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Thread: Glassair II FT Wing Heavy situation

  1. #11

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    Quote Originally Posted by martymayes View Post
    Looks like this was addressed in SH Service Bulletin #131

    http://glasairaviation.com/wp-conten.../07/GSB131.pdf
    Thanks for pointing this out - good find that seems to directly address the OP's issue.

    As an Aeronautical Engineer who's had some exposure to designing complex fuel systems for aircraft (WKII, etc.), I will say that to _ME_, this fuel system design is flawed. The earth is not everywhere flat, and the notion that the pilot is responsible for finding a spot to park where (assuming the aircraft was built perfectly straight and level in the first place, which is a big assumption and possibly in this case not true) one wingtip is not higher than the vent on the other wingtip is just bad design practice. Split the tank, have a L/R/Header/Off valve, and call it good.

    My $0.02.

  2. #12

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    Or don't fill it full if it will be parked.

  3. #13

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    Quote Originally Posted by Bill Berson View Post
    Or don't fill it full if it will be parked.
    Sure, as a workaround. I'd still argue that's a design error. But it also might depend on how long the fuel takes to shift sides. And what if the plane flies slightly one wing low (not rigged perfectly, or not flown perfectly :-) )? Then, even if you fill the tanks just before take-off, you'll pump a LOT of fuel overboard. And the SB131 that Marty pointed to indicates that a siphon will form if you do start pumping fuel, so you'd have to know it's happening, drop the other wing JUST enough to break the siphon on the low side but not enough to start one on the high side. God forbid you want to slip or something.

    If this is my plane, I try to fix the design issue - not slap operational band-aids on it. Maybe that's not possible, or maybe the vent valves that SB131 point to are a good workaround for this issue (seems like that's what they were designed to fix/deal with). If nothing else, I'd install them, or fix them if they're not working correctly.

  4. #14

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    While more susceptible with full fuel, apparently it can happen when there is less than full fuel and the plane is leaning enough to allow fuel to enter the vent line, That's all it takes to get the siphon flow going and siphoning will continue until broken.

  5. #15

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    A small car screw jack under one axel would lift and keep it level. Might be a hassle, but better than a gas leak.
    Last edited by Bill Berson; 10-26-2017 at 09:48 PM.

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