Hello everybody,


I'm working on a large scale project and need some advice on props. The base engine is a 3hp 4 cycle. What would be the advantages or disadvantages of running a 4 bladed prop vs. a 2 bladed prop on an engine as large as this?

None as far as power to airflow conversion is concerned.

The number of prop blades has been a popular topic over the time I've been here. Basically 2 is best and 3 or 4 is used when other factors overpower the need for the maximum efficiency. Things like noise control for pattern models, ground clearance and scale factors being the biggies.

Is there a formula for calculate what 3 or 4 blade prop is needed if you know what 2 blade prop to use?

If you want to keep the same power consumption, the 3 blade prop diameter D3 = D2*.92
while the 4 blade prop diameter D4 = D2*.87

I assume you are holding the pitch constant?

Yes, that's assuming the same pitch and the same rpm.