Supercruise

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The English Electric Lightning was the first aircraft capable of supercruise.

Supercruise is sustained supersonic flight of an aircraft with a useful cargo, passenger, or weapons load performed efficiently which typically precludes the use of highly inefficient afterburners (reheat). Many well known supersonic military aircraft are not capable of super cruise as they are only able to maintain supersonic flight in short bursts (typically with afterburners) while they cruise at subsonic speeds. Aircraft such as the SR-71 Blackbird are designed to cruise at supersonic speed with afterburners enabled.

One of the most prominent and well-known examples of this type of aircraft was Concorde. Due to its long service in commercial airlines, Concorde has the record for the most time spent in supercruise; it has spent more time in supercruise than all other aircraft combined.[1]

Advantages[edit]

Most military aircraft use afterburners (or reheat) to travel at supersonic speeds and cannot reach supersonic speeds using the dry engine thrust. Afterburners are highly inefficient compared to conventional jet engine operation due to the low pressures typically found in the exhaust section. This limits most aircraft to using afterburners for only very short periods. Therefore, an aircraft that can supercruise has generally greater endurance at supersonic speeds than one which cannot. Supercruise capability is also an advantage for stealth aircraft, as an afterburner plume both reflects radar signals and creates a significant infrared signature[2] in addition to being visually conspicuous.

History[edit]

Concorde routinely supercruised most of the way over the Atlantic.

The first turbine-powered aircraft to exceed Mach 1 in level flight without afterburners was the un-reheated Armstrong Siddeley Sapphire powered P.1 prototype of the English Electric Lightning, on 11 August 1954. Previously this aircraft, WG760, flown by Roland Beamont had unknowingly exceeded Mach 1 in the climb on its first flight on 4 August 1954, although due to position error, the Mach meter had only shown a maximum of Mach 0.95, and Beamont, who had not noticed any change in behaviour of the aircraft, was surprised when informed of the fact after the flight data had been analysed.[3] However, this early demonstration of supercruise was extremely limited; the Lightning could supercruise at approximately Mach 1.22[4] while later versions were able to achieve much higher speeds.

The British Aircraft Corporation Tactical Strike/Reconnaissance 2 (TSR-2), which first flew on 27 September 1964, was one of the first military aircraft specifically designed to cruise supersonically; one of the planned mission profiles was for a supersonic cruise at Mach 2.00 at 50–58,000 ft.[5] Supersonic cruise at lower levels was at Mach 1.1 at 200 ft.[6] The TSR-2 used Bristol Olympus engines, a later version of which would also power Concorde.

Many of the fighters listed as capable of supercruise can only marginally exceed the speed of sound without afterburners and may only be able to do so without an external weapons load.

In day-to-day operation the Tupolev Tu-144 and Concorde both used afterburners to accelerate quickly through the high-drag transonic flight regime before deactivating them to supercruise. Doing this minimized fuel use, even though afterburners are relatively inefficient. Both aircraft were capable of achieving supersonic flight without the use of afterburners; however, doing so meant that they spent much longer in the high-drag transonic flight envelope, and this made the short use of afterburners more fuel efficient over the whole flight.

Military use[edit]

The term supercruise was originally used to describe a fighter performance requirement set forth by USAF Col. John Boyd, Pierre Sprey, and Col. Everest Riccioni, proponents of the F-16 Falcon.[citation needed] Following the entry into production of the F-16, they began work on an improved fighter design with the ability to cruise supersonically over enemy territory for a minimum of twenty minutes. As air combat is often the result of surprise, and the speed of the combat is determined by the speed of the surprising aircraft, this would have given a supercruise-capable design a worthwhile performance advantage in many situations. The postulated fighter would have had a top speed of just over Mach 1, and a fuel fraction in excess of 40%, the minimum required to successfully meet the twenty-minute requirement. Meeting the fuel fraction requirement necessitated a very austere design with few advanced electronics. The United States Air Force showed no interest in the proposal at that time, but years later revived the term and redefined it to apply to the requirements for the Advanced Tactical Fighter, which resulted in the F-22 Raptor.

The F-22 Raptor is capable of supercruise (but is seen here running afterburner)
The Eurofighter Typhoon is capable of supercruise at Mach 1.5[7]

The F-22 Raptor's supercruise capabilities are touted as a major performance advantage over other fighters. Even so, supercruising uses much more fuel to travel the same distance than at subsonic speeds: The Air Force Association estimates that use of supercruise for a 100-nautical-mile (190 km) dash as part of a mission would cut the F-22's combat radius from about 600 nautical miles (1,110 km) to about 450 nautical miles (830 km). However, this is still unconfirmed as the altitude and flight profile are classified (as are most of the F-22's capabilities).

