According to the pilot-owner of the amateur-built, tandem-seat airplane, prior to departure, the partially filled main fuel tank contained an estimated 11 gallons of fuel. The pilot-owner based the quantity on the fuel gauge reading and his 9 years' experience with the airplane, but did not "stick" the tank. Another pilot, seated in the front seat, stated that the pilot-owner also observed "some" fuel in the auxiliary fuel tank, as "indicated by the float." After taking off and climbing the airplane to 3,000 feet, the pilot-owner demonstrated some maneuvers, which the front seat pilot then performed. None of the maneuvers were aerobatic, as fuel would have spilled from the non-sealed auxiliary tank. After maneuvering, the pilot-owner advanced the throttle to return to the airport, but the engine remained at what he thought was "low power" with "engine sound continuous - perhaps just above idle." The pilot-owner established a glide, activated the fuel boost pump, moved the fuel selector to the auxiliary tank, checked both magnetos, and tried various throttle settings before advancing the throttle to full and returning the fuel selector to the main tank. The pilot-owner subsequently performed a forced landing to a corn field, and upon touchdown, the landing gear sheared and the airplane nosed over. The following day, a Federal Aviation Administration examination of the airplane revealed damage to the left wing spar and rudder, and no fuel present in the fuel tanks, fuel lines or gascolator. An unknown quantity of fuel had leaked out of the auxiliary fuel tank. The pilot-owner subsequently noted, "it has become obvious that the engine quit for a lack of fuel," and that he felt the reason the auxiliary fuel did not "re-start" the engine was due to vapor lock. He further stated, "the major error I committed, was trusting the…fuel quantity indicated and not refueling the aircraft prior to this flight."