Flutter clearance of the Schweizer 1-36 deep-stall sailplane

A Schweizer 1-36 sailplane was modified for a controlled, deep-stall flight program. This modification allowed the horizontal stabilizer to pivot as much as 70 deg leading edge down. Ground vibration and flutter testing were accomplished on the sailplane with the horizontal stabilizer in the normal flight and deep-stall flight positions. Test results indicated satisfactory damping levels and trends for the structural modes of the sailplane. The modified sailplane was demonstrated to be free of aeroelastic instabilities to 83 KEAS with the horizontal stabilizer in the normal flight position and to 39 KEAS with the horizontal stabilizer in the deep-stall flight position. This flight envelope was adequate for the controlled, deep-stall flight experiments.