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Optimization of Autogyro for Preliminary Development of Personal Flying Vehicle

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  • #16
    Here’s what Prof. JAJ Bennett says about cyclic pitch and the 90 degree phase shift:

    The tilting hub and reflex methods of control are fundamentally Identical because whenever the control lever is moved in any given direction the cyclic variation of the blade incidence is the same in both.
    Inertia prevents a sudden displacement of the tip-path plane, so that when hub is tilted the periodic displacement about the flapping hinges gives the same variation of blade angle with respect to the tip-path plane as is obtained about feathering control hinges in the reflex method.
    It is wrong to imagine that to tilt the hub the pilot must impose a load on the control column sufficient to displace the blades against their own inertia.
    The control mechanism is a relay, in which the moments are relatively small and when the pilot operates this relay he only causes the blades to feather cyclically.
    The result is a cyclic variation of lift in phase with the cyclic variation of blade incidence. The cyclic variation of lift displaces blades from their normal path, but owing to the natural frequency of motion about the flapping hinge being equal to the rotor’s angular speed, the displacement of the blade from its normal path occurs 90 deg. later in azimuth, thus effecting the required tilt of the tip-path plane, and therefore the lift vector which is normal to this plane.

    Prof. Bennett was chief engineer of the Cierva Company and later, designer of the Fairey Rotordyne. The term "reflex" means cyclic pitch via feathering bearings.

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    • #17
      XXavier said:
      Perhaps 'backward tilt of the disk that allows you to have the drag component of the rotor balancing the thrust of the aircraft propeller'... It's a gyro, after all, and not a chopper
      Perhaps I have centered a bit too much on the comparison with light helicopters
      Here's a comparison between the two-seat R-22 and Schweizer 300.
      Thanks for your input Xavier, it was great to meet you!
      J'ai de si grands memmoires du Bois de la Pierre...;-)
      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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      • #18
        but owing to the natural frequency of motion about the flapping hinge being equal to the rotor’s angular speed
        This phrase is equivalent to Prouty's statement that a rotor is a second order system in resonance and it is the reason for the 90° phase shift between input and response. The picture shows the control linkage from cyclic to swash plate. In this case the cyclic stick actually moves the swash plate for and aft but the pitch horns go one quarter around the mast so that the blade feathering takes place when the blade is at right angles with the aircraft, which ultimately causes the for and aft disk tilt.
        (from here: https://www.researchgate.net/figure/Schematic-of-collective-and-cyclic-control-system-of-helicopter_fig3_322887374)
        Click image for larger version  Name:	Schematic-of-collective-and-cyclic-control-system-of-helicopter.ppm.png Views:	1 Size:	49.3 KB ID:	1135706






        A good description can be found on page 7-4 here:

        http://navybmr.com/study%20material/...14008A_ch7.pdf


        As an engineer I found I hard to live with the sloppy drawing above, so I tried to improve it a bit:


        Click image for larger version

Name:	Collective-and-Cyclic-Control-System-of-Helicopter.png
Views:	1
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        Last edited by kolibri282; 07-19-2018, 01:47 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


        • #19
          Pitch/flap coupling, wherein an upflapping blade is depitched, in effect imposes an aerodynamic spring that resists flapping and raises the flap resonant frequency.
          The R-22 has a small amount, reducing the phase shift to ~80º.
          The A&S-18A has considerably more, being the means whereby collective pitch is automatically reduced following a jump which reduces the phase angle to ~70º.

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