I am getting conflicting info on what size engine to use and its probably due to my lack of info I've posted. The aircraft has a wing area of 6.4 sq ft ,total weight of 231 oz including 40 oz for the engine . This would give a wing loading of 36 oz/sq ft ,if my calculations are correct.I was thinking of fitting a Super Tigre 3000 as they are reasonably priced at $350 Aussie dollars.It is possible to convert petrol "weed wackers" and would be cheaper to run but i'am worried about interference from the ignition system and I think the total cost of conversion would not be much under the cost of the Super Tigre.