What's new
Van's Air Force

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

Fuel Smell "Funny"

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
This is something that I have noticed about my -8 for some time, and have been meaning to post - but I always forget by the time I get home from the airport....I think it is peculiar to the -8 because of the under wing NACA vent - not sure if any other models share the same configuration.

I usually fill up with gas at a field a short distance from my home base, and always feed from the left tank for the short return trip. I sometimes have noticed a faint smell of fuel when I turn base to final for landing, and after the first time, I did a little investigating to make sure I didn't have a problem. What I discovered was that it was stronger with the passenger vent open, and almost went away when the passenger vent was closed. It also didn't happen at all if I fed fuel from the right tank on my return.

Putting these little pieces of info together, I surmise that with the tanks freshly filled, and the right tank isolated (not being used), I am getting a "burp" of fuel out of the vent. When I turn make the pattern turns, I must be getting a little plume of fuel vapor, and it is going under the wing and into the under-wing NACA scoop. (Now before anyone gets too worried, I've been a fireman for many years, and I can tell you that this faint smell is WAY below flammability limits. It's just enough to notice.)

Anyone else smelled this? Any alternative theories? the conditions I've stated are the ONLY times I've noticed it, and only in a left-hand pattern (you don't get it with right turns, and since the scoop is on the right, that's why I think my explanation makes sense...

Paul
 
Must be the fuel vent, Paul. But I can't say I've ever noticed this with mine. Are your vents (fuel) configured per the plans?

I sometimes fill up to the bottom of the neck in the tank and will get some spillage from around the cap on the top of the wing. But never any fuel smell.

Using a little problem solving methodology here, what else do you do when approaching to land when you smell the fuel? You switch the boost pump on. Do you have a recirc system? Where does it return? You overfilling one tank or the other? What else happens when returning? Sustained higher angle of attack???

Last, if it only happens in a left hand pattern, then also I'd say you're not flying coordinated regardless of the source of fuel smell. Check that one next time.
 
Paul
I get the same thing if the tanks are full to the brim. I always assumed it was the vents and don't worry about it.
I have noticed the same thing on other planes I have flown.
 
I've noticed the same thing on two -8's, and a -3B. Hmmmm, no NACA duct on the 3B. The best theory I've heard is that it was from the vent, but was coming in through the flap pushrod holes.

BTW, it would be easy to duct tape over the passenger NACA duct to see if that stopped it. Being winter, I doubt the passenger would mind :)

Cheers,
Rusty

PS- Thanks for your excellent work with the shuttle program!!!
 
Of course, Bryan is right, if I just flew more coordinated, I shouldn't get it in the NACA scoop at all!! :eek: (Of course, I learned to fly in airplanes without flaps, so I'm always slipping around on final....or at least that's gonna be my excuse!). To answer your other questions - stock, per-plans vents, no return system, tanks full to the brim every time - I'm nothing if not repeatable....

Interesting to know I'm not the only one that has noticed this though. I might just put some tape over that vent tomorrow - of course, that'll mess up my OAT sensor and real-time TAS...

Paul
 
Just thought of something. Maybe you're getting a little fuel in the vent tubing during your flight home. Then as you slow, the tank depressurizes and burps out the ounce or two of fuel. Think?

Ahh. Slipping to land.. would be a good RV(8) discussion topic. I kind of find it a little uncomfortable myself. I have no reason to believe the plane would do funny things, but just don't feel as comfortable as I do slipping in a slow, high-winger.

Was a beautiful evening for a quick RV mission. My wingman had to try our his new digital SLR with that sunset. We swung by Clover at about 5:30-5:45.
 
Last edited:
Just a thought

Paul,
Since I have read many of your posts, I see you have a carburated engine. When you go full rich (preparing to land), maybe some extra fuel is going into the overflow tube from your carb and out the bottom cowl. I also assume your fuel pump has been activated about the same time as you go full rich. I would then assume your overflow tube is starboard of your exhaust, which on a left bank would not "heat dissapate" the fuel as it would flow away from the exhaust and wrap up the starboard side of the fuselage (and into the NACA vent). On a right bank, the fuel would be heat dissapated from the exhaust and you would never "smell" any. I am really reaching for straws with this theory but would be interested in knowing if your overflow tube is in this configuration from your carb.
I like the duct tape approach to see if this goes away.
Keep up the informative posting.

