Sonex-B Fuel Tank Problem

[gethomas]

This is a re-post under a new topic. Old post was about tank venting but the problem has expanded beyond that. I was going on a previous response by John Monnett to my vent problem post advising that my problem wasn't caused by venting but mounting conflicts caused by too tight straps.

I loosened the straps and reformed the tank with air pressure.

I did some ground runs on the runway to try things out and the engine stopped. The fuel tank had deformed again apparently disrupting the fuel flow. The fuel level was down to about 2gal, the day was hot and I suspected that heat was causing the problem.

So, I did the following test on the tank:

Completely released straps and removed tank bracket attached to glare shield. See Photo 1. This was to eliminate any possibility of tight straps as John described. The tank is simply sitting in the air frame with no mounting conflicts.

Photo 1

Used bicycle pump to pump in air back through vent line to reform tank. Photo 2.

Photo 2

Photo 3 shows reformed tank.

Photo 3

When I released the air pressure the tank deformed some.

Placed airplane in the sun with sun on right side. Ambient temperature 81deg; temperature on right side of fuselage 95deg

After 30 minutes the tank deformed more. Photo 4.

Photo 4

This shows that there is a problem with the tank heating up causing it to change shape. Is the tank too big for the airframe, not allowing expansion in high ambient heat? A tank mounting problem? A manufacturing/quality problem with tank?

Any suggestions on how to resolve this problem? I read on the forum that there are Weix-B builders flying with deformed tanks.