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Gyroplane takeoff techniques

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  • Gyroplane takeoff techniques

    In the 50 or so hours that I have flown gyroplanes, I have had the opportunity to fly with probably 8 different instructors in 3 different countries. There seem to be two different schools of thought on proper (and safe) take-off techniques on "new generation" gyroplanes like the German-made AutoGyro (MTO, Calidus and Cavalon) which are equipped with powerful pre-rotators.

    The technique I learned to fly gyroplanes with (and which seems to be endorsed in Phil Harwood's manuals) essentially calls for pre-rotating to 200 RPM, then bringing the stick back and smoothly advancing the throttle to takeoff power.

    The other technique which I have learned from some of the instructors, particularly the ones who have experience flying gyroplanes with no-prerotators (hand-spinning) or less capable pre-rotators focuses more on bringing the throttle up slowly while closely monitoring the rotor RPM, and then going full (takeoff) power once the rotor is fully sped-up. I appreciate the rationale behind this; the idea being to prevent the unit accelerating to the point that the retreating blade stalls and you end with rotor blade flapping with a potentially disastrous outcome.

    FAA-H-8083-21 Rotorcraft Flying Handbook describes two techniques discussed for "Normal Takeoff". They break the difference down to a description of "most amateur-build gyroplanes" or "certificated gyroplanes."

    The normal takeoff for most amateur-built gyroplanes is accomplished by prerotating to sufficient rotor r.p.m. to prevent blade flapping and tilting the rotor back with cyclic control. Using a speed of 20 to 30 m.p.h., allow the rotor to accelerate and begin producing lift. As lift increases, move the cyclic forward to decrease the pitch angle on the rotor disc. When appreciable lift is being produced, the nose of the aircraft rises, and you can feel an increase in drag. Using coordinated throttle and flight control inputs, balance the gyroplane on the main gear without the nose wheel or tail wheel in contact with the surface. At this point, smoothly increase power to full thrust and hold the nose at takeoff attitude with cyclic pressure. The gyroplane will lift off at or near the minimum power required speed for the aircraft. VX should be used for the initial climb, then VY for the remainder of the climb phase.

    For "certificated gyroplanes" it says:

    A normal takeoff for certificated gyroplanes is accomplished by prerotating to a rotor r.p.m. slightly above that required for flight and disengaging the rotor drive. The brakes are then released and full power is applied.

    While I understand that perhaps better and more experienced instructors will teach both technique to students to instill good habits and of course not knowing what kind of gyroplanes his students will be flying in the future, I wonder if it is truly necessary for safe operations on gyroplanes with powerful rotators, and even if the pilot is not subjecting himself to a performance penalty when operating off shorter runways?

    According to the Pilot Operating Handbook for an MTO Sport equipped with the shorter "Sport" rotor, the rotor diameter is 8.0 meters (the "Standard" rotor diameter is 8.4 meters). Unless my calculations are faulty, that would with a 4 meters length from hub to tip, at 200 RPM the rotor tips would be travelling at 187 mph. Of course, the Rotor blade has a lifting or driven region (the outermost third of the span), the driving region (middle portion of the span) and the stall region which is the inboard part of the span. So lets say that the center of the lift region is at 3 meters, the linear velocity at this point would be around 140 mph. At 2 meters (probably well in the driving region) the linear velocity is about 93 mph and at 1 meter from the hub it is about 47 mph.

    Even with a lift-off speed at 35-45 mph, I wonder what the risk of flapping is at these types of linear velocities, and if there really is a necessity to use the second technique for consistently safe operations? I can't help but wonder whether powerful pre-rotators, sufficient horizontal tail surfaces, and thrust lines close to the Center of Gravity are all part of the design of new-generation gyroplanes to make them safer and simpler to operate.

  • #2
    Good observations and post!
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    • #3
      Ignore the FAA Handbook comments about certificated gyroplanes; they are referring to the A&S 18A and the McCulloch J-2, which almost nobody but me flies these days. They are equipped with collective controls that allow pre-spin with a flat collective blade pitch, and that's not possible in any of the designs you mentioned. Pre-spin above 100% of flight rpm is routine in the old certificated birds and impossible for everybody else. The technique they describe in the Handbook is simply not pertinent to your situation.


      • #4
        Thanks for the background on the take-off techniques for the 18A and J-2. That certainly clarifies the statement in the FAA Rotorcraft Flying Handbook. I get the feeling that the FAA manual is quite dated when discussing gyroplane topics.

