Anonymous asked in Cars & TransportationAircraft · 1 decade ago

Jet engine question and power supply ?.?

How are jet airliner engines started ?. What provides the power to provide electrical supply for all the systems.?. Does a jetliner use batteries or have a more sophisticated way of providing electricity ?.

11 Answers

  • 1 decade ago
    Favorite Answer

    Jet engines have many ways to start. The smaller ones are started by battery (28 volt dc) and the larger ones are air started. An air starter ( for a jetliner) is a small turbine that spools the engine to somewhere around 15% to 22% for fuel on and is released at around 34% during start. The air for the starter is provided by an aircart (a deisel powered compressor) or an APU ( a small battery started centrigal jet engine) using compressor bleed air. A generator with a constant speed drive is mounted to the jet engine gearbox. The CSD is like an automatic transmission for the generator to maintain a constant speed to allow throttle changes. This, along with a control panel and voltage regulator, keep the generator output at a constant 115v/400cycles. Most jetliners have a solid state inverter as back-up for emergecy power (battery)along with a generator mounted to the APU's gearbox.

    Source(s): I work as an aircraft inspector with 27 years of experience. I travel internationally checking out not only aircraft, but audit maintenance bases as well.
  • Jim G
    Lv 4
    1 decade ago

    Jet engines are started using a couple of different methods. The most common among airlines is an internal air supply from the APU (auxiliary power unit). Once the engine is running a generator is engaged to provide electrical power to the aircraft systems. The battery is used for minimal power uses such as emergency lighting and some engine instruments but is disconnect and charged by the generators. Each engine has a generator so that even if you lose an engine you will still have electrical power for lights, galley, rest rooms...the generators provide all electrical power once the engines have been started.

  • 1 decade ago

    Starting a Jet engine depends or the engine type. Typically they are started with an AC starter. However, many military aircraft use a pneumatic start system. This is better suited for fighters or a/c where the engines are closely situated or near an APU.

    The normal way to provide electrics in aviation is to use a gearbox take-off shaft to drive a utilities box where generators are mounted. An APU (Auxiliary Power Unit - a smaller jet turbine that drives a set of critical utilities like AC generators and Hydraulic pumps) is also used but mostly for ground operations and emergencies.

    In short every manufacturer has its own way of designing these systems so there is a huge variety of systems out there. This is what makes our profession so interesting.

    Source(s): 25 yrs of commercial and military aviation engineering experience
  • 1 decade ago

    Jet engines are usually started with an electric motor driven by batteries, or sometimes using pressurized air. when the first engine is started it gives the power required to start other engines(in fact the first engine to be started is Auxiliary Power Unit, that is a small engine used to provide power to the airplane) then the power provided by the engine started is used to start all engines.

    Every engine on jetliners is equipped with alternators and pumps, so the engine provide electricity and hydraulic and pneumatic power (little airplanes usually have no hydraulic-power plant, only electrical plant.). But for example Tornado's main engines are started by the APU using a mechanical gear-box.

    Batteries are needed when the power needed is more than the power produced, and if there is an engine's malfunction, and to start the APU.

    Little planes work like cars, batteries, engine, alternator and the electrical start motor(sometimes there is only a device that acts for both)

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  • 1 decade ago

    Most jet engines are started with compressed air either from an APU or a ground power cart.

    All aircraft have batteries, generally to start the APU. The APU provides electric power on the ground and bleed air for engine start.

    In flight, electric power comes from engine mounted alternators, just like in your car. They're quite a bit larger of course but the concept is the same.

    Source(s): Retired AF. 12 years in acft maintenance.
  • Anonymous
    1 decade ago

    Turbine engines are started with bleed air coming off one of the stages of the APU. The APU generator supplies power to the airplane once they pull the ground power cord. When the aircraft is pushed back, they start the engines with the bleed air. They do not use electric starters.

    Once one engine is started, that engine generator will be brought on line, which takes over electrical power for the aircraft. The second engine is started, and that generator will take over supplying part of the power from the first generator.

    Then they shut the APU down. You can usually tell when power is swicthed between the generators, the lights will usually blink, and there may be one of those audible dings to go along with it.

  • 1 decade ago

    That depends on where you are, On the ground at an airport they use a portable jet turbin to spin the engine to get it fired or they can use a starter motor to get the turbin spinning. once enough air is moved through the engine to create compression the fuel is then ignited. In the tail of jetliners thereis a small jet turbin that runs a generator to power the plane with electricity.

  • Anonymous
    1 decade ago

    well basic answer would be the APU (Auxiliary Power Unit) anyway, with the help of the said generator and the Avionics, you can start your engine thru a generator and engine switches located both in the upper panel and on the throttle lever area

  • 1 decade ago

    Jet engines start with an elecrtic start.

    On the ground, they operate and start by plugging in to ground power.

    In the air I am not sure. They have some type of power generator. I think it is a seperate unit and not driven by the propulsion engines but I could be wrong.

  • 1 decade ago

    Don't forget the B-47, it started with an explosive cartridge, and the turbine APU in the CH-47 helicopter starts with hydraulics from an accumulator.

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