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C. Beaty
Gold Supporter
Last Activity: 10-09-2018, 08:14 PM
Joined: 04-16-2004
Location: Florida
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  • The cyclic control system of the Bell-47 helicopter does not use feathering bearings; cyclic pitch is applied to a pair of pivots of the universal joint suspension system via linkage from the swash plate. The B-47ís feathering bearings are used only for collective pitch.
    ...
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  • With tilt head cyclic control, whether Cierva or Bensen, the rotorhead is the swash plate. Prof. JAJ Bennett, chief engineer of Cierva Autogiros at the time, explains it as follows:

    ďThe tilting hub and reflex methods of control are fundamentally Identical because whenever the control lever...
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  • C. Beaty
    replied to Hang Test
    Equally important is that the stick be more or less centered during normal cruise and under no condition of flight should it be against a stop. An exception was Bensen's wood rotorblades with excess trailing edge reflex which served as a speed limiter.

    The pitching moment of the rotor blades...
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    Last edited by C. Beaty; 10-01-2018, 02:57 PM.

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  • C. Beaty
    replied to Beaty's floating hub
    JM, the feedback provided by a Bensen type rotorhead is most useful when used on an unstable gyro. A stable gyro; one that follows Ciervaís criteria for stability such as CLT, torque-yaw compensaton via tail surfaces, etc doesnít derive much benefit from rotor feedback. An unstable gyro is quite difficult...
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  • No need to get too fancy; a slice from a wood dowel 8-10 inches long will tell you everything you need to know about autorotation and cyclic pitch control.
    As a windmill, hold this thing out of the window of a moving car, give it a flip and it will rotate in whichever direction it is started....
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  • A scale model of a see saw rotor is an excellent way of visualizing its operation. I used to build them from spruce yardsticks, at one time a give away advertisement by lumber suppliers and building material suppliers. There used to be a barrel of these things near the entrance doors of such businesses...
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    Last edited by C. Beaty; 09-28-2018, 11:47 AM.

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  • C. Beaty
    replied to Beaty's floating hub
    This was my first attempt at a floating hub in 1974.

    https://www.youtube.com/watch?v=YnLXL3gmESM

    I donít know where the idea came from; no Internet in 1974 and I had never heard about Doblhoff or Doman but I must have read about floating hubs somewhere. It resulted, in part,...
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  • The military is the primary user of helicopters and they often overlook small companies with clever ideas; they purchase large numbers of helicopters and prefer dealing with major manufacturers.

    However, there was one experimental model financed by the military, the McDonnell XV-1 convertiplane...
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  • Hereís JCís plank with Aerodynamics of the Helicopter terminology.
    ...
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  • Birdsí wings flap, Juan Manuel, but a rotating mass canít; we only imagine rotor blades to flap by viewing them along a false axis. The terminology is confusing.
    The attached picture is from: Aerodynamics of the Helicopter by Gessow & Myers. When a rotor is viewed along its real axis of rotation,...
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    Last edited by C. Beaty; 09-25-2018, 12:33 AM.

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  • Check out the Doman tilting hub rotor system; the need for flap and drag hinges is eliminated by allowing the rotor hub to align itself with the rotor tip plane.
    http://www.helistart.com/helicopters/Doman/LZ-1A

    The first tilting hub rotor appeared on the Doblhof tip jet helicopter...
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  • A simple way of measuring the L/D ratio of a rotor is to measure the rotor disc angle of attack by using something like the method shown in the sketch. Use an electronic inclinometer to measure the angle of the straight edge. The primary source of error is the inaccuracy the typical airspeed indicator....
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    Last edited by C. Beaty; 09-23-2018, 03:05 PM.

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  • Rotor RPM is irrelevant; rotor tip speed is everything. Rotor tip speed depends upon blade loading (not disc loading) and is approximately equal to 66 x square root of blade loading.

    Cierva settled on a blade loading of ~ 35 lb/ft which results in a tip speed of 390 fps, good enough for...
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    Last edited by C. Beaty; 09-22-2018, 09:13 AM.

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  • You deserve the compliment, JC. Youíre the only person I know who has memorized all 4 of Maxwellís partial differential equations postulating electromagnetic radiation. (just being silly)...
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  • Thanks Eddie, I appreciate that. My personal hero is Jean Claude DEBREYER, perhaps the smartest engineer I'íve ever known.

    Actually, most of the engineering was done by Igor Bensen. His rotor system, combining Arthur Youngís teetering, underslung rotor with Ciervaís tilt head cyclic system...
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    Last edited by C. Beaty; 09-17-2018, 05:00 PM.

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  • I have to disagree, Doug; the shape of retail hardware doesnít always say much about the engineering expertise of the designer. Take automobile tail fins for example; I think they first appeared on Cadillacs in the late 1950s and within a short time, all automobiles had to have tail fins. Didnít have...
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  • Here are some rotor drag measurements that I made in the 1970s, showing the influence of airfoil thickness. Measurements were made via a pressure transducer acting along the rotorhead roll pivot axis with an inclinometer mounted on the keel to determine inclination of the roll pivot.

    The...
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