Exhaust smell when powered back

kellyp · #1 01-02-2007, 12:05 PM

Happy New Year everyone! I have a strange occurance that you listers might know the cause of.

When I pull the power back for high speed descent I get exhaust smell in the cabin. It goes away if I add power. My exhaust pipes are cut horizontal and flush with the bottom surface of the cooling air exit (out of the slipstream). I'm guessing that under power the jet of exhaust clears the fuselage, but not when powered back.

This happens with the cabin heat and vents closed so I don't think those are the culprits. My canopy and firewall are sealed well. Anybody have this problem and a solution?

The next place for me to look is the flap rod holes in the fuse. Any ideas or photos on how anyone has sealed these up?

Reply off list if you want. Thanks for your help,

fodrv7 · #2 01-02-2007, 02:30 PM

Kelly,
I haven't had that problem, but it highlights how important it is to have a CO (Carbon Monoxide) monitor.

You cannot smell CO, but it will put you to sleep with out you knowing.

Good luck with the fume problem.

Pete.

akarmy · #3 01-02-2007, 02:40 PM

Quote:

Originally Posted by kellyp

When I pull the power back for high speed descent I get exhaust smell in the cabin ....... Anybody have this problem and a solution?

Yep, same thing with mine. It's only if I really pull the power back quickly while descending. In normal operation I never pull the power that quickly so it's not an issue. Knowing the amount of leaking air into the cabin I suspect it would be hard to seal every last location. I have aileron pushrod seals, canopy seals (as good as I can get it) etc... While you can smell exhaust I have never had the CO alarm go off in flight so that's good I guess... (hopefully it's working!)

kellyp · #4 01-02-2007, 02:49 PM

I should also mention that I have the aileron pushrod seals at the cabin to wing interface. Good to hear it is not enough to register on the CO monitor. If I find a solution I will post it here.

MartinPred · #5 01-03-2007, 01:53 PM

Quote:

Originally Posted by akarmy

Yep, same thing with mine. It's only if I really pull the power back quickly while descending. In normal operation I never pull the power that quickly so it's not an issue. Knowing the amount of leaking air into the cabin I suspect it would be hard to seal every last location. I have aileron pushrod seals, canopy seals (as good as I can get it) etc... While you can smell exhaust I have never had the CO alarm go off in flight so that's good I guess... (hopefully it's working!)

Are you sure it's exhaust and not fuel fumes? I get a good whiff of fuel when I do a steep descent in the pattern with the mixture at full-rich. I suspect some of that carb air is somehow getting to the cabin.

Of course, if I'm going to be doing a lot of pattern work I try to keep it leaned out. That tends to elminate the smell.

-Martin
402BD

kellyp · #6 01-03-2007, 04:48 PM

Quote:

Originally Posted by MartinPred

Are you sure it's exhaust and not fuel fumes? I get a good whiff of fuel when I do a steep descent in the pattern with the mixture at full-rich. I suspect some of that carb air is somehow getting to the cabin.

Of course, if I'm going to be doing a lot of pattern work I try to keep it leaned out. That tends to elminate the smell.

-Martin
402BD

It's exhaust, not fuel. I've had others on board that would smell it also and they agree...it's exhaust. I also stayed leaned out in the pattern, full rich only when climbing in hot weather.

AlexPeterson · #7 01-03-2007, 05:01 PM

I recently reworked my exhaust system, tightening things up, etc.. When I first flew it after this work, I noticed exhaust smell in the cockpit during slower (pattern) flight. I re-rigged the tail pipes a bit lower, and the smell went away. The two positions were only about an inch and a half different vertically. The new position keeps the entire open end of the pipe below the cooling air exit, and maybe 6 to 8 inches aft. The position that was stinky put the open end of the pipe mostly above the lower exit air area.

fodrv7 · #8 01-03-2007, 06:38 PM

There is connection between this thread and Paul's thread, "Fuel Smell "Funny" . http://www.vansairforce.com/communit...ght=fuel+smell

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.