RV-3: F-1 Style Fuel Tank Vents
 

Here?s a quick picture of the vents we are going to try on the RV-3 project. Instead of running the vent lines into the cockpit and up (then back down) the sidewalls, we decided to give the F-1 Rocket ?coiled vent tube? a try. Pretty simple to execute, and I have heard of no reported problems for the Rocket guys with this design.



We?ll let folks know how it works once we have some flight experience with it!

Paul

That's what I'm planning to do on my -7, although I'm not planning on the vent extending that far.

I did puzle a bit over how long I wanted the vent, and in the end, copied the ones on my RV-8. We can always cut them down or replace them with somehtign fancier in teh future!

I have these on my F1. For what it's worth, the only negative I have found is that I cannot fill the tanks to the brim or an impressive amount will vent when the fuel expands due to temperature changes. I can also notice a fuel smell when leveling off after a climb when the tanks are near full. Burn a little off, however, and this all goes away. My RV, which has the Van's standard vent arrangement (the loop inside the fuselage with its apex high above the wing) will also spurt fuel when full, but not to the same extent as my F1.

Mark Olson RV-7A F1-EVO Rocket

How many loops do you have in your vent line Mark?

I used 2 loops, similar to the picture above. I read on one of the Rocket Forum threads that this tended to minimize fuel venting, especially in turbulence.

I have heard that 3 loop would help prevent some of the issues you've mentioned, but I'd imagine that those cases are rare as the added volume from the third loop is minimal. I'm going to use two loops.

You need to add these!



You can find them here: http://www.aircraftextras.com/

I looked at (drooled over) some of the cool vents like those Randy, but alas...the tank flange is just too narrow to comfortably drill holes for the AN fittings. And down here where the mud-dauber's live, it's nice to have a tube over which to slip a cover!

Those things are pretty neat though....

Where is the open end in the fueltank?
 

Hello

I just remember this, the Vans serie of planes are designed as tailwheel plane. So the tube ends in the fueltank in front of the filler opening. This is the highest spot when the tailwheel is on the bottom.

If you build a nosewheel, then the highest spot is closer to the spar. If you fill a A-Version up really full, then the tube opening is underneath the fuellevel.
If you put the plane into the sun, then the air in the tank expands and push out quite an amount of fuel!

Really look where the opening is, otherwise do not fill higher than the opening.

Regards, Dominik

Threaded Fittings
 

The ones from Aircraft Extra are threaded for an AN3 bolt. I am using a remove before flight flag on a drilled headed bolt. Still doesn't solve the wing flange issue that Paul describes though. But they work great on the side by sides.

I thought I'd revive this old thread.

I'm getting ready to to make my vent lines for my -7 and I thought the OP may like to update us on how this method worked for him. It looks much simpler to construct and I like the idea of minimizing the fuel lines in the cockpit.

If Paul is busy flying his little jet around ;), maybe someone else could lend their experience with the coiled vent method.

Four years ago I was rebuilding an already-built RV4, and I needed to replace the vent lines inside the fuselage due to damage. I decided to try the ?F1? vent installation because it was easier to accomplish than replacing the internal lines.

The F1 vent system spits more fuel on the ramp than the original installation did and seems to vent more fuel at high AOA. At my next condition inspection I?m planning to re-do the system and go back to the vent system as shown on the plans.

Fuel vents
 

I used Paul?s vent suggestion and is working just fine on my rv3b.

Steve

Rv3B
100 hours

Outboard vent
 

Why carry the vent line all the way through the tank and through the root rib?

Seems the simplest installation would be a 90 degree fitting in the most outboard tank rib at highest point and straight down and out a hole in the tank/wing skin with a 45 degree cut on outside end.

Or a fitting in bottom outboard tank skin with inside tube going to the highest point in the tank (a bit more drag from fitting).

I chickened out and did the conventional RV-4 installation because of these unknowns:

Vent hole could ice over? (no hot engine air passing over vent opening)

RV-4 is a taildragger (is it possible to get inside end of vent line at a point where fuel won't siphon out with full tank tail up and tail down?)

Less drag with inboard vent? (already turbulent air from engine and gear)

I understand the RV-10 has a straight down vent with no loop.

Finn

Full tanks
 

I have the Rocket/Dye/etc two loop system on 3B. It works very well for me because I normally store the ship with tanks half full. When topped of for travel, I have not noticed anything objectionable ( gas odor). Completely full, sloped ramp or hot sun is ?no win scenario?. That said, Fynnflyer?s idea for outboard vent at the apex of the airfoil would optimize the condition, but only on perfectly level ramp if ?no leakage? is the objective. Just my $0.02.

I implemented a slightly different version of this in my -8. Works great. I've never seen a drop of gas in almost 200 hours. I would definitely do it again

Sounds good, what was the slightly different version...Photo??

The Lancair folks run the vent line out to the wingtip and then down to an NACA inlet in the bottom of the wingtip to supply some elevated pressure. But also, they put a check valve in the line, so air can get pulled in to replace fuel as it burns, but fuel can not come out the vent.

I don't know if the check valve has a pressure relief function, so that expanding fuel in a full tank in the sun won't overpressure the wing?

If you were to omit the check valve and just run the vent to the tip, as I think FinnFlyer is suggesting, only slight mis-coordinated flight would send a substantial amount of fuel flowing out the vent line. A few moments in a slip with a 5-degree bank and you could lose 1/4 tank!

No, no. Just like the newer RVs have a vent line straight down at the tank root rib, I was thinking straight down at the outermost tank rib. Or a 90 degree fitting on the tank bottom facing into the wind, and inside the tank a tube from fitting up to very highest point in the tank. No reason you couldn't coil that tube a few times inside the tank too.

Of course the ultimate in simplicity would be to drill a 1/4" hole in the fuel cap and press a 1/4" tube, bent 90 degrees into the wind, into the cap But that would attract a lot of dirty looks from other RV builders and owners and cost you at least 10 mph top speed. :)

Finn

And how is it that does not simply drain the tank down to the level of the fitting in the root rib? Set aside uncoordinated flight for now, just consider dihedral.

It must be that the vent line still starts at the high point of the tank at the outboard end, and runs inboard to the root, then down. Without a couple of coils, it will tend to burp more fuel