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Chris Lord October 31, 2018

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  • #76
    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


    • #77
      I've been pondering further my theory of in-flight rotor rpm degradation.
      Another possible cause of that in N198LT could have been an involuntarily engaged prerotator.
      It's happened before in a Cavalon (although without causing a crash), as Desmon Butts described in 2016:


      I know of a Cavilon in the states that the pneumatic system kept the pre rotator engaged and got so hot the shaft turned blue. The whole system had to be replaced.

      This gyro is one that was built with issues. When I was asked to look at it the pre-rotator would engage at random times while on taxi. I told the owner not to fly it until it was fixed. It however had been flow that way by the building organization and dealer then delivered that way to him. They had the flights like that .
      PP - ASEL complex (C172RG, Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), 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


      • #78
        Whether or not the pneumatic system contributed in this case, I must admit the brake and prerotator system design were significant factors in my decision to go with a Magni. The rotor brake is simple: off a Vespa scooter, I understand, with a cable activation, panel warning light, and connection to the RRPM gauge (which doesn’t come on until the brake is off). The prerotator is also cable activated so you have a good sense of the force being applied (vs. a pneumatic system, where you have no sense of this and I’ve seen several broken prerotator brackets on MTOs). Also, the flex cable for the prerotator means there’s no restrictions on pulling the stick back (and certainly no locking mechanism to hold/keep the stick forward) while the prerotator is engaged.

        Magni isn’t the only one with these attributes (seems to me the AR-1 has similar features). This is not at all to say I’m speculating this was involved in this accident; only that, to me, these design features have their advantages over the pneumatic systems and rigid prerotators beyond the potential of this type of possible in-flight failure.

        /Ed

        Comment


        • #79
          A Magni would be my second choice of gyro, and it's a good machine.
          I also prefer the flex-shaft prerotator for those reasons.
          No 90° drive-shaft linkage to prevent prerotation with the rotor fully back.
          (The AR-1 does not have a flex-shaft, but an ELA/AutoGyro/etc. type drive-shaft.)
          PP - ASEL complex (C172RG, Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), 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


          • #80
            Originally posted by Kolibri View Post

            (The AR-1 does not have a flex-shaft, but an ELA/AutoGyro/etc. type drive-shaft.)
            True but IIRC the rigid drive on the AR-1 is able to accept a good amount of back-stick with the prerotator engaged. If I recall it’s from a combination of a spline-type joint (or two) on the shaft(s) plus universal joint(s). I recall Abid saying there’s no problem keeping the stick back but it did shorten the life of the u-joint to several hundred (500?) hours. But the end result is attributes I found acceptable and seeming to be better than the fixed systems.

            /Ed

            Comment


            • #81
              Hi just found this thread and in particular the comments around the operation of the BRAKE/FLIGHT switch and the effect on trim or rotor brake whilst in flight. I’ve no idea on this accident and if this is even relevant to it but I thought I’d share my own experiences, for context I’m a UK gyroplane instructor.

              Around 2 years ago I made a flight with a reasonably experienced gyroplane pilot who had recently purchased a Calidus. I say reasonably, he had circa 500hours from 15 years of flying one. He had just over 10 hours in the Calidus and just wanted someone in the aircraft to act as safety pilot / critique / help him with the navigation / local procedures on a flight to a new airfield. Fairly unremarkable stuff.

              During the climb out from the airfield I was generally aware that our rate of climb was poor and I commented to the pilot, with an additional comment about airspeed verse Vy, we were quite fast.

              Some seconds later, certainly less than minute the situation hadn’t improved significantly, we were still slightly fast and now it wasn’t only the rate of climb that was on my mind but our overall height. Things weren’t so dramatic as needing to get involved just yet but I did say to the pilot, that he needed to remedy the situation PDQ.

              This time the pilot replied that he had been trying to fix things but the aircraft just wouldn’t climb. I checked the throttle position from the rear seat and confirmed that we had full throttle and said to him I suppose a little despairingly “Set pitch attitude to give the airspeed we want and trim…” to which he replied that he couldn’t. At this point I said “I have control”.

