I'm an A/P mechanic, also a student pilot, taking lessons in my brothers 67' Cherokee 180. We did a lot of slow flight today, and I've always noticed in the past that when approaching stalls, there's an exhaust odor in the cockpit, never happens any other time even with heat on, full power takeoffs, cruise, ground idling etc... Only in slow flight just a hair above stall speed, or right after a stall.
The exhaust system appears to be in good shape (gaskets, runners, muffler) I just assumed that at such a low airspeed with the nose pointing up at 2000 rpm, the exhaust hovers under the front of the aircraft rather than smoothing flowing twards the rear and the smell comes into the cabin. But it got me thinking further today when my instructor commented about it several times.
I didnt have much of a chance when we got back, but I'm going to inspect it further, like check the fire-wall for any openings, take another look at the exhaust manifold gaskets, perhaps take the muffler shroud off and examine. I'm aware that this is something that can be very critical.
Has anybody experienced this at slow flight? I did a google search and found 2 results of people smelling exhaust in the cabin at slow flight, but they weren't cherokees.
Just wondering if anybody has experienced this or if there is anything else that I should look into?
Any advice/comments appreciatied.
Thanks!
- Andrew
Check the condition of the rubber gaskets that seal the wingroot to the fuselage. If the bottom side is leaking, exhaust fumes will enter the cabin through the aileron cable openings.
JimC
Cherokees are also notorious for exhaust fumes coming back thru the hole in the tailcone and traveling backwards into the cabin due to lower air pressure inside the cabin while in flight. Slow flight is likely to aggravate this condition. A handheld portable Carbon Monoxide meter confirms this phenomenon in my plane as the CO level increases in the back seat when you hold the meter near the hatch door in the rear baggage area/hatrack which has a poor seal. My remedy is to always fly with either the left side vent open a bit, or the heater on just enough to bring the inside cabin pressure up enough to force some air back out the various cabin leaks. Also the wing root seals can let some exhaust in too, just as JimC mentioned. I taped up all the lightening holes in the front of the spar carry-thru under the rear seat with duct tape, which also helps to keep cold air from freezing my rear passengers' feet in the winter time.
I experience the same in my PA32. Great way to test my CO detector! I'll be interested to learn if you find a definitive source of the leak. I know it's not my exhaust system - could be any of the other seals mentioned I suppose.
I too have the same problem in my Warrior. I get exhaust in the cabin any time my nose is pitched up. I use a digital co2 meter and keep a close eye on it. I've loaned the meter to other friends with Cherokees and they also had the same results.
Another issue I have is cold air coming into the cabin through the bilge area. There is a vent down there on the belly, but plugging that didn't make a difference. I'm going to experiment with it this winter because I'm determined to get it sealed up.
That cold air is coming forward through the tailcone from the vertical slot for the stabilator mass balance. The area at the aft end of the tailcone is higher pressure than the inside of the aircraft.
JimC
Do you know of an effective way to block that air? The tailcone has the bulkhead installed and there is a nice little boot around the counterbalance shaft. It seems like a lot of air is coming from underneath my rear bench seat. Thanks
