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.

[kazansky22]

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.

I have parked the plane in various locations on the airfield to see if it was just the spot I was in, and then I went into the same spot points in different direction to see if it would alter the pilot side of the wing tank being more full but it didn't seem to make any difference. I also left it there with the fill caps off to vent in case the vents were clogged and it also didn't seem to make any difference.


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

I thought maybe the left main tire might have been low but I checked both mains and the nose tire while I was at it and they are all about the same.

[Marc Zeitlin]

I thought maybe the left main tire might have been low but I checked both mains and the nose tire while I was at it and they are all about the same.When parked on known flat ground, measure the height of the left wingtip and the right wingtip off the ground. There's not a lot of geometric dihedral in a II FT and if one wingtip is only a few inches below the other, there can be substantial fuel transfer from one side to the other.

This is just ONE of the many reasons that having a "BOTH" setting on a fuel valve on a low wing airplane is generally (although not always) a bad idea.

You may want to take a look at CFR 14 Part 23.2430 (the new version of Part 23) - although EAB aircraft are not required to comply with Part 23, generally the rules are written for good safety reasons. Your fuel system would not meet the requirements of 23.2430.

I am not familiar with the II FT fuel system, and couldn't find a specification on-line. To those who know - what connects the left and right tanks in the wings? (and then connects them both to the fuel valve, which apparently is a "Header", "Both", "Off" setup)? Knowing this might help debug this problem.

Just out of curiosity, how long have you been flying this plane for before noticing this issue (which can be a serious safety issue, depending on the answer to the above questions, since draining ONE tank dry may [again, depending upon configuration], lead to an inability to draw fuel from the other wing tank). And did you have a complete Pre-Buy Examination performed on the plane? If so, what was their report on the fuel system?

[cub builder]

I am not familiar with the II FT fuel system, and couldn't find a specification on-line. To those who know - what connects the left and right tanks in the wings? (and then connects them both to the fuel valve, which apparently is a "Header", "Both", "Off" setup)? Knowing this might help debug this problem.



To the best of my recollection, the GlassAir II has a single tank that spans the center section and both wings, so the fuel selector has header/main/off positions only. The fuel caps at both wing tips are there so you can top off the tank from either side once the center section is full, but unless your plane was modified, both caps lead to the same tank. However, as I stated previously, and you didn't say whether you have tip tanks or not. If tip tanks are installed, there is some pretty complicated valving that will make the tip tank overflow regardless of the plane's position if the valving is having problems.

As Bill Berson pointed out a couple of posts earlier, you may have a low landing gear. The gear may not sit level for whatever reason. Measure the wing tips from the ground to see if the plane is level. Fuel doesn't flow up hill unless there is a pressure pushing it. If it does this with both caps off and there are no tip tanks installed, then gravity is pulling the fuel to the low wing.

Another possibility may be that the drain from the header tank to the main may be open, so when you fill the header tank, it may be draining into the main causing it to overflow.

It's been a few years since I've worked on a GlassAir fuel system, so it is possible that I may not recall all the details for your specific model, and many builders modify the fuel system, so diagnosing it blind is a bit of a crap shoot. But if you can provide a complete description of your fuel system configuration, it would be helpful in determining the problem.

[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-content/uploads/2016/07/GSB131.pdf

[Marc Zeitlin]

Looks like this was addressed in SH Service Bulletin #131

http://glasairaviation.com/wp-content/uploads/2016/07/GSB131.pdfThanks 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.

[martymayes]

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.

[Bill Berson]

A small car screw jack under one axel would lift and keep it level. Might be a hassle, but better than a gas leak.