Sonex-B Fuel Tank Vent

[Area 51%]

Gentlemen,

Perhaps Sonex should put out a notice to not over tighten the tank straps and we can avoid any more builder angst from this condition.

Page G01 on my plans (Legacy) view C-C states "Only Snug Bolts enough to secure Fuel Tank in place. (overtightening will deform Tank and Longerons)"

[dirkverdonck]

Hi Guys,
I was unhappy with the tank straps for my Waiex-B, tried to adjust them but replaced them in the end with 4 half-straps that bolt together in the middle. Much easier to install the tank and the fit around the edges is a lot better.
The vent line will exit under the cowling as in my Onex and will have a 45°cut to the front to slightly pressurise the tank in flight.
About the plans: one should consider the fact that Sonex kits are not 'plug and play' kits but some common sense and fiddling is sometines needed to achieve the required results. I applied this in the build of my Onex and it still works as a dream after two years of puttering around!

PS: I hope my Waiex-B tank doesn't collapse in a year or two during the first flight.

[pappas]

Well,

Color me embarrassed... again, for not seeing the reference in the legacy plans you found. That same warning may be in my "B" plans. I'm not even going to check! I will assume that it's in there.

I defer to the position on these subjects that I usually do, which is: I probably screwed it up! :-)

[gethomas]

While doing ground runs on the runway the engine stopped. The fuel tank had deformed 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 as John Monnett suggested. Maybe the vent is not causing a problem.

So, I did the following test on the tank:

Released straps and removed tank front bracket attached to glare shield. See Photo 1. This was to eliminate the possibility of tight straps as John described.

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

Placed airplane in the sun with sun on right side. Ambient temperature 81deg; temperature on right side of fuselage 104deg

After 30 minutes the tank deformed. Photo 4.

Photo 4

This shows that there is a problem with the tank heating up causing it to change in shape. Is this a compatibility issue between airframe and tank? 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.

[GordonTurner]

Hmmmmmm. They have been making these tanks for a very long time. It doesn’t seem like people have complained about this all these years, I never saw it anyway. So did they change the chemistry of the tanks? Compared to the pictures, my old tank circa 2012 looks more pale-ish and translucent-ish than what I am seeing in the pictures above.

Gordon

[dtibbo]

My tank collapsed too, never flown, open vent line. I’ll try loosening the straps and see what happens

[fastj22]

I will report that my B-model tank has not deformed. I placed my vent near the fill neck and routed it through the firewall and down the side edge with a 90 degree turn facing into the airflow. It was made with a 3/8th inch steel automotive brake line.

[gethomas]

ditibbo: Were you able to get your tank reformed?