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Main Gear distance back from CG?

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  • Main Gear distance back from CG?

    When looking in top view, is there a generally accepted distance that the main gear be from the craft's CG? Most single-place gyros rock back on their tails without pilot, others like the Sport Copter do not. When watching someone balance on the mains during takeoff it might be assumed that the gear should be located directly under the CG, but as with many things gyro related appearances may be deceiving.

    Regards,
    Brian Jackson

  • #2
    A general rule is with the gyro at a 10 degree nose up attitude the mains should be located directly under the rotor head.

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    • #3
      A round about way of answering your question Brian.

      When beginning the takeoff roll once some reasonable rotor rpm is achieved and I move the cyclic fully aft the rotor thrust vector (right angle to the center of the rotor disk) is pointed at the front wheel.

      As rotor rpm increases and lift increases the nose lifts and I begin to move the cyclic forward to balance on the mains and my rotor thrust vector moves aft. This is a gyroplanes way of telling the pilot when she is ready to lift off.

      At some point the rotor thrust vector will get close enough to the center of gravity and the gyroplane will lift off. If I have too much aft cyclic or the mains are too far forward I will lift off at less than the target airspeed with the nose high. If the mains are too far aft I may lift off at higher than my target air speed.

      A heavy person in a single seater likely need the mains further forward and a light person may need the mins further aft because the pilot is well ahead of the center of gravity. In a single seater the pilot is a larger percentage of the all up weight than a tandem.

      Part of the reason for the hang test is to find out where the rotor head needs to be.

      In this picture of The Predator the horizontal center of gravity is about eight inches ahead of the rear black fuel tank strap and the mains are about two feet behind that center of gravity.

      If I have the nose tire about an inch above the ground on my takeoff roll she will lift off at just about 50kts. With a heavy passenger and full fuel she will lift off closer to 60kts because the center of gravity has moved forward in relation to the mains.
      Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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      • #4
        Using Alanís method of measurement The Predator has the rotor head over the mains at six degrees.

        This is the same picture rotated six degrees.
        Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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        • #5
          Brian you could have the mains under the tail if you wanted to,with the wheels back that far when the rotor develops lift the gyro would take off

          at a level attitude.I watched a video of a Chinese guy with the wheels at the very rear and he got off just fine.

          On my RAF I moved the gear aft 6" to help keep the nose wheel on the ground during the take off run,it made things more manageable for me

          and it shortened my distance by quite a lot,by allowing me to achieve a better angle of attack on the rotor,rotor RPM was achieved faster.
          Best Regards,
          Eddie Sigman,Polvadera,nm
          (575) 835-4921

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