Inlets and Diffusers Questions and Answers

Answer: C

Keeping the compression internal avoids the cowl drag of external turning and can give excellent recovery. The difficulty is that the shock system must be started and held in place, and a small disturbance can expel it violently.

Answer: D

It combines the robustness of external compression with the low cowl drag of internal compression, which suits sustained high supersonic flight. The penalty is complexity, since variable geometry and bleed are needed to keep the shock system positioned.

Answer: A

The intake loses its designed shock structure abruptly, recovery collapses and the engine may surge or flame out. Restarting usually requires slowing down or repositioning the variable geometry, and the transient loads can be severe.

Answer: B

The shock moves rapidly in and out of the duct, producing violent pressure fluctuations that can damage structure and upset the engine. It typically appears when the intake is operating well below its matched mass flow, which is a throttled condition at speed.

Answer: C

Boundary layer air is low in total pressure and highly distorted, and ingesting it degrades both recovery and compressor stability. The diverter costs drag and weight, which is the price paid for keeping that air out of the engine.

Answer: D

A shock impinging on a boundary layer thickens it and can separate it entirely, destroying the shock structure. Bleeding that low energy air away keeps the interaction manageable, at the cost of the drag associated with dumping it overboard.

Answer: A

A blade passing through a low pressure sector sees a momentarily higher incidence and may stall, even though the average condition looks acceptable. That is why distortion is quantified separately from recovery and treated as a stability rather than a performance issue.

Answer: B

Swirl changes the incidence on the first rotor row directly, either loading or unloading it depending on its direction. Modern intake assessments treat it alongside pressure distortion because either can trigger a surge on its own.

Answer: C

Accretion disturbs the flow field the intake was designed around and a shed fragment can damage the fan directly. Hot bleed air or electrical heating keeps the leading edge above freezing, which is why anti-icing is a required system rather than an optional one.

Answer: D

A mismatch appears as spillage drag if the intake supplies too much or as poor recovery and instability if it supplies too little. Matching must hold across the whole flight envelope, which is precisely why variable geometry appears on high speed aircraft.