can someone please explain how prop sizes work

thank you,
jason

the first number is the diameter. the second number is the pitch. pitch is the distance forward that the prop will go in one revolution. so a 10x6 prop is 10 inches in diameter and it will cause the plane to go forward 6 inches every time it turns once. A 10x7 prop has more "twist" in the blades, so it will cause the pane to go forward 7 inches every time around.

The load a prop puts on an engine is actually determined with a lengthy calculation... but you find a prop that works well, then if its a .40 size (or close) you can trade 1 inch pitch for in inch dia within the 9 to 12 inch dia range and get decent results.

The primary rules of thumb for for props tend to center on appx .40 ci engines. Power has a cubic factor... prop blade areas have squared factors with dia change (blade "span"). It just happend that they tend to match up well in the range where a .40 engine is used.

And that one inch forward per revolution for every inch of pitch is subject to a lot of limiting factors, like drag on the plane, friction on the prop, etc, etc....

But those are the basics. Larger diameter allows for more "pull", or will help your climb rate; while higher pitch will move the plane faster.

What FH was saying is, if you add an inch in diameter, drop an inch in pitch; or vice versa.
Dennis-