I've never heard of an FS aircraft that can't get off the ground, unless the author REALLY screwed up the flight dynamics.
Can you check your engine gauges to make sure you've got 100% power? If not, maybe recalibrate your joystick.
The .cfg file should contain entries under [Engine Data], or something like that. Or, the parameter you need to tweak is in the .air file.
You'll need an .air file editor for that one.
Hope this helps.
