Supercruise

Supercruise is sustained supersonic flight of a supersonic aircraft with a useful cargo, passenger, or weapons load performed efficiently, which typically precludes the use of highly inefficient afterburners or "reheat". Many well known supersonic military aircraft not capable of supercruise can only maintain Mach 1+ flight in short bursts, typically with afterburners. Aircraft such as the SR-71 Blackbird are designed to cruise at supersonic speed with afterburners enabled.

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

One of the best known examples of an aircraft capable of supercruise was Concorde. Due to its long service as a commercial airliner, Concorde holds the record for the most time spent in supercruise; more than all other aircraft combined.[1]

Advantages

The main advantage is the ability of an aircraft to fly at supersonic speed without using its afterburner which consumes large amounts of fuel and limits its range.

Supercruise capability also provides advantages for stealth aircraft, because an afterburner plume reflects radar signals and creates a significant infrared signature.[2]

History
Concorde routinely supercruised most of the way over the Atlantic, enabling it to travel from London to New York in three hours, a record which has yet to be surpassed by any other commercial aircraft.

On 3 August 1954, a Gerfaut research aircraft powered by an SNECMA Atar 101D2A engine exceeded Mach 1 on level flight without using afterburners.[3][4] The first production aircraft intended to exceed Mach 1 in dry level flight was the Lockheed F-104 Starfighter which featured a radical design, with razor-thin, stubby wings attached substantially farther back on the fuselage than most contemporary aircraft. The wing provided excellent supersonic and high-speed, low-altitude performance, but resulted in poor turning capability and high landing speeds. It was the first production aircraft to achieve Mach 2, and the first aircraft to reach an altitude of 100,000 feet after taking off under its own power. The Starfighter established world records for airspeed, altitude, and time-to-climb in 1958, becoming the first aircraft to hold all three simultaneously. The un-reheated Armstrong Siddeley Sapphire powered P.1 prototype of the English Electric Lightning, exceeded Mach 1 on 11 August 1954. A week previous, on 4 August, the P.1, WG760 flown by Roland Beamont on its maiden flight, had unknowingly exceeded Mach 1 in a climb, although, due to position error, the Machmeter had only shown a maximum of Mach 0.95. Beamont, who had not noticed any change in behaviour of the aircraft, was surprised when informed after the flight data had been analysed.[5] However, this early demonstration of super sonic flight was extremely limited, as the Lightning could only cruise without reheat at approximately Mach 1.02,[6] while later versions were able to achieve much higher speeds, but only for very short time periods. Since it could not sustain supersonic speed for 20 minutes, as specified in the original definition of "supercruise", inclusion of the EE Lightning in the category has remained controversial.

The BAC TSR-2 strike and reconnaissance aircraft, 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 2.0 at 50,000–58,000 ft (15–18 km).[7] Supersonic cruise at lower levels was at Mach 1.1 at 200 ft (61 m).[8] The TSR-2 used Bristol Olympus engines, a later version of which would also power Concorde.

Qualitative variation in Cd factor (drag coefficient) with Mach number (speed) for aircraft; supercruising above Mach 2 is efficient.

Only the supersonic transports (SST), Concorde and the last version of the Tu-144 (the Tu-144D), spent most of their time cruising at their design speeds without needing afterburning. Some combat aircraft that are listed as capable of supercruise may only be able to do so without an external weapons load, for example. Reheat was added to Concorde for take-off to cope with weight increases that came after the initial design. As it was available, it was also used for transonic acceleration to reduce the time taken and fuel used to reach cruise. The upgraded Tu-144D had more economical engines than the Tu-144, which did not require afterburners during cruise, as well as a more advanced intake design, which increased the full payload range from 3,080 to 5,330 km (1,910 to 3,310 mi) (Concorde's operational range was 6,470 km or 4,020 mi).[9]

Military use

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. 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 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 meet the twenty-minute requirement. 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,[10] which resulted in the F-22 Raptor.

The F-22 Raptor is capable of supercruise at Mach 1.8 (but is seen here running afterburner).
The Dassault Rafale is capable of supercruising with four missiles and a belly drop tank.[11]
The Eurofighter Typhoon is capable of supercruise at Mach 1.5.[12]

The F-22 Raptor's supercruise capabilities are touted as a major performance advantage over other fighters, with supercruise being demonstrated up to at least Mach 1.8.[13] Virtually all current and past jet fighters, prior to the F-22, cruise at approximately Mach 0.8–0.9 with militarily significant weapons loads.[14] However, supercruising uses more fuel to travel the same distance than at subsonic speeds, with the Air Force Association estimating that use of supercruise for a 100-nautical-mile (120 mi; 190 km) dash as part of a mission would cut the F-22's combat radius from about 600 nautical miles (690 mi; 1,100 km) to about 450 nautical miles (520 mi; 830 km). This reduction is unconfirmed because the altitude and flight profile are classified, as are most of the F-22's capabilities, but it is still far less of a reduction than would result from the use of afterburner.

