Jet aircraft
A jet aircraft (or simply jet) is an aircraft (nearly always a fixed-wing aircraft) propelled by one or more jet engines.
Whereas the engines in
The idea of the jet engine was not new, but the technical problems involved could not begin to be solved until the 1930s.
History
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.[2]
After other jet engines had been run, Romanian inventor Henri Coandă claimed to have built a jet-powered aircraft in 1910, the Coandă-1910. However, to support this claim, he had to make substantial alterations to the drawings which he used to support his subsequently debunked claims.[3] 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.[3]
During the 1920s and 1930s a number of approaches were tried. A variety of motorjet, turboprop, pulsejet and rocket powered aircraft were designed. Rocket-engine research was being carried out in Germany and the first aircraft to fly under rocket power was the Lippisch Ente, in 1928.[4] The Ente had previously been flown as a glider. The next year, in 1929, the Opel RAK.1 became the first purpose-built rocket aircraft to fly.
The turbojet was invented in the 1930s, independently by Frank Whittle and later Hans von Ohain. The first turbojet aircraft to fly was the Heinkel He 178, on August 27, 1939 in Rostock (Germany), powered by von Ohain's design.[5][6] 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.[7][8]
The first flight of a jet-propelled aircraft to come to public attention was the Italian Caproni Campini N.1 motorjet prototype which flew on August 27, 1940.[9] It was the first jet aircraft recognised by the Fédération 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.
The British experimental
The Messerschmitt Me 262 was the first operational jet fighter,[15] manufactured by Germany during World War II and entering service on 19 April 1944 with Erprobungskommando 262 at 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 British Gloster Meteor entered 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 the World 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-propelled Messerschmitt Me 163 Komet was a faster operational aircraft during the war.[citation needed]
Around this time, mid 1944, the United Kingdom's Meteor was being used for defence of the UK against the V-1 flying bomb – the V-1 itself a pulsejet-powered aircraft and direct ancestor of the cruise missile – and then ground-attack operations over Europe in the last months of the war. In 1944 Germany introduced the Arado Ar 234 jet reconnaissance and bomber aircraft into service, though chiefly used in the former role, with the Heinkel He 162 Spatz single-jet light fighter appearing at the end of 1944. USSR tested its own Bereznyak-Isayev BI-1 in 1942, but the project was scrapped by leader Joseph Stalin in 1945. The Imperial Japanese Navy also developed jet aircraft in 1945, including the Nakajima 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, the Lockheed P-80 Shooting Star into service and the UK its second fighter design, the de Havilland Vampire.
The US introduced the
Turbofan aircraft with far greater fuel efficiency began entering service in the 1950s and 1960s, and became the most commonly used type of jet.
The
The fastest military jet aircraft was the
Other jets
Most people use the term 'jet aircraft' to denote gas turbine based airbreathing jet engines, but rockets and scramjets are both also propelled by jet propulsion.
Cruise missiles are 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 unmanned X-43 scramjet at around Mach 9–10.
The fastest manned (rocket) aircraft is the
The Space Shuttle, while far faster than the X-43 or X-15, was not regarded as an aircraft during ascent as it was carried ballistically by 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.
The
Jet-powered wingsuits exist – powered by model aircraft jet engines – but of short duration and needing to be launched at height.[18]
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, either
Jet aircraft are usually designed using the
Jet engines
There are several types of engine which operate by expelling hot gas:
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, typically
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 to turboprop and turbofans for subsonic flight. The last major aircraft to use turbojets were Concorde and Tu-144 supersonic 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 than
One difference is that jet engines respond relatively slowly.[citation needed] 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 early BOAC Comet pilots.[16]
Propulsive efficiency
In aircraft overall propulsive efficiency is the efficiency, in percent, with which the energy contained in a vehicle's propellant is converted into useful energy, to replace losses due to
Mathematically, it is represented as [19] where is the
For jet aircraft the propulsive efficiency (essentially energy 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,[20][21] is
where c is the exhaust speed, and v is the speed of the aircraft.
Range
For a long range jet operating in the stratosphere, the speed of sound is constant, hence flying at fixed angle of attack and constant Mach number causes the aircraft to climb, without changing the value of the local speed of sound. In this case:
where is the cruise Mach number and the local speed of sound. The range equation can be shown to be:
which is known as the Breguet range equation after the French aviation pioneer Louis Charles Breguet.
See also
- Coanda-1910– Aircraft
- 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
Citations
- ^ CWN, Chris Studman for. "Sir Frank Whittle - Jet Engine Inventor - Born In Coventry". www.cwn.org.uk. Archived from the original on 20 October 2017. Retrieved 6 May 2018.
- ^ Jet Propulsion of Aircraft Part III Archived 2012-11-05 at the Wayback Machine G Geoffrey Smith Flight September 25th 1941
- ^ a b Winter, Frank H. (6 December 2010). "Coanda's Claim:The story of a jet flight in 1910, just seven years after Kitty Hawk, may be too good to be true". airspacemag.com.
- ^ "Lippisch Ente."[permanent dead link] The Internet Encyclopedia of Science: Experimental Aircraft. Retrieved: 26 September 2011.
- ^ Warsitz, Lutz: The First Jet Pilot – The Story of German Test Pilot Erich Warsitz (p. 125), Pen and Sword Books Ltd., England, 2009 Archived 2010-06-03 at the Wayback Machine
- ^ "Heinkel He 178".
- ^ Experimental & Prototype US Air Force Jet Fighters, Jenkins & Landis, 2008
- ^ Foderaro, Lisa W. (10 August 1996). "Frank Whittle, 89, Dies; His Jet Engine Propelled Progress". The New York Times.
- ^ "Flight 28 August 1941". flightglobal.com. Archived from the original on 20 October 2017. Retrieved 6 May 2018.
- ^ "No Airscrew Necessary..." Archived 2012-10-25 at the Wayback Machine Flight(flightglobal.com), 27 October 1949 p554
- ^ Butler, 2006, p.8
- ^ Butler, 2006, p.23
- ^ Radinger, 1996, p.33
- ^ Radinger, 1996, p.49
- ISBN 0-88740-234-8.[page needed]
- ^ a b "Jet! When Britain Ruled the Skies". BBC. Retrieved 17 February 2023.
- ^ Thomas Lawrence; David Jenney (31 Aug 2010). "The Fastest Helicopter on Earth". IEEE Spectrum. Archived from the original on 30 January 2017. Retrieved 1 August 2017.
- ^ "'Jetman' Yves Rossy Shows Us How to Fly His Carbon Fiber Jet Wing". Wired. 31 July 2013. Archived from the original on 2 January 2017. Retrieved 1 August 2017.
- ^ ch10-3 Archived 2010-09-14 at the Wayback Machine
- ^ K.Honicke, R.Lindner, P.Anders, M.Krahl, H.Hadrich, K.Rohricht. Beschreibung der Konstruktion der Triebwerksanlagen. Interflug, Berlin, 1968
- Rolls-Royce plc, 2003. Retrieved: 21 July 2012.
Bibliography
- Butler, Phil; Buttler, Tony (2006). Gloster Meteor: Britain's Celebrated First-Generation Jet. Surrey, UK: Midland Publishing. p. 23. ISBN 1-85780-230-6.
- Lutz Warsitz: The First Jet Pilot – The Story of German Test Pilot Erich Warsitz, Pen and Sword Books Ltd., England, 2009,
- Radinger, Will; Schick, Walter Schick (1996). Me 262 (in German). Berlin: Avantic Verlag GmbH. ISBN 978-3-925505-21-8.