Pat Garboden
Ozark, MO
RV9-A 942 WG (reserved) slider w/O-235
RV9-A 942PT (reserved) tip-up w/O320
 
More Variables

I noticed on reaching cruise level recently that when I turned OFF the cabin air I could smell fuel vapour.
Turning it back ON the smell dissappeared.

I assumed at the time- and still think I am right- when the cabin vent was turned ON the cabin was slightly pressurised (over coming the normal slight negative pressure in the cabin) and the vapour could not enter.

Perhaps what is happening Paul, is that something is changing the pressure in the cabin -flaps down, reduced airspeed- and the airflow into the cabin is increased.

I mean. I would never suggest that you don't always have the ball absolutely nailed in the middle. Tut! Tut!

Pete.
 
Interesting, and for me at least timely. I am just about ready to route the soft aluminum vent tubing through the fuel tanks. I'm thinking that at the outboard end of its run, which as you know is a few inches past where it is held by a clamp riveted to the filler flange, I should cut the tube at a bit of an angle and orient the tube so that its angle is somewhat parallel with the top of the tank. This, it would seem, minimize the chance of fuel sloshing up and finding its way into the vent tube. Whattaya think?
 
Maybe the increase in atmospheric pressure from the descent increases the pressure in the tank pushing any fuel that has sloshed into the vent line out of the vent.
 
Paul, one thing that nobody has mentioned is that the rudder cables could have sliced into the vent line(s).

This has been a problem with the -4's and as I recall, the -8's are similar.

Might want to check that. Can't hurt any!

:D CJ
 
Val pukes fuel!

Paul,

I was in the hangar late Tuesday night installing my landing light. It was quiet except for the cursing as I stripped and crimped wires in a very tight space. All of a sudden I hear this "splaaat" noise and look over quickly to see fuel shooting out of your fuel vent.

Easily explained by physics, but very creepy at midnight........

Glad you made it home safely!
 
I love the discussion that a simple observation can generate! Even though many of these ideas might or might not apply in this particular case, they are still things for people to think about in the future if they have their own problems....I call these "archive building" threads!

The Carb ideas are interesting, but for this particular case, I think it is more likely the fuel vent, since it only happens with a full right tank that hasn't been touched. Next time I come back with after filling, I'll burn off the right side first and see if it happens!

petehowell said:
Paul
I was in the hangar late Tuesday night installing my landing light. It was quiet except for the cursing as I stripped and crimped wires in a very tight space. All of a sudden I hear this "splaaat" noise and look over quickly to see fuel shooting out of your fuel vent.

Easily explained by physics, but very creepy at midnight........

Glad you made it home safely!
Click to expand...

Well that's a cool piece of data Pete! Once again....I fueled the airplane upon landing at ANE(and I always "put a heap on it" when I fill it - fuel left at the pump doesn't do much good...), so when the fuel warmed up in the hangar, I bet it expanded out the vent line.


I don't think I've ever had it so quiet in my hangar that I could hear the airplane make noises.... :eek:

Paul
 
ahhh.... the smell of 100LL in the morning

I have never noticed any fuel smells during flight even with leaking fuel hoses forward of the firewall. However, I do get a good smell when I first open the canopy. I figure this might have been from the leaking hoses, time will tell.
 
Seal the NACA duct.

Paul,
Here's another thought.
If some builders find a need to fit Aileron Pushrod boots the maybe your fuel vapour is finding it's way into the wings and entering through the aileron pushrod holes.
You could easily check this by duct taping over your NACA duct and doing a flight test.

It also raises the option for those flying in the figid North American winters with leaking eyeball vents.
Tape over the NACA duct. You might pick up 0.01 of a Knot.
Pete.
 
A few years ago I was under my plane cleaning or some such thing. I heard a gurgle, and got a splash of 100LL right in the face. I was directly under the vent, and I guess as the plane warmed up in the hangar, some fuel glob in the vent line puked out right onto me. I respect those buggers a bit more now...

I will also smell a little fuel if I climb steeply with full tanks. In a steep climb attitude, the vent line is submerged and the air on top of the fuel expands. My standard procedure is now to switch tanks after I've burned a gallon or two, just to minimize this. I don't know where it comes in, but probably in the wing root fairings or flap holes.
 
I have noticed the fuel smell on the base/final turn many times. I have had several passengers mention it and have never figured out where its coming from. I definately think it is from the fuel vent but it could be coming in several places. The wing NACA vent or flap pushrod holes sound like good possibilities. BTW, I have an IO-360... pretty sure the carby is not the problem.

