On May 26, 2003, approximately 1100 mountain daylight time, a Beech A36, N2106L, was substantially damaged when it struck a sign during takeoff at Afton Municipal Airport, Afton, Wyoming. The private pilot and three passengers were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal flight being conducted under Title 14 CFR Part 91. The local flight was originating at the time of the accident. According to the pilot, he had 50 gallons of fuel on board and the density altitude was reported to be 7,200 feet msl when he took off with three passengers for a local scenic flight. When he returned about 45 minutes later, three other passengers asked to go on a similar flight. No fuel was added, and the pilot estimated he had approximately 38 gallons of fuel remaining. Engine start, taxi and run-up were uneventful. Density altitude was reported to be 8,500 feet msl, and the mixture was leaned. The pilot said "the plane did not develop the same amount of power as on the previous takeoff" and the takeoff roll was longer. "The plane rotated approximately 200 yards before the departure end of the runway," he wrote, "and did not accelerate beyond 70 knots." He lowered the nose to gain airspeed. Airspeed slowly increased and the airplane "was ascending at about the same rate as the terrain. Approximately eight seconds after take off, I felt a slight surge in power and lifted the nose." He then heard a "pop" and "felt a slight shudder." He concluded he had "grazed over the top of some object with the stinger at the rear of the plane." Concerned about possible damage to the airplane, the pilot radioed the airport manager and asked him to inspect the airplane when he made a low pass over the airport. He lowered the landing gear and flew over the runway. The airport manager advised him that "everything looked fine." The pilot then proceeded with his scenic flight which lasted about 25 minutes. After an uneventful landing and as the passengers disembarked, they noticed the rear foot step had been knocked off. Further investigation showed a gash under the right wing, 2 feet outboard from the fuselage, that extended from just aft of the leading edge to the flap. The pilot said he had struck a "highway sign." The performance charts in the Beech A36 Pilot Operating Handbook/FAA Approved Airplane Flight Manual were consulted. 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 approximately 600 feet per minute. According to Teledyne Continental Motors, a full power setting is to be used for pre-takeoff leaning on all their normally-aspirated reciprocating engines. This information is contained in the various engine handbooks. If the engine were to be leaned at a lower power setting, the mixture would become richer as power was increased beyond the setting used for leaning, and would result in lower rpm and reduced horsepower.