Building Tip - Fuel Tank Vent Line

[f1rocket]

Here's a tip for running your vent line on your fuel tanks that keeps the line out of the cockpit, reduces the number of fittings, and simplifies the installation.

This is a picture of my wing upside down. Inside the root, I ran a double loop of 1/4" aluminum tubing to a AN919-6D reducer fitting that I Prosealed to the skin. The 3/8" end has been sanded smooth using an electric drill and a bench grinder. The end has been cut at a 45 degree angle and rounded.

Many of the Rocket guys are using this set up and it works great. The double loop prevents most, if not all, fuel leakage from a full tank in the hot sun. As usual, all disclaimers apply. YMMV.

[Bob Axsom]

Interesting - with the top of the fuel in the dihedral oriented tanks placing fuel above the top of the loop it does cause some concern. Do you extend a vent line on the inside of the tank from the fitting to the high point in the tank at the outboard end?

[f1rocket]

Yes, the tanks are built with the vent line running inside the tank all the way up to the top side of the farthest outboard end.

The only thing the line in your cockpit does is create a loop of line higher than the tank, thus preventing fuel expansion from pushing fuel out of the vent. The doule loop of line does the same thing effectively.

[rv8ch]

Many of the Rocket guys are using this set up and it works great.

What did they use to determine this? Did they try flying in several different
attitudes with a chase plane to ensure no fuel was flowing out? I guess if
your tank was still off the wing you could move the thing around to see
if anything leaks.

This looks a lot simpler than the way I did it, for sure.

[Mel]

Let's play "devil's advocate" for a minute. What happens if you are forced to park with one wing low with full tanks putting the fuel level above the inside vent opening and also above the loop? Now with heat expansion fuel begins to flow through the vent line? Would this not creat a siphon effect?
Mel

[PJSeipel]

For a siphon effect, air would have to be able to get into the tank to replace the fuel going out. I'd guess you'll lose whatever fuel the expansion pushes out of the tube and that's it. Same situation as if you ran the tubing through the cockpit.

PJ

[f1rocket]

Originally Posted by rv8ch

What did they use to determine this? Did they try flying in several different
attitudes with a chase plane to ensure no fuel was flowing out? I guess if
your tank was still off the wing you could move the thing around to see
if anything leaks.

This looks a lot simpler than the way I did it, for sure.

Over 30 Rockets flying with this set up. The Rocket plans show this as the standard way to vent the tank. I thought the RV folks might be interested in using this. If not, that's okay by me.

[rv8ch]

Over 30 Rockets flying with this set up. The Rocket plans
show this as the standard way to vent the tank. I thought the RV
folks might be interested in using this. If not, that's okay by me.

That's good enough for me. Unfortunately this tip will have to wait
for my next RV, since I've already done vents on my 8.

Thanks for sharing it with us, and please feel free to send over
any other rocket tips!

[Radomir]

is this how they do it on RV-10? I thought I saw something like this on teh -10... but may be wrong..

[Davepar]

That is tempting. I haven't even drilled the hole in the side of the fuse for the vent line yet. Hmmm...