Inlets and Diffusers Questions and Answers

Answer: C

The flow must turn hardest around the lip when the aircraft is stationary and the engine is drawing from a wide region ahead of it. A sharp lip separates there, which is why supersonic aircraft often need auxiliary doors for take-off.

Answer: D

Correct answer: Additional shocks give steadily smaller gains for added complexity

The gains fall away sharply: the second shock is worth 15 points of recovery, the third five, and the fourth two. Since each additional ramp adds weight, mechanism and cost, there is a point beyond which another shock is not worth having - which is why practical intakes use two or three rather than a dozen.

Answer: A

None of these features is free, and each is fitted only where the problem it solves outweighs what it costs. That balance shifts with the flight envelope, which is why intakes on aircraft of different mission look so unlike one another.

Answer: B

Both statements are true and the second is the reason. Splitting the deceleration across several weak oblique shocks keeps the product of their pressure ratios high, where one strong shock would waste an unacceptable fraction of the available pressure.

Answer: C

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. The intake has no moving parts and burns no fuel, so it can add nothing. What it does is convert kinetic energy the air already possesses into static pressure by slowing it down, and the total pressure recovery measures how much of that energy survives the conversion.

Answer: D

Both are true and the second is the reason for the separate treatment. Recovery is an average and says nothing about uniformity, yet a blade passing through a low pressure sector sees a momentarily higher incidence and may stall.

Answer: A

Both statements are true and the second is the justification. Ingesting that air would degrade both recovery and stability, so the airframe accepts a drag penalty in exchange for keeping it out of the compressor altogether.

Answer: B

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

Both are true and the reason gives the mechanism. At high speed the free stream delivers a large streamtube to a capture area that cannot change; throttling reduces what the engine will swallow, and the surplus must be turned aside around the cowl. The momentum lost in turning it is the spillage drag.

Answer: C

Both are true and the second is the reason. Bleeding away the low energy air keeps the shock boundary layer interaction manageable, so the penalty buys the intake's stability rather than any improvement in its performance.

Answer: D

The reason is true but it does not support the assertion, which is false. At supersonic speed a rounded lip increases cowl drag, which is why fast aircraft use sharp lips and add blow-in doors for the take-off case instead.