Prop change? pitch vs diameter

[Bigbore]

What's the difference between a variation of prop pitch vs prop diameter?
I mean I can get two props with the same diam. and different pitch for example X440 and X640.
The question is: is there a X4xx that behaves like X640?

[Flying Scotsman]

No


But with a lot of modification an X4xx MAY give simillar results. I will let the prop experts chime in with their advice as to what you want to acheive.

Douggie

[m4a1usr]

The question is: is there a X4xx that behaves like X640?

The answer is you could get it to behave like the the 640 but you would pay for it in other ways. First you have to understand the difference between the two.

The 640 travels further in direction for every 360 deg of rotation. Nothing complex there. They both have about the exact same surface area. By changing the edge cupping and tip profile you could concievably narrow the thrust cone of the 440 prop. This would be similar in effect to the higher pitch prop. But you would not be able to duplicate the same performance. The 640 would always have the greater pitch by shear design.

To get a 4xx series prop to behave the same as a 640 you would need to increase the diameter. That means an increase in blade surface area and that requires more force. So motor loading increases just like with the 640, but the larger diameter prop may want to do weird things like increased prop walk or no cavitation upon start up (props when sized correctly typically cavitate for a bit) or you end up with RPM limitations, heat, etc. The list can be long.

So to answer your question, yes you can trade diameter Vs pitch for an increase in performance. But there can be penalties. So why bother?


The rule of thumb would be that "One inch on diameter would absorb the torque of 2-3 inches of pitch" or vice versa. This is only a quide and for full sized boat props but the model fits. You could not use this rule for proper propeller selection.

John

[carlcisneros]

I run the ABC series of props and love them. They have different pitches per size/series if you will of props.
Check out their web site.
They are great folks to work with.
Jim Schaefer will talk you ear off if you got the time on prop selection and useage.

www.abcprops.com