I’ve been busy designing a custom heating system for my plane, which is why I haven’t posted in a little while. My Sling 4 kit would normally include a cuff-style heater, which heats air by passing it over the exhaust pipe. It’s a basic system, but many small airplanes use this arrangement, including the 47-year-old Cessna 172 I fly currently.
Continuing with the theme of bringing high technology into my plane, I decided I wanted something that would offer more control, taking advantage of technology and designs common in cars. Like automotive systems, I’m going to capture heat from the Rotax engine’s liquid cooling system rather than blowing air over the muffler. To that end, there will be a heater core inside the cabin, with a blower motor and air handling unit to allow directing air to the floor, the console, or up to the windshield, just like in a car. The only thing I’m not putting in is air conditioning, which adds considerable weight and would take up more space. But, at least with a blower, I’ll be able to keep the cabin at a reasonable temperature even when on the ground.
I’ve designed the components to fit in the space between the firewall and the instrument sub-panel, so it will be pretty compact. Rather than use push-pull wires to direct flow, I’m using servos and stepper motors, along with a computer controller, to open and close doors in the air handling unit, and to control the speed of the blower motor.
I’m getting pretty close to finishing the design. It has been a bit tricky since I’m trying to achieve a few different goals: (1) efficiency in moving air, (2) light weight, and (3) ability to manufacture it in my workshop. The HVAC system casing in most cars is made of polypropylene, a great material known for its durability and temperature resistance. These parts are usually cast in a mold, and at present I’m not planning to do that, instead using 3D printing. Designing parts for additive manufacturing vs. cast molding has some challenges, especially with big hollow pieces that need to move large volumes of air.
A few months ago I posted about an HVAC system that I bought from a salvage vehicle. I’m planning to re-use multiple components from that system, which has helped speed the development of my system.