Inlets and Diffusers Questions and Answers

Answer: A

A sharp lip is right for supersonic cruise but wrong for static conditions, where the flow must turn hard into the duct from a wide region ahead. Blow-in doors provide extra area at low speed and close once the aircraft is moving fast enough.

Answer: B

Recovery is an average and says nothing about how uniform the flow is across the face. A blade passing through a low pressure sector sees a momentarily higher incidence, which is precisely how a compressor surges with acceptable average conditions.

Answer: C

A shock impinging on a thickened boundary layer can separate it entirely and destroy the shock structure. Bleed removes that low energy air to keep the interaction manageable, so its weight and drag buy the intake's stability.

Answer: D

It is the single figure expressing how much of the available energy the intake preserved. A loss of one per cent typically costs rather more than one per cent in thrust, which is why intake design receives such attention on high speed aircraft.

Answer: A

Above Mach one the area velocity relation reverses, so a diverging passage accelerates the flow rather than slowing it. The shock supplies the discontinuous transition, and its total pressure loss is the price of making the change at all.

Answer: B

The excess air must be turned around the intake, and the pressure forces of that turning appear on the airframe. It is worst when the engine is throttled at high speed, since demand falls while the capture area stays fixed.

Answer: C

Recovery collapses, distortion rises sharply and the engine may surge or flame out within moments. Restarting normally requires slowing down or repositioning the variable geometry, and the transient loads can be severe on the structure.

Answer: D

It is assessed separately from recovery because a compressor can surge on it even when the average condition looks entirely acceptable. A blade passing through a low pressure sector momentarily sees a higher incidence and may stall.

Answer: A

The three are indistinguishable at 0.85 and close at 1.4, but the single normal shock loses badly by Mach 2. That divergence is exactly why multi-shock intakes appear on aircraft designed to cruise above about Mach 1.6.

Answer: B

Correct answer: A mechanical compressor becomes unnecessary

At Mach 3 the intake alone delivers a pressure ratio of 36.7, which exceeds what many turbojet compressors provide. Since the compressor and its turbine exist only to raise that pressure, both can be dispensed with - which is the ramjet, an engine with no rotating machinery at all.