I think it is much more mundane. The mythology around secret aircraft makes them out to have super-performance or strange advanced characteristics, when these

I think it is much more mundane. The mythology around secret aircraft makes them out to have super-performance or strange advanced characteristics, when these things probably weren't true at all. I would believe exactly the opposite. Things like "flying saucers" were attempts at secret advanced aircraft which worked, but not particularly well, and never really went on to be anything more than experimental aircraft. Leaks happened from time to time to prod adversaries to worry and try to develop competing technology to waste their time and resources. The F117 looks pretty alien, that one worked though. https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk There are probably a handful of other examples, aircraft that were tried but never made to work very well, work on new principles of design that haven't been figured out yet, and are still on the drawing board with various attempts to make them work ongoing.