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"Arerodynamics of Gyroplanes"

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  • #16
    Brian-> It surprises me that not a lot was discussed about the Houston study, after all, I believe it was mentioned that it took 500,000 punds to compile it plus wind tunneling, many years work etc and yet it provoked so little response about such an important issue.

    Am I missing something here, I would appreciate comments on this .
    Brian,

    this report would surely be of great benefit to the gyro community and I have gone to quite some length to make good use of it. Unfortunately Dr. Houston has declined all requests for support regarding his report (see #4 of this thread)
    http://www.rotaryforum.com/forum/showthread.php?t=25941
    If a report is not backed up by anyone it's very hard to make any use of it. I have also tried to get the program that was used but have not been successful here either. In March I have started to develope a mathematical model for gyros which I would like to match against the results (both computational and experimental) of this report because then one would be able to discuss the results on a scientific basis but unless I find some more people to support the effort (see http://www.rotaryforum.com/forum/showthread.php?t=27391) it will take at least another half year before that model is available. I hope I'll make it...;-)
    Last edited by kolibri282; 10-22-2010, 10:52 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


    • #17
      The translation of this text requires too much time for me (Google translator), but the ideas of Peter Lovegrove are false. As Mike said, it is wrong to separate lift and drag. His sketches are misleading. Ratio lift/drag is without interest in this stories.
      Jean Claude

      Comment


      • #18
        Stick force depends upon cyclic flapping angle.

        Rotor lift/drag ratio has nothing to do with it.

        If the TV weather babe said; “The component of wind out of the East is 7.07 mph while the component of wind out of the North is also 7.07 mph,” instead of a “NE wind of 10 mph,” most people would at least flip channels.

        Comment


        • #19
          JC -> As Mike said, it is wrong to separate lift and drag.
          It is sound and well proven engineering practice to resolve vector quantities into components in a cartesian coordinate system. If the forumlae for the components are correct the resultant will also be correct and may simply be calculated by good old Pythagoras (but in fact that formula was known hundreds of years before Mr. P stepped in, as far as I know)
          Last edited by kolibri282; 10-22-2010, 10:38 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


          • #20
            Juergen, Observe the sketch 5. You understand that Mike and I want to say: It is wrong to separate lift and drag, as long as to lose one of them.

            Comment


            • #21
              Jean Claude,

              as usual I am a bit confused since there is no sketch labeld 5 and in answer #5 there is no sketch. If you have a vector that has two non zero components it is of course rubbish to drop one of them. Please elaborate if this is the case.
              PS: much of the confusion seems to lay in translation. Veullez vous, chère Jean Claude, svp attacher votre texte aussi en français, merci!
              Last edited by kolibri282; 10-22-2010, 12:24 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 -

              Comment


              • #22
                Juergen, je voulais parler de la fig 5 dans le texte de Peter Lovegrove:
                http://www.autogyro.com/technic/offsetg.htm

                Comment


                • #23
                  Dans fig. 5 l'auteur essai d'expliquer comment la commande de l'autogir soit arracher du pilot par la force de trainé, la pousse n'as pas de bras de levier en ce cas es apparait pas.

                  Figure 5 explains how control is wrenched from the pilot by drag force, the thrust does not have a lever arm and therefore does not appear.
                  Last edited by kolibri282; 10-22-2010, 10:09 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 -

                  Comment


                  • #24
                    Juergen, Comme l'auteur, vous oubliez la portance. Ici la résultante rotor (RTV) n'a pas de bras de levier, mais la portance en a un.
                    La trainée n'est pas la cause qui tire le manche. Pas de trainée sans portance.
                    Juergen, as the author, you forget The Lift. Here, RTV has no lever arm, but the lift has!
                    Drag is not the cause that put the stick. No drag without lift.
                    Last edited by Jean Claude; 10-23-2010, 01:08 AM.

                    Comment


                    • #25
                      I didn't forget lift, I just set the lever arm to zero since it is very small anyway and the thrust would counteract the moment generated by the drag force so you err to the safe side. This is good engineering practice and probably more important in this case since we are considering a dynamic phenomenon where you can not be sure, whether the static formula for H force gives a good approximation. That way you get a safer estimate.
                      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


                      • #26
                        Originally posted by kolibri282 View Post
                        I didn't forget lift, I just set the lever arm to zero since it is very small anyway
                        No very small. About 1/5 lever arm to Drag

                        Originally posted by kolibri282 View Post
                        the thrust would counteract the moment generated by the drag force .
                        The thrust or the lift? is not the same thing. Difference 10° is not negligible.

                        Originally posted by kolibri282 View Post
                        so you err to the safe side.
                        I did not say not to shift the axis of bearing. I said that the cause is not the ratio Lift / Drag. The real cause is the flapping angle, which can reach 8 degrees in certain flight conditions. The safety offset is therefore that indicated by Lovegrove, but for an entirely different reason.

                        Jean Claude

                        Comment


                        • #27
                          JC->The thrust or the lift? is not the same thing. Difference 10° is not negligible.
                          The cosine of 10° is 0.9848 the difference between lift and thrust is therefore 1.5%, that is why the so called small angle assumptions are almost invariably used in rotorwork since the errors in calculating the forces are usually much larger unless you use a numerical rotor model that takes into account a plethora of variables.
                          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


                          • #28
                            Juergen, I agree with you: difference on value is negligible. But difference on the lever arm is basic, as shown in my sketch post #24
                            A good engineering practice is certainly having an understanding of basic phenomena and, better yet, secondary phenomena. Chuck thinks like me : "Rotor lift/drag ratio has nothing to do with it", contrary to the reasoning of Peter Lovegrave and yours.
                            Last edited by Jean Claude; 10-23-2010, 07:04 AM.

                            Comment


                            • #29
                              Mr. Lovegrove also states that rotor drag increases with airspeed. That’s also backwards.

                              Cyclic flapping angle increases with airspeed.

                              So we now have a rotor-head and the machine which dangles from it, in beautiful balance. it will happily fly 'hands off' in that situation. If we want to fly faster and still 'hands off', the rotor drag may increase, so we will have too much effort trying to pull the torque-beam into the 'climb' mode. But, Hey , presto! we simply relax the tension on the trim spring with our inflight pitch trimmer, and its contribution to the rearward moment is reduced and the head system comes nicely back into balance.
                              Last edited by C. Beaty; 10-23-2010, 07:41 AM.

                              Comment


                              • #30
                                Most modern day trainee gyro pilots have experienced the brutality of the forces developed when they mess up their rotor starting and their little 22 foot (6.7 m) rotor decides to start flapping.
                                To me this sentence seems to state very clearly that the author sees flapping as the source of the rotor force component which the pilot has to control (or may no longer be able to control) or do I get the meaning of the sentence wrong?

                                He uses the term "Drag" for the force component in the negative x direction which is consistent with using lift for the upward component. If you carefully study the drawing you see that this "Drag" force is almost as large as the lift force and the resultant is not aligned with the axis of rotation but inclined backwards. So his "Drag" force includes the component of rotor flapping. I feel that the confusion comes from the fact that in rotor work "Drag" is not the inplane force component that is perpendicular to thrust but sums up all force contributions along the x axis. That inplane component of a rotor wich lays in the tip path plane is called H-force therefore the L/D ratio of the rotor alone is thrust devided by H-force (thrust/H-force).
                                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

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