Fumes In Cockpit

[blakecarl]

Flying our BC12-65 we smell what is most likely exhaust fumes in the cockpit. Our CFI has commented that he usually has a low grade headache after flying in the Taylorcraft (for the purpose of this discussion, let's assume that it's not the students giving him the headache!). We have a carbon monoxide detection card which remains normal during flight. There doesn't appear to be any significant openings in the firewall where exhaust could come through. The cabin heat isn't the source since we had a piece of foil tape over the opening into the cockpit to keep from adding heat on warm days. The most likely source I can come up with is the opening around the landing gear bungee cords. I've attached some photos of the exhaust pipe and underside of our cockpit. Is there some type of sealing system that should be used to eliminate this? Has anyone experienced something similar? Any ideas on what could be done to eliminate the fumes would be appreciated.

Thanks
Blake

[magman]

Re: Fumes In Cockpit

I think you may want to try another CO detector. They are only effective for a few months. If you DO have fumes it should activate. You may want to assure that all openings in the firewall are sealed. I think there is a "boot" that goes over the bungees inside the cockpit. I'm NOT a fan of extending the exhaust stack as this may lead to cracking.
Ron

[robbie]

Re: Fumes In Cockpit

Anyone have a boot or cover over the bungees cords inside of the plane???
Sounds like it might be a good idea.
I think alot of my cold air comes in from that spot.

[mikeg]

Re: Fumes In Cockpit

Look for broken exhaust stacks at the cylinders, leaking exhaust gaskets, remove the heat muff and look for cracks in the exhaust system.
Mike
NC29804
NC27451

[Pearson]

Re: Fumes In Cockpit

There is supposed to be a cover across the tubes just under the front edge of the seat. I am sure it is not meant to be airtight, but it will help keep fumes or cold air from comming into the cockpit. Originally it was pressed paper, but most have been replaced with aluminum or just removed.

[ClipWing_T]

Re: Fumes In Cockpit

I had the same problem on my Taylorcraft many years ago. I would
get headaches after flying and a there was a smell of exhaust . I removed
the heat muff and found cracks in the exhaust pipe. Try a CO dector and
maybe block off the front seat area. That should be the easiest
first thing to do.

[RobertP]

Re: Fumes In Cockpit

I had the same problem with my F22A all be it I wasn't smelling exhaust fumes! but on a 50 hr check I found the exhaust stack was holed and cracked just where the muffler goes around the stack and had to have a new piece welded in by a licensed aircraft welder. It was also welded up previously as a result of a pre purchase inspection before I bought the aircraft so obviously this is a weak spot and it seemed to me that it could possibly be caused by the stack vibrating against the muff under certain conditions.

It is very difficult to see the damage without actually removing the muffs but it is one of the inspections to do on a 50 hr with my aircraft.

If you find the stack is cracked / holed and you need to have it welded or a new piece welded in make sure it is put in a jig before heat is applied or it will warp and the exhaust will not fit the engine block and you have to start all over again! (yes it happened to me when I let a friend who was a very good car welder have a go first time around! ) The licensed welder let me watch whilst he repaired it and explained it all to me plus they use special tube ordered up from the States. It cost £260 in total so not cheap but I felt I had my monies worth when I saw the work involved and you couldn't tell a piece had been inserted when they had finished.

[magman]

Re: Fumes In Cockpit

It does appear that your CO detector is NOT functioning.
If you are going to check your heat muff don't do only part of the job.
Recently did a F22A that looked good but a Pressure Test revealed at
least 6 inches of a spiral crack.

Get a Leaf Blower or use the pressure side of a Shop Vacuum Cleaner.
Hook up to exhaust stack with duct tape.
Turn pressure on & squirt a soap & water solution EVERYWHERE.
If you close the throttle you can check intake hoses & gaskets in addition to the exhaust system & gaskets.

Easy & cheap to do.

Ron Ciura

Buffalo NY

[rotaxflyer]

Re: Fumes In Cockpit

I had a similar problem a couple years ago. The CO detector with the spot is simply too slow - by the time the dot changed colour, it was too late and I would have the headache.

In the end it turned out that a couple exhaust studs needed to be heli-coiled. I also stuffed the space around the shock cords with foam rubber and added an extension to the exhaust, but that only marginally improved things.

I strongly recommend that you get a CO detector that is battery operated and displays the concentration. There is a home model from Kiddie that fits the bill and costs around $40. There are aircraft ones available, but I found the kiddie one works pretty well if a little bulky. Three AA batteries last the season.

