Incident Summary
A pilot conducted two scenic flights on the same day. The first flight carried three passengers and 50 gallons of fuel at a density altitude of 7,200 feet mean sea level (msl). The second flight, with three passengers and 38 gallons of fuel, occurred at a density altitude of 8,500 feet msl. During the second takeoff, the pilot reported that the aircraft did not develop the same amount of power as on the previous takeoff. The takeoff roll was longer, and the airplane rotated approximately 200 yards before the departure end of the runway, failing to accelerate beyond 70 knots.
Pilot's Account
The pilot lowered the nose to gain airspeed, which slowly increased. The airplane ascended at about the same rate as the surrounding terrain. Approximately eight seconds after takeoff, the pilot felt a slight surge in power and lifted the nose. Immediately after, he heard a "pop" and felt a slight shudder. The pilot concluded that he had "grazed over the top of some object with the stinger at the rear of the plane." Concerned about possible damage, he radioed the airport manager and requested an inspection during a low pass over the airport. The pilot lowered the landing gear and flew over the runway. The airport manager advised that everything appeared fine, so the pilot proceeded with the flight.
Inspection and Damage
After landing, as passengers disembarked, they noticed the rear foot step had been knocked off. Further investigation revealed a gash under the right wing, located 2 feet outboard from the fuselage, extending from just aft of the leading edge to the flap. No other damage was noted.
Performance Considerations
Based on a maximum gross weight of 3,600 pounds and a density altitude of 8,500 feet, it was computed that the airplane would require 2,100 feet for the takeoff roll and would climb at approximately 600 feet per minute. According to the engine manufacturer, a full power setting should be used for pre-takeoff leaning on all normally-aspirated reciprocating engines, as stated in various engine handbooks. If the engine were leaned at a lower power setting, the mixture would become richer as power was increased beyond the setting used for leaning, resulting in lower rpm and reduced horsepower.