RE: Bigger engine on P-51 PTS RTF?
The way the wing is built retracts are out of the question.
Full throttle airtime? about 8 to 10 minutes depending on how your engine is running. (assuming a 45 to 46 size engine)
Before you ask, if you want to mount the battery and receiver in the premade foam tray you can't change to a bigger fuel tank (the tray sits right against the tank)