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The angle of attack (AoA) plays a major role in designing a propeller for specific uses, such as if it is to be designed for aircraft propulsion the AoA must be high, while the AoA must be low if it will be utilized for generation. Can a single AoA be chosen for a fixed propeller so it can be utilized for both generation and propulsion uses?

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  • $\begingroup$ What sort of generator? $\endgroup$
    – Koyovis
    Dec 18 '21 at 6:17
  • $\begingroup$ As the airflow velocity plays a critical role in angles of attack, it's important to understand at which wind velocity the generator blades will be used. Without further indication from you, it can only be assumed you want to use the propeller like a RAT, meaning in a glide velocity range, and you have no constraint on torque or rpm. $\endgroup$
    – mins
    Dec 18 '21 at 12:33
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    $\begingroup$ There are two close votes, but zero feedback on the reason. Please offer constructive criticism if you think this should be closed. $\endgroup$ Dec 18 '21 at 18:29
  • $\begingroup$ @MichaelHall without further constraints like "at the same airspeed" or "same rpm" etc, the answer is simply "yes" with no additional useful information to provide $\endgroup$
    – Abdullah
    Dec 19 '21 at 5:28
  • $\begingroup$ @Abdullah, I agree, but this wouldn’t be the first question with a very basic answer. Yet there seems to be no shortage of people willing to draft lengthy explanations to such simple inquiries. Don’t like the question? Offer a suggestion to improve it, or downvote it for not being useful. This isn’t a great question, but why close it? $\endgroup$ Dec 19 '21 at 6:15
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Long story short: Indeed a propeller can be used in both ways - as propeller or turbine. To achieve good performance the blade profile normally deflects the air flow. And there is the main difference: for propeller and turbine this deflection is opposite. In the design condition the air follows the propeller profile very well, if you use the same as a turbine the flow will stall and the aerodynamic performance is quite bad. That means either you have a good propeller and a bad turbine or vice versa. As a compromise you can minimize this effect by using a non deflecting profile and a small stagger angle of the blade. As a result the specific power of propeller resp. turbine will be relatively small. Coming back to your initial question the aoa resp. stagger angle should be small enough so that no stall occurs for turbine operation. The onset of stall is depending on the actual profile used and the flow inlet conditions. A lot of stuff you need to know to get a specific angle ;) Cheers

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  • $\begingroup$ "the blade profile normally deflects the air flow. And there is the main difference: for propeller and turbine this deflection is opposite". That doesn't seem correct. For the same relative flow and airfoil, the deflection is the same. $\endgroup$
    – mins
    Dec 19 '21 at 11:45
  • $\begingroup$ @Rednose won't you guide our sleigh in the right direction by editing "propeller and turbine deflection is opposite". Remember, the airstream drives the prop in the event of engine failure. (windmilling). $\endgroup$ Dec 20 '21 at 0:11
  • $\begingroup$ "the propeller deflection drives the airstream and the airstream drives the turbine blades" i get it, but what happens to the direction of rotation of propeller and the direction of torque in both cases? are they same or reverse @RobertDiGiovanni please answer!!! $\endgroup$ Dec 25 '21 at 14:28
  • $\begingroup$ @MohammedSiddique to the delight of one restarting their engine, the direction of rotation is the same. This is because the "push" from the airstream moves the blade the same way as the torque of the (live) engine tries to "pull". Visualize with a diagram, it works regardless of direction of engine rotation. Focus on the blade angle and how the airstream would move it if the engine stopped running. $\endgroup$ Dec 25 '21 at 15:02
  • $\begingroup$ @RobertDiGiovanni thank you for your explanation sir. $\endgroup$ Dec 25 '21 at 16:44

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