Building Tip - Fuel Tank Vent Line

[RudiGreyling]

This setup looks very tempting, thanx for the tip.

Now if we can just have more views from people Pro's & Con's and then one would be able to make up their own mind.

[dan]

I noticed in the photo what looks like your spars not being primed. Or am I just seeing things?

)_( Dan
RV-7 N714D
http://www.rvproject.com

[f1rocket]

Originally Posted by dan

I noticed in the photo what looks like your spars not being primed. Or am I just seeing things?

)_( Dan
RV-7 N714D
http://www.rvproject.com

I guess you haven't seen my posts on priming?
They are anodized at the factory along with all the internal parts of the wing.

[RV_7A]

The only issue I can see with this setup is that when fuel flows into the tube, a certain amount of fuel will always be trapped in the line. Since the viscosity of fuel is quite thin, air equalization needed in the tank or out will gurgle past the trapped fuel indefinitely. The factory setup allows excess fuel that enters the line to either run back in the tank or out into the air or ground. Trapped fuel will either evaporate inside the line and could quite possibly gather dust or dirt.

Those are just my thoughts, and certainly not intended as unfriendly criticism or to start a "serious" discussion.

[f1rocket]

When you fly, (especially at "Rocket" speeds ) the air pressure pushes any fuel in the line back into the tank.

[dan]

Originally Posted by f1rocket

I guess you haven't seen my posts on priming?
They are anodized at the factory along with all the internal parts of the wing.

Ah...nope, hadn't seen your priming posts. I'm used to seeing gold anodizing. You must have used clear or something like blue or gray just to mess with us.

)_( Dan

[arffguy]

OK, so I assume that you are using capacitance fuel senders. But where are the fuel pick-up tubes? What am I missing here? That is the inboard part of the wing, correct?

[f1rocket]

Originally Posted by arffguy

OK, so I assume that you are using capacitance fuel senders. But where are the fuel pick-up tubes? What am I missing here? That is the inboard part of the wing, correct?

No, on this tank the float sender is placed in the back baffle of the tank so as to not interfere with the flop tube, which is in the nose of the tank.

[BJohnson]

Another advantage of this setup is it appears that in the accidental flipping of the plane during a emergency landing, the vent exit will be above the tanks, preventing the vent line from turning into a drain line. I have read many stories of the plane flipping and subsequent fuel draining from the tanks. Is this accurate?

[mlw450802]

Originally Posted by 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.

Randy,
I like this idea but I am wondering (for those of us building our tanks) why one could not simply place the three loops inside the outboard bay and place the vent hole out there also?

It would reduce fittings and tubing usage and I can't see where it would be hydraulically different relative to siphon etc. I suppose slips with full tanks might spill a little more but who knows?

-Mike

Oops! I do see a big difference in the wing down situation (parked or uncoordinated). With the vent line running inboard (as in the Rocket design), the fuel has to climb up the vent line and would equalize level with the fuel in the tank before beginning to spill.

Your idea and implementation is better!