RE: Smallest gasoline engine?
mazer,
allot depends on the plane but a 120 size is about the smallest for gas engines depending on the plane. Now others are putting the new Evolution 1.6 engines into 90 size planes, mainly the Showtime and now the Funtana90 and getting good results but thses planes have large wings and loads of wing area for their size.
As an example I own 2 Carl Goldberg Sukhoi's. One has a YS140 glow engine and the other a lightened G26 in it. Both weigh within 1/2 pound of each other but the G26 powered one required a lot of C/F to get it lighter. Why lighter, well wing loading is a big factor. The gas enigne is 20 ounces over what the glow engine is, so I had to put the gas engined version on a serious diet by replacing everything I could with Carbon Fiber, Li-Ion batteries and allot more
Now both fly very well and are about equal in power but the gas powered one requires me to land a little faster as the stall speed is higher due to the higher wing loading. Given the same size tank in each more. I get way more flight time on the gas engine than I do with the glow engine
Now on the other hand, Great Planes make a very nice Super Stearman that is built around the OS120 glow engine. In the manual for this plane they say you need approx. 18 ounces of nose weight just to balance it. So now you have an option:
Do you add 18 ounces of dead weight or do you go with a heavier more powerful engine. I went with a G26 which turned out to be exactly what I needed and so did several others. Wing loading was not an issue for this particular plane.
So you must ask yourself several things. Gas engines are heavier than glow engines, glow engines burn allot more fuel, gas engine burn considerably less fuel but you need a bigger gas engine to get the same power as you would with a much smaller and lighter glow engine. Remember weight and wingloading are everything. Lighter is alwys better.