# What is the force to change the pitch of a variable pitch propeller?

At the moment I am struggling with the problem that I do have an idea how to calculate this force by using the blade element theory and going over a whole propeller blade in order to calculate the torque inside the blade. I need this torque in order to calculate the force necessary for changing my pitch inflight. Is the blade element theory the correct way to calculate this?

Source: Nelson, Wilbur C.: Airplane Propeller Principles (John Wiley & Sons, 1944).

Also I do lack information regarding the airfoil data. Is there a good estimate on how high the coefficient of torque will be? Is there a good airfoil database for propellers online?

The assumption that cm=-1/4*ca does not work, as profiles on propellers are not even plates.

• depends on the propeller, on the speed you're flying, on the arm available to apply the force (same force, but twice the arm gives twice the torque) Jan 11, 2017 at 9:18
• Edited question to clarify Just to get it correct: I am not looking for the torque my engine has to deliver to get the propeller spinning, but I am searching for the torque my blades generate, in order to calculate the force for an electric servo/hydraulic mechanism I need to change my pitch in flight. As this is a variable pitch propeller, the speed I am flying should be of lower importance, since my angle of attack (and thus my coefficient of torque) as well as the rotational speed are way higher. I do hope for a general method, but in my application case it will be a plane with Ma<0.3 Jan 11, 2017 at 18:21
• Per this post, the X-Plane flight simulator uses blade element theory on the prop disk, which gives the drag and therefore torque. Jan 11, 2017 at 19:05
• This doesn't answer the question, but this link provides great info on how a Constant Speed Propeller and it's Governor work. I don't know how much engine oil pressure is needed to change the pitch, or what the formula might be for 2,3,4 blae propellors.<boldmethod.com/learn-to-fly/aircraft-systems/…> Apr 1, 2018 at 15:28
• Are you scratch building a variable pitch propeller?! Nov 30, 2022 at 17:01