Heater System Preliminary Design

I’ve completed the preliminary design of my automatic heater system. I’ve been concentrating on this for the last few weeks, which is why I haven’t posted much progress on the plane itself.

This system recovers the heat from the engine’s cylinder head water cooling loop, forces air over a heater core, then directs the heated air to one or more outlets as desired. A microcontroller handles the operation. The user interface will be similar to that found in cars: temperature select, fan speed select, and airflow controls – with a full auto mode as well. I’ve decided against attempting to install air conditioning components due to the added weight, complexity, impact to engine power, and lastly, there are no A/C systems that I’m aware of that have been designed for the Sling and Rotax engine. One exception is a Sling TSi operating out of Australia that has a custom A/C system. There’s a video about it YouTube, but that’s about all I could find for details.

Luckily, A/C is not terribly necessary up in the Northeast. Once at altitude, the air temperature is usually pretty comfortable, even on hot summer days. The air scoops on each side of the fuselage will feed this outside air into the cabin. But, when it’s hot on the ground and there’s little airflow, the blower motor will provide a little bit of relief to the cabin.

My goals were to keep the assembly light, to fit in the space between the firewall and the dash subpanel, and to use off-the-shelf components especially for critical parts like the heater core.

Overview of the heater system installation
Overview of the heater assembly (without hoses)

To ensure this design fits in my plane, I modeled the firewall and the subpanel, any any protrusions in the vicinity. The result is a nicely packaged assembly that will install easily, as well as be accessible for servicing in the future.

The assembly fits in the compartment behind the firewall

I intend to make a prototype of this design in the coming days, to verify fit and function, then to integrate the mechatronics (microcontroller, servos, temp sensors, etc.).

First set of parts coming off the printer

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