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Chris Lord October 31, 2018

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  • #61
    As I tried to clarify, "graveyard spiral" was just my rough visual metaphor for what the witness described (going round and round, and descending).
    It's reassuring, however, that gyros are not prone to the phenomenon.


    ________
    In my experience when a gyroplane is trimmed properly; it needs no rotor control input to fly straight and level at whatever airspeed is desired.
    Well, yes, Vance, that's what trim is for.
    But the scenario I'm musing about assumes not only compromised pitch authority, but possibly trim as well.



    I take off without trim in a Cavalon and it does not nose dive (rotor dumped forward?) and flies with very little cyclic back pressure.
    At something near cruise AS, I can see how rotor blowback effect can negate the need for trim (at that particular AS).

    But N198LT was not flying anywhere near cruise AS in its last 20 seconds.
    In fact, witnesses reported very little forward speed. Winds were light. Thus, AS was low.

    We all know that slow flight requires considerable back cyclic (or nose-up trim) in comparison to cruise.
    If control authority were compromised at a low AS, it would present a real challenge.
    Trim may not provide enough compensation.

    I don't know the strength and length of arm of the Cavalon pitch trim cylinder rod.
    Would it be sufficient to, for example, pull back the torque tube for a vertical descent? Or is it less powerful than that?
    I'm trying to explore the limits of what Cavalon pitch trim could do in the event of loss of cyclic.


    _______
    loftus, thanks for your description of that personal incident.
    I'm wondering if something like that happened onboard N198LT.


    _______
    It would helpful if pictures of the Cavalon control system were posted, especially of the lower area.

    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."

    Comment


    • #62
      Originally posted by Kolibri View Post
      As I tried to clarify, "graveyard spiral" was just my rough visual metaphor for what the witness described (going round and round, and descending).
      It's reassuring, however, that gyros are not prone to the phenomenon.


      ________

      Well, yes, Vance, that's what trim is for.
      But the scenario I'm musing about assumes not only compromised pitch authority, but possibly trim as well.


      We all know that slow flight requires considerable back cyclic (or nose-up trim) in comparison to cruise.
      If control authority were compromised at a low AS, it would present a real challenge.
      Trim may not provide enough compensation.

      I don't know the strength and length of arm of the Cavalon pitch trim cylinder rod.
      Would it be sufficient to, for example, pull back the torque tube for a vertical descent? Or is it less powerful than that?
      I'm trying to explore the limits of what Cavalon pitch trim could do in the event of loss of cyclic.[/COLOR]

      _______
      loftus, thanks for your description of that personal incident.
      I'm wondering if something like that happened onboard N198LT.


      _______
      It would helpful if pictures of the Cavalon control system were posted, especially of the lower area.

      Regards,
      Kolibri
      That is why I mentioned the pneumatic trim was at the top where the FAA confirmed the controls were in place.

      The Cavalons I have flown could be trimmed for a vertical descent.

      Somehow Chris was able to go from near VNE to slow flight.

      Pictures of nearly every part of the Cavalon are available on line from AutoGyro GMBH.
      Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

      Comment


      • #63
        Pictures of nearly every part of the Cavalon are available on line from AutoGyro GMBH.
        Not that I've been able to so far find. Please post some links, thanks.


        That is why I mentioned the pneumatic trim was at the top where the FAA confirmed the controls were in place.
        I'm not talking about the pitch trim arm connecting to the torque tube (and rotor brake).
        I've been wondering about something in the cabin.

        Question: In "Brake" mode, is the pitch trim cylinder pressurized to force the rod up, thus moving the rotorhead forward and activating the rotor brake?
        Or, does "Brake" mode completely depressurize the pitch trim cylinder, and the rotorhead falls forward all on its own?

        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."

        Comment


        • #64
          My recollection is neither.

          There is an air cylinder that pushes the rotor head forward and a rotor brake cylinder that are activated in the brake mode.

          When the switch is made from brake to flight it dumps the pressure in the system.

          There is a different cylinder that pulls the head back for trim in the flight mode when pressure is added to the system.

          It has been more than a year since the last time I flew a Cavalon so hopefully someone else will confirm or correct my recollection.

          I don't care for pneumatic trim systems.
          Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

          Comment


          • #65
            Originally posted by Vance View Post
            My recollection is neither.

            There is an air cylinder that pushes the rotor head forward and a rotor brake cylinder that are activated in the brake mode.

            When the switch is made from brake to flight it dumps the pressure in the system.

            There is a different cylinder that pulls the head back for trim in the flight mode when pressure is added to the system.

            It has been more than a year since the last time I flew a Cavalon so hopefully someone else will confirm or correct my recollection.

            I don't care for pneumatic trim systems.
            There is a pneumatic cylinder that trims the roll axis and a larger cylinder that provides for pitch trim, which also engages the rotor brake and pushes the head forward in brake mode.

            Details can be found in the Cavalon Maintenance Manual which can be downloaded here:

            https://www.manualslib.com/manual/11...o-Cavalon.html

            Comment


            • #66
              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


              • #67
                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 (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."

                Comment


                • #68
                  Very interesting!!!

                  Comment


                  • #69
                    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


                    • #70
                      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 (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."

                      Comment


                      • #71
                        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


                        • #72
                          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 (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."

                          Comment


                          • #73
                            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


                            • #74
                              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


                              • #75
                                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 (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."

                                Comment

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