# 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)
– Federico
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.
– fooot
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