Spin testing
The PAC 750 test aircraft in NZ had two large water drums and an electric pump fitted in the fuselage,so they could vary the C of G in flight. They told me they had spun it more than 100 times during the testing.
In the days before concorde, the english were researching delta wings etc, and they built a small jet powered delta wing research aircraft to gather data. They actually built three of them. Each one crashed and killed it's pilot.
The project was considered a sucess!!!!
The idiot proof aircraft has not yet been built.
And the bull**** proof pilot has not arrived yet either.