Chapter 7 is devoted entirely to a discussion of undercarriage design.

1.24 Nacelle and Intake

A nacelle is the structural housing for an aircraft engine. In civil aircraft, nacelles are invariably externally pod-mounted, either slung under or mounted over the wing or attached to the fuselage (see Figure 4.28). The front part of the nacelle is the intake and the aft end is the nozzle. Military aircraft engines are invariably buried in the fuselage; the front is called the intake in the absence of a nacelle. Chapter 10 discusses the nacelle in detail.

In addition to housing the engine, the main purpose of the nacelle is to facili­tate the internal airflow reaching the engine face (or the fan of gas turbines) with minimum distortion over a wide range of aircraft speeds and attitudes. For subsonic turbofans, the intake acts as a diffuser with an acoustic lining to abate noise gen­eration. The inhaled air-mass flow demanded by an engine varies considerably: At idle, just enough is required to sustain combustion, whereas at maximum thrust, the demand is many times higher. A rigid intake must be sized such that during critical operations (i. e., takeoff, climb, and cruise), the engine does not suffer and gener­ates adequate thrust. Supersonic intakes are even more complex and are designed to minimize loss resulting from shock waves.

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