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Chris Lord October 31, 2018

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  • #61
    From the manual:
    "Trimming is effected by varying trim pressure in the pneumatic trim actuator which is installed in parallel with the rotor head tilt for pitch control.
    Aft or nose-up trimming activates the electrical compressor and increases trim pressure, causing the actuator to contract, and tilting the rotor disc aft.
    Forward trimming opens the pressure relief valve to reduce trim pressure and allows the rotor disc to flatten, due to the spindle head offset and the gyroplane's weight."

    Sounds like a loss of pressure would put things into full forward trim.

    Comment


    • #62
      I researched my above question, and found the answer in an AutoGyro maintenance manual.
      When switched to "BRAKE" the pneumatic trim is pressurized, but with reverse effect (my emphasis is in bold):


      63-51-00 Rotor Brake System

      The rotor brake system consists of a brake pad mounted to a bracket which is hinged to the rotor head
      bridge. With the pneumatic mode selector in BRAKE position the operation of the pneumatic trim
      actuator is reversed so that increased pressure causes the actuator to push the rotor head up (or
      level) and presses a brake pad against the rotor head disc.
      In order to increase brake pressure,
      move the 4-way trim switch to aft. Note that this action will also push the control stick forward. At full brake
      pressure the control stick will be maintained in its full forward position.
      IF . . . the pneumatic mode selector in N198LT somehow failed and went into "BRAKE" mode in flight,
      then Chris would have involuntarily lost altitude from a flattening rotor disk.

      More alarming (and confusing) would have been decaying rotor rpm from the engaged rotor brake.

      This may explain the odd power fluctuations heard in the Mayday call.
      Chris may have been trying to maintain altitude and rotor rpm via the throttle.

      If the rotor brake was engaged in flight, he could have lost enough rrpm to explain the otherwise inexplicable plummet from 150' AGL.

      Those who may be skeptical of my "trim runaway" theory may be interested to learn that AutoGyro's
      latest Cavalon POH is version 3.1, announced on 5 November 2018 (several days after the crash).


      SECTION 3 - EMERGENCY PROCEDURES has some new material from the previous version 2.2 (my emphasis is in bold):


      SECTION 3 - EMERGENCY PROCEDURES
      3.8.4 Trim runaway


      Failure of a trim selector switch or pneumatic valve may result in trim runaway (where the
      trim system runs to one extreme and pushes the control stick accordingly).
      Although the
      average pilot is able to resist the out-of-trim stick force and continue to fly the aircraft it may
      be possible to reduce the stick load by intervention:

      (i) High forward stick load required to prevent aircraft nose rising (this will be
      coincident with a high air-pressure reading) – briefly turn the Flight/Brake selector
      to “Brake” to deplete system air pressure. If the air compressor is heard to start
      and the pressure rises again then pull the circuit-breaker marked “Comp” to stop
      the compressor. Repeat the brief selection of “Brake” to deplete system air
      pressure as required.

      (ii) High aft stick load required to prevent aircraft diving (this will be coincident with
      low or zero air pressure) – check “Comp” circuit breaker, if activated push to reset
      then try to trim aircraft nose-up. If unsuccessful then continue to expedited
      landing. Note: reset the circuit-breaker once only.

      Not a word was mentioned in scenario (ii) about a possible pressurization of the pitch trim cylinder in reverse, pushing up the actuator arm.

      Also new in this Cavlon POH version 3.1 SECTION 3 - EMERGENCY PROCEDURES is:

      3.9 Pitch oscillation recovery
      3.10 Vibration
      All three of these items may have been relevant for N198LT.
      I find this very interesting.

      Regards,
      Kolibri
      PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

      Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

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

      Comment


      • #63
        Very interesting!!!

        Comment


        • #64
          The Cavalons I have flown dump the pressure when operating the brake to flight switch because it is porting the pressure in the opposite direction.

          The nose down trim button on the cyclic also reduces the pressure.

          If the trim pump is running away it is easy to pull the breaker to stop the pump. The pump will stop by itself when a given pressure is reached.

          With no pressure the trim system doesn't do anything and it is easy to fly the aircraft. Most of my initial takeoffs were done with the trim pressure at zero.

          When a Cavalon is trimmed incorrectly it is easy to overcome the trim and fly the aircraft.

          I have not tried to fly a Cavalon in the brake mode. I suspect it would not be a problem.

          There is an overdrive button that relieves the pressure in the rotor brake that allows you to reposition the rotor if you are not happy with where it stops.
          Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

          Comment


          • #65
            If the trim pump is running away it is easy to pull the breaker to stop the pump.
            If one remembers to do so during an in-flight emergency.


