Truthfully, under the right conditions a pair of 50cc engines set up and propped correctly will handle the 100lbs and then some. It all depends entirely on how the aircraft is to be flown, and the type of departure and arrival with terra firma. I used the term aircraft instead of airplane deliberately to allow for extreme differences in flight profiles. I have this strange and unsubstantiated feeling that the need for information will not be used for what most of us consider to be a normal flying platform or profile. I'm thinking either aeronautical competition or UAV development. If someone was to have the thousands of feet of available runway like they do at Moffett then small engines and high weights aren't much of a factor.