              Faithful to my instruction to him and with a 15-20mph higher airspeed than required I pulled some back stick to give a high nose up attitude. On reflection, with that initial irritation that a pilot whom I had a level of expectation with couldn’t climb accurately, my stick force was probably higher than normal and with the pitch attitude set to that I wanted I trimmed. Now my trim process is usually a couple of second rearwards trim at a time with aircraft operating normally, i.e. to account for student errors, laziness or even leaky pneumatics etc. It was after that initial trimming that I remember thinking “Wow this aircraft is trimmed miles away! (heavily nose down).” Of course with the conversation that had taken place before it simply re-enforced a view that the pilot was rusty and couldn’t climb away accurately and now my thinking that his problem was he just hadn’t trimmed the aircraft.

              By now we are crosswind and our intention was to depart the circuit to enroute broadly in that direction. With the pitch attitude as I wanted I set about trimming but with the thinking that it was so far out it would need 5-6 seconds of rearwards trim. As I was trimming the stick force became very large indeed to the point that it was not manageable with one hand anymore and even with 2 hands with the more relaxed and unplanned way I had been sat it wasn’t easy.

              I am confused to be honest and of course with hindsight I could have just tried to reverse the inputs but I guess that’s confusion for you.

              Back in the aircraft I said to the pilot that something wasn’t correct and I would continue flying the aircraft if he could look and see if there was anything obviously wrong, bearing temperature perhaps?

              I made a PAN call and turned downwind in the circuit with the intention to get back on the ground but at this point I have to say I was struggling with the stick forces, even two handed. We were circa 5-600ft and I was not clear on the issue, it felt like a control restriction and not being clear on how that would develop I thought it would be sensible to get on the ground sooner than later and I cut the throttle to idle and intended to land in a field. At about 2-3ft the front seat now passenger exclaimed “I’ve found it” and flicked the BRAKE/FLIGHT switch to FLIGHT and the high control forces went away and we climbed away.

              In our subsequent discussion it became apparent how this had happened. The runway in use made a reasonable taxi necessary and on reaching the hold board the pilot was going to line up when I stopped him, suggesting it would be better to wait for landing traffic as we would be less rushed. However he had already flicked the switch to FLIGHT. Then when we actually lined up he went through his lining up process mechanically and flicked the BRAKE/FLIGHT switch, except this time it was now back in the BRAKE position. Of course in the Calidus that is not an easy spot from the rear.

              In summary, the aircraft will pre-rotate in this state, and will fly, except that when you trim you are now forcing the trim piston up into the rotor brake and stick forces are too high to maintain controlled flight for very long, worse there is a lot of confusion around what the problem actually is. I articulated the above to UK hierarchy at the time not being a Calidus owner and not flying one often I’ve no idea how that has been feed back and actually in the UK the process of wider communication has room for improvement.


              As it relates to comments on this thread you would not easily over come the stick forces involved and actually it is so un-natural that you would not feel comfortable doing so because unless you know what the issue is (and in which case the remedy is very easy you just flick a switch) but without knowing you would not want to remain airborne. Closing the throttle and landing is the best option, which then depends on where you are flying to how that works out.

              The other element of discussion seems to centre on the Teleflex control cables which can be pinched but that is a focus for trained maintenance personal. I think one snag could be loose articles restricting at this point (I have a picture but cant upload its basically the point underneath the seat of the Cavalon where the control cable runs). That would seem a more likely snag than the control cable.


