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Fuel vent location

rjcthree

rjcthree

Well Known Member
I need a little help understanding something.

I'm looking over drawing 36A, studying the plumbing. Bringing the fuel vent into the cabin, up forward then down and out seems like a waste of space and time. Why not vent straight down and out at the wing root?

Are we trying to keep exhaust out of the tanks? Prevent leakage out the vent at low bank (uncoordinated flight) angles? It's gotta be something good to go through the trouble . . .


Thanks, Rick 90432
 
You want fuel in your tanks!

So, fuel enters the vent line and reaches the same level of the tank. If you, for instance, make a roll, part of fuel will then go down (i.e.: in the upper part of the U tubing) and the, when roll is completed, will come out from the bottom.

If you run tubing from wing root down, you will empty your tanks.

Camillo
 
Alternative vent design

An alternative to the in-cabin vent design is to put a 3-loop coil of tubing in the wing root, and mount the vent fitting on the bottom tank flange. This was first used by a Rocket builder. Do a search - there are pictues and discussion of how/why it works (so I won't repeat all that here).
 
Rick,

This has been brought up before and the reason for the routing is to put a loop higher than the tanks is to help keep them from siphoning off your fuel, should you park it on an uneven surface or the fuel in the tanks heats up enough and starts to expand while sitting in the sun.

The vent lines really don't take up any cabin room, so that wasn't an issue for me.

The Rock mod looks good but may get in the way of any future service requiring the removal of the tank inspection panel.

One other thing to consider, most power losses associated with new homebuilts is traced back to the fuel system. Think twice before doing anything non-standard with the fuel system.
 
Rick,

I agree with the others. The main point (except for the rocket mod) is that there must be part of the vent line above the fuel tank to keep things from siphoning out. Doesn't matter where that high point is (I moved both of mine to go up and back down in the front corners rather than as on the plans) but it has to be there.

greg
 
rjcthree said:
Bringing the fuel vent into the cabin, up forward then down and out seems like a waste of space and time.
Click to expand...

Hi Rich,
I can't help you with the waste of space, but I can certainly help with the time. Do a thread search on the term "Bonaco". There are a lot of posts and pictures of pre-made brake lines, fuel lines AND fuel vent lines. They're very inexpensive and are of excellent quality.
 
Fuel vent

I believe the vent line in the cabin is essential. First the length is needed for Acro, the 9 is a dupe of the previous models so the vent line was used there.
The 10 uses the same in tank setup but has a 90 degree straight down to the root fairing and does not enter the cabin.
Tad Sargent
 
I didn't like the vents coming into the cabin. I opted for the rocket method in my RV7. I riveted a plate on the wing skin and mounted the fuel vent fitting there. The coiled tubing is held in place with 1/4" adel clamps and vinyl tubing spacers to keep the tubing from rubbing. I match drilled the wing fairing with a hole that slides over the vent fitting. An additional very small hole could be drilled in the top of the tube nearest the exit fitting to allow an alternate source of vent air in the event of a stoppage at the fitting (ie ice). I haven't done this yet, but am thinking about it.

 
Rockyjs said:
I didn't like the vents coming into the cabin. I opted for the rocket method in my RV7.
Click to expand...

I guess I'm old school...:)

After nearly 40 years of installing gas lines thoughout interiors of homes and commercial buildings, and dealing with contained open flames in furnaces; it just doesn't bother me at all, to run a few vent lines though the cabin; especially when it allows the "loop" to be much higher above the fuel tanks, than a coiled wing method. Afterall, you've still that fuel piping coming directly from the wings, that goes to the "in cabin" fuel selector, then off to the pumps and back out through the firewall to the engine.

L.Adamson
 
I'd like 'em in the warm air

I.e for freeze protection..Lots of warm air ..>Why wouldn't you put them close to the middle?

Frank
 
Relief hole?

Seems like I read a thread where a "backup" hole was put in the vent line in case the vent gets iced over. Where does this relief hole go? Not crazy about having gas possibly leak into the cabin.
 
No open vent lines in the cabin.

There should be NO holes in the vent line inside the cabin. Even if you didn't get fuel in there, there would be fumes. NEVER vent fuel tanks to inside the cabin. Period!
 
Webb said:
Seems like I read a thread where a "backup" hole was put in the vent line in case the vent gets iced over. Where does this relief hole go? Not crazy about having gas possibly leak into the cabin.
Click to expand...


Look at post #8 of this thread.

Regards,
Brett
 
Last edited:
Thanks

Mel - thanks - I would not have gone there, just a curiosity question regarding the "what if" of a fuel vent blockage. Darn fumes are even more dangerous than the liquid. "boom"

Brett - Interesting install - where did the design come from? I like the ideal of not having those long lines travel along the cockpit walls. Now would be a very very easy time to move. Just would have to "patch" the bottom of the fuselage. Would have plenty of aluminum line to reuse (lol). Also as I get ready to rivet the skin to the firewall, I'll have some fuel tank sealant mixed, no problem to reseal the screw holes for the clamps
 
Webb said:
Mel - thanks - I would not have gone there, just a curiosity question regarding the "what if" of a fuel vent blockage. Darn fumes are even more dangerous than the liquid. "boom"

Brett - Interesting install - where did the design come from? I like the ideal of not having those long lines travel along the cockpit walls. Now would be a very very easy time to move. Just would have to "patch" the bottom of the fuselage. Would have plenty of aluminum line to reuse (lol). Also as I get ready to rivet the skin to the firewall, I'll have some fuel tank sealant mixed, no problem to reseal the screw holes for the clamps
Click to expand...

Webb,

To be totally honest, I myself do not know where that method stemmed from. In reading Rockyjs thread he seems to have co-opted the idea from Rocket builders. I had read his posting and then saw yours. Perhaps you could send a note to Rockyjs ( I still laugh at that) and ask him were He saw it.
Not much help I know?but heck I tried.

Regards,
Brett
 
Brett,
The more I look at this, the more I like it. Multiple coils which would be easy to make. Instead of using the cover screws, I think that I would just use the skin and install some clamps that way. No sense in disturbing the screws which passed pressure testing.... As far as any leak out, hot day and full tank maybe but any fuel that might make it into one of the loops stand a good chance of getting drawn back into the tank as you fly. The part I would like to consider is the tiny vent hole incase the intake became blocked. Here is a concern that Mel brought up - you have the potential for fuel vapor in an enclosed area between the wing and the fuselage and a potential leak into the cabin. Not good. Perhaps it is best to bypass the thought. I've never had a problem having vent lines get clogged but I really don't want a first.....Of course there would always be the option to break the vent line if you had to because it iced over since it was in the cabin. Just make sure you grabbed the vent instead of the fuel feed (lol). Geez, I think we think too much.

Thanks,
Webb
 
Webb said:
...As far as any leak out, hot day and full tank maybe but any fuel that might make it into one of the loops stand a good chance of getting drawn back into the tank as you fly...
Click to expand...
I haven't tried to follow the physics of the various venting schemes but I do know that the standard Van's setup will spew fuel onto pavement on a warm day after a fill-up. There is the solution of not filling quite to the top.
 
Rockyjs said:
Here is the link to the Rocket fuel vent where I "borrowed" the idea. This I believe is their standard fuel vent system. There's a lengthy discussion of the pros and cons.

http://www.vansairforce.com/communi... was looking for that thread. Regards, Brett
Click to expand...
 
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