Inlets and Diffusers Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Ram compression alone gives a pressure ratio near 37 at Mach 3, comparable with a whole compressor. Once the intake supplies that, the compressor and the turbine driving it can be removed - leaving an intake, a combustor and a nozzle, which is the ramjet.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the intake slows the flow and raises its static pressure, and recovery measures how much total pressure survived. Statement 3 is precisely what an intake cannot do - with no shaft and no fuel it has no means of adding energy, only of converting the kinetic energy already present.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: supersonic flow cannot decelerate to subsonic without a shock, and several weak oblique shocks destroy far less total pressure than one strong normal shock - 0.92 against 0.72 at Mach 2. Statement 3 has it the wrong way round: it is the internal compression intake that is prone to unstart, since its shock system is swallowed and can be expelled.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: distortion is non-uniformity at the compressor face, and swirl changes the angle at which air meets the first rotor blades. Statement 3 is the assumption that has caused trouble in practice - recovery is an average and distortion a spread, so a high average can conceal a badly distorted profile that will surge the compressor.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 describe the streamtube correctly at the two extremes. Statement 3 has the sense of spillage inverted: it arises when the intake captures less than the approaching streamtube offers, so the surplus is turned aside. Air the intake actually captures is not spilled.

Answer: B

The progression is one of splitting the deceleration across more and weaker shocks as Mach number rises. Each step buys recovery at the cost of complexity, which is why the simplest type that will do the job is always preferred.

Answer: C

Correct answer: A-1, B-2, C-3, D-4

Four distinct faults with four distinct causes. Spillage drag comes from turning aside air the intake does not capture. Buzz is an unsteady oscillation of the shock system, usually at reduced mass flow. Unstart is the shock system being expelled forward of the cowl, with an abrupt loss of recovery and thrust. And distortion is non-uniform total pressure arriving at the compressor.

Answer: D

Correct answer: A-1, B-2, C-3, D-4

Four features answering four requirements. The diverter keeps the fuselage boundary layer out. Bleed removes the low-energy air that collects under the shock, where the adverse gradient would otherwise separate it. Variable ramps move the shock system as the flight condition changes. And blow-in doors open at static and low speed, when the fixed intake area is too small for the airflow the engine demands.

Answer: A

The intake is sized so that the fourth condition falls at the most important point of the envelope. Everywhere else the streamtube departs from the capture area, and the departure is what produces lip loading or spillage drag.

Answer: B

An inlet converts kinetic energy already present into static pressure and adds nothing. The best it can achieve is to perform that conversion while losing as little total pressure as possible, which is exactly what recovery measures.