John,


If it was this simple and scale was to engines as it was to flight, your engine would have to be 1/5 of the size in every direction, which means 1/5 cubed, or 1/125 of the displacement.

That would make a 20 cc engine the 'scale' size.

But would this engine size be suitable to fly your 1/5 scale aircraft?

Also, the full-size engine is a multi-cylinder four-stroke, possibly a VW air-cooled engine.

Within the 20 cc bracket, most model engines are single cylinder.

Could a 20 cc ~ four-stroke, like an OS1.20, Saito 1.25, YS1.10FZ suit that model?