A/c train
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Posts: 674
Joined: Sun Jun 10, 2001 7:57 am

Electrical Loads - Fuel Burn

Mon Jan 31, 2005 5:50 am

Ive quite recently done some engine courses and during morning Q +A session we got on to the subject of fuel burn influenced by taking air off the engines etc etc, this is easily understandable.
Then our instructor said that that if you use a bigger electrical load, say when you get icing conditions and your particular aircraft is fitted with leading edge electrical anti-icing blankets, the aircrafts fuel burn with no change in TLA, WILL increase.
So an extra load i.e anti-ice, nose cowl L/E being used will cause higher fuel burn, this surely cant be a significant amount ?
My question is, if so, why ?

I was under the impression, each IDG supplied 90 kva, and the galley will take 20 kva etc etc, but is it a problem with higher torque transmitted back through the engine from the IDG ? ive never been that bothered about this, im just interested. I can notice in cars sometimes, the RPM drops with higher electrical load used.
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Electrical Loads - Fuel Burn

Mon Jan 31, 2005 6:57 am

It will take more torque to turn a generator when you are extracting watts from it than when you are not. That's what you see in your car and that's what happens in aircraft.

RPM and shaft torque decides the power which goes through a driveshaft. The RPM doesn't change, but more power is extracted from the generator. As the sum of the energy is constant, the energy going out as electrical power must be matched by mechanical power going in through the driveshaft. This means more torque on the shaft which means you will have to pour more fuel into the engine to keep the RPM the same.

I thought I was doing good trying to avoid those airport hotels... and look at me now.

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