News: Added Links For Twin Commander and Facebook Pages

Login  |  Register

Author Topic: GCUs  (Read 1213 times)

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3269
GCUs
« on: May 26, 2024, 10:39:51 pm »
I lost a GCU a while back (generator wouldn't come on line) and Aero Air was able to replace it right away (maybe they even had one in stock? Not sure). Anyway, after the replacement, the left generator won't come on line unless the right generator is turned off. Then it comes on line normally.

Barry Lane pointed out to me that there are different part numbers of GCUs, and at least one of them has this issue.

So, at this 150 hour, I am having them swap the GCUs from left to right. That way, at least, when I start the right engine first, the switchology will be normal. If I happen to start the left engine first (which I never do), I would have to turn the other generator off... but most of the time, that should be a non-issue.

Barry also pointed out that this isn't an incorrect part number for a 980, just that it happens to have this issue.

Adam Frisch

  • Administrator
  • Hero Member
  • *****
  • Posts: 1677
    • Adam Frisch FSF
Re: GCUs
« Reply #1 on: May 27, 2024, 01:41:31 am »
Why start the right always? Is it in POH for the 980 to do so? I alternate mine.
Slumming it in the turboprop world - so you don't have to.

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3269
Re: GCUs
« Reply #2 on: May 27, 2024, 09:56:22 am »
There is nothing in the AFM about it.

I always start the right engine because you can still access the door if you need to, and if someone were to approach the airplane they would be more likely to do so on the left side. I think most Commander guys do it that way, at least in my experience.

JMA

  • Sr. Member
  • ****
  • Posts: 482
Re: GCUs
« Reply #3 on: May 28, 2024, 08:58:13 am »
Funny DonV, every single engine start on our 980 since new is on the right, and my father always mentioned that by the book, you should rotate starting each side, but never has for the same exact reasons you gave (almost word for word).

schrambow

  • Full Member
  • ***
  • Posts: 120
Re: GCUs
« Reply #4 on: May 28, 2024, 02:24:58 pm »
I agree with the normal start of the right engine first due to what is stated above already.  Though I have started experimenting of trying the left engine first (parallel) in warm conditions and find that it spools up slightly faster than the right one does under the same weather environment for whatever reason.  Obviously, a series start spools up both very fast, I use series start when i get to a warm (> 80)  or a cold start (< 30) environment.
But when i am doing a normal parallel start, I am opting to starting the left one first due to a faster start and i would believe being easier ultimately for both engines during the start process?

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3269
Re: GCUs
« Reply #5 on: May 28, 2024, 02:30:54 pm »
I was searching for some history (involving a similar N Number), and I ran across this accident:

https://aviation-safety.net/wikibase/2837

Narrative: "Pilot did not shut off l.Eng bfor de-planing pax.Pax bld.Alc.Lvl 0.19pct.Pax failed see/avoid prop."

This was a piston 680, so presumably just had the rear door, but still...