Aircraft Engine Preheater Remote Switch

N6500E has a engine preheater installed on it and it gets cold enough in the winter around here that the use of it is required. There is much debate as to whether it's fine to leave any engine heating system on all of the time or not, and some of the debate depends on a variety of conditions and variables. I'm not going there, because no one argues that it is perfectly fine to preheat a cold engine before firing it up.

The problem: it takes 2-8 hours to fully preheat the engine, depending on how cold it is in the hangar. My hangar is not close to home; I can't just swing by the day before (much less 2-8 hours before) a flight to turn on the heater. I wanted an app on my phone that I can instruct to: "Turn on the heater at 02:00 tomorrow," it will do as instructed, then I can just show up at the airport and go flying. Surely there is such a product...

I found a few that sort-of looked like they might do what I wanted, but to be sure, I opted to make my own. My solution is a Raspberry Pi connected to a relay-switched power cord. The Pi checks an application on my website to determine what it should be doing, then it triggers the relay appropriately. I also added some "premium" features such as status lights and a countdown display so that I could plug it in and verify that things were working before leaving the hangar.

The absolute worst part of this project was internet connectivity. WiFi in the hangar would have made this project much easier, but I don't have that. My initial plan was to use a $15 Huawei E303 USB 3G modem (which theoretically is "supported" by Linux). That was a colossal waste of time. These USB modems were designed work with Windows, not Linux. Current documentation is nonexistent and I could never get everything working reliably.

Plan B was to use a basic WiFi hotspot. The hotspot connects to the Internet and the Pi connects to that over WiFi. This approach worked perfectly!

The Hardware

Prototype 2, complete with status lights.

The "production" version. For durability, the components were soldered directly to the prototyping board that connects sits on top of the Raspberry Pi.