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Author Topic: 980 Won't Fill to Capacity  (Read 2932 times)

ghancock

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Re: 980 Won't Fill to Capacity
« Reply #15 on: July 26, 2016, 07:56:46 am »
I'm of the opinion that unless you have perfectly installed bladders you're never going to get the full load specified in the manual, and I carry that as far as thinking you'll never get perfectly installed bladders for numerous reasons.  If you consider how they are installed and what they actually are, I bet only a hand full of planes actually got the listed amount of gas when filled.

My airplane has 33.5gal aux tanks and if I fill them completely to the top I get 30gal even in both of them.  I still don't know exactly how much fits into my main tank and hoping to figure that out soon.  I can guarantee it is not 156gal though. :-)

Glenn
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You can't win an argument with an ignorant person,  they'll just drag you down to their level and beat you with experience.

JimC

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Re: 980 Won't Fill to Capacity
« Reply #16 on: July 26, 2016, 10:15:36 am »
This should be a fixable problem. I can fill aux tanks in my Cessna to stated capacity - and it's a similar complicated arrangement of two connected bladder tanks with one filler.

Up to 1-2% short, sure. But people are talking about being 10% short on capacity - can't that be fixed?
C206, C340

donv

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Re: 980 Won't Fill to Capacity
« Reply #17 on: July 26, 2016, 03:03:57 pm »
Bruce-- That's what I think as well. We looked at the flight logs the original German owners kept, and they logged every flight. After the tanks were installed, they started flying about 20-30 minutes more, so that did make a difference.

Don, I was taking to Mike G in Indy and he recalled planes being short of capacity when new. In fact the plane I was picking up, a 1000, has one wing that differs much more than I would have expected from the other.  I can get the numbers for you.  Not a great answer but makes me want to ask Geoffrey P at Twin if he recalls any solutions.

Bruce Byerly

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Re: 980 Won't Fill to Capacity
« Reply #18 on: July 26, 2016, 04:12:36 pm »
This should be a fixable problem. I can fill aux tanks in my Cessna to stated capacity - and it's a similar complicated arrangement of two connected bladder tanks with one filler.

Up to 1-2% short, sure. But people are talking about being 10% short on capacity - can't that be fixed?

You'd think - same as me -  but it's a bit more complicated unfortunately.  Funny thing is I've seen well over 400 gallons go into a 690A/B vs the 389 they are supposed to hold in 22 bladders. 

ghancock

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Re: 980 Won't Fill to Capacity
« Reply #19 on: July 27, 2016, 08:10:40 am »
I'm sure you could fix them.  Remove all bladders and try to square the corners as best as possible.  The question:  Will this actually fix the issue are or you throwing money at a completely unknown?  I personally just figure out what I can carry exactly and deal with it.  It would be nice to have the extra gas for sure but knowing that I can only fly 4.5 hours instead of 5 hours is sufficient enough for me.

Glenn
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You can't win an argument with an ignorant person,  they'll just drag you down to their level and beat you with experience.

SKYFLYER

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Re: 980 Won't Fill to Capacity
« Reply #20 on: July 27, 2016, 10:06:37 am »
If I recall correctly when I had all the bladders replaced in the 680FL, several years back, they hooked up a compressor attached to special fuel caps and inflated them like a balloon to make sure the bladders filled all the cavities flush. Not sure how they blocked the overflows but you could hear them "pop" into the corners of the cells. Clearly they knew the max air pressure to apply before any damage could be done.
Not sure if you could get that done on yours or not but it seems that maybe a few corners of one or more cells are not sitting in the corners and bunched up. Also if there had ever been an issue with the vents you could get negative pressure in a cell and cause it to not retake the same position it had been in before especially the corners.

ghancock

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Re: 980 Won't Fill to Capacity
« Reply #21 on: July 27, 2016, 01:05:35 pm »
That sounds very interesting, but would have no idea how they did it.  I guess if you had rubber plugs you could shove into the holes of each feed and vent line you could pull that off and sounds like an awesome way to make sure things were pushed out.

Thanks for sharing,

Glenn
--glenn
You can't win an argument with an ignorant person,  they'll just drag you down to their level and beat you with experience.