Where is the blade angle of a fixed-pitch propeller the smallest?

Where is the blade angle of a fixed-pitch propeller the smallest?

• A. At the hub
• B. At midspan
• C. At the leading edge
• D. At the tip

Answer: (D)

With a fixed-pitch propeller the blade’s pitch is the same along its length, but the air flowing past it changes with radius because the tangential (spin) speed increases with radius (Vt = ωr). The result is the inflow angle seen by the blade getting more dominated by tangential velocity toward the tip and more dominated by axial velocity near the hub. That means the relative wind meets the blade at a smaller angle to the blade’s surface at the tip, so the blade angle (as experienced by the flow) is smallest there. Near the hub, the tangential speed is almost zero, so the flow is more axial and the effective angle to the fixed blade is larger. Hence the smallest blade angle occurs at the tip.

With a fixed-pitch propeller the blade’s pitch is the same along its length, but the air flowing past it changes with radius because the tangential (spin) speed increases with radius (Vt = ωr). The result is the inflow angle seen by the blade getting more dominated by tangential velocity toward the tip and more dominated by axial velocity near the hub. That means the relative wind meets the blade at a smaller angle to the blade’s surface at the tip, so the blade angle (as experienced by the flow) is smallest there. Near the hub, the tangential speed is almost zero, so the flow is more axial and the effective angle to the fixed blade is larger. Hence the smallest blade angle occurs at the tip.