Podded engine

The nacelle consists of an inlet, an exhaust nozzle and a cowling which opens for access to the engine accessories and external tubing.

It has opening doors which allow access for regular maintenance such as adding oil as well as unscheduled replacement of engine accessories and external tubing.

The shape of the lip on the inlet, the minimum internal area and the internal profile, are established with different engine airflows at cruise to keep pressure losses acceptable, and different incident airflow angles such as in cross-winds and during take-off rotation to keep variations in pressure across the fan face acceptable.

Pressure losses in the exhaust nozzle also affect the engine performance by increasing the fuel consumption.

Instead, in these cases it is common to mount two (or occasionally four) podded engines on the rear of the fuselage, where they are less likely to be damaged by ingesting foreign objects from the ground.

The local airflow at the airplane's tail is typically descending with respect to the centerline of the aircraft's fuselage.

This placement uses the Coandă effect to give a lower minimum flight speed and decrease the length of runway needed for takeoff and landing.

In general, the idea is to mount the engine where it will receive good air flow, be distant from the ground to avoid foreign object damage, and not occupy fuselage space.