Glassair II FT Wing Heavy situation

[kazansky22]

Hello guys, I wanted to ask if any of you fine gentlemen had any ideas about my issue here.

My plane it parked on the ground, I put some gas in 1 side and put some gas in the other, equal amounts on both sides. I park the plane, wait a minute or two, check the fuel level and the pilot side tank starts pouring gas out of the top when I open it and the passenger side looks almost empty.

I've parked in the same spot each time and turned the plane every which way in the parking spot to see if that would effect all the fuel going into 1 wing. It didn't.

I'm a little afraid to fly the plane with all the fuel in one wing since their is a bulletin out about that very specific occurrence. I'm not exactly sure what to do. I'm not the original builder so my knowledge of aircraft construction is a bit limited. But thats why I'm here

[martymayes]

I would not fly it either. Need to find out the how it’s plumbed bring it up to factory specs

[CHICAGORANDY]

The emptying tank and its cross-over plumbing would need to be higher than the fill point of the other tank for it to over-run it. Also it would seem that there is no fuel tank selector on the airplane? Sounds like both tanks are joined with a "T" going to the engine or a 3rd 'header' tank under the cowling?

[vaflier]

The vent line on the tank that is emptying is plugged. Mud dauber would be my guess. Check the tank vents. If the caps have vents check those as well or just replace the tank caps. Problem solved. Reasoning is as follows, tank with plugged vent is warming up in the sun and building pressure since the vent is plugged and forcing the fuel over into the other tank.

[cub builder]

If you only have the main and header tank, the GlasAir only has one main tank that spans across the wings. Whichever wing is downhill is going to want to overflow. Leave the caps on and check it again on a level surface. The tanks should level out again and should also equalize once you taxi onto the runway to take off.

If you have the tip tanks installed, they have some rather complicated antisiphon and anti-overflow plumbing between the tips and the main tank. If the tip tank is overflowing, the valving that controls that is mounted just under the seam where the tip tank attaches to the wing. The tip tanks should feed into the mains during flight automatically if the valving is all working correctly.

However, since I don't know your specific plane's configuration, please put the plane on level ground and check that the fuel tanks level out again.

[Bill Berson]

If the landing gear is low on the pilot side it won't matter how many ways you position it on the ramp.

[martymayes]

Hello guys, I wanted to ask if any of you fine gentlemen had any ideas about my issue here.

My plane it parked on the ground, I put some gas in 1 side and put some gas in the other, equal amounts on both sides. I park the plane, wait a minute or two, check the fuel level and the pilot side tank starts pouring gas out of the top when I open it and the passenger side looks almost empty.

Looks like this was addressed in SH Service Bulletin #131

http://glasairaviation.com/wp-conten.../07/GSB131.pdf

[Marc Zeitlin]

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.

[Bill Berson]

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

[Marc Zeitlin]

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.