Easy Heater Box Control


Our Dream Tundra project is a good example of how it is hard to think of everything when designing a firewall layout with a blank slate. The design and kit are excellent overall, but – as is typical of many homebuilt aircraft – there is little information on what to do in the engine compartment. This is primarily because homebuilders have many different ideas of what is going to go on the front end, and every single one is probably going to be a little different.

I have built, modified, and maintained enough aircraft that I have a pretty good idea of what is needed – but as to what goes exactly where, well – structural differences between airplanes prevents having a “one size fits all” solution. So each job is custom. And that means that you inevitably end up putting something where something else would like to be. On this job, I ended up with a fuel pump location that would have made it tricky to install the Bowden cable that controls the cabin heat door. I could make it work – but it wouldn’t be pretty.

Fortunately, there was an option – TCW Technologies offers a servo-control system that uses a little electronic servo and a rheostat-like control in the cockpit to open and close the door. And you can run the wires just about anywhere – solving the problem of yet another push-pull cable running through the busy engine compartment.

TCW servo
TCW servo

Installation of the little servo was easy – one picture is worth a thousand words. There are many different variations on the lowly heater box, but almost any of them can be made to work easily. In our case, we needed to extend the bolt from the flapper door arm up to above the body of the box – this was easily done with a long #8 bolt and a piece of aluminum tube as a spacer. The control knob has a small circuit board on the back of it – this installed easily using the template from TCW in our center panel – right where the two front seat occupants can argue if it is too hot or too cold in the cockpit.

TCW is a business founded and run by homebuilders – check them out at www.tcwtech.com.

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Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra and an electric Xenos motorglider they completed. Currently, they are building an F1 Rocket. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, FAA DAR, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.


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