Airplanes consume a substantial amount of energy during flight. Not all of this energy, however, is spent on powering the engines. Airplanes consume energy to power all their electronic devices, including cabin lights, exterior lights, cockpit controls and more. Thankfully, most airplanes are designed a special component that’s responsible for powering these devices Known as an auxiliary power unit (APU), it plays an important role in the function of modern-day airplanes.
Overview of APUs
An APU is a component found on medium- and large-sized airplanes that’s designed to power electrical devices and systems. They typically produce around 115 volts of alternating current (AC), which is used to power the airplane’s electrical devices and systems.
An APU isn’t just a generator, though. It’s actually a miniature engine. Typically found on the tail or around the wheel well, it provides power to the airplane’s electrical devices and systems as needed. Most airplanes, of course, are equipped with at least one generator. The generator is the main source of power for the airplane’s electrical devices and systems. If the generator fails, though, the APU make take over to ensure the airplane’s electrical devices and systems function as intended.
You can think of an APU like a wind generator. During flight, wind will spin the APU’s turbines. The spinning of these turbines then generates electricity that can be used to power the airplane’s electrical devices and systems. As long as an airplane is in the air, the APU will produce electricity.
Why Airplanes Have an APU
The main reason airplanes have an APU is redundancy. Airplanes need power to run their electrical systems and devices. From cabin lights and exterior lights to air conditioning, cockpit controls and more, countless devices and systems in airplanes require power to run. If an airplane’s generator fails, these devices and systems will stop working, which could create a safety hazard for the airplane’s crew and passengers. An APU serves as a backup source of power. When the generator fails to produce a sufficient amount of power, the APU will provide supplemental power to the airplane’s electrical devices and systems.
Some airplanes have an APU to assist with startup as well. Starting an airplane, of course, consumes a substantial amount of power. For particularly large airplanes, an APU may be used to provide supplemental power during takeoff. It provides an additional boost of power that’s often required by large airplanes when taking off.