Most commercial jetliners have a small hole in the tail. Have you ever wondered what this hole is there for ? The number of engines in an airplane differs with the size of the plane. Some plane has 2 engines while and big planes like Boeing have 4 engines.

But there is one more engine which you do not know. Let me introduce you the smallest engines in an airplane which plays a prominent role in smooth running of an airplane. Airplanes have a secret engine hidden in the tail.

Read: Why Planes Dim Their Lights When Landing? Here’s The Reason

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Airplane Has A Secret Engine Hidden In The Tail:

If you observe most jetliners have a hole in the tail. In fact, it’s part of what’s called an auxiliary power unit (APU). An airliner’s APU is a hidden extra engine, typically a gas turbine engine like jet engines themselves.

But the APU doesn’t help the plane move. It helps when the airplane is parked. The pilots will use the APU to power onboard electric systems from cabin lights and coffee makers to various cockpit systems as well as to provide airflow to the air conditioning systems.

APU Heps To Start Main Engines:

The APU is typically used to start the main engines. Once the engines are running, the APU is normally switched off, to be restarted only when the plane is on the ground at its destination. When it comes to cooling and lighting a parked plane, the APU is much more efficient than the main engines.

Your mind might be puzzled with one question at this moment. If the APU starts the main engines, then what starts the APU ? Typically an aircraft’s batteries. So next time when you take off thank that tiny engine in the tail.

Also Know: Why Airplanes Are Painted White In Color ?

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