Robbert,
You might try going to an engineering library at a University. You can probably find all kinds of test results and research on supersonic props. You can probably find info on some of the old projects like the one with a jet engine in the back and the supersonic prop on the front, I can't remember what it was. You'll probably find info on more modern projects also. I have found quite a lot of design information on many different helicopters from older to more modern at the University af Washingtons engineering library.