# Can a propeller with 90° pitching and symmetrical airfoils generate thrust?

Imagine we have a plane that is already moving at a speed $$v_{plane}$$. At a certain time $$t=0$$, a motor starts moving a propeller whose blades consist on symmetrical airfoils with $$90^\circ$$ of pitching (that is, their chords are perfectly parallel to the fuselage of the plane). Under which conditions (if any) would this propeller produce thrust?

Intuitively, one may think that, with $$90^\circ$$ of pitching, this will just be impossible. Note however that we start from the condition that the airplane is already moving.

Imagine that the rotating speed of the propeller was $$\omega_{prop}$$. If we analysed the forces generated by a blade in a cross section at radius $$R$$, they should look like the following (blue for the velocity of air and red for forces produced by the airfoil):

Since the plane is moving and the propeller is rotating, from the perspective of the blade the incoming air will have a nonzero apparent angle of attack. This will produce lift and, if $$\frac{c_L}{c_D}$$ is sufficiently large, the direction of the resulting force vector ($$F_{TOTAL}$$ in the diagram) will point slightly to the direction of movement, hence generating thrust.

Is this correct? If so, would a propeller with long blades spinning sufficiently fast generate thrust under these constraints?

The horizontal component of the total aerodynamic force $$F_{TOTAL}$$ would indeed be a thrust.
• For how it is drawn in the picture, the AoA is positive since the blade is moving forward ($V_{plane}$) and downward ($\omega_{prop}$). On the opposite side $\omega_{prop}$ would be the other way around so $F_{total}$ would point downward and slightly forward $\rightarrow$ still a lot of torque and few thrust. Commented Jul 7, 2023 at 18:46