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. Many well known supersonic military aircraft are not capable of super cruise as
they are only able to maintain supersonic flight in short bursts 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.
Advantages Most military aircraft use afterburners 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 in addition to being visually conspicuous.
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 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. However, this early demonstration
of supercruise was extremely limited; the Lightning could supercruise at approximately
Mach 1.22 while later versions were able to achieve much higher speeds.
The British Aircraft Corporation Tactical Strike/Reconnaissance 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. Supersonic cruise at lower levels was at Mach 1.1 at
200 ft. 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. 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'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
dash as part of a mission would cut the F-22's combat radius from about 600 nautical miles
to about 450 nautical miles. However, this is still unconfirmed as the altitude and flight
profile are classified. The F-22 has demonstrated supercruise speeds
of at least Mach 1.7, a difference of 320 knots indicated airspeed at 40,000 ft. 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. 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 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 engines used in 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-litre belly
tank and even in the naval version; it can supercruise while carrying six air-to-air
missiles. The EJ200 engine built by EuroJet Turbo GmbH
gives the Eurofighter Typhoon supercruise capability. It is capable of supercruising
at Mach 1.5 in clean configuration, though this drops to Mach 1.3 with typical air-to-air
armament. The General Electric F414G in JAS 39 Gripen
NG is designed for supercruise and has been shown to achieve Mach 1.2.
Although the Pratt & Whitney F135 F-35 engine was not designed to achieve a supercruise
capability, the F-35 is able to maintain Mach 1.2 for a dash of 150 miles without using
afterburners. 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.
All known supercruise aircraft can only do so at considerable altitude, which restricts
the use of terrain mask and so makes any non-stealth aircraft very obvious.
Aircraft designed to cruise on afterburner The Pratt & Whitney J58 turbojets used on
the Lockheed A-12 and SR-71 Blackbird needed afterburner to sustain supersonic cruise speeds.
The XB-70A Valkyrie also used afterburning turbojets for a cruise design point of Mach
3.0. Convair B58 Hustler also used the J58 powerplant.
Ramjets and scramjets 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 ability In service:
Eurofighter Typhoon Dassault Rafale
Gripen NG F-22 Raptor
Formerly in service: English Electric Lightning
SR-71 Blackbird Prototype/experimental only:
A-12 YF-12
BAC TSR-2 General Dynamics F-16XL
Northrop YF-23 Lockheed YF-22
Civilian: Concorde
Future: F-35 Lightning II
TAI TFX Advanced Medium Combat Aircraft
AIDC F-CK-1 Ching-kuo Zero Emission Hyper Sonic Transport
SonicStar Sukhoi/HAL FGFA
Sukhoi PAK FA Chengdu J-20
Shenyang J-31 Mikoyan LMFS
References
See also Fuel fraction
Supersonic transport