Karl
 
Fuel smell

Fellow RV'rs:

A few weeks ago, about the time of the fuel fire on an RV at Falcon Field (KFFC) near Atlanta, I smelled 100LL a couple of times during taxi back to my hangar after flight. Having EXTREME aversion to becoming a "Crispy Critter", I thought it prudent to check it out.

I have an IO-360-A3B6D with Bendix FI on my 8. I checked all the fuel fittings, lines, etc with the boost pump on with the mixture in the idle cut off position----nothing. Not satisfied, I walked around and moved the mixture toward the rich position. By the time I got back around to the engine, there was maybe a thimble full of fuel on the floor!

The leak was coming around the mixture shaft, dripping close to the exhaust. Apparently the smell was coming out of the cooling air ramp and into the cockpit through the bottom wing skin/fuselage overlap and into the cockpit thru the aileron push/pull holes and the flap actuating rod holes.

The "O" rings on the shaft had hardend and turned into "D" rings allowing the fuel to be pushed by. Don Rivera and the guys at Airflow Performance in Spartenberg, SC. did a superb job of rebuilding the fuel servo and flow divider.

This hasn't much to do with Paul's problem, except that the smell MAY be coming from the overflow vents, then thru the above mentioned route. I doubt that even a Champ or Cub could slip enough to get the smell thru the underwing air vent!!!!!

Mannan Thomason
RV-8 N161RL
 
mannanj said:
This hasn't much to do with Paul's problem, except that the smell MAY be coming from the overflow vents, then thru the above mentioned route. I doubt that even a Champ or Cub could slip enough to get the smell thru the underwing air vent!!!!!

Mannan Thomason
RV-8 N161RL
Click to expand...

Mannan makes a really important point - if you have a fuel smell, you should track it down!

The reason I suspect the NACA scoop is that the smell comes and goes in direct proportion to the opening and closing of the rear seat vent, and it comes right out of the vent. I absolutely agree that fuel itself isn't making it to the vent - but the smell appeas to be. I've tracked down lots of fuel smells in my years as a firefighter, and it's amazing how far they reach.
 
Ironflight said:
Mannan makes a really important point - if you have a fuel smell, you should track it down!
Click to expand...
Last time I smelled fuel, I had a loose fitting on an injector...check it out sooner rather than later!
 
related post "Exhaust smell when powered back"

There is connection between this thread and Kelly's thread "Exhaust smell when powered back".
http://www.vansairforce.com/community/showthread.php?p=95438&posted=1#post95438

The exhaust smell and the fuel smell have both occurred when throttle back and entering the circuit.

It has also prompted me to remember that I once had a warning from my CO monitor and it too occurred on downwind leg.

This all seems to confirm that there is a change in airlfow into the cockpit when reducing power and speed to enter the circuit.

Pete.
 
Angle of attack is larger at slower speeds. Somehow, that curls airflow in a way that it gets in the cockpit. Don't know if it is the flap holes or where, but it gets in.
 
gas smell

I have had the same problem and found that the quick drain on the right side was leaking a few drops of gas. it wasn't until I used some fuel lub on the "O" rings that it stopped.

Gas lub is a fuel prof lubrication that will not desolve in gasoline

Marvin RV8A
 
Captain_John said:
Paul, one thing that nobody has mentioned is that the rudder cables could have sliced into the vent line(s).

This has been a problem with the -4's and as I recall, the -8's are similar.

Might want to check that. Can't hurt any!

:D CJ
Click to expand...

The 4's and 8's are not the same. Yes it could and has happened on 4's, but I don't see how this could happen on the 8's. They are buried in the gear boxes nowhere near the rudder cables. (just wanted to clear that up).
 
Fuel tester

Paul -

The only time I have had a fuel smell I isolated it to the fuel tester stored behind my seat. I only seemed to get a wiff on landings and always soon after fueling. I left it behind in the hangar a couple of times to test my theory and the odor did not appear.
 
Last edited:
I wouldn't doubt that Paul's conclusion is on the money.

I know that if I top my tanks off and park the plane they will leak fuel out of the vents when the plane is parked. This is very common. This is why whenever I fill up at the nearby cheap airport I always try to remember to swap tanks on the way home even though it's a 5 minute flight. No sense wasting that liquid blue gold. :)
 
Fuel smell in cockpit RV4

I, also, thought I was smelling to much fuel. Full tanks, high angle of attack seemed to be the worst. I was constantly checking the fuel system. In the middle of this, I replaced the fuel selector valve. I did find a small seep at the new valve and fixed it. Last Saturday, I couldnt fly because of low clouds, wind and rain in the area - it was cool temps. I was sitting in the seat working on my GPS when the sun came out and quickly warmed the uninsulated tin roof to the hanger. Shortly after, I heard a girgle-girgle-SPIT. Fuel squirted on my bare leg! (had shorts on) The fuel vent was broke at the very top of the loop. So, I am embarrased to say, the left fuel tank was venting into the cockpit! The alum tubing must have been over stressed when the 180 degree bend was made. The moral of this story is obvious... hope this helps out in RV land.
 
