An intake ramp is a rectangular, plate-like device within the

air intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...

of a jet engine, designed to generate a number of

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

s to aid the inlet compression process at supersonic speeds. The ramp sits at an acute angle to deflect the intake air from the longitudinal direction. At supersonic flight speeds, the deflection of the air stream creates a number of oblique shock waves at each change of gradient along at the ramp. Air crossing each shock wave suddenly slows to a lower Mach number, thus increasing

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

. Ideally, the first oblique shock wave should intercept the air intake lip, thus avoiding air spillage and pre-entry drag on the outer boundary of the deflected streamtube. For a fixed geometry intake at zero incidence, this condition can only be achieved at one particular flight Mach number, because the angle of the shock wave (to the longitudinal direction) becomes more acute with increasing aircraft speed. More advanced supersonic intakes feature a ramp with a number of discrete changes of gradient in order to generate multiple oblique shock waves. In the case of

Concorde The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC). Studies started in 1954, and France an ...

, the first (converging) intake ramp is followed by a diverging ramp. After the air passes the end of the first ramp it has become subsonic such that the diverging ramp further contributes towards the reduction in airstream velocity and consequently its increase in pressure. This intake design thus ensures excellent pressure recovery and contributes to Concorde's improved fuel efficiency whilst cruising supersonically at up to Mach 2.2 (beyond which airframe heating effects limit any further increase in speed). Variable geometry intakes, such as those on Concorde, vary the ramp angle to focus the series of oblique shock waves onto the intake lip, control of which is accomplished by complex non-linear control laws using the ramp void pressure (the pressure of the air in the gap between the two ramps) as a control input. The intake ramp for rectangular intakes has its equivalent in the

inlet cone Inlet cones (sometimes called shock cones or inlet centerbodies) are a component of some supersonic aircraft and missiles. They are primarily used on ramjets, such as the D-21 Tagboard and Lockheed X-7. Some turbojet aircraft including the Su-7 ...

for circular intakes. Much lighter fixed-geometry alternatives are used on modern aircraft which are designed with greater emphasis on durability and survivability (stealth). These inlets preserve the performance of variable intake ramps by controlling shock position using the downstream pressure. They include the caret compression surface, used in the

Boeing F/A-18E/F Super Hornet The Boeing F/A-18E and F/A-18F Super Hornet are twin-engine, carrier-capable, multirole fighter aircraft variants based on the McDonnell Douglas F/A-18 Hornet. The F/A-18E single-seat and F/A-18F tandem-seat variants are larger and more ad ...

and

Lockheed Martin F-22 Raptor The Lockheed Martin F-22 Raptor is an American single-seat, twin-engine, all-weather stealth tactical fighter aircraft developed for the United States Air Force (USAF). As the result of the USAF's Advanced Tactical Fighter (ATF) program, th ...

inlets, and the diverterless supersonic inlet used on the

Lockheed Martin F-35 Lightning II The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather Stealth aircraft, stealth multirole combat aircraft that is intended to perform both Air superiority fighter, air superiority and attack ...

and Chengdu J-20.

Intake gallery

Image:Concorde Ramp.jpg, The ramps in two of the Concorde intakes are visible and clearly labelled as such. Image:F-14_3_Yokota_Tokyo.jpg,

F-14 The Grumman F-14 Tomcat is an American carrier-capable supersonic, twin-engine, two-seat, twin-tail, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experimental (VFX) program after the ...

with internal ramps forming upper surface of intake duct Image:North American XB-70 above runway ECN-792.jpg, Vertical ramps on inboard surface of intake duct

XB-70 The North American Aviation XB-70 Valkyrie was the prototype version of the planned B-70 nuclear-armed, deep-penetration supersonic strategic bomber for the United States Air Force Strategic Air Command. Designed in the late 1950s by North Ame ...

Image:F-15E Strike Eagle is parked by a crew chief from Elmendorf Air Force Base.jpg,

F-15 The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather tactical fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force selected McDonnell Douglas's ...

internal ramps form upper surface of intake duct behind the intake upper lips which are shown in different positions

Intake gallery

References

See also