[cc438]

I know of one plane so crazy that it has to make this list even though it never left the drawing board, the Lippisch P.13A.

We all know the Nazis had crazy ideas, we know that had overambitious ideas, this is one of those crazy AND overambitious ideas that kinda, sorta made sense. It was a delta winged, pyramid shaped, supersonic interceptor powered by a coal-fueled ramjet: https://en.wikipedia.org/wiki/Lippisch_P.13a

It was basically an amalgamation of half-baked construction and propulsion ideas but the aerodynamic principles were fundamentally sound and incredibly advanced for their time. The aero research and data from this program was used with great effect by the US and USSR. It was basically the common ancestor from which all future delta-wing designs evolved.

[halviti]

Looks like they had a working prototype. Pretty impressive.

https://www.youtube.com/watch?v=MvtxjSrImHw

[smegel]

...coal?

[Tuna-Fish]

Coal has a reasonable enough energy density to be used as aircraft fuel. The reason it isn't, and liquid fuels are used instead, is that solid fuels require very laborous processing and complex systems to produce the kind of even continuous combustion that liquid fuels can do with just a pump.

In peacetime, with oil as cheap as it is on the world market, it would never make sense to produce a coal-powered aircraft. At war, with no oil imports coming in, and in desperate need of operable aircraft, the investment of processing coal into even granules to burn in a ramjet might.

[maemre]

Germans did not have much oil in WW2 [1], they even converted coal to synthetic fuels [2].

[1]: https://en.wikipedia.org/wiki/Oil_Campaign_of_World_War_II [2]: https://en.wikipedia.org/wiki/Synthetic_fuel