RE: ParkZone P-51 Mustang RTF
Prob your battery is fully charged . Did you charge it on the charger that came with the plane or you're own. If the one that came with it is the only one you got, check the battery when the PZ charger shuts off, battery should be warm. If hot, it is overcharging, and if cold, prob not charged enough. I found that often unplugging a charged but cool battery and then replugging it in sometime tops off the battery better. Better yet, invest in a better charger, possibly one that does lipo so you can upgrade.
The plane does feel nose heavy, but when in the air, it flys fine.
You could charge it on someone Astro charger or something and check out the batt. I had a bad batt come with my old aerobird challenger that would never seem to provide much power. I checked it's status and one of the fancy chargers. It would charge to the right volts, but wouldn't hold the amps. If that's the case with your's, call PZ and I'm sure they'll send you a new one ROW.
My advice, switch to lipo power asap, as it just fly better with them, and you'll be much more satisfied. It will provide much more power and double the flight times. Next upgrade, I think I may stick in a Mega brushless. hmmm..