A flight instructor and student pilot departed on an introductory instructional flight towards a training area where they performed basic flight maneuvers. They then flew to Flying U Ranch Airport, Union Mills, Indiana, where the flight instructor demonstrated a simulated forced landing which was to be followed by a go-around to runway 18 (2,745 feet by 100 feet, grass). The runway was reportedly covered with about 12-14 inches of snow. During the demonstration, the flight instructor reduced engine power to idle from an altitude of 2,000 feet mean sea level and executed a descent to an altitude of about 5 - 6 feet above ground level at 60 knots indicated airspeed. The flight instructor did not increase engine throttle during this descent to "clear the engine." The flight instructor applied full throttle during the go-around, but the engine hesitated and the airplane continued to descend. The main landing gear wheels followed by the airplane nose contacted the snow. The left wing followed by the right wing then contacted the ground. Both wings buckled from the ground contact resulting in substantial damage to the airplane. The flight instructor accumulated a total flight time of 2,163 hours as an instructor.