On September 14, 1996, at 1430 central daylight time, a Piper PA-25, N7753Z, operated by the St. Louis Soaring Association, landed on top of a Blanik glider, L-23, N7906, also operated by the St. Louis Soaring Association, that had just touched down on the airstrip. The were no injuries to the pilot of the PA-25, or to the instructor pilot and the student pilot in the glider. The glider received substantial damage and the PA-25 received minor damage. Both aircraft were operating under 14 CFR 91 flight rules and had departed the Highland-Winet Airport, Highland, Illinois, on local flights. Visual meteorological conditions prevailed and no flight plans were filed. The pilot of the PA-25 reported she had towed the Blanik to an altitude of about 1,200 feet above ground altitude (AGL). After the sail plane executed a release, she entered the right hand traffic pattern for runway 36. She reported that she was making an approach to land on runway 36. She reported that sail planes normally land on the parallel sail plane runway, except in emergencies when they land on the powered runway. She reported that she did not see the sail plane that was underneath and in front of her on the final approach to runway 36. As the Blanik touched down on the runway, the PA-25 landed on top of the sail plane. The landing gear of the PA-25 straddled the empennage behind the wings and the nose of PA-25 rested on the top of the sail plane just behind the cockpit of the sail plane. Both aircraft rolled out for about 150 feet before stopping. The pilot in command of the Blanik sail plane reported that he had been towed to an altitude of about 1,200 feet AGL to an area west of the airport where "good lift" had been found earlier in the day. The pilot reported he did not get the lift he had expected after the release, and as a result, was back at the entry point for landing within 10 minutes. He reported that he was at about 800 feet AGL on left downwind, west of the sail plane runway. The pilot reported that another sail plane, a Schweizer 1-34, was ahead of him in the pattern and was making an approach to the sail plane runway. He elected to extend the downwind to gain separation from the Schweizer. The pilot reported that when he turned base leg, the sail plane was further from the runway and lower than normal. He reported he saw the PA-25 on a right base leg east of the field for the parallel powered runway. The Blanik pilot determined it was necessary for him to land on the powered runway since the Schweizer had just landed. He reported that he had expected the pilot of the PA-25 to execute a go-around. Neither the Blanik nor the PA-25 were equipped with radios. He reported that the sail plane was in front and lower than the PA-25 on final approach to runway 36. As the Blanik touched down on the runway, the PA-25 settled on the T-tail of the Blanik, and they rolled out for about 150 feet before coming to a stop. A witness on the ground reported seeing the Blanik sail plane approaching final for runway 36 about 100 yards from the runway threshold. Immediately behind and above the Blanik was the PA-25 tow plane approaching from the same direction. The PA-25 was slowly overtaking the Blanik. He reported that at the instant the Blanik touched down, the PA-25 gently made contact with the top of the Blanik. The PA-25's engine stopped immediately and the two rolled to a stop. The St. Louis Soaring Association owned and operated both the Blanik and the PA-25. Neither aircraft were equipped with radios.