 April 1944 withErprobungskommando 262at Lechfeld just south of Augsburg. An Me 262 scored the first combat victory for a jet fighter on 26 July 1944, the day before the BritishGloster Meteorentered operational service. The Me 262 had first flown on April 18, 1941, but mass production did not start until early 1944, with the first squadrons operational that year, too late for any effect on the outcome of theWorld War II.While only around 15 Meteors were operational during WW2, up to 1,400 Me 262 were produced, with 300 entering combat. Only the rocket-propelledMesserschmitt Me 163 Kometwas a faster operational aircraft during the war.

Around this time, mid 1944, the United Kingdom's Meteor was being used for defence of the UK against theV-1 flying bomb– the V-1 itself apulsejet-powered aircraft and direct ancestor of thecruise missile– and then ground-attack operations over Europe in the last months of the war. In 1944 Germany introduced theArado Ar 234jet reconnaissance and bomber aircraft into service, though chiefly used in the former role, with theHeinkel He 162Spatzsingle-jetlight fighterappearing at the end of 1944. USSR tested its ownBereznyak-Isayev BI-1in 1942, but the project was scrapped by leaderJoseph Stalinin 1945. TheImperial Japanese Navyalso developed jet aircraft in 1945, including theNakajima J9Y Kikka,a modified, and slightly smaller version of the Me 262 that had folding wings. By the end of 1945, the US had introduced their first jet fighter, theLockheed P-80 Shooting Starinto service and the UK its second fighter design, thede Havilland Vampire.

The US introduced theNorth American B-45 Tornado,their first jet bomber, into service in 1948. It was capable of carrying nuclear weapons, but was used for reconnaissance over Korea. On November 8, 1950, during theKorean War,United States Air ForceLt. Russell J. Brown, flying in anF-80,intercepted twoNorth KoreanMiG-15snear theYalu Riverand shot them down in the first jet-to-jetdogfightin history. The UK put theEnglish Electric Canberrainto service in 1951 as alight bomber.It was designed to fly higher and faster than anyinterceptor.

TheConcordewas the longest running commercialSSTproviding service from 1976 to 2003

BOACoperated the first commercial jet service, fromLondontoJohannesburg,in 1952 with thede Havilland Cometjetliner.This highly innovative aircraft travelled far faster and higher than propeller aircraft, was much quieter, smoother, and had stylish blended wings containing hidden jet engines. However, due to a design defect, and use of aluminium alloys, the aircraft suffered catastrophicmetal fatiguewhich led to several crashes,which gave time for theBoeing 707to enter service in 1958 and thus to dominate the market for civilian airliners. The underslung engines were found to be advantageous in the event of a propellant leak, and so the 707 looked rather different from the Comet: the 707 has a shape that is effectively the same as that of contemporary aircraft, with marked commonality still evident today for example with the737(fuselage) andA340(single deck, swept wing, four below-wing engines).

Turbofanaircraft with far greaterfuel efficiencybegan entering service in the 1950s and 1960s, and became the most commonly used type of jet.

TheTu-144supersonic transportwas the fastest commercial jet aircraft at Mach 2.35 (2,503 km/h (1,555 mph)). It went into service in 1975, but was withdrawn from commercial service shortly afterwards. The Mach 2Concordeentered service in 1976 and flew for 27 years.

The fastest military jet aircraft was theSR-71 Blackbirdat Mach 3.35 (3,661 km/h (2,275 mph)).

Other jets

Most people use the term 'jet aircraft' to denote gas turbine basedairbreathing jet engines,but rockets and scramjets are both also propelled by jet propulsion.

The Sikorsky S-69 was acompound helicopterwith auxiliary turbojets

Cruise missilesare single-use unmanned jet aircraft, powered predominantly by ramjets or turbojets or sometimes turbofans, but they will often have a rocket propulsion system for initial propulsion.

The fastest airbreathing jet aircraft is the unmannedX-43scramjet at around Mach 9–10.

The fastest manned (rocket) aircraft is theX-15at Mach 6.85.

TheSpace Shuttle,while far faster than the X-43 or X-15, was not regarded as an aircraft during ascent as it was carriedballisticallyby rocket thrust, rather than the air. During re-entry it was classed (like a glider) as an unpowered aircraft. The first flight was in 1981.

TheBell 533(1964),Lockheed XH-51(1965), andSikorsky S-69(1977-1981) are examples ofcompound helicopterdesigns where jet exhaust added to forward thrust.TheHiller YH-32 HornetandFairey Ultra-light Helicopterwere among the many helicopters where the rotors were driven bytip jets.

Jet-poweredwingsuitsexist – powered by model aircraft jet engines – but of short duration and needing to be launched at height.

Aerodynamics

Because of the way they work, the typical exhaust speed of jet engines is transonic or faster, therefore most jet aircraft need to fly at high speeds, eithersupersonicor speeds just below the speed of sound ( "transonic") so as to achieve efficient flight. Aerodynamics is therefore an important consideration.

