On May 9, 2008 at approximately 1220 central daylight time a single engine Schweizer 269D helicopter, N584PM, was substantially damaged during a hard landing following a practice autorotation. The flight instructor and private pilot receiving instruction were not injured. The helicopter was owned and operated by the San Antonio Police Department. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local pattern flight originated at Stinson Municipal Airport (SSF), San Antonio, Texas. In a statement provided by the flight instructor, while demonstrating a 180 degree right autorotation the helicopter entered a "down draft" resulting in a loss of altitude. Due to low altitude the pilot elected not to roll power on and decided to continue the autorotation to a touchdown. The pilot was unable to arrest the descent rate and the helicopter touched down level, bounced 2 to 3 feet and came to rest in the upright position. Damage was discovered to the helicopter skids and supporting structure. At 1253 an automated weather observation station at SSF reported winds from 160 degrees at 10 knots gusting to 17 knots, visibility 7 miles, clear skies, temperature 90 degrees, dew point 68 degrees, and a barometric pressure of 29.78 inches of Mercury.