Ever wondered about that loud jet-like noise you hear as you board a plane? It’s not the engines starting up, but the noise of the Auxiliary Power Unit, or APU. It’s a small turbine engine typically located near the rear of an aircraft’s fuselage. Hence, the jet-like noise from the APU. While it may seem like a mini jet engine, it’s not designed to propel the plane forward. Instead, the APU provides additional energy for various functions when the aircraft is on the ground.
The Many Roles of an APU
Here are some of the primary functions of an APU:
- Engine Starting: The APU generates the power needed to start one of the aircraft’s main engines, making it essential for preparing the plane for takeoff.
- Onboard Power: When an aircraft is parked at the gate, the APU supplies electricity for onboard lighting, cockpit avionics, and galley equipment. This ensures that the plane remains functional and comfortable for passengers and crew, even when the main engines are turned off.
- Climate Control: The APU also plays a crucial role in maintaining a comfortable cabin temperature. It draws air from its own compressor, which is then used to heat or cool the aircraft’s interior.
One of the biggest advantages of using an APU is that it helps conserve fuel and reduce maintenance costs by eliminating the need to start one of the main engines while waiting for passengers or during pre-flight preparations.
The APU is mostly used when the aircraft is on the ground. In most cases, it’s shut down before takeoff and restarted once the plane has landed and cleared the runway. However, in some situations, the APU can also serve as an emergency electrical power source during flight.
A Brief History of APUs
The concept of an APU has been around for quite some time. Early versions of APUs could be found on the B-29 Superfortress and Convair XP5Y-1. The Boeing 727 was the first Boeing aircraft to be equipped with an APU.
These days, APUs can be found on a wide range of medium to large civil and military jets, some turboprop aircraft, and even a few military fighters. However, smaller civilian jets, such as the Cessna Citation CJ or One Aviation’s Eclipse jet, don’t have APUs due to the added weight, which can significantly impact the airplane’s useful load.
The Future of APUs
As aircraft technology continues to advance, APUs will likely become even more efficient, quieter, and environmentally friendly. With ongoing research and development, we can expect to see further improvements in APU performance and capabilities, making them an even more integral part of modern aircraft.
The APU may be a relatively small and often overlooked component of an airplane, but its role is undeniably crucial. It keeps passengers comfortable, powers essential onboard systems, and helps conserve fuel and reduce maintenance costs.
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
