As with most NiCD/NiMH powered planes, the battery must be reconditioned before its first flights or the plane will seem to be very underpowered.

Novices typically make this mistake as do some more experienced flyers.

Charge the battery well over the amount of time recommended, then put it in the plane and run the plane at 75% power until the ESC cuts off flow to the motor.

Repeat several times.

You'll find that the power will seem to improve with each successive cycle.

Most experienced RC'ers own fancy computer controlled chargers/cyclers/conditioners/balancers which do all of the work for you automatically and also report back the state, capacity and condition of the battery.

Since the battery has probably been sitting in the box for a few months during transport and shipping, all of this is normally required.