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For a variable pitch propeller where the angle of attack can be adjusted during flight, are the individual blades similar in design to standard propellers, with a low angle of attack at the edge of the propeller (3-6 degrees), and gradually increases towards the root (14-16 degrees); or are the propeller blades one singular angle of attack throughout the entire length of the blade?

I'm presuming the blades have a differing angle of attack at the root and tip, but of a lower magnitude to prevent the root AOA exceeding the critical angle?

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  • $\begingroup$ All aircraft propeller blades are designed with a varied angle between the hub and tip because the tips are turning faster than the hub. The Wright Brothers were the first to figure it out sometime around 1902. $\endgroup$
    – Mike Sowsun
    May 28, 2022 at 2:19
  • $\begingroup$ Are you asking if the root-to-tip difference in blade pitch is less on a variable pitch prop than on a fixed pitch prop? (Other respondents so far seem to have fixated (heh) onto "one singular AoA throughout the entire length.") $\endgroup$
    – Camille Goudeseune
    May 29, 2022 at 0:03

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A couple of important distinctions here:

  • Angle of Attack (AoA) is the local angle of the blade profile relative to the airflow.
  • Blade pitch is the local angle of the blade profile relative to the propeller rotation axis
  • Variable pitch propellers can offset the whole blade with an additional angle. The shape of the blade will remain constant.

enter image description here

Picture above is from this link, which contains a good explanation on propeller blade shapes. It shows the AoA, with the two velocity components Relative Wind and Rotational Velocity. And the Rotational Velocity increases with increasing local blade radius. So in order to have a constant local AoA at every point of the blade, the local blade pitch must be a (linear) function of distance from the centre. Which can be seen in all propeller designs, old and new, fixed blade or variable pitch.

enter image description herePic source

The term Variable Pitch may cause some confusion. All propellers have a local profile pitch angle relative to the spinning axis that changes with local radius, like in the pic above. But Variable Pitch means: the whole blade can increase its pitch angle, to keep the AoA constant with increasing airspeed.

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