At about 1146 eastern time, a Piper PA-25-235 and a Robinson R22 Beta collided in flight at North Palm Beach County General Aviation Airport. The pilot of the Piper sustained serious injuries. The flight instructor and pilot-rated student of the Robinson helicopter both sustained minor injuries. The pilot of the glider being towed by the Pawnee released and landed uneventfully. The helicopter instructor said she announced on the common frequency that she would be making a 180-degree autorotation to runway 8L. She said she saw the Pawnee and glider in position and holding on runway 8L. She continued the autorotation and recovered to a hover, at which time she felt the impact. The Pawnee pilot said he cleared for traffic in his entire field of view and was also cleared by wing walkers. He saw the helicopter on downwind, announced departure and took off. He saw the helicopter when he was about 100 feet agl and felt the impact. He then released the glider and the airplane crashed.