              Comment


              • #82
                When I started to fly German gyros back in 2009 I (it's a habit) used to study them for possible inflight problems, how to avoid them and how to sort them out. The question "what if this selector is turned to BRAKE in flight appeared in the first month of getting familiar with this brand of gyros (I met ELA years later). I've siimply tried this in flight - unpleasant but nothing serious if you know how this happens (praemontis praemunitis). After that I use to show how it goes to each my student. At least 2 or 3 times it happened in real when student for unknown reason really turned it to BRAKE. And they always don't agree that they did this! The proof is usually easy since I also use to have an action camera installed so controls and instrument panel are seen. This is very useful for student to review his/her flight soon after landing. Students were very confused when they saw them switching FLIGHT to BRAKE, usually this happened on a take-off roll.
                One more tip for a Calidus: I'm 176 cm man and I found out that it's more comfort for instructor to sit in the back seat a bit higher. Thus I have a 8-10 cm custom made pad under me while flying back seat. This makes possible to see most of instrument panel. And I use to look at airspeed indicator mirrored image on the canopy glass - it is seen clear enough for most days.
                Alex Lameko
                Russian gyroforum
                Visit my collection of gyro videos

                Comment


                • #83
                  Thank you for sharing your experience Phil Bennett.

                  It is a good flight instructor story well told.

                  I did not know you could pre-rotate with it in the "brake" mode.

                  It is nice to know that the Calidus was still flyable with it in the "brake" mode despite adding to the pressure in an effort to trim her out.
                  Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                  Comment


                  • #84
                    I like the way you think Alex.

                    It had not occurred to me that someone might try to fly in the brake mode.

                    I will add that procedure to my syllabus.
                    Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                    Comment


                    • #85
                      I have not tried to fly a Cavalon in the brake mode. I suspect it would not be a problem....Because the trim force is not very hard to overcome.
                      Well, now we know better.

                      I'm not surprised to read from Phil's account that it was indeed a physically difficult and mentally confusing event:


                      As I was trimming the stick force became very large indeed to the point that it was not manageable with one hand anymore and even with 2 hands with the more relaxed and unplanned way I had been sat it wasn’t easy.

                      I made a PAN call and turned downwind in the circuit with the intention to get back on the ground but at this point I have to say I was struggling with the stick forces, even two handed.

                      In summary, the aircraft will pre-rotate in this state, and will fly, except that when you trim you are now forcing the trim piston up into the rotor brake and stick forces are too high to maintain controlled flight for very long, worse there is a lot of confusion around what the problem actually is.

                      As it relates to comments on this thread you would not easily over come the stick forces involved and actually it is so un-natural that you would not feel comfortable doing so because unless you know what the issue is...but without knowing you would not want to remain airborne.
                      Phil, this was very illuminating, thank you for posting about your experience.

                      Do you recall what rotor rpms were? How much degradation due to rotor braking?



                      __________
                      The wisdom of AutoGyro's FLIGHT/BRAKE common switch is by now openly suspect.

                      It reminds me of this Far Side cartoon:

                      Click image for larger version  Name:	wings stay on, wings fall off.jpg Views:	1 Size:	66.5 KB ID:	1141748






                      ___________
                      The other element of discussion seems to centre on the Teleflex control cables which can be pinched but that is a focus for trained maintenance personal. I think one snag could be loose articles restricting at this point (I have a picture but cant upload its basically the point underneath the seat of the Cavalon where the control cable runs). That would seem a more likely snag than the control cable.
                      Good point to consider.

                      It's still not been confirmed if N198LT had previous tip-over or rotor strike damage which may have compromised the cables.
                      Perhaps the NTSB will be able to inspect them. Previously frayed wires inside the sheath, for example, should be discernible.

                      Regards,
                      Kolibri

                      PP - ASEL complex (C172RG, Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), 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


                      • #86

                        Comment


                        • #87
                          Sorry for the mash up of posts - my picture was too large to attach and now the orientation is poor! The photo above is from a Cavalon and it is under the seat showing the control for pitch the position as photographed is full aft stick and you can see that any foreign object or loose article finding its way into this area between the control rod and the composite structure will cause restriction.

                          On the BRAKE/FLIGHT point. Rotor RPMs were not significantly affected but that would be an impression rather than an absolute recollection. Ultimately the friction material and surface area are insignificant verse the aerodynamic forces at play. It is the physical restriction of the control movement aft that is the issue and worse it isn't just trying to stop the stick moving but it is actually pushing the other way.

