Microlighters

I have a 35 l Bushbaby fuel tank in one of the Cub's wings. This tank has a fairly long pipe (about 50mm) at the refill cap. The tank is composite but the filling pipe seems to be some kind of plastic, with the cap (with breather pipe in the cap) screwing directly onto this pipe. The pipe goes into the tank about 25mm or more.

The one problem is that if we fill the tank with fuel touching this pipe, the tank can not breath (out) when the fuel becomes warmer than it was when we filled the tank. What happens is that the air/fumes mixture which is trapped in that top portion of the tank can not get out when it expands. It then pushes some of the fuel in the neck out onto the wing. The tank burps fuel .

The other problem is that the tank can not be filled to capacity. As soon as the fuel touches the bottom of this problem pipe, the air is trapped and no more fuel can be added. It leaves this tank with about 25mm air where fuel should be. On a cross country trip this additional fuel might just be needed.

To solve the problem a hole of about 6mm in the neck of the pipe just below (inside) the tank will do the trick. To get a drill in there using one of those 90 degree air tools can be done, but then we have a lot of drill dust inside the fuel tank.......not nice Another option cold be to melt a hole into the pipe using a soldering iron. Or install an internal breather pipe inside the refill pipe to end 6mm below the cap. All these options have some or other problem and baggage.

I am sure I am not the first to have this problem.
What do you suggest please?

I had some of those tanks. Drilled 5mm holes in the plastic tube towards the rear of the tank. Problem solved. Eventually all the drilling dust will be taken care off by the petrol filters. On the topic of filters: The GUD BC 31 is a nice beeeeg filter that will trap a lot of crap before clogging up. Way to go, man, and fly safe. Enjoy.

Dankie Boet, sal so maak en laat weet.

Problem solved!

Stuffed a rag into the throat of the tank, used a soldering iron to melt a hole into the (front) side of the filler pipe just below the top of the tank, used my pocket knife to remove the burr and there..........4.5l additional fuel (and about 15 minutes additional flight) and no more burping of fuel onto the wing via the breather.

Remove the rag carefully not drop any debris into the tank and go fly

Slem tjent. There is always a better way of doing it!!!