The pilot reported that had commenced the takeoff run with no flap selected but felt that the aircraft was slow to accelerate to takeoff speed. He then selected flap and the aircraft became airborne. There were trees and high ground beyond the end of the strip and the pilot turned the aircraft right to avoid this area. As the aircraft turned, it struck a powerline and then impacted the ground in a nose down attitude. The pilot and passenger were uninjured. The pilot stated that the aircraft was about 100 lb under maximum weight with the centre of gravity within the envelope. He believed that the aircraft encountered wind shear and a downdraft leading to loss of performance. The ambient air temperature was 34 degrees C, with less than 5 kts wind at the time of the accident.