ORIGINAL: Skribnod
Wouldnt a company make a ton of cash and save the modeler a lot of money if they produced a gas engines (not glow) in the 40-90 size displacement range? Seems to me a gallon of pre-mix fuel is 6 times cheaper than a gallon of glow fuel. Some company out there could make a ton of money if they did!! I see the smallest on the market is the 1.3 first place engine, scale that in half and you would have a perfect 60 size engine that saves a lot of money. Just a thought and wishfull thinking.
The real issue here is power to weight ratio. Oldtimers will tell you of spark ignited engines in that size.
If you create a gasoline powered, 0.60 cubic inch spark ignited engine, it will have about half the power of a 0.60 cubic inch displacement glow engine, and the ignition coil and timing system will weigh about as much as the engine, without the extra battery. Even with a new LiPo battery, that's a power to weight ratio about a fourth as much as the glow engine of comparable displacement. To get similar power, you need that 18cc engine, which is larger and weighs more.
The disparity comes from the way the fuel burns. It combines with and burns with a fixed amount of oxygen. Your 0.60 cubic inch engine will accept (very roughly) about four times as much alcohol as gasoline - which makes for about (again very roughly) twice the power with an alcohol 0.60 as with a gasoline powered 0.60.
So, the reason there aren't a lot of .60 size spark ignited gasoline engines around is that they'd only have the power of a .30 glow engine, and would weigh as much as a 1.20. Roughly.
Or so it seems to me,
Dave Olson