The private pilot stated that, during the initial climb after takeoff, after "leveling out" and seeing an increase in airspeed, "the [flight] control got mushy, and the airplane began to sink slightly." The pilot added flaps and verified engine throttle position; however, the airplane continued to sink, and the flight controls continued to feel mushy. The pilot pushed the nose forward and retracted the flaps. The airplane descended and hit a ditch and gravel road before coming to rest adjacent a chain-linked-fence. Both wings were bent down and partially separated, both main landing gear collapsed, and the fuselage was impact damaged. The pilot stated that there were no mechanical failures or malfunctions of the airplane. A video of the accident corroborated the pilot's statement. An examination of the airplane, conducted by the National Transportation Safety Board investigator in charge and Federal Aviation Administration inspectors, revealed no mechanical anomalies that would have precluded normal operations.