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A piston-engine aircraft will continue to run as long as its magnetos still work, even if there is zero electricity in the battery and the alternator is broken, because magnetos are independent of the aircraft's electrical system. Since turbine engines don't have magnetos, do jet aircraft (including turboprops) work the same way?

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    $\begingroup$ I think a clarification of the question could help narrow down whether the question is asking about any electrical power at all (i.e. purely mechanical), or if the question is only about electrical power provided from a source external to the engine housing itself. The questions so far seem to indicate that electrical power is typically required, but is usually provided internally by the engine itself. $\endgroup$
    – Milwrdfan
    Mar 21 at 20:23

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Yes, a jet engine can operate without electrical power. Or at least they used to be able to...

A jet engine uses igniters (like electric spark plugs) to initiate combustion in the combustor. Once initiated, the igniters are not needed anymore and the combustor should stay operating as long as the engine is operating.

Modern jet engines use a FADEC (Full Authority Digital Electronic Control) to control the engine. The FADEC is a computer that monitors everything about a jet engine and simplifies its operation to the pilot.

Older jet engines used different combinations of mechanical, pneumatic, and hydraulic control. A modern FADEC is better all around, improving engine performance, life, and safety.

Modern FADEC are redundant and are extremely reliable.

The FADEC requires electricity, but it will have a separate generator analogous to the magnetos.

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  • $\begingroup$ Are the fuel pumps mechanical or electrically operated? If they're electrical, the combustors will stay lit while they've got fuel, but as soon as the pumps stop, the fire will go out. No? $\endgroup$
    – FreeMan
    Mar 21 at 14:17
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    $\begingroup$ @FreeMan The high-pressure fuel pumps within the engine are mechanically connected to the accessory gearbox and will continue to run. The low-pressure fuel pumps in the tanks might not, but as Therac said, gravity and suction from the high-pressure pump is enough for under-wing-mounted engines. I think tail-mounted engines might have problems though. $\endgroup$
    – Bianfable
    Mar 21 at 14:32
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    $\begingroup$ From faa.gov/sites/faa.gov/files/2022-01/… If the FADEC fails, the engine fails. However, system redundancy makes it much less likely for a FADEC system to fail than a traditional magneto system. In fact, a double magneto failure is statistically more likely than a FADEC failure. $\endgroup$ Mar 21 at 21:32
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    $\begingroup$ "They used to be able to" does not answer "can they?" $\endgroup$ Mar 22 at 5:26
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    $\begingroup$ @user253751 I think the context of modern engines using a FADEC (which uses electricity) makes it clear the possible exception I'm referring to. The OP allows a spark ignition piston engine to operate 'without electricity' because it has a self-contained power source (magnetos) independent of the aircraft's electrical system. If the same allowance is made for a FADEC's independent power source, then Yes, it can operate independent of the aircraft's electrical system. If however, all electricity is forbidden from use in this question, then no a modern jet engine will not operate. $\endgroup$ Mar 22 at 6:08
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Jet engines have magnetos too (alternators with permanent magnets). Combustion can be sustained without igniters, but a permanent electrical power supply is required to feed engine electronic components, in particular each engine controller (EEC, ECU, FADEC).

This controller adjusts the engine parameters, according to the thrust demand selected by the crew with the throttle (fuel flow, variable vanes...)

Each engine has its own dedicated electrical alternator for the controller. If this power supply is not operative on the ground, the crew cannot take off (see A320 minimum equipment list).

enter image description here

(Source: CFM56-7B Engine systems)

A controller has two redundant channels fed by different sets of stator windings in the alternator. The controller is initially fed from the aircraft power supply, and the dedicated alternator takes over when the engine spins (> 12% N2 on CFM56).

If any set of windings fails:

  • The corresponding controller channel is switched back to the main aircraft supply (IDG, or whatever currently feeds the main electrical bus). If this happens while in flight, the flight can continue.

  • An ECAM message ENG 1(2) FADEC ALTERNATOR is displayed. If this message appears before takeoff, the crew is not allowed to take off.

Both the regular high-power generator (IDG) and the small controller generator are driven by the engine using the accessory gearbox, e.g for CFM56-7B of a Boeing 737 NG:

enter image description here

(Source: CFM56-7B engine manual)

This gearbox is located at the bottom or (like here) on the side of the fan case:

enter image description here

Source.

For more details about the accessory gearbox, see this question: Where is the generator in a large turbofan of a commercial airliner?

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