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  • SC Rotor Brake

    I installed full SC rotor system on my RAF. The rotor brake is ineffectual. The rotor spins even in a light breeze while pulling VERY hard on the brake handle. Once, I pulled so hard the ferrule broke. Initially, the brake shoe only made contact on the outer edge. I sanded the brake shoe to match the brake shoe/PR gear application angle on a flat bed belt sander and now have a more uniform contact surface on the whole shoe. This helped very little. I also roughened the contact surface on the PR ring gear. Nothing has helped so far. Looking for ideas, perhaps refabricating the brake handle, or anything else.
    CFI-ASMEL-IA, A&P
    @ 6450' MSL in W. Colo.

  • #2
    Hi Rob,
    My old sportcopter had the same issue and I did exactly what you have done. The reason they don't hold still as well is two-fold. One, inefficient leverage design and second,
    and more importantly; those blades are over 100 pounds. Unlike my old Dominator with Dragon Wing blades which weighed about 1/2 that, Sport blades are just plain heavy and once they start moving, they keep going. My current AR-1 is the same way with Averso blades of approx. the same weight. Rotor brake is one step above useless no matter how tight I adjust it. The blades are just too heavy for the mechanism.
    Taxing in a very slight turn will start the 'locked down' blades rotating. I find I have to 'bump' the prerotator from time to time just to keep them fore/aft. I can be parked with the blades locked and the brake adjusted as tight as I can get it and a gust will still move the rotors. I simply live with it, annoying as it may be. Also, when my blades are 'spinning down' after a flight, I never engage the rotor brake until the rotor is lower than 30 rrpm. Not much drag then either. If there was a 'fix' for that feature, I would have done it ages ago. It's the only constant annoyance about my gyro, otherwise, a fantastic machine.
    Mark
    __________________

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    The speed in which a woman says "nothing" when asked "What's wrong?" is inversely proportional to the severity of the storm that's coming.
    No tyrant, foreign or domestic, should be permitted to die a natural death.

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    • #3
      Originally posted by mark treidel View Post
      Hi Rob,
      My old sportcopter had the same issue and I did exactly what you have done. The reason they don't hold still as well is two-fold. One, inefficient leverage design and second,
      and more importantly; those blades are over 100 pounds. Unlike my old Dominator with Dragon Wing blades which weighed about 1/2 that, Sport blades are just plain heavy and once they start moving, they keep going. My current AR-1 is the same way with Averso blades of approx. the same weight. Rotor brake is one step above useless no matter how tight I adjust it. The blades are just too heavy for the mechanism.
      Taxing in a very slight turn will start the 'locked down' blades rotating. I find I have to 'bump' the prerotator from time to time just to keep them fore/aft. I can be parked with the blades locked and the brake adjusted as tight as I can get it and a gust will still move the rotors. I simply live with it, annoying as it may be. Also, when my blades are 'spinning down' after a flight, I never engage the rotor brake until the rotor is lower than 30 rrpm. Not much drag then either. If there was a 'fix' for that feature, I would have done it ages ago. It's the only constant annoyance about my gyro, otherwise, a fantastic machine.
      Mark:
      I'm so glad to hear of someone else having the same issue with the AR-1 rotor bake. I've tightened it about as far as I can and the rotor still swings when I turn while taxiing. My next step is to try and pull the cable tighter but there is little guidance about how tight it should be.
      George

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      • #4
        I am thinking about extending the brake lever arm at the rotor head, as well as modifying the brake handle to increase the brake pad pressure. I was just hoping I would not have to reinvent the wheel, er.... brake, assuming it was a common problem. I would have brake handle mechanism go over-center to serve as a parking brake. This may already be done with the SC setup, but is just a simple lever on the RAF. High rotor weight is certainly desirable aspect of rotor inertia to inhibit RPM decay when flying, but is troublesome here.
        CFI-ASMEL-IA, A&P
        @ 6450' MSL in W. Colo.

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        • #5
          The Predator uses thirty foot, eight and a half inch chord Sport Rotors with a bicycle caliper for the rotor brake operated by a bicycle lever and held on by a tie wrap.

          Terry Brandt would not teach me in The Predator without a rotor brake so it is one of those quick solutions (a few hours) that has held up well for 1,700 hours of flight.

          The pads are cheap and typically last five hundred hours. They grab the ring gear.

          The cable is a standard cable from a tandem bicycle.

