Intake ramp

An F-15 with its two intake ramps in different positions

An intake ramp is a rectangular, plate-like device within the air intake of a jet engine, designed to generate a shock wave 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 an oblique shock wave at the forward end of the ramp. Air crossing the shock wave suddenly slows to a lower Mach number, thus increasing pressure.

Ideally, the 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.

Some supersonic intakes feature two or more ramps, operating in series, to generate multiple oblique shock waves. Each downstream ramp is steeper in inclination than the previous ramp. These intakes are usually more efficient than single (oblique) shock wave inlets. For a fixed geometry it is feasible to use curved intakes without any shocks before the final normal shock. Modern fighter jets (like the F-22 Raptor) have engines so powerful that top speed is not limited by them, thus spillage at the intake is acceptable and a lightweight fixed geometry chosen. The nacelle has a round outer lip to defect spillage back into the longitudinal direction. The nacelle thus gets a very large cross section with more volume than needed for the engine and in the F-22 the nacelles are combined with the fuselage to create a large weapon bay, place for fuel, and a wide body, which generates some lift. Modern jets have a horizontal ramp thus spillage at least produces some lift. In case of the F-22 the inlet has two ramps placed in a diamond shape, thus for most Mach- and thrust-conditions spillage occurs only at the aft / lower corner of that diamond. In case of the F-22 the leading edges of the wing become supersonic at Mach 1.8 and certainly are as large a source of wave drag as the inlet.

Variable geometry intakes, such as those on Concorde aircraft, vary the ramp angle to focus the oblique shock wave/s onto the intake lip.

Intake gallery

Concorde ramp moves down on higher Mach numbers
The ramp of the Concorde is clearly visible
F-14 with internal ramp
At subsonic speeds the ramp of the F-15 points downwards
Vertical ramp on the XB-70

References

Aircraft components and systems

Airframe structure	Aft pressure bulkhead Cabane strut Canopy Cruciform tail Dope Empennage Fabric covering Fairing Flying wires Former Fuselage Hardpoint Interplane strut Jury strut Leading edge Lift strut Longeron Nacelle Rib Spar Stabilizer Stressed skin Strut T-tail Tailplane Trailing edge Twin tail Vertical stabilizer V-tail Wing root Wing tip Wingbox

Flight controls	Aileron Airbrake Artificial feel Autopilot Canard Centre stick Deceleron Dive brake Electro-hydraulic actuator Elevator Elevon Flaperon Flight control modes Fly-by-wire Gust lock Rudder Servo tab Side-stick Spoiler Spoileron Stabilator Stick pusher Stick shaker Trim tab Wing warping Yaw damper Yoke

Aerodynamic and high-lift devices	Active Aeroelastic Wing Adaptive compliant wing Blown flap Channel wing Dog-tooth Droop Flap Gouge flap Gurney flap Krueger flap Leading edge cuff LEX Slats Slot Stall strips Strake Variable-sweep wing Vortex generator Vortilon Wing fence Winglet

Avionic and flight instrument systems	ACAS Air data computer Airspeed indicator Altimeter Annunciator panel Attitude indicator Compass Course deviation indicator EFIS EICAS Flight data recorder Flight management system Glass cockpit GPS Heading indicator Horizontal situation indicator INS Pitot-static system Radar altimeter TCAS Transponder Turn and slip indicator Vertical Speed Indicator Yaw string

Propulsion controls, devices and fuel systems	Autothrottle Drop tank FADEC Fuel tank Gascolator Inlet cone Intake ramp NACA cowling Self-sealing fuel tank Splitter plate Throttle Thrust lever Thrust reversal Townend ring Wet wing

Landing and arresting gear	Arrestor hook Autobrake Conventional landing gear Drogue parachute Landing gear Landing gear extender Oleo strut Tricycle landing gear Tundra tire

Escape systems	Ejection seat Escape crew capsule

Other systems	Aircraft lavatory Auxiliary power unit Bleed air system Deicing boot Emergency oxygen system Entertainment system Environmental control system Hydraulic system Ice protection system Landing lights Navigation light Passenger service unit Ram air turbine Weeping wing

This article is issued from Wikipedia - version of the Saturday, April 02, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.

Intake ramp

Intake gallery

References

See also