Warbird Information Exchange

Hi guys,

I had a discussion with someone about the operating procedure for a generator, and he said that to prevent damage to the generator control unit, it should be switched off during the approach, in base or on final.

I never heard of such a technique before, but apparently it was common "back in the day".

What do you think?

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Olivier Lacombe -- Harvard Mk.4 C-GBQB

Doesn't seem to be a large failure rate that I have experienced or heard of with them and we leave them on.
Radios and such back then drew a bigger load so that it could suck power and overload the generator at low RPM. Particularly if you were doing pattern work shortly after startup so the battery would still be drawing high amps to recharge after the start.
Back in the day the batteries were also rated lower in capacity IIRC.
I would guess apples and oranges in operation.

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Rich Palmer

Remember an Injured Youth
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Don't Be A Dilbert!

Generator output is based only on RPM. Is RPM that low on approach or base? The generator should come on line at about 1400 RPM as I recall.

If the reverse current relay is operating, that should prevent the battery from feeding the generator below the coming-in speed, right? I just don't understand how the generator can be harmed if everything is working properly.

If that statement is true, the generator should always be switched off when it isn't charging like during taxi.

Thanks guys.

Brandon, that's how I understood the operation of a generator. In final, RPM can be below 1 400, and it will stay below that limit until shut down, but as you said, if the reverse current relay is serviceable, no harm should be done.

This all started when our Beaver came back from flying with a smoke-filled cockpit, the GCU had just left for a better world.

I'm not a fan of switching stuff on final mind you.

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Olivier Lacombe -- Harvard Mk.4 C-GBQB

In my experience, stuff usually fails when you are messing with it! Unless the operating handbook says differently, I'd leave it alone. I don't think that kind of failure is too common, but I could be wrong.