RE: propane weedeater engines in planes?
My experence with anything internal combustion engine ran on LP is they run hot, very hot. The only thing I could imagine sticking it on would be an open engine plane. The LP cylinders are not as light as our plastic tanks but the weight of the liquid is quite a bit. As far as the regulator, not needed, most run straight tank pressure, the regulator doesn't have enough flow to keep up with the rpm's of the engine. Last thing you'll have to think about is it's a 4 cycle, with oil in a crankcase, even fuji who makes a 4 cycle gasser states that the engine has to be mounted with cylinder upright, so you can't put it any other way except upright. You can still do aerobatics, but sustained vertical climbing and inverted flight would kill the engine. Conversion cost are mild if done right, but cobbled together adapters are unsafe in any way or being. I thought many times of taking the 32cc leaf blower enging and converting it, but declined because there are way too many cheap great running gassers on the market to bother investing my time into making a flying turd.