                          Of course it is easily fixed once / if you know about it but the point is there are times when you are not aware - ask a group of instructors "Can you pre-rotate with the switch in BRAKE mode?" and you will get a range of views, including outright guessing. It really isn't well understood and of course there are times when you are not instructing, merely a passenger with an experienced pilot and so you simply pay less attention to what is being done. In which case when you get asked for your assistance you are less prepared for what you are being handed. OR perhaps the gauges look normal, or you are not looking for a particular gauge OR [and this is a big criticism in many of these aircraft] the switches and gauges are NOT in a standard place / layout. Incredible as it may seem I've flown aircraft in the UK that have rotor RPM and engine RPM gauges switched.

                          I think from problem becoming apparent to closing the throttle was <20sec. and to less than 100ft maybe <40sec. It isn't the same as planning a failure and I'm not sure if any of this is relevant to the Chris Lord accident but if this aircraft was unfamiliar or it wasn't a training flight where events are more prepared and planned then I could well understand how you get handed some odd situation with huge stick force and if you are unaware that you can pre-rotate with the switch in BRAKE mode why do you even look there?

                          It is not something I would practice because any small lapse or relaxation on the stick will see the aircraft bunt. Merely explaining that this flight mode is sub-optimal should be enough and as a checklist item I do not get students to dump trim pressure before the take off roll as the only mechanism to stop pre-rotation with the switch on BRAKE is residual pressure in the system.

                          Comment


                          • #88
                            I just completed my MTO 2017 build on Monday and I took the time to run through some scenarios:

                            1. You cannot pre rotate in brake mode. There is a micro switch on the control shaft that prevents the prerotator from engaging until you move the stick back. The prerotator only engages when the stick is within range. Too far back or forward and prerotation stops. There is also a pressure switch to prevent prerotation with any pressure in the system. You must have the stick in the correct position AND no pressure in the system so you cannot prerotate in brake mode. You can learn it with engine off and key on. I don't understand the comment that it is not understood and involves guessing.


                            2. Switching to brake on takeoff roll. The pressure switch is set at about 2 bars. It will allow pre rotation at 2 bars or less but at that low pressure there is no braking pressure and the stick is easily pulled back. This is likely what happened to Phil. The PIC may have put it in brake mode but didn't build pressure. If he was trimming on climb out, it was poor technique.

                            2. Nothing happens immediately and suddenly when you engage brake mode in flight. The "Brake" position is really "Brake Armed". You have to take a second action to apply the brake. Rather than asking "Can you prerotate in brake mode?" the question should be "If a student engaged brake mode in flight, what would happen?". You do not fall out of the sky, nor does the stick go full forward with maximum force. Absolutely nothing happens. You would never know it was in brake mode if you never needed aft trim during your flight. Until you take the second step and build pressure use the trim switch, you wouldn't know the switch was in brake mode. If and when you trim aft in flight you will start to feel forward stick pressure when trimming aft. Again, with the engine off, it can easily be simulated. I imagine that if I pulsed aft trim in flight and the result was more forward pressure instead of less, I would notice it and probably bump the trim again. It would get slightly heavier and responding the opposite of what I intended so I imagine that I would try forward trim. I hope I would not panic and hold the aft trim button until stick forces required two hands but I can see how that scenario would cause confusion. However, a student could/should be taught not to mess with any trims during take off. Level off and then set trim. I will practice today in the hanger with engine off by switching to brake mode and then applying aft trim to get a feel for it and practice switching back to flight mode to feel the instant release of forward stick forces.

                            I have a brand new MTO sitting here that I know very well having just built it so if anyone wants me to test other scenarios that I may have not covered above, I would be happy to run through them in an effort to keep us all safer. I encourage everyone with an autogyro to sit in the seat, flip on power without starting the engine, and run through the scenarios that I did. I have a much better understanding of what to expect. We are all here to learn and help each other.