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

  • The two Pratt & Whitney F119 that power the F-22 Raptor make it the most capable supercruiser fighter aircraft in service. The F-22 Raptor can supercruise up to Mach 1.8 without external stores.[15][16] (Note: General Electric YF120 supercruise capable engines also powered an F-22 prototype during this fly off, but were not selected for production.)
  • The EJ200 engine built by EuroJet Turbo GmbH mounted in the Eurofighter Typhoon. It is capable of supercruising at Mach 1.5 with an air superiority missile load.[12] Typhoon pilots have stated that Mach 1.3 is attainable in combat configuration with external stores.[17]
  • The General Electric F414G in JAS 39 Gripen NG is designed for supercruise and has been shown to achieve Mach 1.2.[18]
  • The Snecma M88 that power the Dassault Rafale. The twin engines enable the Rafale to supercruise with four missiles and a belly drop tank.[11]
  • The two AL-41F-1S engines of the Sukhoi Su-35 can achieve supersonic speed without engaging afterburners. But without any external weapons load.[19]

Independently, Russia is working on Izdelje 30 (after AL31F and AL41F derivatives modifications, like 117S turbofan) and RD33MKRU Morskaja Osa; an all new AL-41 engine with a complete redesign underway to add supercruise ability to the Sukhoi Su-57. This has yet to bear fruit, but the stop-gap 117S engine, produced by this program, seems to achieve the supercruise goal already. It was recently announced that during testing of a Su-35BM fighter equipped with these engines it was travelling at just past supersonic speed it continued to accelerate without the use of the afterburner, thus suggesting that it had supercruise capability, though it has yet to be seen whether this will be possible with a combat load.[20]

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 for eluding detection.

Aircraft designed to cruise on afterburner

The Lockheed A-12, SR-71 Blackbird, and YF-12, were designed for sustained operation at supersonic speeds using an afterburner. SR-71 missions flew at maximum range cruise, with afterburner settings in the lower portion of the range, about 98% of the time.[21]

The North American XB-70 Valkyrie used six General Electric YJ93 engines for sustained flight at Mach 3.0, its design point.[22] Unlike the J-58 engine in the SR-71, the YJ93 did not need special fuel, as it used JP-6.[22] Partial afterburner was used for cruise.[23] The XB-70A AV-2 prototype sustained speeds in excess of Mach 3 for 32 minutes on one flight. The type was designed to operate at its design point speed for periods of hours over intercontinental ranges.[24] At 100% military thrust (maximum throttle without afterburner), at 35,000 ft (11,000 m), the XB-70 would exceed M1.03 so long as its mass did not exceed 400,000 lb (180,000 kg), rising to M1.2 as the mass dropped to 250,000 lb (110,000 kg)[25]

The Mikoyan-Gurevich MiG-25 was designed for supersonic cruise at Mach 2.35 with partial afterburner in operation. The engines used an extremely low pressure ratio of 4.75, but this was boosted by ram air pressure during supersonic flight.[26] The low pressure ratio of the compressor meant poor efficiency at subsonic speeds, and high efficiency at supersonic speeds.

The BAC TSR-2 was designed to cruise at M2.0 using afterburners, and had a predicted top speed of M2.35. It could also cruise supersonically without afterburner, as demonstrated on a delivery flight.[27][28]

Aircraft with supercruise ability

In service:

Formerly in service:

  • General Dynamics F-16N Fighting Falcon[35]

Prototype/experimental only:

Civilian:

References
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  2. "Stealth design of airplanes / stealth aircraft". fighter-planes.com. Retrieved 2015-09-04.
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  4. "1956 - 0414 - Flight Archive". flightglobal.com. Retrieved 2015-09-04.
  5. "English Electric - Armstrong Siddeley - Rolls-Royce Avon - 1957 - 0541 - Flight Archive". flightglobal.com. Retrieved 2015-09-04.
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  10. The Cutting Age, p.141
  11. French Ministry of Defense Orders a Further 59 Rafale Fighters
  12. "Eurofighter Typhoon - Luftüberlegenheitsrolle - Austrian Eurofighter Site in German". web.archive.org. Archived from the original on August 15, 2009. Retrieved 2015-09-04.CS1 maint: unfit URL (link)
  13. Ayton, Mark. "F-22 Raptor". AirForces Monthly, August 2008, p. 75. Retrieved: 19 July 2008.
  14. "Gallery of USAF Weapons", pp. 147–155. Air Force Magazine, May 2006.
  15. General Jumper qualifies in F/A-22 Raptor, af.mil, January 13, 2005
  16. Last of its kind. Flightglobal.
  17. "EuroFighter Typhoon". fighter-planes.com. Retrieved 2015-09-04.
  18. "Gripen Supercruises." Gripen International, 21 January 2009.
  19. "AL-41F-1C."
  20. "О ходе испытаний нового российского истребителя Су-35БМ: Наука и техника: Lenta.ru". lenta.ru. Retrieved 2015-09-04.
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  41. "Saab 35 Draken". Saab.com. 2015-12-14. Retrieved 2018-03-24. At that time there was limited understanding of supersonic aviation, which is why the "double delta" configuration had been tested earlier in 1952 using the specially developed Saab 210 "Little Dragon" experimental aircraft. The maiden flight was carried out on 25 October 1955 by Bengt Olow and shortly afterwards, in January 1956, the Draken broke the sound barrier while climbing and without afterburner!
  42. 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.
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