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Q-talk 143 - Cabin Heat on a Bent Pipe

Building a cabin heat muff to go around a bent exhaust pipe.

by Sanjay Dhall

The exhaust system I have installed on my Q-200 is a 4 x 4 - each cylinder exhausts directly to the outside without any joints or connections to other cylinders. I made this choice as it appeared to be the simplest for me to make by myself, and required the least number of fitting related rework.

During fabrication, I welded on several lugs on the exhaust tubes since I wasn't sure where I would attach the carb or cabin heat muffs. The following pictures show the process of trying to locate and build a cabin heat muff. There is a great deal more effort involved with making the cabin heat muff as compared to the carb heat muff. This extra effort is required since you want to ensure that air from within the engine compartment stays out of the cockpit cabin, whereas carb heat can draw ambient air from the engine compartment.

My first attempt was to locate the cabin heat muff on the straight section and wrap it around both right hand exhaust pipes. The picture above shows a screen door spring wrapped around the pipes and attached to the lugs.

From that I figured out the size of the heat muff, made a cardboard model, and installed it. Unfortunately, this design would have put it too close to the cowling surface for my comfort. No go.

My second attempt was to fabricate a heat muff for a bent section of the exhaust pipe on cylinder #3. As you can see, I made a cardboard template just to get the general shape, but this was not the final shape of blank.

Wheaties - it's the breakfast of champions, and I found a great way to recycle the cardboard box. As you can see, the folded version shows a triangular gap inside elbow.

Above is the final blank made of 0.030" 6061 Aluminum. Note that this has a slightly different shape than the original cardboard template to avoid the triangular gap.

Next it was time to cut and fold. Doing this on a sheet metal brake required some planning.

Then I made the second half. On the other side I was able to use the same template, but all of the bends were reversed.

Then I re-wrapped the screen door spring around the bend in the new location and hooked it on the lugs.

I placed both halves into position, around the exhaust pipe and admired my work for a few minutes.

Then I took everything back off and installed 1-1/4" Aluminum flanges with pop rivets. This created an air inlet and outlet, that I put as far apart as I could to allow for heat transfer.

This is what the two "clam shell" halves looked like when I bolted them together.

To finish up, I attached 1-1/4" scat hose with hose clamps. Then I sealed off any gaps on both ends with 1-1/2" hose clamps.

[Editor's Note: This is a fine looking job Sanjay! We look forward to hearing about your taxi testing!]