            The pump will stop by itself when a given pressure is reached.
            If all systems are functioning properly.


            I have not tried to fly a Cavalon in the brake mode. I suspect it would not be a problem.

            I have not flown a Cavalon in the brake mode. I suspect it would not be a problem.
            Perhaps you're not sufficiently thinking through the scenario.
            The affected pilot would have to muscle against what could be an effectively locked up pitch actuator.

            Also, the AutoGyro rotor brake pad has a lot of surface area, and the new rotorheads have a double pad.
            Their braking power seems ample.

            Why do you
            "suspect it would not be a problem" to fly a Cavalon in "BRAKE" mode?

            Regards,
            Kolibri

            PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

            Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

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

            Comment


            • #66
              Originally posted by Kolibri View Post

              Why do you[/COLOR] "suspect it would not be a problem" to fly a Cavalon in "BRAKE" mode?

              Regards,
              Kolibri
              Because the trim force is not very hard to overcome.
              Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

              Comment


              • #67
                Are you not assuming that the "BRAKE" actuator-up force is similar/equal to the "FLIGHT" actuator-down force?
                And that a malfunctioning system would not add additional force than normal?
                PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

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

                Comment


                • #68
                  Originally posted by Kolibri View Post
                  Are you not assuming that the "BRAKE" actuator-up force is similar/equal to the "FLIGHT" actuator-down force?
                  And that a malfunctioning system would not add additional force than normal?
                  Yes I am imagining the force would be the same in both directions because I have felt the cyclic with the switch in both "flight" and "brake" positions.

                  I haven't flown a Cavalon with it in "brake" mode.

                  I had a client pump the Cavalon to maximum pressure for takeoff by accident and it was easy for me to fly the aircraft.
                  Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                  Comment


                  • #69
                    I do tend to agree here with Vance, a malfunction might create difficulty but should be flyable, especially by an experienced pilot like Chris. Everything considered so far I'm still thinking a control system failure.
                    It could be so valuable if Autogyro would chime in with anything they know. Autogyro owners, particularly Cavalon and Calidus, but also MTO would really like to know I'm sure. I'm sure liability issues make it difficult for them to do. MTO has a similar pneumatic brake and trim system to the other two, except no roll trim in the older MTO. Would be interesting to know how a runaway pump would occur all of a sudden in flight. It would be very difficult to accidentally change the control from Flight to Brake unintentionally. Thank you for the interesting discussion. I keep thinking of Chris,and what catastrophic failure could have occurred that was beyond his abilities.

                    Comment


                    • #70
                      because I have felt the cyclic with the switch in both "flight" and "brake" positions.
                      When it was functioning normally . . .

                      I haven't flown a Cavalon with it in "brake" mode.
                      Perhaps somebody would be brave enough to try it and report their experience?


                      __________
                      It could be so valuable if Autogyro would chime in with anything they know. Autogyro owners, particularly Cavalon and Calidus, but also MTO would really like to know I'm sure. I'm sure liability issues make it difficult for them to do.
                      loftus, they've not even announced an In Memorium that their USA COO died in one of their products.
                      I doubt they'll "
                      chime in with anything they know".

                      But they sure were busy revising the Cavalon POH at about the same time.

                      PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                      Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

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

                      Comment


                      • #71
                        Originally posted by Kolibri View Post

                        loftus, they've not even announced an In Memorium that their USA COO died in one of their products.
                        I doubt they'll "
                        chime in with anything they know".

                        But they sure were busy revising the Cavalon POH at about the same time.
                        Yeah agreed but not surprised. At the same time I know Autogyro have tended to stay off the forum because as you know it can become a ****show.
                        I'd still like to know the mechanism of a runaway pump etc. Clearly electrical, just don't understand quite how it happens.

                        Comment


                        • #72
                          It is not hard for me to imagine one of the little wires to the buttons on the cyclic shorting out or the buttons themselves sticking.

                          In my opinion the brake to flight switch seems pretty bullet proof with the most likely failure being to lose pressure altogether.

                          If the detent failed and it switched from "flight" to "brake" in flight it would be disquieting rather than catastrophic.

                          It is hard for me to imagine enough force generated by the trim system for it to be a problem for an experienced pilot.


                          Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                          Comment


                          • #73
                            I'm wondering what max air pressure would be if the limiting valve/device failed and the compressor never cycled off.
                            That pitch trim cylinder is quite large, and reportedly quite powerful.



                            8 December 2018___________________

                            The Calidus, MTOsport, and MTOfree POHs do not have the new Emergency Procedure items of Trim runaway, Pitch oscillation recovery, and Vibration.
                            Seems odd since they also use the pneumatic trim system with FLIGHT/BRAKE switch, and would require such text in their POH.

