Inlets and Diffusers Questions and Answers

Answer: C

A rounded lip prevents separation when the flow turns hard into the intake on the ground, which is why subsonic aircraft use one. Supersonic aircraft accept a sharp lip for its lower cowl drag and add blow-in doors for the take-off case.

Answer: D

Internal compression is the most fragile of the arrangements, because its shock system must be started and then held in place. A small disturbance can expel it violently, which is exactly what makes external compression more forgiving.

Answer: A

Recovery is an average across the compressor face and carries no information about uniformity. A blade passing through a low pressure sector momentarily sees a higher incidence, which is precisely how a surge occurs at acceptable average conditions.

Answer: B

Correct answer: Ingesting the fuselage boundary layer

Boundary layer air arrives already depleted in total pressure, so taking it in lowers recovery rather than raising it - and distorts the flow besides. The other three all help: preventing separation preserves what the shocks left, an oblique shock ahead of the terminal one weakens it, and bleed removes the low-energy air the shock would otherwise separate.

Answer: C

The intake captures only what the engine demands, and the remainder of the approaching streamtube flows around the outside. Turning that air produces the pressure forces that appear as drag on the airframe rather than as anything useful.

Answer: D

Variable geometry exists precisely to improve recovery across the envelope, which is why it is fitted at all. The other three are the genuine penalties that keep it off aircraft whose envelope a fixed intake can cover adequately.

Answer: A

Loss across a normal shock rises steeply with upstream Mach number, and by 2.5 a single shock keeps only about half the total pressure. Multi-shock arrangements recover well over 0.8 at the same condition, which decides the matter.

Answer: B

A uniform reduction is a loss of recovery and affects performance rather than stability. Distortion specifically describes variation across the face, which is what threatens the compressor by changing blade incidence sector by sector.

Answer: C

Bleed dumps low energy boundary layer air overboard, so the engine receives less than the intake captured. What it buys is a manageable shock boundary layer interaction, without which the intake could separate and unstart entirely.

Answer: D

Recovery collapses rather than improving, since the designed shock structure has been lost altogether. The other three are exactly the consequences that make an unstart a serious event rather than a mere performance excursion.