What is the hole in the tail of the planes?

You may have noticed that there is a small hole in the back of most commercial aircraft. But, do you know its name and its function?

It's name

The name of these devices mounted in the tail of the airplanes is the unit of auxiliary power or APU (abbreviations in English of Auxiliary Power Unit). The APU provides power for functions other than propulsion. In addition to being used in airplanes, they are also present in ships or some large land vehicles such as trains or trucks.

It's functions

In the case of airplanes, the APU is a relatively small part but with an important function. It is responsible for generating electricity, hydraulic pressure and air conditioning while the engines are off. In addition to supplying energy to rotate the compressor and thus start the engines. And not only that, but they are also used in many cases to keep the aircraft's most necessary systems operating in mid-flight during a possible loss of power. For example, the APU would supply electricity to the hydraulics, lights, or cockpit instruments.

APU cockpit

The first reactor to incorporate an APU

The Boeing 727 was the first jet to incorporate an APU in 1963. This improvement allowed the aircraft to operate in small airports regardless of the facilities they had.

Boeing 727