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Author Topic: Lost a GCU  (Read 600 times)

seanmcgillivray

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Lost a GCU
« on: October 28, 2021, 10:55:11 pm »
On my last flight I landed for fuel about 600NM short of home. Went to start and could not get my right gen to come online.

Troubleshooted annunciation and flip flopped the GCUa and the problem followed. For some unknown reason what ever took out the GCU took out the start control relay. Or the relay took out the GCU.

New relay and new GCU will be in tomorrow. Hope got this problem fixed.

donv

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Re: Lost a GCU
« Reply #1 on: October 28, 2021, 11:51:59 pm »
Sorry to hear that!

I remember when I was picking up my (then) employer's brand new Citation Sovereign, at the factory. Delivery flight. Generator failed on the ramp, just like what happened to you.

The good news was that at the Cessna factory, parts were no problem and we were on our way within about an hour!

seanmcgillivray

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Re: Lost a GCU
« Reply #2 on: October 29, 2021, 08:47:18 pm »
Installed overhauled GCU and still have the problem.

Flip flop cannon plugs and it flips the bad gen. How can a overhauled GCU be bad out of the box?

Got another coming on Tuesday.

seanmcgillivray

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Re: Lost a GCU
« Reply #3 on: November 04, 2021, 11:13:10 pm »
Overhauled GCU and a bit of tuning to get the load share right.

Anyone have overheating issues when doing long ground runs?

donv

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Re: Lost a GCU
« Reply #4 on: November 05, 2021, 11:50:10 am »
What sort of overheating? Are you referring to oil temps?

In very hot conditions, I have seen oil temps start to get too high. The key is to keep forward flow through the engines. If you are in flat pitch, then it can be an issue. I suppose with the start locks on, it would particularly be an issue-- I haven't experienced that. But I do remember long taxis in 100+ degree weather where we ran into the heat issue, and again, the key was just to keep forward flow through the engines.

seanmcgillivray

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Re: Lost a GCU
« Reply #5 on: November 05, 2021, 11:13:02 pm »
Don, yes oil temps. Should of specified.

Was on the start locks, to balance the GCUs you have to run the engine at 96% RPM. Guess if I was off the locks I might get better airflow across the cooler.



donv

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Re: Lost a GCU
« Reply #6 on: November 05, 2021, 11:19:18 pm »
Yes, in that circumstance I would be off the locks, and with just a bit of forward flow, so you have to be on the brakes. But Bruce or some others with more maintenance experience might have a different thought.

I assume your oil cooler doors were open?

seanmcgillivray

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Re: Lost a GCU
« Reply #7 on: November 06, 2021, 10:17:01 am »
Doors open. Have a little more adjusting to do as I have a 20 amp split.

Will take the props off the locks.

Bruce Byerly

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Re: Lost a GCU
« Reply #8 on: November 11, 2021, 10:48:39 pm »
Yes, in that circumstance I would be off the locks, and with just a bit of forward flow, so you have to be on the brakes. But Bruce or some others with more maintenance experience might have a different thought.

I assume your oil cooler doors were open?

Yes just a little airflow takes care of that right away.