If you look a little deeper within the Help Center - Asking Questions, you'll see where it says:
Questions related to the maintenance and repair of motor vehicles and their accessories, internal combustion engines, even in applications other than automotive so long as the question is related to engine or engine accessories.
This allows, in my mind, for the broader sense of any type of conveyance, even airplanes, so long as the question is about the maintenance of the engine and such. I don't recall any questions specifically about airplanes on here, but we have questions about lawn mowers and weed eaters which don't fall into the big three (cars, trucks, motorcycles), as well as things like John Deere tractors. I personally don't see as how airplanes are any different as long as it's about an ICE. I mean, I don't think you'd want to ask about how the control surfaces work or how to do maintenance on the gauges in the cockpit. I don't think most people who are here would be even able to start to answer questions like this.
Mind you, there is an Aviation stack where such questions would probably be on-topic.