What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel Smell

Did you have very full tanks, or at least a full one on one side? If you burp fuel out the vent, it can flow back and get in to the rear seat NACA scoop (under the wing). Just one posible cause - others include an imporoper (leaking) fitting in the cockpit, so definitely somethgin to pin down!

Paul
 
Also at steep climb angles...I get a smell every now and then. After much angst and searching, I traced my odor to the vents squirting a bit.
 
how did you trace that down? i have had similar issues with gas odors and thought it was the fuel vents too.
 
tigerair25 said:
Has any one had an experience of smelling fuel when doing aileron rolls???If so what was the problem??
Click to expand...

Look very carefully at where the rudder cables go by the vent line in the cockpit. If they have rubbed a hole in the vent line it will cause a fuel smell in the cockpit if you drop one wing very much with a full tank on the opposie side.
 
Turbo,
I was freaked out the first time that I smelled fuel, so I traced all of my lines with the aux pump running and found nothing. This sent me down the path of the fuel vents. I took some pipe cleaners and shoved them up the vents immediately after shutting down and they came out wet. This was the only way that I could come up with to test the vents...un-scientific, but I sleep better now...
 
Paul, could you elaborate a bit on the path of fuel smell in your scenario? I, too, get a whiff of avgas in the cockpit, especially right after topping off, and usually when doing rolls. I've crawled around and found no leaks in any tubing inside the cockpit.

The smell seems to permeate the air even with the rear vent closed. I'm not seeing how fuel vapor could get from the vent tubes to the NACA vent in the right wing in flight with any real concentration. Help me see the light, O Wise One ... :D
 
Well Don, I came to the conclusion after discovering this in the pattern after "flying out" for fuel. I discovered that if the right tank was full to the brim, and I didn't use anything out of it, I'd get the fuel smell while turning base and final (probably with a little slip). If I burned something out of it on the way back (even just a little), I got no smell in those turns. This was repeatable time after time. My theory is that as the vent burps, in a turn, th fuel vapors slip outboard to get in to the NACA scoop. It takes very small amounts of fuel vapor to generate a smell (I learned this in my firefighting days), and I could make the smell diminish by closing the passenger vent. Very few vents close all the way, so some smell remained. There may be another explanation, but the evidence and experimental results sure point to the NACA scoop and the right fuel vent.

Paul
 
tinman said:
Also at steep climb angles...I get a smell every now and then. After much angst and searching, I traced my odor to the vents squirting a bit.
Click to expand...

I have seen this more than once, flying formation on an -8A while climbing after a fuel stop. Every 20 seconds or so for the first few minutes there will be a little "puff" of fuel vapor from the vents--usually one or the other but hitting a bump will cause them both to burp.
 
The fuel vents will burp a bit of fuel if you happen to go upside down. It can be worse if the tanks are full.
Also if you have the standard fuel valve: When both tanks are full, five minutes into the flight, especially on sunny days, you will get a whiff of fuel.
The tank that is NOT being used is pushing a bit of fuel past the fuel valve and out around the handle stem. This tank is being pressurized by the vent and also by sun heating the fuel, which causes the fuel to expand. Check it sometime by touching a kleenex to the stem of the valve. It is a very small amount and not worth worrying about. To stop this fuel smell, take off and fly for five minutes or so and then change tanks. This will relieve the pressure on the unused tank and you will get no odor.
 
Interesting thesis, Paul. I guess I've never paid enough attention to exactly where and when I smell it. Maybe I'll start.

I'm wondering if there's any other portal of entry for fumes besides the rear seat air vent? I sure wish I'd modified the gear towers with a large access panel to be able to investigate that area further. I'm still not convinced that my issue isn't in the fittings there ...
 
I've noticed right after I gas up that I get a fuel smell also. I found that after I fly briefly, it goes away but if I taxi back to hangar it, I will open the gas cap latch and it prevents the fuel smell. I think the fuel is cold and when it goes into the warm gas tanks there is an increase in pressure with the increase in temperature. I have also found that if I don't release the cap, I get back flow out of the vent tubes.

Bill Near
 
N8RV said:
I'm wondering if there's any other portal of entry for fumes besides the rear seat air vent? I sure wish I'd modified the gear towers with a large access panel to be able to investigate that area further. I'm still not convinced that my issue isn't in the fittings there ...
Click to expand...

I'm also wondering if you get the fuel burping form the vents, if it might not get in through the wing/fuselage joint? The smell would easily migrate in to the cabin. But....there is such a strong and fast correlation between the smell and closing/opening the rear passenger vent (in my case) that I think it is getting rammed in there.

Paul
 
I had the fuel smell after acro and was unable to locate where it was coming from. I too thought it was from the fuel vents and being sucked into the air vents. I checked the vent lines in the gear tower and found one of the fittings that attaches on the floor thru fitting loose. I tightened it and flew again and still had the smell. I checked the same fitting again and found the nut tight but the line had a little play in it when I pulled on it. Further investigation revealed that the fitting was cross threaded. New fitting, new flight, no smell. Now I don't have fuel smell in any flight regime and I do a lot of acro.
 
Last edited:
OK, did an hour in the -8 tonight and got the strong odor when doing standard rate turns (coordinated, half fuel), then again when slowing for pattern work and stalls. It appears to follow AOA more than anything. No leaks inside or out. Most of you are reporting nearly full tanks and this makes sense, but half fuel? I don't remember this smell from the last time I flew it... Any more insight?

BTW, I put a camera under the Hiperbipe once and happened to notice the fuel venting out of a topped off tank on descent. The HB and the -8 share the same vent location, and on my airplane it pushes a LOT of fuel unless I burn it down a little.
 
You must log in or register to reply here.
Back
Top