Fuel Lube

Marvin said:
I have had the same problem and found that the quick drain on the right side was leaking a few drops of gas. it wasn't until I used some fuel lub on the "O" rings that it stopped.

Gas lub is a fuel prof lubrication that will not desolve in gasoline

Marvin RV8A
Click to expand...

I'm not familiar with "fuel lube", but would like to try it on the O-ring on my fuel caps. Can you tell me where to get it and under what trade name(s)?

Thanks,
 
Fuel Lube

Dean -

Fuel Lube appears to be unavailable these days. EZTurn is available in tubes and tins from Wicks, AC$, etc.
 
Don't do it, too sticky!

I have some experience with some fuel caps whose O-rings were "lubricated" with EZ-Turn Fuel Lube. I say "Lubricated" because the stuff is like a cross between honey which has been boiled for an hour to make it twice as thick and sticky, and spray adhesive. The stuff is WAY sticky, and does not lubricate at all. This made the fuel caps almost impossible to remove. If I'm not mistaken, O-rings need to be lubricated to slide well, so that they seal properly. In the process of leak-checking my tanks, my fuel caps leaked with the EZ-turn on them. After cleaning all this gunk off there, I applied some light oil to the O-rings, and walla, the caps sealed fine. My theory is that the O-rings were unable to slide when they were expanded via the cam-lock mechanism of the fuel cap, leading to the leaks.

The stuff is great for sealing pipe threads in the fuel system, but I don't think it's appropriate for O-rings. If I'm all wet about the light oil being the most appropriate thing to use on fuel cap O-rings, somebody please chime in and correct me.
 
I use "Lubriplate" to lube my fuel cap "O"-rings. Never had a problem. I re-lube them once a year.
 
fuel line to fuel pressure gauge broke

hempy.4 said:
I, also, thought I was smelling to much fuel. Full tanks, high angle of attack seemed to be the worst. I was constantly checking the fuel system. In the middle of this, I replaced the fuel selector valve. I did find a small seep at the new valve and fixed it. Last Saturday, I couldnt fly because of low clouds, wind and rain in the area - it was cool temps. I was sitting in the seat working on my GPS when the sun came out and quickly warmed the uninsulated tin roof to the hanger. Shortly after, I heard a girgle-girgle-SPIT. Fuel squirted on my bare leg! (had shorts on) The fuel vent was broke at the very top of the loop. So, I am embarrased to say, the left fuel tank was venting into the cockpit! The alum tubing must have been over stressed when the 180 degree bend was made. The moral of this story is obvious... hope this helps out in RV land.
Click to expand...


Almost didn't write this up since I didn't see any lessons learned from my experience and my reaction. I had a strong smell of aviation fuel yesterday when I was turning downwind after turning on the boost pump and switching tanks. When inverted with negative Gs, that's not unusual, but upright got my attention. I switched back to the other tank, went to idle and was preparing to pull mixture and turn the fuel selector to off when I knew I had the field made. I had already unlatched the right side of the canopy (slider like an -8). The smell decreased turning base so made a normal landing and pulled off the runway. By then I didn't smell it any more. I was almost sure it was a leak with the fuel line to the fuel selector and pulled the boot around the stick to look before I got out of the airplane. Didn't see anything, so figured the next step was to remove the cowling. As I got out of the airplane, I saw the blue streaks from the left lower cowling and down the left gear fairing like my toy had wet its britches. Mine may not have been dry then either. With the cowling off and tracking back from the blue streaks, I found the copper tubing to the fuel pressure gauge on the mechanical fuel pump had broken right at the top of the fitting. A very rare event when properly installed according to the two A&Ps that did the repair. Looking back, what I didn't notice even though I scanned the instruments, was that the fuel pressure gauge would have been reading zero. Have no idea whether there was a chance for a fire, but it was definitely on my mind during the event. Will have to make the check out flight tomorrow early before the temps hit the triple digits in Alabama.
Bill McLean
RV-4
 
You must log in or register to reply here.
Back
Top