12.99 Cabin Heat

This entry is part 48 of 48 in the series 12 - Engine / Propeller

Update at the bottom of the post.

Even after the recent modifications, I’ve still got issues getting cabin heat. Here’s what (I think) is happening:

While I am getting hot air from the system, I’m not getting enough volume. On our recent flight to Atlanta, Ann was getting cold so I turned on the heat.  After a while, it didn’t seem like it was getting any warmer. I asked her to put her foot down where the air outlet was to see if any hot air was coming out. She said that she wasn’t feeling any but she wasn’t sure if she was checking in the right place. It’s down on the very bottom of the canard bulkhead between the rudder pedals but you can’t really see where it is.

On the trip back, while we were taxiing out, I turned on the heat and asked her to check if she could feel any hot air coming out. She said there was a definite blast of hot air. Once in the air, I had her check again. Nothing!


Here’s what I think is happening:

On the ground, the damper which blocks the hot air from going out the bottom of the fuselage and diverts it into the cabin works fine. But once in the air, the shape of the outlet at the bottom of the fuselage creates a vacuum.  Because the damper doesn’t create an airtight seal in the duct, I think that vacuum is literally sucking the hot air out the bottom.

My solution is to create a lip or flange that the damper can seal against to block the air from being sucked out.

So while the nose gear doors were out, I disassembled the nose oil cooler ducts to access the damper. I sanded the duct area around the damper and then applied a liberal amount of release agent (AKA, Vaseline) to the damper.  Then I mixed up some epoxy, cabo and some flox and applied it to the duct around the bottom of the damper. Once it cured, I broke the damper loose and cleaned up the excess.

Because of the tight working area, I had to repeat this a few times to get the required coverage.

2017-02-14 IMG_20170214_1313582017-02-14 IMG_20170214_131445

Now I just need to test it out.  I’ll attach an extension duct to the co-pilot side outlet. That way I’ll be able to tell if this fix worked.


I connected a 6′ shop vacuum hose to the copilot side heater duct. The OAT was about 50f. With the outside NACA blocked and the diverter closed to allow heated air into the cabin and the fan on max, I was feeling hot air coming out at a noticeable flow.  It definitely needs more flow though.  I’ve got a pair of 1.5″ centrifugal fans that should increase that flow.  But that will be for a later day.

For now, I think that I’ve got enough hot air for anything above 30F.

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