Can anybody please explain the principle behind inverted flight or what forces of flight are involved in inverted flying?
Think Newton's third law. Think angle of attack. Don't get hung up on Bernoulli and don't do what Tex Johnson did!
In truth this was a co-ordinated roll but Tex was flying a 707 upside down at one point without appreciable altitude loss.
If you really want to go into this look at the Kutta condition as well.
Kutta condition - Wikipedia, the free encyclopedia