Power Electric
Sunday, July 10th, 2011How the electric Power needed to a Jet Air craft generated the engines generate or some other devices deployed?
Assuming using reductions gears for dynamos to a generate electric power would be difficult @ high revolutions of the engines?
Jason has the best answer: "Yes, for most large commercial aircraft, each engine has an IDG or Integrated Drive Generator unit. This electrical generator is attached directed to the turbine gearbox and employs a CSD or Constant Speed Drive which forces the generator to spin at a constant speed (despite whatever the engine is doing) and to provide the 400hz frequency required for aircraft power supply.
The APU is generally only used on the ground, or in emergencies below 18,000ft (depending on the aircraft)."
However, modern aircraft can operate the APU at high altitudes. It's part of the test flight after overhaul to test the APU at high altitude. It depends on the particular APU unit what the maximum altitude is that it can operate at. The electrical system also employs various power inverters to turn AC into DC where needed and also the RAT, Ram Air Turbine mentioned usually only provides emergency hydraulic power to one actuator of the flight controls, the ailerons, elevators, and the rudder. Especially to the rudder. The other flight controls have two systems going to them but the rudder will have all three systems if so equipped. I believe it is Blue system that goes to all three flight controls if so equipped. The electrical system does "load shedding" if the plane loses a generator. The system sheds load down ot essential systems only. The electrical power priority is as follows, Engine driven generators, external power, APU, Emergency hydraulic generator if so equipped, and then the aircraft battery is the last resort. Lots of things work off of the so called "hot battery bus" until the battery runs down, but it should be enough time to get on the ground. Things like, the stand-by attitude. It is electric. The standby altimeter is an air instrument and operates on it's own system. However I think the pilot's pitot tube is heated by the battery because the system MUST be protected from ice. Also the number one radio is run off of the battery. Also basic emergency lighting. Basic flight instruments and a radio. That's your last resort.