On July 12, 1997, about 1515 eastern daylight time, a Schweizer SGS-1-26B glider, N9927J, registered to a private owner, crashed after an in-flight separation of the right wing at Eustis, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the Title 14 CFR Part 91 local personal flight. The airline transport-rated pilot was not injured. The airplane was destroyed. The flight had originated from the Mid-Florida Airport, about 1 hour and 30 minutes before the accident. The flight was tracking northward, when the pilot said he experienced "minimal lift" at an altitude of about 4,000 feet mean sea level (msl). A ground witness said there was a cumulus cloud in the vicinity just before the accident. The pilot said that when he got near the cloud the lift increased, at first to about 300 feet per minute (fpm), then to about 600 fpm. As the glider passed 4,000 feet msl, there was a rapid rate of increase to over 1,000 fpm. The pilot estimated that the glider climbed from 4,000 feet msl to about 6,200 feet msl in about 20 seconds. At peak altitude the right wing separated from the glider, at the root. The pilot said he believed the wing separated upward, and made contact with the top of the canopy. He attempted numerous combinations of control imputes. The glider yawed, rolled and pitched with little response to the controls, and finally became upright in a high yaw rate condition. The glider impacted in a thick stand of 80- to 100-foot tall pine trees. The reported cloud bases at the time of the accident were reported to be 4,300 feet msl. The floor of the Orlando Class B airspace was 3,000 feet msl at the location of the accident, and the aircraft was operating at the time of the accident without gyro instruments. A section of the right wing front spar was sent to the NTSB Materials Laboratory, Washington, DC, for examination. The examination revealed that the fracture features and deformations were all consistent with "overstress separations." No evidence of fatigue or any type of cracking was found.