The pilot reported that during the takeoff roll, shortly after rotation, he cycled the gear up. The airplane then descended and contacted the runway, which resulted in substantial damage to the lower fuselage. The flap control lever and the flaps were found in the “UP” position following the accident. Review of the Airplane Flight Manual (AFM) directed the flaps to be set to MID during the before taxi check and to check flaps MID during the before takeoff check. The AFM ALSO stated, in part, “No takeoff authorized without flaps, or with non-symmetrical flap configuration or annunciated flap asymmetry.” The pilot said he could not recall setting the flaps to “MID” position prior to takeoff. The pilot reported that there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation.