Once upon a time there was a secret subsonic stealth aircraft that made 38 demonstration test flights. This aircraft had NO KNOWN manufacturer or military official designation. Instead, it was known only by the manufacturer's assigned name. Design goals were new stealth and new manufacturing parameters.
Only one aircraft demonstrator was built that made 38 test flights over a four year span. The range of stealth concepts were a generation beyond those of the American fighter- F-117. And, it pioneered new 'lean manufacturing' methods and concepts. This one/sole aircraft was kept secret, and details of it's successful flight tests were Classified.
However, I will reveal some known operating parameters/specifications when a true answer is forthcoming. What aircraft am I thinking of?
1. Manufacturer?
2. Name assigned by manufacturer?
3. Years of flight tests- (Beginning and Ending years?)