On November 27, 1999, about 1615 Eastern Standard Time, a Bell 47G, N940B, was substantially damaged when it struck a tree while departing from a clearing near Coudersport, Pennsylvania. The certificated private pilot and a passenger were not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the personal flight conducted under 14 CFR Part 91. Earlier in the day, the pilot and passenger departed a private heliport in Glen Rock, Pennsylvania, and flew to the Grand Canyon State Airport (N38), Wellsboro, Pennsylvania, where the helicopter was refueled. They then departed N38, and landed in a clearing, located about 1/2 mile northwest of Coudersport. According to the pilot, the clearing was about 40 feet wide, by 150 feet long, and was surrounded by "very tall trees." The pilot said he made a normal run-up and lifted the helicopter to a hover. He used full throttle and maintained 3,100 RPM. When the helicopter started to accelerate forward, at about 12-15 knots, the RPM dropped to 3,000 and the pilot lowered collective to keep the RPM from dropping further. The helicopter's main rotor blades contacted a pine tree about 30 feet above the ground. The helicopter then rolled to the left and impacted the ground. According to a Federal Aviation Administration Inspector, the elevation at the accident site was about 1,800 feet msl. The pilot did not report any mechanical malfunctions with the helicopter's airframe or engine. After the accident, the pilot stated that the helicopter was with-in it's maximum gross weight; however, the helicopter did not have enough power available to climb and he should have never landed in the clearing.