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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]
Contents
Advantages
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 of time. 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]History
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 August 11, 1954. However, this early demonstration of supercruise was extremely limited; the Lightning could supercruise at approximately Mach 1.22[3] while later versions were able to achieve much higher speeds.
The British Aircraft Corporation Tactical Strike/Reconnaissance 2 (TSR-2), which first flew on September 27, 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.[4] 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
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 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).[6] 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.[7]
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.
- The Pratt & Whitney F119 in combination with the F-22 Raptor
- The Snecma M88 engine in the Dassault Rafale allows it to supercruise in dry power, even with four missiles and a 1000-liter belly tank and even in the naval version; it can supercruise while carrying six air-to-air missiles (MBDA MICA).[8][9]
- The EJ200 engine built by EuroJet Turbo GmbH adds the supercruise capability in the Eurofighter Typhoon, and is capable of supercruising at Mach 1.5.[5] Typhoon pilots have stated that Mach 1.3 is attainable in combat configuration with external stores.[citation needed]
- The General Electric F414G in JAS 39 Gripen NG is designed for supercruise and has been shown to achieve Mach 1.2.[10]
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-31 117S engine, produced by this program, seems to achieve the supercruise goal already.[citation needed] It was recently announced[13] 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
The Pratt & Whitney J58 engines of the Lockheed A-12 and SR-71 Blackbird were designed for sustained and efficient operation at supersonic speeds using afterburners with air that was diverted past the turbojet core of the engine. This gave a good compression ratio and higher efficiency simply due to the ram effect at the high operating speed of the aircraft. The afterburners acted essentially as ramjets and these types of engines achieve peak efficiency at around Mach 3.In a somewhat similar vein, the XB-70A Valkyrie made use of specially designed turbojets (six General Electric YJ-93 engines) to sustain speeds in excess of Mach 3. Unlike the J58 engines powering the SR-71, the YJ-93 engines of the XB-70A did not require the use of special fuel, and did not radically modify the intake/exhaust geometry in order to achieve Mach 3 flight. The YJ-93 engines did operate in afterburner at Mach 3; however, the engines were specifically designed to be very efficient in afterburner, and the XB-70A AV-2 prototype sustained speeds in excess of Mach 3 for 32 minutes on one flight. Furthermore, the type was designed to operate at such speeds for periods of hours over intercontinental ranges.[14]
Ramjets and scramjets
Ramjet and scramjet powered aircraft have to date been mostly experimental (with exceptions such as the SR-71 and its turbojet/ramjet hybrid J58 engines, as noted above; and there have been numerous ramjet missiles), but these engines operate most efficiently 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
Aircraft with supercruise include:- English Electric Lightning (The first aircraft capable of supercruise)
- Saab Draken
- Lockheed Blackbird (A-12, YF-12 and SR-71)
- Tupolev Tu-128[citation needed]
- Tupolev Tu-144
- Tupolev Tu-160
- Concorde[15]
- BAC TSR-2
- F-16XL
- Eurofighter Typhoon
- Dassault Rafale
- Chengdu J-10[citation needed]
- Gripen NG[16][17]
- F-22 Raptor
- YF-23 Black Widow II
- Sukhoi Su-35BM
- Mikoyan MiG-31
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