The F-22 has demonstrated supercruise speeds of at least Mach 1.7, a difference of 320 knots (593 km/h) indicated airspeed (KIAS) at 40,000 ft (12,000 m).[8] Supercruise in militarily significant parlance is meant to imply a significant increase in effective combat speed with a full weapons load over existing types. Virtually all current and past jet fighters, prior to the F-22, cruise at approximately Mach 0.8–0.9 with a militarily significant weapons load. The F-22 represents a significant advance in cruise speed over previous types.[9]

The key challenge in attaining supercruise is not simply attaining a high static thrust-to-weight ratio. Engine thrust and efficiency can vary greatly with speed and altitude. In order to achieve significant dry thrust at high supersonic speed, the engine (and airframe) must be built purposely with this goal in mind. Conversely, there is nothing special about being able to marginally exceed the speed of sound with a "standard" jet engine, as any supersonic engine is capable of surviving supercruise conditions, even if they may not provide enough dry power to maintain supersonic flight.

There are a few engines in production that are designed to facilitate tactically significant supercruise.

Although the Pratt & Whitney F135 F-35 engine was not designed to achieve a supercruise capability,[13] the F-35 is able to maintain Mach 1.2 for a dash of 150 miles without using afterburners.[14]

NPO Saturn is developing a supercruise-capable derivative of its AL-41 engine for the Sukhoi PAK FA and the Indo-Russian Sukhoi/HAL FGFA. This is yet to bear fruit, but the stop-gap AL-41F1S 117S engine, produced by this program, seems to achieve the supercruise goal already.[citation needed] It was recently announced[15] that during testing of a Su-35BM fighter equipped with these engines it was traveling in the ~M1.1–1.2 airspeed range at nominal power and was still accelerating, thus suggesting that the supercruise was possible at even higher speed. Further testing will show the extent of this possibility.[citation needed]

All known supercruise aircraft can only do so at considerable altitude (where the air is thinner and so offers less resistance), which restricts the use of terrain mask and so makes any non-stealth aircraft very obvious.[citation needed]

Aircraft designed to cruise on afterburner[edit]

The Pratt & Whitney J58 turbojets[16] used on the Lockheed A-12 and SR-71 Blackbird needed afterburner to sustain supersonic cruise speeds.[17]

The XB-70A Valkyrie also used afterburning turbojets (six General Electric YJ-93 engines) for a cruise design point of Mach 3.0.[18]

Ramjets and scramjets[edit]

Ramjet and scramjet powered aircraft have to date been experimental. There have been numerous ramjet missiles, but these engines only operate at supersonic speeds and therefore would be theoretically ideal for an aircraft intended to spend long periods in supersonic flight. Due to the exotic nature of the engines, whether this would be considered "supercruise" is largely semantic.

Aircraft with supercruise[edit]

Aircraft with supercruise include:

Projected aircraft:

References[edit]

  1. ^ [1][dead link]
  2. ^ Stealth design of airplanes / stealth aircraft
  3. ^ http://www.flightglobal.com/pdfarchive/view/1957/1957%20-%200541.html
  4. ^ English Electric Aircraft and their Predecessors, Stephen Ransom & Robert Fairclough, Putnam, London, 1987, (p.227)
  5. ^ http://nuclear-weapons.info/images/tna-air2-17329e53a_02.JPG
  6. ^ http://i.imgur.com/ddSy1.jpg
  7. ^ a b Austrian Eurofighter Site in German
  8. ^ F-22 Raptor.com
  9. ^ "Gallery of USAF Weapons", pp. 147–155. Air Force Magazine, May 2006.
  10. ^ "Air defense mission for flotille F12." Fox Three, issue 8, pg. 8. Retrieved: 2011-03-30.
  11. ^ Desclaux, Jacques and Jacques Serre (2003). M88 – 2 E4: Advanced New Generation Engine for Rafale Multirole Fighter. AIAA/ICAS International Air and Space Symposium and Exposition: The Next 100 Years. 14–17 July 2003, Dayton, Ohio. AIAA 2003-2610.
  12. ^ "Gripen Supercruises." Gripen International, 21 January 2009.
  13. ^ Frequently Asked Questions about JSF, jsf.mil, retrieved March 2011
  14. ^ Tirpak, John A. (November 2012). "The F-35’s Race Against Time". airforce-magazine.com. Air Force Association. Retrieved 6 November 2012. 
  15. ^ Su-35BM testing report on Lenta.ru (in Russian)
  16. ^ http://www.enginehistory.org/Convention/2013/SR-71PropulsionSystem-2013.pdf
  17. ^ "Flying the SR-71 Blackbird" Col. Richard H. Graham, USAF (Retd), ISBN 0-7603-3239-8 p132
  18. ^ Jenkins, Dennis R.; Tony R. Landis, Alvin S. White, and Fitzhugh L. Fulton (2005). Valkyrie: North American's Mach 3 Superbomber. Speciality Press. various pages. ISBN 1-58007-072-8. 
  19. ^ Powerplant, ConcordeSST —describes full cycle of Concorde's engine from takeoff to touchdown, including the turning off of reheat to begin supercruise at Mach 1.7.
  20. ^ "A Totally Superior Product" (PDF). Gripen News: 2. June 2001. 
  21. ^ "Gripen Supercruises" (press release). Retrieved 2009-12-04. 

See also[edit]