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fuel odor after looping

Jake14

Well Known Member
I do just basic positive-g acro in my 14, but notice that after a couple of loops (+4 to 0 g) I get a faint smell of fuel in the cockpit which disappears in a minute or so. Don't get this with other maneuvers. I've checked all the fuel system connections but can't find any evidence of leaks (odor or blue stains)
Wondering if this is common or cause for concern and any suggestions where to look would be appreciated
 
I don't loop but you're doing the right thing to find the source of the fuel smell. Anytime you smell fuel, find the source.
 
I have the same problem sometimes on my 8 usually as I approach 0 G's. I think it's from the fuel vents. I checked all my fuel lines and made sure there was no leaks. Mine also only happens during acro.
 
I get this occasionally to but only on the first climb out on real full tanks. After that nothing. Figured it came from one of the vents as there are no other system leaks.
 
With full tanks, in the sun, I have found that there is a very small leakage of fuel around the stem of the Van?s standard fuel valve. Check with a small bit of Kleenex at the top of the valve

This is a very tiny amount of fuel, the odour, is distinctive.

Typically it happens about two or three minutes into the flight with full tanks. Changing tanks will eliminate the issue

I have also experienced, occasionally, the fuel smell, from fuel vents, during aerobatics.
 
Tom, yes probably the fuel caps. When I fill to the brim and then bring my RV into the heated hanger I can get a pretty good fuel stain in a few days off the left cap - gas expands. I don?t do this anymore.
 
Thanks for the suggestions, I fly with fairly full tanks so I think the vent may be what's causing it. On a pull-up to vertical with plenty of fuel in the tanks, the vent intake at the top/rear/outboard of the tank probably gets submerged. Then the positive g at the bottom pushes the fuel out.
Thanks again.
 
Thanks for the suggestions, I fly with fairly full tanks so I think the vent may be what's causing it. On a pull-up to vertical with plenty of fuel in the tanks, the vent intake at the top/rear/outboard of the tank probably gets submerged. Then the positive g at the bottom pushes the fuel out.
Thanks again.
On your next fill up, try to see if you can lift of the nose wheel and observe. With the 14 tanks, you will get two cups or more of fuel coming out of the vent. The fuel goes to the back and outer corner of the tank where the vent line is terminated at. I noticed this during my phase one and testing.
 
I?ve noticed the same fuel smell during Acro with all 5 RV?s I?ve owned, regardless of the fuel level. None of them had an inverted fuel pickup. I?m pretty sure that a little fuel is sloshing into the vent line and coming out the vent fitting right under my feet. This is the only time I?ve had a fuel smell, so it has to be the vent, or the cap. Neither is serious. If it?s the cap, you should see staining somewhere around that area.
 
I installed the Rocket style fuel vents in my wing roots and they have worked well for me.
 
I caught that moment on video: https://youtu.be/uMyGyqhU7Yc

I usually fly with one tank half full and second half empty so thermal expansion has nothing to do with fuel coming out. First I cut drainage line inside of cockpit and put line going from the tank into transparent bottle using AN fittings. I brought about 2 oz of perfect 100LL after just about 15 minutes of aerobatics.
I tried rocket style vent inside cockpit but it did not work at all. It does not matter which tank is active at the moment. I think about some expandable tank connecting both vent lines.
Extra has 5 tanks and very complicated vent system. Did not have a chance to look at drawings. May be some solution is there.
 
I do just basic positive-g acro in my 14, but notice that after a couple of loops (+4 to 0 g) I get a faint smell of fuel in the cockpit....
Technically 0G is not positive. :D All the RV's I have flown (mostly with Carbs) I never smell fuel doing aerobatics. I'm able to manage at least -0.5G on all my maneuvers, except a proper Cuban-8, on the inverted 45 down line, before you 1/2 roll upright. It is hard to stay positive. I believe IAC requires you establish and hold the inverted down line before rolling upright even in sportsman. A lot of non-inverted fuel system planes sputter.
 
Fuel Vents

I believe that the vapor from the fuel vents gets sucked in to the cockpit where the flap actuator rods are. I also believe that the cockpit has slightly lower pressure which helps the vapor come in. I have had it on both my RV's and have never been concerned about it.

Steve
 
CO intake?

I believe that the vapor from the fuel vents gets sucked in to the cockpit where the flap actuator rods are. I also believe that the cockpit has slightly lower pressure which helps the vapor come in. ...
Wouldn't that also allow CO to come in from the exhaust pipes?
 
Amazing video!

I caught that moment on video: https://youtu.be/uMyGyqhU7Yc
...
Great video! Shows the fuel coming out very clearly. Looks like you've done a lot of research on this. My vents are "pressurized" - facing forward. I wonder if that will have any influence on this - not flying yet but looking forward to testing. Thanks for sharing the video!
 
Wouldn't that also allow CO to come in from the exhaust pipes?
Difficult to say. Those who use smoke systems should shed light on how airflow distributes around the cockpit. Try to drive a car with trunk open. You will be surprised.
 
Great video! Shows the fuel coming out very clearly. Looks like you've done a lot of research on this. My vents are "pressurized" - facing forward. I wonder if that will have any influence on this - not flying yet but looking forward to testing. Thanks for sharing the video!

Mickey, you are not alone. Everybody who builds according to plans has vents "pressurized". In my opinion it makes things even worse. You have slightly higher pressure in the tanks due to vents facing forward. At some maneuvers like hammerhead when you fly slowly that extra pressure pushes everything you have collected in your vent lines out.
 
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