On November 3, 2002, about 1706 Pacific standard time, a Lewis Barnett J4B, N23152, descended into an open field approaching the Nut Tree Airport, Vacaville, California. The experimental rotorcraft (gyroplane) was substantially damaged, and the private pilot received minor injuries. The rotorcraft was being operated on a personal flight by the pilot/builder under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed. No flight plan had been filed for the planned local area flight that began from Vacaville about 1630. The pilot indicated to the National Transportation Safety Board investigator that when he was on the base leg to the airport, at 80 miles per hour, his gyroplane suddenly pitched upward. The pilot stated that he reduced engine power and the gyroplane started rotating in a clockwise direction. He then reduced cyclic and applied engine power to lower the nose and arrest the spin. This technique did not work. The nose would not drop, and the added engine power increased the spin rate. As the gyroplane neared ground level, the pilot applied full engine power to decrease the descent rate and to obtain forward motion. The gyroplane made a hard impact with the ground while in a tail low pitch attitude.