Most aircraft have a small hole in the tail, but what effect do they have?

If you notice, you will see a small hole with the tip of a commercial plane. It is the smallest engine place but it is very important for operation throughout the flight.

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Most aircraft have a small hole in the tail, but what effect do they have? Picture 1

The engine is located in the small hole at the tail of the aircraft called APU (Auxiliary Power Unit) - an auxiliary electric motor that provides energy to activate the main engine and power the electrical equipment in the carrier. Guests like air conditioning, lighting . when the plane is parked on the ground. When the plane runs on the runway, the main engine will replace APU.

APU's electricity also helps pilots, mechanics to check the aircraft, contact the airport from the cockpit, operate gates, pay goods, and power the kitchen and toilet. fly.

Most aircraft have a small hole in the tail, but what effect do they have? Picture 2

When the plane landed, the main engine was returned to the small station mode, one engine was turned off, only one engine operated when the aircraft rolled into the parking lot. 2 minutes before the plane stops, the APU auxiliary engine is started, re-energizing the aircraft as it did not take off.

Military aircraft also have APU but simply to save fuel, saving the main engine hours only, not as important as commercial aircraft.