Tall Paul - I didn't see anything that had a max or min size for the plane - just fuel quantity. I'll bet if you designed a plane right, you could get an O.S. .26 4-stroke to carry 32 oz of fuel which should give you some long flights. But then it might be so slow that it is counter-productive. I guess the secret is finding a system that gives the best balance of speed to fuel consumption. Too bad I live on the wrong side of the country. I'd like to give this one a shot to see how I do.