          Some of my clients find it awkward.

          We are supposed to have a week of rain so I won't be able to post a picture anytime soon.

          Brake is probably not the most descriptive word for what it does. I put it on when I am below a hundred rotor rpm mostly just to get it done. There is very little braking going on. Its main job is to keep the rotors front to back during taxi. If they get sideways in any wind it puts a lot of load on the controls, blades and stops.

          Because of how it works it is possible to squeeze it at just the right time to get the blades to stop front to back. This is still hit or miss and the squeeze is done on what would be the last revolution. I often have to bring it around with the pre-rotator.

          There have been times when I have forgotten to release the rotor brake before takeoff and the extra time it takes to spool up is barely noticeable. I feel this is a feature rather than a weakness.

          I have always been able to get the rotor stopped in high winds; it just takes a while and sometimes reorienting the aircraft in relation to the wind.

          I have not flown a gyroplane with an effective "rotor brake."

          The rotor brake has always been for taxiing rather than stopping the rotor.
          Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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          • #6
            I would think that a brake that works to well could bend the mast. Just a thought!
            PRA member 41204
            PRA Chapter 16

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            • #7
              I have 25' SC rotors on my Vortex and 30' SC rotors on my RAF/Sparrowhawk. The 25' rotors certainly slow to a stop quicker.

              My Vortex rotor brake has become more effective over time. I scuffed up the brake contact surface of the ring gear with a dremel tool and didn't notice much improvement, but as the scuffed surface developed a slight haze of oxidation, it definitely became more effective.

              Once I accidentally left the rotor brake on and didn't notice until I had been flying for several minutes. That ruined the brake pad and it had to be replaced.

              Once I over-greased the prerotator bendix and got some grease on the ring gear which then got on the brake pad which ruined it and had to be replaced.


              On my Vortex, the brake handle is essentially on/off, but the tension is adjustable and there is a sweet spot where it works best.

              On my RAF/Sparrowhawk like yours, it is a matter of pulling the brake handle and locking it down. My guess is if you are pulling hard enough to break the cable or ferrule, you may be expecting too much from the rotor brake. Patience my friend. ; )

              Eric

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              • #8
                Reading all your fine comments is indeed enlightening, but there is still the simple fact my rotor brake is insufficient in even the slightest breeze, or taxiing. Next to worthless. I have already roughened the surfaces, etc. I offer the attached photo indicating the direction I now plan to try. The stock RAF PR brake lever arm (at bottom) is slightly more than twice the length of the SC arm, measured from the fulcrum bolt. I plan to simply lengthen the SC lever arm, and mount the old RAF cable attach bracket as far away as possible. This will double the force applied to the brake pads. I plan to measure any effectiveness change by measuring the time required to stop the blades from 60 RPM. Sadly, I need to remove the entire hub assembly in order to accurately drill the new bracket holes. Wish me luck!
                CFI-ASMEL-IA, A&P
                @ 6450' MSL in W. Colo.

                Comment


                • #9
                  Originally posted by dunc View Post
                  ... the brake shoe only made contact on the outer edge. I sanded the brake shoe to match the brake shoe/PR gear application angle on a flatbed belt sander and now have a more uniform contact surface on the whole shoe. This helped very little...
                  The braking force will be proportional to the pressure on the pads and the coefficient of friction of the two materials.
                  The area of the contact surface is immaterial.
                  A smaller surface will wear out faster but will not supply any less braking action.

                  The pounds per square inch will be higher and the number of square inches will be smaller. They cancel each other out.

                  To increase braking action...
                  Increase the clamping force or...
                  Increase the coefficient of friction by changing the braking surface materials or texture.

                  If the brake pad itself is glazed over. try giving it a "Skuff Job".



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                  • #10
                    Rob,

                    I thought of another thing for you to check. There is a barrel pulley in the RAF rotor brake system that the cable wraps around near the brake handle in the cabin -- see pic. It needs to be free to rotate. Mine was locked up and the cable was dragging. I lubed it so it was free to rotate which allowed more tension to easily be applied to the rotor brake. Winds do not rotate my SC rotors with the rotor brake applied.

                    Eric

                    Click image for larger version

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                    • #11
                      Great tip, Eric S., thanks.

                      Regards,
                      Kolibri
                      PP - ASEL complex (C172RG, Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, Sport Copter II, M912), soloed in gliders

                      "
                      When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

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