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Why does it roll to the left?

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  • Why does it roll to the left?

    This gyro is apparently trying to take off with insufficient rotor revs, but why does it roll to the left? Is that perhaps due to the dissymmetry of lift, that can't be compensated because the blade flapping is limited by the stops?

    ​​​​https://youtu.be/TVu8Ubcuol0
    Last edited by XXavier; 08-19-2018, 01:10 AM.

  • #2
    In my opinion once the rotor blades started hitting the ground they pulled it left because of the direction they are turning.

    It is my observation the tendency in a divergent blade event is to roll to the retreating blade side. Most people call this flapping; a gyroplane has to flap the blades to fly forward so I feel that is misleading. It appears to me the gyroplane has exceeded the available flapping angle just before the blades struck the ground. Without being at the controls it is hard to know exactly what was going on. The mishandling is so severe that for me there is not much related to normal operations.

    If there was an instructor on board he would be saying "NOSE DOWN, STICK FORWARD" and trying to overpower the pilot's apparent tendency to freeze on the controls. I have had students do this very thing no matter how the "nose is going to come up and you need to begin bringing the cyclic forward" is explained.

    Almost all of my clients do this on their first takeoff attempt and hit the tail wheel hard in The Predator. Most take about three takeoffs before they get it. There are various exercises to do if they are not getting it. The next mistake many make is to plant the nose wheel and the aircraft out accelerates the blades leading to a divergent blade event caused by too much forward airspeed for the rotor rpm. The aircraft is trying to explain what it wants and the pilot is not listening.

    It is my observation that most side by sides hit the tail wheel harder and faster because of the lower polar moment.

    In a fixed wing these control inputs would likely lead to a stall/spin with possible fatal results.
    Last edited by Vance; 08-19-2018, 05:16 AM.
    Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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    • #3
      The gyro rolls to the left before the blade tips contact the ground...
      Last edited by XXavier; 08-19-2018, 05:29 AM.

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      • #4
        Flapping velocity is highest at rotor position 3-9 o’clock. Teeter pivot friction, if teeter pivots use plain rather than ball/roller bearings, tries to lay the stick over to the left.
        Another factor is the result of striking the teeter stops at 6 o’clock; displacement resulting from gyroscopic precession shows up 90 degrees later.
        Last edited by C. Beaty; 08-19-2018, 08:45 AM.

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        • #5
          Seems like torque. Just off the ground with nose is straight up in the air, full throttle and very low airspeed.

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          • #6
            The gyroplane in the video appears to me to have an anticlockwise turning propeller as viewed from behind. In my opinion torque would turn the gyroplane clockwise (roll right) rather than roll anticlockwise (roll left).
            Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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            • #7
              You’re right, didn’t really look closely.

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              • #8
                Hello Chuck,

                good to hear from you again.Lets see if I havet fully understood.
                The rotor is below the required RPMs, and therefore, the rotor plane axis would be tilted too much backwards against the rotor bearing axis. This is due to the asymmetric lift, between advancing and retreating blades.
                So the rotor is hitting the back stops, or in other words, the back stops try to tilt the the rotor forward. The rotor behaves like a gyroscope or a spinning top.
                When you push the top of a spinning top forward, it tilts not in the direction it is pushed, but 90 degrees further in the rotation, direction.
                Thus left in this case.

                Kai.

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                • #9
                  You’ve got it, Kai. Banging the teeter stop at 6 o’clock is effectively an upward impulse and since the rotor is a resonant system, displacement lags force by 90º, i.e., gyroscopic precession.
                  Striking the teeter stop at 6 o’clock always tilts the rotor to the left when the rotor rotates CCW viewed from above.
                  The same behavior applies to satellites in Earth orbit, rocks being twirled on a string, etc.

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                  • #10
                    Originally posted by Vance View Post
                    If there was an instructor on board he would be saying "NOSE DOWN, STICK FORWARD" .
                    Yes, but push forward the stick when the blades already hit the stops will aggravate the violence of the shocks in the hand.
                    In my opinion, first of all, It should reduce speed forward, by immediately stop throttle: Less flow trough the disc, less flapping angle

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                    • #11
                      A gyro is not ready to climb out immediately after breaking ground; that’s the reason there are so many flap/roll accidents.. The rotor does not reach full flight RPM until full load has been applied for several seconds; until the rotor reaches full flight RPM, it should be held in ground effect at low speed as RPM builds up. It is a mistake to apply full throttle and initiate a climb immediately upon leaving the ground.

                      Part of the fault lies with digital rotor tachs; blinking digits don’t show a clear image of the rotor’s behavior. A cable driven mechanical tachometer presents a much clearer picture of the rotor’s progress.

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                      • #12
                        Originally posted by Jean Claude View Post
                        Yes, but push forward the stick when the blades already hit the stops will aggravate the violence of the shocks in the hand.
                        In my opinion, first of all, It should reduce speed forward, by immediately stop throttle: Less flow trough the disc, less flapping angle
                        I feel it is important to get the cyclic forward at the first signs of hitting the teeter stops Jean Claude.

                        I have not experienced what you describe.

                        What I was taught and what I teach is as soon as I feel the tapping in the cyclic; reduce power to idle and mover the cyclic full forward before the rotor collides with something. In my experience this will immediately stop the tapping against the stops.

                        In my quote from the instructor who should have been on board; nose down sometimes doesn’t register so the suggestion is followed by stick forward in case they have forgotten how to get the nose down and forgotten what the cyclic is. The suggestion comes long before the teeter stops hit.

                        For most this is a step in learning to takeoff in a gyroplane. Some can grasp it intellectually and by example, most have to experience the nose coming up too far on takeoff and premature flight at low indicated air speeds as part of the learning process.

                        If a client is having trouble with balancing on the mains; we will practice balancing the full length of the runway using the reduction of power to stop lift off. Often we encounter blade flap doing this exercise and moving the cyclic forward stops it immediately. Sometime the sudden forward cyclic leads to untidy directional control but in my opinion that is easier to manage than a rotor blade colliding with the propeller or rudder.
                        Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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                        • #13
                          Pushing the stick forward reduces the angle of attack of the advancing rotor blade and increases the angle of attack of the retreating blade.

                          How does this reduce teeter stop pounding that results from a stalled retreating blade?

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                          • #14
                            Originally posted by Vance View Post
                            ...reduce power to idle and mover the cyclic full forward before the rotor collides with something. In my experience this will immediately stop the tapping against the stops.
                            That's exactly what I said, Vance.
                            Regarding the stick quickly pushed forward:
                            If the flapping angle reaches 9 degrees and the flapping stops leave only 8 degrees of freedom, then at each touch the stop pushes the stick back of 1 degree and you can move the stick forward only between two successive shocks. If, in this time interval, you have moved the stick forward 3 degrees, the next shock will push the stick back by almost 4 degrees instead of 1 degree. Thus, more violent for the pilot.

                            Chuck,
                            Here is my simulation of take off without level flight for my tractive poject with Rotax 503 2C:
                            Pre-launch : 265 rpm
                            Stabilised in flight: 410 rpm
                            I takes into account the ground effect, the decrease of traction of the propeller with the forward speed, the rolling drag in the grass, the parasitic aerodynamic drag, the inertia of rotation of the blades, the autorotative torque
                            Click image for larger version  Name:	Sans titre.png Views:	1 Size:	11.1 KB ID:	1137049

                            Last edited by Jean Claude; 08-20-2018, 10:11 AM.

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                            • #15
                              What would recommend at the onset of hitting the teeter stops Mr Beaty?
                              Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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