Certain planes are more agile than others
When you're trying to do a flip, your plane type makes the difference. Look at their stats. The small propeller-based stunt plane can turn on a dime, where as an F-22 Raptor, not so much.
My biggest complaint is you inreased the volume on the music so much it's clipping beyond 0db, causing distortion. Sounds horrible, and had my ears blown out when the game started loading. When increasing the volume of anything using a sound program (EG: audacity), if you use volume increase to the point where parts of the sound wave start squaring off on either side of the wave then it's going to sound horribly distorted.
This game reminded me of the old IBM Sopwith Camel. It was ok, but didn't really catch my interest as much as Sopwith. In Sopwith you could dog-fight and bomb enemy installations as standard game play. This is a good foundation, just needs more to it.