        Back to my question- given the powerful prerotators on most European-production gyros, what is the real risk of blade flap given the linear velocities of the blades when pre-rotated to 200-220 RPM? Beyond my own piloting technique, I am trying to study for my CFI and would like to be fully conversant on the topic and be able to defend my position.


        • #5
          There's a further distinction to be made. Some prerotators are built to remain engaged after the takeoff run begins. With both the airflow and the prerotator accelerating the rotor, the buildup of RRPM during a run will be rapid. This type of prerotator will disengage automatically via the Bendix unit once the RRPM is being sustained primarily by airflow alone. Keeping the prerotator engaged governs engine RPM and therefore makes premature airspeed on the runway essentially impossible. In such craft, you may indeed keep the spinup clutch engaged and go straight to brakes-off and full throttle.

          If the prerotator is a model that does not allow continued engagement during the takeoff run, then, even at 200 RRPM, it's possible to overrun one's rotor by applying immediate full throttle at brakes-off. It's even possible to leave the ground with the rotor still hitting the teeter stops rather forcefully. So I believe that throttle must be applied with some caution if the prerotator is disengaged at the very beginning of the takeoff roll. 200 RRPM is not enough to prevent violent blade flapping at higher airspeeds.


          • #6
            Originally posted by Uwe Goehl View Post
            Back to my question- given the powerful prerotators on most European-production gyros, what is the real risk of blade flap given the linear velocities of the blades when pre-rotated to 200-220 RPM? Beyond my own piloting technique, I am trying to study for my CFI and would like to be fully conversant on the topic and be able to defend my position.
            For avoid the flapping risk, just read the manufacturer's recommendations:
            For example Magni M16: Pre-launch at 200 rpm and then full throttle with stick at rear stop, until lift the front wheel. It is in page 59- 60


            • #7
              If I read into the question a little bit? There is always a potential for the flapping angle to exceed the control limits; this being referred to as a "blade flap". The greatest risk of this is a lower rotor rpm and feeding too much air too quickly into the disk. The rotor is only doing what it has to do to compensate for dissimilar lift (Dissymmetry of lift) and flapping on the teeter bolt. As rotor rpm is increased the centripetal forces and coning angle increase the separation between the retreating blade and the tail section; also the flapping angle decreases.
              Generally, once in flight this is not a concern; however, a really slowed rotor being exposed to high power engine thrust settings can exceed the controls flap/teeter angle and an "in flight" "blade flap" could be experienced. It is highly likely in this scenario the gyro will enter into a PPO (push over).
              Bottom line, improper rotor speed and energy management can cause this; while spinning up or spooling down or even in flight!
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              • #8
                The "blade flap" is only the late warning that the rrpm does not longer increase, due to the excessive stall of the retreating blade (Lack of autototative torque)
                Then, as said David, the dissymmetry of airspeed is no longer compensated by the dissymmetry of A.o.A due to longitudinal flapping angle.
                But therefore the low centrifugal force has nothing to see in the longitudinal flapping angle, or the hits on the stops. Just on the coning.
                If it were not so, it would be sufficient to build heavier blades, or set more far the stops, isn't it ?
                Last edited by Jean - Claude; 05-24-2017, 05:25 AM.


                • #9
                  A gyro will not PPO, even in the presence of excessive in-flight blade flapping and low RRPM, unless its prop thrustline is higher than its center of mass. PPO is caused by misalignment of prop thrustline and center of mass, period.

                  This is not to say that it is wise to maneuver in a way that causes low rotor RPM -- but the two problems are unrelated and should be considered separately.


                  • #10
                    Originally posted by Gyro28866 View Post
                    As rotor rpm is increased the centripetal forces and coning angle increase the separation between the retreating blade and the tail section
                    My spreadsheet shows the opposite: For example when the run reaches 25 mph, rrpm is no longer that 180 while the rotor thrust is about 300 lbs. So, the coning is 1.5 degree larger than in level flight close to 340 rpm


                    • #11
                      If you put aside the risk of the blades becoming unstable, gently increasing power whilst monitoring rotor rpm provides a final line of defence against setting off down the runway with the stick fully forward if you are flying an AutoGyro machine. If you just go "200rpm / full power" then by the time you realise you have missed something it is generally too late .......