The power supply is certainly one of the most complex parts of an aircraft. To be power supplied while on the runway, planes have a large number of systems that complement each other and operate redundantly. Everything is designed so that other alimentation systems can take over in the event of the failure of one or more sources.
Airplanes today are filled with electronics, and for some, the flight controls are even fully electric. Airbus was the first manufacturer to offer electric flight controls managed by digital computers, with its A320. Let’s see now what are the different ways to power an aircraft.
The Aircraft batteries
Like most vehicles, planes have batteries. These are mainly lead, Nickel Cadmium (Ni-Cd), or Lithium-Ion (Li-ion).
Unfortunately, the large number of electrical systems onboard an aircraft does not allow to rely entirely on the batteries. These can very quickly be discharged, and would not support the energy required by the ignition of the engines of an airliner either. For small planes, the ignition can be supported by batteries.
Auxiliary Power Unit (APU)
It is a small turbojet that is generally located at the rear of the fuselage. It is powered by the same kerosene as the engines. The APU provides the aircraft with electricity, but also air conditioning when its engines are off. Due to its small size, an electric starter powered by batteries is sufficient to start it.
In turn, the APU will provide the pneumatic energy needed to ignite the engines. After the engines start, the APU is usually shut down. Indeed, the reactors will take over the air conditioning and power supply.
The air outlet of the APU materializes on the majority of aircraft through the hole at the end of the tail. And if there is an exit, there is of course an entrance, which is located nearby.
Ground Power Unit (GPU)
Runway generators provide electrical power to aircraft on the ground for economic as well as ecological purposes, taking over from APUs. Thus, the availability of these groups is crucial to minimize the downtime of the aircraft on the ground.
Why use the GPU?
- Not all aircraft are equipped with APUs.
- It saves fuel, unlike the APU.
- Some airports prohibit the use of the APU in the parking lot.