                            However, the MTOsport 2017 (POH-M17_1.1_EN.pdf) does have them.
                            AutoGyro_POH_MTOsport-Model2017 Revision 1.1 – Issue Date 13.04.2018

                            What's interesting, however, about the Cavalon POH 3.1 is although it does have the same verbiage, it hasn't the MTOsport 2017 POH's careful layout.
                            The text looks very sloppily copied/pasted. Also, the Cavalon POH 3.1 in German has the better layout, however, the concurrent English version seems rushed.
                            This reinforces my hunch that it was done consequently to Chris's crash, and hurriedly so.



                            ___________
                            If the detent failed and it switched from "flight" to "brake" in flight it would be disquieting rather than catastrophic.
                            Perhaps some curious yet brave AutoGyro owner could take off from a long runway, maintain 5' AGL and try it.

                            Nevertheless, what I'm postulating is a much different scenario than the Cavalon POH's 3.8.4(ii) where the compressor popped a breaker and the pitch trim cylinder had little/no pressure.
                            Rather, not only is there "BRAKE" pressure on the up-actuator, but it also refuses to dissipate.

                            I've recently carefully inspected an AutoGyro rotorhead, and talked to some folks.
                            When the "BRAKE" mode is active, the actuator arm is pressurized to slide up, and moves the pair of hinged levers flush with
                            the underside of the inner torque tube to hinge up the rotor brake. These levers are about 35mm long, providing significant leverage.
                            As it pushes up the rotor brake, it simultaneously pushes the rotorhead forward to the stop.

                            If Chris added nose-up trim, in "BRAKE" mode (accidental or failed) this would have been backwards and moved the actuator further up.



                            Click image for larger version  Name:	AutoGyro rotor brake.png Views:	1 Size:	744.3 KB ID:	1140662



                            If that pitch trim actuator arm had been pressurized up, even if overcame by muscled aft-cyclic the actuator would still be braking the rotor.
                            Furthermore, as I understand the mechanism, increasing aft-cyclic would also increase the braking force by pulling the rear of the torque tube into the actuator. (This was not described in any AutoGyro POH.)

                            Again, I don't know if the pneumatic selector (or switch) failed and locked up the actuator, but it would explain a lot.
                            Such a malfunction would have presented a very confusing in-flight situation, with little time to diagnose it.

                            I think it a bad idea to combine trim and rotor braking under one switch and valve. IMO, they should be separate controls and systems.
                            As Einstein once quipped, "
                            Everything should be made as simple as possible, but not simpler."


                            ____________
                            N198LT dropped out of the air from 150' AGL.
                            That has never been adequately explained.

                            The only thing that seems to make sense of this NTSB witness statement:


                            In an interview and a written statement, a witness stated he was driving southbound on the highway that paralleled the shoreline of the lake at the time of the accident.
                            He said the gyrocopter was travelling northwest bound, about 300 feet above ground level "with very little airspeed" and appeared to be turning to the east.
                            The gyrocopter then "entered an autorotation" then, when it reached "… about 150 feet the nose of the aircraft dropped immediately turning toward [the] east then back toward the north."
                            The gyrocopter descended from view [and crashed].
                            . . . is decayed rotor rpm.

                            And what so far seems to me the most plausible reason for decayed rotor rpm is that the rotor brake was engaged.

                            Chris seemed to be ruddering around in those last moments.


                            when it reached "… about 150 feet the nose of the aircraft dropped immediately turning toward [the] east then back toward the north."
                            This portion may be telling.
                            An engaged rotor brake would cause the Cavalon to yaw left, so he may have been fighting that with right rudder.
                            If the rotor rpm had decayed sufficiently, and the Cavalon began to fall, he may have then had too much right rudder, which swung the nose east.
                            As he quickly corrected, the nose swung left back north.
                            I think during those very last seconds, all he had was power and rudder, and neither one could help him by then.
                            PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                            Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

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

                            Comment


                            • #74
                              Sometimes "stupid simple" is not so stupid.

                              For comparison: The original Wunderlich rotor brake was quite fail-safe. It was/is engaged by manually pushing a plastic puck up against the forward edge of the rotor head. It would only stay there (and stay engaged) as long as full forward stick held it there. Back off stick pressure, and it simply dropped down and disengaged. If worse came to worst, the casting that held the actual brake pad pivoted on the forward end of the torque bar on two rather thin ears of cast pot metal. If engaged hard, the ears it would just break off, again disabling the brake.

                              Comment


                              • #75
                                The problem with simple, straightforward designs Doug, is that they don’t sell. The general public likes to think their expensive toy is high tech, state of the art; therefore, all the superfluous bells and whistles.

                                Comment

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