Pete Cock, who won the first-ever Gold Trophy stunt contest in Britain, described going inverted by means of a half-roll with his 1949 Kan-Doo. Powered (if that's the right expression) by a 2cc ED diesel, it could be made to turn to the right, under the influence of rudder and engine offset, if he slackened the lines by running towards it. When it was heading in exactly the opposite direction, he would step back, pull on the lines and - bingo - inverted flight. I never had the nerve to try it with my Mills 1.3-powered Stuntmaster (a 1948 Bill Dean design), but with the slow flight and low line-tension of those early diesel models, I could probably have got away with it.