Who says they are experimental? Classified doesn’t necessary equal experimental.
I see. So, in 2004 (at least), the US had developed a novel propulsion system on an aircraft that employed no fixed wings nor rotors that allowed the craft to loiter in fixed space for an hour or more and then accelerate to 15k-knots in an instant to then resume a stationary and fixed position and/or minimal forward velocity and this was not experimental, but instead, was a fully operational aeronautical platform that was capable of navigating mixed-use air space?
For almost 20-years, they’ve managed to maintain the secrecy of technology that would win any number of Nobel Prizes and revolutionize aviation moving that field forward by generations (or more)? Fascinating.
Does that sound likely?
For some historical perspective, under the cover of darkness and in absolute secrecy, the B-2 Spirit made its first flight in 1989. It remained secret until 1997 when it was finally revealed to the public after being tested for almost a decade by the US Air Force. Why reveal it to the public? So they could put it into operational service (IOC). It’s tough to put an airplane into service in civilian airspace without giving it a transponder and it’s tough to give a transponder to an aircraft that doesn’t publicly exist.