DIY Experimental Aircraft Heat Muff

There's a fun-flying aircraft that's occasionally seen in the wild blue, and once spotted, it's immediately recognized for its missing cockpit. It's called a Breezy. The only thing that separates N11018 from "Breezy" status is the fact that it has a cockpit. Because of this, it can never be referred to as a Breezy, but as long as N11018's cockpit remains intact, it shall be called a Drafty because, well, this sucker is drafty. There's yet a place I've flown to where either my core or my extremities haven't experienced the sensations that happen when exposed to temps as the mercury approaches zero. I'm not complaining though. The 1965 construction has held up quite well, though over the years there's no denying, this ship has become drafty.

The two left side exhaust stacks were rigged up for the carb heat box so that left me only the right side exhaust system from which to build a heat muff. The forward exhaust stack was completely unusable, but the rear stack had about 6" of almost-straight, nearly-unobstructed pipe so that was the best place to work with. Wittman Tailwind O-200 exhaust

I got two aluminum 2-piece shaft collars from Grainger... aluminum collar

... and one 6" x 8" x 0.032" sheet of aluminum, one 2" x 7 " x 0.032" sheet of aluminum, four #4 rivets, and two 2" hose clamps.

The 2" x 7 " x 0.032" sheet of aluminum was cut into 1" strips and then riveted into 2" diameter cylinders that would become the inlet and outlets for the heat muff. heat muff inlet and outlet

The shaft collars were clamped onto the exhaust and the 6" x 8" x 0.032" sheet of aluminum was wrapped around them. Sorry, I don't know why I don't have a better photo of this, but if you look at the hose clamps on this photo, underneath is where the collars were attached. experimental aircraft heat muff

Using one of these sanders...

I shaped the inlet and outlet parts to fit against the heat muff... heat_muff_inlet_outlet_shaped

The inlet and outlet were then welded to the muff. If you look carefully, you can see the aluminum collars inside and how they help shape the heat muff. Finished heat muff

This patch shows that maybe possibly once upon a time this ship had a heating system. Wittman Tailwind firewall

Digging through an old pile of airplane parts, I found this abandoned Piper heater box. I think it came from a Super Cub. Super Cub heat box

Next I needed a way to control the heat box. Digging through the same pile of old airplane parts, I found a cable that was suitable for the task, and an empty spot on the experimental canvas to place it (to the right of the mag switch). heat_muff_heat_control_before

To finish the installation, well... let's just say that I used the creative freedom allotted to me in the Experimental Category.

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  1. Thomas Tipton Says :
    November 22, 2023 at 10:08am
    I've been researching heat muff designs for a future build. Your design is by far the best I've seen yet. Obviously the only shortcoming in your situation was the short six inches of available straight exhaust. Pretty sure I'll be following your lead on my build. Thank you.”

  2. Ralph McMorris Says :
    December 16, 2021 at 4:47pm
    “Hello there. I need to make a better heat muff for my Murphy Elite. I was wondering if that muff actually delivered the amount of heat you were looking for. The mighty Murphy is mighty drafty as well!

    • Dorian Jepsen Says:
      December 28, 2021 at 9:15pm
      “The volume was just too small. The air coming into the cabin was lukewarm at best so I got rid of it and have since installed new exhaust. When time allows, I'll try making another heat muff.”
  3. Steve Yoho Says :
    November 12, 2019 at 2:51pm
    “It may be a little late to ask this question, but how did the aluminum collars hold up to the heat of the exhaust pipe?”
    • Dorian Jepsen Says:
      November 19, 2019 at 11:02am
      “I'm not a metallurgist, but when it came time to remove this heat muff, it disassembled without issue and I don't recall seeing any discoloration of the parts so I'm inclined to believe they held up well. The biggest problem was the small volume.”

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