The pilot stated that after departure he proceeded to the local practice area then elected to return. Two airplanes were in the traffic pattern and a third airplane was about 10 miles to the east inbound. In order to sequence with the 2 airplanes in the pattern and the third airplane on the extended downwind, he entered the traffic pattern close to the approach end of the intended runway rather than midfield downwind. He lowered the flaps, but “…failed to lower the gear at the ‘key’ point….” He turned onto base where he extended full flaps then turned onto final approach. While on final approach he had a sense that the airplane was fast, but did not detect that the landing gear was retracted. He continued the approach and sensed that the sight picture was lower than usual, but did not recall hearing the landing gear warning horn. He heard the propeller contact the runway and attempted to lower the landing gear but it was too late. He heard the landing gear warning horn after the airplane came to rest. Postaccident inspection of the airplane revealed a main stringer and leading edge rib inside the right wing were damaged.