The Hondas have been known to fly, - their best feature in my opinion is the seperate oil tank with an agitator which whips the oil into a mist in the air and gets pumped through the crankcase by the action of the piston and one way valves, then returns to the tank. This allows a four stroke to be used at any angle, and the oil is kept out of the combustion chamber with a normal oil scraper ring.
Their power to weight ratio is another story though.

Take a look here:- http://www.auav.net/honda/index.htm

http://www.auav.net/engines.htm