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 (reheat). Many well known supersonic military aircraft are not capable of supercruise 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.

Most military aircraft use afterburners (or reheat) to occasionally travel at supersonic speeds and cannot reach supersonic speeds using the dry engine thrust. In these cases afterburners are highly inefficient compared to conventional jet engine operation due to the low pressures typically found in the exhaust section, but their engines are more efficient when the afterburners are not operational, although also less powerful.

However, this higher fuel usage limits most aircraft to only using afterburners for 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.

On 3 August 1954 a Gerfaut research aircraft powered by an ATAR 101D2A engine exceeded Mach 1 on the level without afterburner.). The first production intent 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 the P.1, 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 1.02 while later versions were able to achieve much higher speeds.

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Wikipedia