Sources of Electrical Power in Aircraft: An In-Depth Guide
Aircraft utilize a diverse range of electrical power sources to operate their sophisticated systems and ensure smooth operations. This guide delves into the primary sources of power used in modern aeroplanes, providing a comprehensive overview of the systems and processes involved.
Engine-Driven Generators
Engine-Driven Generators: Most commercial and large aircraft rely on engine-driven generators to convert mechanical energy from the aircraft engines into electrical energy. These generators, located under each wing or in the tail cone, typically produce alternating current (AC). These generators play a crucial role in powering the various electrical systems during flight.
APU Auxiliary Power Unit
APU (Auxiliary Power Unit): The APU is a small turbine engine located in the aircraft that provides electrical power and pneumatic pressure when the main engines are not operating. It is particularly useful during ground operations to supply power for systems such as lighting, avionics, and cabin air conditioning.
Batteries
Batteries: Aircraft have onboard batteries, typically lead-acid or lithium-ion, which provide essential power for starting the engines and can supply electrical power during emergencies or when external power is not available. These batteries are crucial for ensuring the aircraft can start its engines and operate in critical situations.
External Power Sources
External Power Sources: During ground operations, aircraft can be connected to external power units (GPU) that supply electricity for systems like lighting, avionics, and cabin air conditioning before the engines are started. This is a convenient and efficient way to power up the aircraft without the need for engine operation.
Solar Power
Solar Power: In some cases, solar panels can be integrated into modern or experimental aircraft to supplement power, particularly for smaller UAVs (Unmanned Aerial Vehicles) or specific applications. Solar power provides a renewable energy source that can reduce the dependency on conventional power systems.
Fuel Cells
Fuel Cells: Research and development in aviation have seen the exploration of fuel cells as a potential power source, especially for future environmentally friendly aircraft. Fuel cells offer a cleaner and more efficient alternative to traditional power generation methods.
These various sources of power work together seamlessly to ensure that all electrical systems in the aircraft, including navigation, communication, and environmental controls, function effectively throughout the flight.
Power System Overview on a Boeing Twin Jet
On a typical Boeing twin jet, there are three engines: one under each wing and a small jet engine (APU) in the tail cone. On the ground, the plane is plugged into ground power supplied by the airport through a big fat electrical cable. Ten minutes before departure, the APU is started to provide electric power and air for the air conditioning, disconnecting the big fat electric cable.
Engine-Driven Generators
To start the main engines, air conditioning is switched off, and the air from the APU is used to start each engine. Once an engine is running, the next one is started in the same way. Then, the APU is switched off.
Hydraulic Systems
Each main engine drives an electric generator which provides electric power. There are two engines, so there are two generators and therefore two electrical systems (Left and Right). However, each generator can run both systems if needed. If an engine fails, you also lose the generator on that engine. In that case, the other engine will supply electric power for both L and R systems. Additionally, the APU can be started, which has its own generator and can power the whole plane if necessary.
Hydraulic System
Each engine has a hydraulic pump that drives its own hydraulic system. There are three hydraulic systems: Left, Center, and Right. L and R are powered by their respective engine-driven pumps and also an electric pump. The Center system is purely electrically powered. Hydraulic systems are critical because they power flight controls and brakes. It’s important to note that even with three hydraulic systems, you can safely fly and land the plane on just one of those systems.
Emergency Power
If an engine fails, you lose the engine-driven hydraulic pump on that side, but the entire system remains powered by the electric pump from the other engine. The APU can also power the hydraulic system. If both engines fail, all three hydraulic systems can be powered by the APU supplying electricity to the pumps. However, starting the APU can take a few minutes, so if both engines fail simultaneously, a small turbine will pop out of the bottom of the plane. This is called the Ram Air Turbine (RAT). It enables you to still control the plane and even land it if the APU does not work.
Even though this is a simplified version of the power system of a typical twin jet, there are additional power sources like hydraulic-driven generators, air-driven pumps, and power transfer units, which vary depending on the specific aircraft type. Additionally, there are numerous batteries that provide essential backup power for various situations.