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The Legacy of Martin Hollmann

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  • #31
    No integrate around the disc, Juergen. Drag opposes to the forward flight. Integrate transversally an edge of the disc to the other and you will see that the load of the rotor disk is not the same as a circular wing.
    Last edited by Jean Claude; 04-02-2013, 02:35 PM.

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    • #32
      The full derivation is in naca 716 up to equation 25 roughly. The main point is that you have to stay consistent with Glauert's inflow calculation
      Last edited by kolibri282; 04-02-2013, 02:52 PM.
      Cheers,

      Juergen

      ..Il semble que la perfection soit atteinte..
      ....non quand il n'y a plus rien à ajouter,...
      ...mais quand il n'y a plus rien à retrancher...
      - Antoine de Saint-Exupéry -

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      • #33
        Here’s what Gessow & Myers says, JC:
        Attached Files

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        • #34
          Yes Chuck. They say: "Consider the rotor of a helicopter as a fixed airplane wing. Then, if it is assumed that the downwash is distributed uniformly across the rotor span..."
          It seems to me this is not a affirmation but just a assumption to simplify. Is not it?

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          • #35
            Yes of course it is, but at that time only analytical expressions could be used. Wind tunnel measurements show that the induced velocity has a very marked longitudinal distribution. Mangler and Squire developed a Fourier series expansion that is the best analytical solution available (as far as I know to the day). They showed that the induced velocity component of the flow field can be treated as a small perturbation and for that case the flow field satisfies Laplace second order differential equation. Using this series Bramwell showed ("Helicopter Dynamics" p. 137ff) that induced power is 11% higher than for the constant case. If the lateral distribution is to be modeled as well you have to take recourse to numerical methods, e.g. the flat wake theory www.rotaryforum.com/forum/showthread.php?t=36560 or to a full fledged 3D CFD solution.
            One must keep in mind though that very successful Helicopters like the Flettner Fl-282 and the early Sikorsky types R-4B and S-51 have been designed using the assumption of a constant induced velocity.
            Last edited by kolibri282; 04-03-2013, 01:01 AM.
            Cheers,

            Juergen

            ..Il semble que la perfection soit atteinte..
            ....non quand il n'y a plus rien à ajouter,...
            ...mais quand il n'y a plus rien à retrancher...
            - Antoine de Saint-Exupéry -

            Comment


            • #36
              Juergen, Glauert neglects too, the distribution on the disk span. This is what, in my opinion, gives a induced drag optimistic

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              • #37
                Everybody knew that the assumption of constant induced velocity would give a value that was too low. An increase of 15% seems to have been the accepted figure but nobody really cared since the error in fuselage drag was even larger and the error introduced by blade flexibility was as about the same magnitude. That is why the analytical solutions for two per rev flapping angles a2 and b2, which were availabel even in the early thirties, were also neglected.

                The last equation on your page is by the way a simplified longitudinal distribution of induced velocity.
                Cheers,

                Juergen

                ..Il semble que la perfection soit atteinte..
                ....non quand il n'y a plus rien à ajouter,...
                ...mais quand il n'y a plus rien à retrancher...
                - Antoine de Saint-Exupéry -

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                • #38
                  Originally posted by kolibri282 View Post
                  Everybody knew that the assumption of constant induced velocity would give a value that was too low. .
                  Everybody did not know, Juergen, since Hollman does not take into account in its calculations. Power just about 10% optimistic. Thank you for your confirmation. Watching his calculations, I had a doubt on my spreadsheet
                  Also note that the longitudinal distribution (last equation) does not change the drag of the disk. Instead, the lateral distribution greatly influences the induced drag.
                  Last edited by Jean Claude; 04-03-2013, 05:03 AM.

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                  • #39
                    Don’t put too much faith in Hollmann’s calculations, JC. He was confused by simple vectors.

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                    • #40
                      I only met the man once, at a conference in New York, knowing then nothing of his background or reputation. He was trying to sell the audience some theory he had cooked up that relied on achieving a vortex ring state in gyroplanes, and it seemed pretty bizarre to me. Ray Prouty was sitting near me, and when I asked him for his reaction, he was equally baffled by the whole thing.

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                      • #41
                        Also note that the longitudinal distribution (last equation) does not change the drag of the disk
                        The report below shows that this is not strictly correct, just almost:
                        http://www.rotaryforum.com/forum/showthread.php?t=37118
                        Cheers,

                        Juergen

                        ..Il semble que la perfection soit atteinte..
                        ....non quand il n'y a plus rien à ajouter,...
                        ...mais quand il n'y a plus rien à retrancher...
                        - Antoine de Saint-Exupéry -

                        Comment


                        • #42
                          Unfortunately, the address is not found, Juergen.

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                          • #43
                            Sorry, somehow the URL was corrupt, it should work now.
                            Cheers,

                            Juergen

                            ..Il semble que la perfection soit atteinte..
                            ....non quand il n'y a plus rien à ajouter,...
                            ...mais quand il n'y a plus rien à retrancher...
                            - Antoine de Saint-Exupéry -

                            Comment


                            • #44
                              There seems to be a personal account of Martin Hollmann building his autogyros. This is a bit surprising as the date on the page is /2017/03/07. Perhaps someone has an idea who the admin is who posted it?
                              http://www.buildagyrocopter.com/2017...-rotor-blades/
                              from here:
                              http://www.buildagyrocopter.com/
                              Cheers,

                              Juergen

                              ..Il semble que la perfection soit atteinte..
                              ....non quand il n'y a plus rien à ajouter,...
                              ...mais quand il n'y a plus rien à retrancher...
                              - Antoine de Saint-Exupéry -

                              Comment


                              • #45
                                Build a gyro is a very strange site. Most of the posts are articles about dead people or dead designs. AND Air Command pilots NEVER got the girls.
                                Tom Milton, PRA Director, Need a DAR, Seat tank, Prerotator, Rotor Brake, or Rotor Tach?
                                Have Airworthiness Certification questions?
                                gyroplanes@aol.com or
                                Visit www.calumetair.com

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