Jet aircraft are usually designed using theWhitcomb area rule,which says that the total area of cross-section of the aircraft at any point along the aircraft from the nose must be approximately the same as that of aSears-Haack body.A shape with that property minimises the production of shockwaves which would waste energy.

Jet engines

Main article:Jet engine

There are several types of engine which operate by expelling hot gas:

TheLockheed SR-71was one of the fastest jet flying at Mach 3.35 (3,661 km/h (2,275 mph)

• turbojet
• turbofan(which come in two main formslow bypass turbofanandhigh bypass turbofan)
• rocket

The different types are used for different purposes.

Rockets are the oldest type, and are mainly used when extremely high speeds are needed, or operation at extremely high altitudes where there is insufficient air to operate a jet engine. Due to the extreme, typicallyhypersonic,exhaust velocity and the necessity of oxidiser being carried on board, they consume propellant extremely quickly, making them impractical for routine transportation.

Turbojets are the second oldest type; they have a high, usually supersonic, exhaust speed and low frontal cross-section, and so are best suited to high-speed, usually supersonic, flight. Although once widely used, they are relatively inefficient compared toturbopropand turbofans for subsonic flight. The last major aircraft to use turbojets were Concorde and Tu-144supersonic transports.

Low bypass turbofans have a lower exhaust speed than turbojets, and are mostly used for high sonic, transonic, and low supersonic speeds. High bypass turbofans are relatively efficient, and are used by subsonic aircraft such as airliners.

Flying characteristics

Jet aircraft fly considerably differently thanpropeller aircraft.

One difference is that jet engines respond relatively slowly.This complicates takeoff and landing maneuvers. In particular, during takeoff, propeller aircraft engines blow air over their wings and that gives more lift and a shorter takeoff. These differences caught out some earlyBOAC Cometpilots.

Propulsive efficiency

Main article:Propulsive efficiency

In aircraftoverall propulsive efficiency$\eta$is the efficiency, in percent, with which the energy contained in a vehicle's propellant is converted into useful energy, to replace losses due toair drag,gravity, and acceleration. It can also be stated as the proportion of the mechanical energy actually used to propel the aircraft. It is always less than 100% because of kinetic energy loss to the exhaust, and less-than-ideal efficiency of the propulsive mechanism, whether apropeller,a jet exhaust, or a fan. In addition, propulsive efficiency is greatly dependent onair densityand airspeed.

Mathematically, it is represented as$\eta =\eta _{c}\eta _{p}$where$\eta _{c}$is thecycle efficiencyand$\eta _{p}$is the propulsive efficiency. The cycle efficiency, in percent, is the proportion of energy that can be derived from the energy source that is converted to mechanical energy by theengine.

Dependence of the propulsive efficiency ($\eta _{p}$) upon the vehicle speed/exhaust speed ratio (v/c) for rocket and jet engines

For jet aircraft thepropulsive efficiency(essentiallyenergy efficiency) is highest when the engine emits an exhaust jet at a speed that is the same as, or nearly the same as, the vehicle velocity. The exact formula for air-breathing engines as given in the literature,is

$\eta _{p}={\frac {2}{1+{\frac {c}{v}}}}$

wherecis the exhaust speed, andvis the speed of the aircraft.

Range

Main article:Range (aircraft)

For a long range jet operating in thestratosphere,the speed of sound is constant, hence flying at fixed angle of attack and constantMach numbercauses the aircraft to climb, without changing the value of the local speed of sound. In this case:

$V=aM$

where$M$is the cruise Mach number and$a$the local speed of sound. The range equation can be shown to be:

$R={\frac {aM}{c_{T}}}{\frac {C_{L}}{C_{D}}}ln{\frac {W_{1}}{W_{2}}}$

which is known as theBreguet range equationafter the French aviation pioneerLouis Charles Breguet.

See also

• Coanda-1910– AircraftPages displaying short descriptions of redirect targetsPages displaying short descriptions with no spaces
• Commercial aviation– Transport system providing air transport for hire
• Contrail– Long, thin artificial clouds that sometimes form behind aircraft
• Jet airliner– Passenger aircraft powered by jet engines
• Jet noise– Noise caused by jets
• Jumbo jet– Airliner with two aisles
• Very light jet– Class of small jet aircraft under 10,000 lb.
• List of jet aircraft of World War II

References

Bibliography

• Butler, Phil; Buttler, Tony (2006).Gloster Meteor: Britain's Celebrated First-Generation Jet.Surrey, UK: Midland Publishing. p. 23.ISBN1-85780-230-6.
• Lutz Warsitz:The First Jet Pilot – The Story of German Test Pilot Erich Warsitz,Pen and Sword Books Ltd., England, 2009,ISBN978-1-84415-818-8,English Edition
• Radinger, Will; Schick, Walter Schick (1996).Me 262(in German). Berlin: Avantic Verlag GmbH.ISBN978-3-925505-21-8.

External links

• The official Erich Warsitz website (the world's first jet pilot), inclusive rare videos (Heinkel He 178) and audio commentaries