The pilot of the gyrocopter reported that, during the takeoff roll, the rotor rpm was not increasing. He continued the takeoff and kept the gyrocopter on the ground to gain airspeed by not moving the stick to the full-aft position. He added that this was an "old existing airplane habit." Subsequently, during the takeoff, the gyrocopter developed a "rotor flap," and he lost directional control. The gyrocopter came to rest on its side to the left of the runway. The pilot added that not having the stick full aft prevented the rotor rpm from increasing and that the appropriate corrective action would have been to apply full-aft stick. The gyrocopter sustained substantial damage to the fuselage and rotors. The pilot reported that there were no preaccident mechanical failures or malfunctions with the gyrocopter that would have precluded normal operation. The gyrocopter's Flight Manual stated that, during the takeoff roll, the pilot must "bring the control stick fully aft."