The pilot and his support crew arrived at the site in the late afternoon and decided to only carry out taxi trials. This was to allow the pilot to get the feel of the controls of his recently purchased, powered hang-glider before flight testing it the next morning. During the last taxi run, it appears that the aircraft became airborne inadvertently. The aircraft climbed steeply to a height of about 150 to 200 feet. Large pitch changes were noted before the attitude stabilised in near level flight. Almost immediately, a shallow right turn commenced which rapidly deteriorated into a descending spiral. The aircraft struck trees and the ground in a vertical dive. Total flight time was 15 to 20 seconds. The pilot had held a Private Pilot Licence some 18 years previously. An offer of flight training had been made by an experienced powered hang-glider pilot, but this offer has been refused because the pilot wanted to teach himself. The control logic of the powered hang-glider was exactly opposite to that of the conventional aircraft on which the pilot had experience.