Welcome Guest. Sign in or Signup

2 Answers

How would a airplane propeller without twist stall at the blade tip as airspeed increases?

Asked by: 5645 views , ,
General Aviation

In the Pilot's Handbook of Aeronautical Knowledge, pages 6-4 and 6-5 state: "A propeller blade designed with the same angle of incidence throughout its entire length would be inefficient because as airspeed increases in flight, the portion near the hub would have a negative angle of attack while the blade tip would be stalled." As I've come to understand this somewhat recently, the relative airflow, with regards to the propeller, is a combination of the rotational speed of the propeller and the forward movement of the aircraft. So, as the airspeed (the forward movement of the aircraft) increases, the angle of attack of the propeller decreases. Conversely, as the RPM (the rotational speed of the propeller) increases, the angle of attack of the propeller increases. I understand that the portion of the propeller near the hub could eventually have a negative angle of attack as airspeed increases. What I don't understand is how the blade tip would be stalled if the AOA continues to decrease. Could anyone explain this to me? Thank you.

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

2 Answers



  1. Russ Roslewski on Apr 16, 2015

    I noticed nobody has taken a stab at this one yet.

    I think you’re right. Aerodynamic stall occurs when the angle of attack increases past the critical AOA. Propeller AOA decreases with increasing airspeed regardless of where on the blade you’re measuring or what the pitch is, so I also can’t see how it would stall. In a constant-pitch propeller blade, the AOA at the tip would be less than near the hub. If the speed increases to where the AOA near the hub is negative, it would be “less” negative at the tip (so, possibly still positive).

    Admittedly, I’m having a hard time figuring out how an airplane could get up to this speed anyway. Maybe in a dive, since once the AOA goes negative on part of the blade, that part of the blade is no longer producing forward thrust. Could even be producing backward thrust. I imagine that would cause some interesting aerodynamics as well as interesting forces on the prop.

    It wouldn’t be the first time someone’s found an error in an FAA publication.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  2. McCluskey on Dec 27, 2022

    I’m currently studying for my CFI initial, and this statement has always puzzled me too. Here’s how I have recently come to think about it:

    Imagine a plane in level cruise. If the propeller could be gradually “untwisted” in flight towards a uniform AOA, the hub end would move toward a smaller AOA and the tip end would move toward a larger AOA. In theory, the hub end could reach a negative AOA and the tip end could exceed the critical AOA and become stalled.

    I still find this a complicated idea to wrap my head around, but I think all they’re trying to reinforce is that as you move inward from the propeller tip, blade angle must increase because of the decreasing speed of inner portion of the blade. If you think about it in terms of a wing, the inner part of the blade is in slow flight (low speed and high AOA) and the outer part is in cruise (high speed and low AOA).

    0 Votes Thumb up 0 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.