Andy

[blakecarl]

Re: Fumes In Cockpit

Thanks for the suggestions! Here’s an update on where I’m at with this. To definitely confirm there was CO present in the cockpit, I took a battery operated detector from home—great idea by the way—with me on a flight. The peak reading from start up to shut down was about 109 ppm. This occurred prior to take off. During flight the readings were around 50 ppm. This was with the windows partially open, all openings through the firewall well sealed and outlet of the cabin heat taped over.

I hooked up exhaust end of a vacuum to the exhaust pipe and used soap solution to look for leaks. There was one small leak in a weld at the point where the two sides join into one, a problem but not big enough to be the primary source. The major leaks I discovered were at the junction of the exhaust pipe with the two back cylinders.

At this point my theory is that the escaped exhaust is exiting at the bottom rear of the cowling where it flows adjacent to the fuselage and a portion is coming into the cockpit via the bungee covers and seams along the landing gear. I have some ideas on how to seal this area but eliminating leaks in the exhaust is the priority.

The local advice I’ve received so far is that the existing exhaust pipe cannot likely be repaired to address the leak at the cylinder heads. I have looked a bit to get an idea what the cost of replacement will involve and am planning to do more research on the forums to see if this has been addressed in the past.

[Pearson]

Re: Fumes In Cockpit

Why can't it be repaired?

Is there any reason you can't drop the whole exhaust system down 3-4 inches and resurface the offending flange with a large flat file or even a small grinder. As difficult as it is to completely remove the original exhaust on most Taylorcraft, I would go to great lengths to repair it without removal. Of course, if it just can't be avoided, you gotta do what you gotta do. I think if I had to go to the trouble of removing my exhaust system, I would spring for a whole new system or a complete rebuild of my old one before putting it back on.

I had problems with my exhaust shortly after I bought my plane. I replaced the gaskets, but discovered the studs were stripping the threads in the cylinders. After installing a couple of helicoils and a set "blow proof" gaskets, I have had no other problems. The blow proof exhaust gaskets are well worth the extra $. I actually had to do a little bit of welding on one of my flanges while I had the exhaust dropped down a few inches. It isn't easy, but it is better than removing the engine to get the exhaust off.

[flyguy]

Re: Fumes In Cockpit

Sure would be nice if there was a STC out there to convert to Luscombe exhausts. That is, with one exhaust pipe on each side.

That is what I have on my "-85," and it makes it easy to work on, new parts are available, including heat muffs, cleans up the back of the engine, and I think they are a lot less likely to fail in any of the typical modes.

Fortunately for me, mine was done on a 337 with the engine change.

Having had both types I think if I had the stock one I would do WHATEVER was necessary to change to the duals. It is that much better.

Darryl

The "silver" coated exhausts are really nice looking.

[blakecarl]

Re: Fumes In Cockpit

"Why can't it be repaired? " It's a question I haven't gotten a good answer to yet.

As far as "dropping it down to work on it", I haven't done this yet. When I located the leak I wasn't able to visually see how wide a gap I'm dealing with between the flange and the gasket / cylinder. How much of a gap can be addressed by sanding down? My partner and I also discussed the possibility of bending the pipes to fit. Assuming they fit properly at one time and have somehow gotten bent out of shape, you should be able to bend them back, right?

When I questioned the A&P who last had the engine apart, he stated that "it has the good blow proof gaskets on it".

[Pearson]

Re: Fumes In Cockpit

My suggestion is to remove the nuts from the studs and drop the whole thing down where you can get a good look at the surface of the flange and the surface on each cylinder where the exhaust bolts up to. Look for cracks in the flanges or pitting that would allow the exhaust gases to blow by. Check the cylinders to see if the hot gases have created a groove or trough in the aluminum. Also jam two nuts together onto each stud and put some torque on them to see if the studs are tight, or will tighten up. If they don't tighten up, get some helicoils for the threads. Take your time and install them correctly and the helicoils work great. If you have to take a stud out, it is a good time to replace it with new. Or you can clean the old ones up on a wire wheel mounted on a bench grinder. It is also a good time to replace all the nuts with the extra thick brass ones made for this exact application. Some people advise using loctite on the threads when screwing the studs back in, but I don't think it works very well in high heat areas like this. The blow proof gaskets can be reused, but check them over carefully. If you have had a leak across them for awhile, they may be damaged.

[NY86]

Re: Fumes In Cockpit

The exhaust gasses tend to follow the bottom skin of the fuselage to the tail area, where there is a low pressure area inside the fuselage. Any openings along the bottom skin aft of the cabin will pull air in from the outside "boundry layer". If the exhaust gasses are there, in they come. Two ways to address the problem: Close the holes; or extend the tailpipes a couple of inches away from the skin.