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Expert seeking expert to bounce design ideas off

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  • Expert seeking expert to bounce design ideas off

    I've released a Fusion360 add-in called "airfoil tools" which makes use of 8 years worth of CFD preprocessing to insert "ideal" foil sections for users.

    I've completed the foils and struts, and I'm overjoyed at how well my turbines function.

    I a now up to the point where I do propellers. They're a lot hard than turbines (which always want to extract as much power as they can, which the betz limit allows us to calculate).

    Is anyone on this board obsessive and knowledgeable about optimal design?

    My goal is to interrogate the user so I know how they plan to use their prop, then to use that with math to give them the one best suited - kindoflike "props for dummies" I guess: I'm not asking for reynolds numbers or fluid densities etc - none of that make sense - I'm asking for things people know (speed ranges, altitudes, medium, etc).

    The work I'm about to embark on involves power and torque and size constraints etc, so I can give them reduction ratios, blade counts, and the completed design in return.

    Ideas I feel like I need to talk over with other experts include tip wiglets, trailing edge uniformity, variable pitch considerations, computing disc fluid velocity at chord stations while taking tip loss into account, and so on...

    To whet you appetite, see attached chart. If you run a few hundred thousand hours of genetic design on 1440 operating regimes optimising for CL/CD over a bell-weighted +/-6-degree AoA target, you can then draw an interesting table. (I wonder if anyone has ever done that before? Do let me know if you've seen it!! - clue - what is the best Reynolds Number ? Answer - see attached screenshot

    My add-in is here, (assuming I, a new user, can post links):
    Attached Files

  • #2

    Not an Expert. Just an observer. First observation is that the person you want is probably sitting on a bar stool next to Elvis and Marilyn. A lot of effort went in between 1916 and 1946 to understand, develop and optimise blade design. Modern props derive from this basic data and perhaps most folks today might not know as much as a blade designer in 1946, or really a room full of designers with slide rules and an interconnecting passageway to a flight test hangar. If the object is to test the efficiency of your app then going into competition with the ghosts of the 1946 design bureau might be a good way to test this out. How? By using a known 1930-1950 blade design on a known engine on a known aircraft with a known history of effective, safe use. Of course you will have your blindfold on and be given the performance parameters. Then you independently come up with a result and compare this to what was evolved by the room full of experienced designers ‘back then’. Comparing the two solutions will then evolve your app. Probably start with a fixed pitch, timber blade designed by Watts, who wrote the book in the 20’s that everybody had on their desk in the 30’s. I can pose a design problem to you that Watts evolved, leaving his book, a design drawing and an application with an extensive service history to compare against your solution. You could even 3D print small versions of each solution and test them in a small wind tunnel. Watts is the guy you want, get ‘the design of screw propellers for aircraft” by HC Watts, Longmans publishers 1920. Ed.


    • #3
      learning from the past

      Thanks! I am using 3D printing with a test rig, so that's actually a good idea. One thing I have noticed, is there's a huge amount of misinformation about this topic - it's almost impossible to trust anything about prop design that's around the internet. I guess too many sketchy opinions, armchair experts, and bogus-claim commercial operators have drowned out the rare voices of people who know.


      • #4
        I've got quite a few early publications on propeller theory that I'm more than happy to donate to someone who wants to try to understand them.

        I'll have to dig up the quote from Spencer Heath (of Paragon propellers) from sometime shortly after WW1 claiming that the design of propellers was as perfect as it will ever be, or something to that extent.