The pilot reported that the airplane was on short final approach for landing on runway 35 when he experienced a "sudden loss of airspeed and rapid increase in descent rate that was not altered by the application of power." The airplane landed hard on the runway, all three landing gear collapsed, and the airplane slid off the left side of the runway. The wing spar and engine firewall were substantially damaged. The pilot further stated that he was flying from the right seat, which made referencing the instruments more difficult, and he "encountered windshear." The winds at an airport located 10 miles northeast of the accident airport, about the time of the accident, that were recorded as 280 degrees at 17 knots, with gusts to 34 knots.