markejackson02 Posted December 11, 2017 Report Share Posted December 11, 2017 Is there any reason I couldn't run a bladder dry? Want to make sure the tanks hold the advertised 27 gallons and I've never had them down below like 10 gallons remaining. Quote Link to comment Share on other sites More sharing options...
N6758N Posted December 11, 2017 Report Share Posted December 11, 2017 No reason you can't run them dry. The fuel pickup in the bladders is basically the same as a wet wing setup. Most of us on here have found that useable fuel is closer to 26 per side after a fill up, however waiting a few hours allows more fuel to be put in. 1 Quote Link to comment Share on other sites More sharing options...
Captnmack Posted December 30, 2017 Report Share Posted December 30, 2017 Depends on how old your Bladders are. Mine were installed in 92 and the cross over tubes are about an inch off the bottom thus trapping more fuel that is unusable. The later installs the tubes were re-designed and are the bottom thus gaining more usable fuel. What you can do is take the drain off but unless you also take the covers off you still will not know how much fuel is trapped. If you do that you will(should) replace the cork gaskets. Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 30, 2017 Report Share Posted December 30, 2017 One thing about the OP's question... What happens when the bladders are empty, do they collapse and change shape, or move around? Watching the bladder install pictures posted on MS recently you get a feeling for how the bladders are supported at the top. There is also a couple of screws in the top access panels related to this support. And some pieces of foam that go under the bladder. The best installation practices have definitely evolved over the decades. Like Any fuel tank.... you still want to test it’s ability to hold the amount of fuel promised, and deliver every useful gallon it has... no exceptions allowed... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Mooneymite Posted December 30, 2017 Report Share Posted December 30, 2017 After a discussion with @Marauder about actual bladder capacity, I ran my right tank empty recently. There was no issue whatsoever. Keep an eye on the fuel pressure and you can catch the stumble before your wife notices. I did determine that after the bladder had been empty for a couple of days, the bladders initially only held about 26 gallons, but the next day after the bladders stretched, I was able to add one more gallon. While close, I never quite got all 27.4 placarded gallons into the tank. 1 Quote Link to comment Share on other sites More sharing options...
Bob_Belville Posted December 30, 2017 Report Share Posted December 30, 2017 2 hours ago, carusoam said: One thing about the OP's question... What happens when the bladders are empty, do they collapse and change shape, or move around? Watching the bladder install pictures posted on MS recently you get a feeling for how the bladders are supported at the top. There is also a couple of screws in the top access panels related to this support. And some pieces of foam that go under the bladder. The best installation practices have definitely evolved over the decades. Like Any fuel tank.... you still want to test it’s ability to hold the amount of fuel promised, and deliver every useful gallon it has... no exceptions allowed... PP thoughts only, not a mechanic... Best regards, -a- When we had finished the installation of the add on bladders we first leveled the plane (which meant raising the tail). We added 1.25 gal. per side per the unusable as defined in the STC. Since we were calibrating the CiES level sensors I then wrote down the reference # as the Zero usable quantity for each wing. I had calibrated several 5 gallon and 1 gallon jugs and the new usable was 64 gallons per the STC. That was conveniently 8 gallons x 4 per side. After putting 8 gallons in each side I noted the reference # as 1/4 full. Ditto for 1/2 and 3/4. The final 8 gallons per side did fit though the right side was very full. What I did find was that after taking the plane off the jacks and opening the filler cap on the right side in the tail lower attitude there was some, not much, overflow. As to the original question, the bladders in my plane, originally installed in '97 were identical to the new ones as to stiffness/flexibility. The 5 gallon+ rectangular cell can be stuffed through the standard access hole in the top of the wing. The cell is supported from the top as shown in this pic. 2 Quote Link to comment Share on other sites More sharing options...
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