The pilot reported that the purpose of the flight was to return to his home airport and that there was a military helicopter and another small single engine airplane in the traffic pattern. While the pilot was landing, the military helicopter was in a hover on the ramp adjacent to the runway. The pilot reported that the airplane touched down normally and that he had positive control of the airplane during the initial landing rollout with all wheels on the ground. Once the airplane passed abeam the helicopter, the pilot described that the airplane “levitated” off the ground in a nose high attitude and began to turn to the right. The pilot attempted to regain control of the airplane, but it continued to the right and departed the runway surface. During the runway excursion, the airplane sustained substantial damage to the fuselage. The pilot reported there were no mechanical failures or anomalies with the airplane that would have precluded normal operation. Based on this information, it is likely that during the landing roll, the airplane encountered the rotor wash of the hovering military helicopter that was adjacent to the runway.