Concerning the Airfoil of Variable Pitch propellers

[Jarfi]

Hello, I am not an expert in aerospace engineering, merely a hobbyist so bear with my ignorance.

lately I have been thinking of creating my own propeller and variable pitch system using a CNC machine as a longer term goal. This desire arose due to the fact that there are no commercially available variable pitch systems for RC-aircraft on the electric scale. You get variable pitch helis, but no real systems out there that suit my needs.

The idea of creating a fixed pitch propeller seems simple at first sight, find some propeller files, there's plenty of standardized propellers for a given pitch you can find online, then turn it into a CNC file and cut some wood or plastic for a prototype.

But then there's the Variable Pitch propeller which is the real milestone, and concerning their airfoils.

Airfoils on fixed props can be found online for a given pitch. Variable propellers change pitch by tilting the blade, my idea was thus to download or create a simple fixed pitch prop, then split it in the middle and install a mechanism which tilts the blade(using the same methodology helicopters use).

Would this concept make sense or are variable pitch propellers specifically designed to have a linear pitch in relation to their angles of attack, that is,
is there any fundamental difference between variable pitch props and fixed ones besides the mechanism which turns the blades?

To further elaborate: Assume two props with the same diameter had the same angle of attack, and the equal pitch for that angle, one being fixed and the other being variable, Would the airfoils be identical?

 

[russ_watters]

Yes, variable pitch props still need to be twisted. The issue variable pitch solves is that as the plane speeds up, the angle of attack decreases, so at some point they produce no thrust. But they still have the same issue of different relative wind along the span due to the rotation. That's the reason for the twist.

 

[CWatters]

I saw variable pitch props used on solar powered models back in the 1990s in Switzerland. May still become info online. No battery was used. The pitch changed to keep the load on the cells at the optimum for the cell as light levels varied. So if you made a shadow with your hand on the cells the pitch changed. They were tricky to fly.