                            Comment


                            • #89
                              HighAltitude, good experimentation and info, thanks for posting.
                              (Do be aware that stick forces in the hangar are not identical to stick forces in flight.)
                              Congratulations on your new build, and I wish you many happy hours of safe flying.


                              The "Brake" position is really "Brake Armed". You have to take a second action to apply the brake. Rather than asking "Can you prerotate in brake mode?" the question should be "If a student engaged brake mode in flight, what would happen?". You do not fall out of the sky, nor does the stick go full forward with maximum force. Absolutely nothing happens. You would never know it was in brake mode if you never needed aft trim during your flight. Until you take the second step and build pressure use the trim switch, you wouldn't know the switch was in brake mode.
                              Fair enough, noted.
                              "
                              Brake Armed" seems accurate, as switching to BRAKE only reverses the air pressure direction within the pitch trim cylinder.
                              From there, application of aft trim begins to move the rotorhead forward, while actuating the rotor brake.

                              If, however, N198LT's trim system somehow malfunctioned, then who knows what it did.


                              ______________
                              Cockpit confusion can spiral quickly from bafflement to panic, especially during multiple conflicting elements.
                              It takes a very cool head to singularly/sequentially unravel things while continuing to safely aviate.

                              I'm reminded of the the fatal crash of
                              Birgenair Flight 301, in which a blocked pitot tube caused disparate airspeed readings
                              for the pilot and co-pilot. The autopilot was slaved to the pilot's faulty gauge, erroneously indicated excessive airspeed.


                              Results from a number of simulations with experienced pilots found that the combination of the overspeed warning horn
                              and underspeed stick shaker while in flight was an overly confusing contradictory set of messages for many pilots;
                              My impression of the N198LT audio was of increasing confusion and desperation as the situation progressively worsened.

                              On the BRAKE/FLIGHT point. Rotor RPMs were not significantly affected but that would be an impression rather than an absolute recollection.
                              Ultimately the friction material and surface area are insignificant verse the aerodynamic forces at play.
                              Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.
                              What I'm wondering here in relation to N198LT was if they had descended from 900 feet to about 150 feet and then found themselves over the trailer park.
                              Chris may have been naturally reluctant to then add power with such strong nose-down pitch. As you explained, "
                              any small lapse or relaxation on the stick will see the aircraft bunt."
                              This trepidation could have allowed his airspeed to decrease, thus decaying RRPM and resulting in that plummet.

                              If this accident were related to runaway pitch trim (and actuated rotor brake), then the question is whether the pilots turned on the BRAKE switch over the lake,
                              or if something in the Cavalon's trim system failed.

                              Pilot error seems unlikely as they attained 1000 feet after an apparently normal takeoff and ascent. I.e., they didn't spool up in BRAKE mode.
                              It begs credibility that either of two rated gyro pilots (one of whom a CFI) would have switched to BRAKE and the other accepting that.
                              It was a side-by-side Cavalon, so the panel is visible to both.

                              To my reckoning, the issue still seems mechanical in nature, whether runaway trim or a restricted control system.
                              I lean towards a trim malfunction, whereby application of nose-up trim dramatically increases stick forces to the bafflement of the pilot.
                              This may explain the significant power modulations as Chris no doubt tried to maintain level flight.

                              However, had the control system been jammed somehow in the area shown by Phil's photo, application of trim and power would have seemed sufficient to at least level out.

                              The cockpit audio suggests to me that more was going on than that.
                              Trying to input nose-up trim with the result of nose-down stick (while braking the rotor) would be the epitome of "
                              an overly confusing contradictory set of messages".

                              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.
                              Full nose-up trim in BRAKE mode means full rotor braking force and the rotor disc at full forward position.
                              This was not addressed in AutoGyro's POH section 3.8.4 Trim runaway.
                              In my opinion, it should be, while they rethink their entire FLIGHT/BRAKE system.

                              Regards,
                              Kolibri
                              PP - ASEL complex (C172RG, Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), 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


                              • #90
                                Originally posted by Kolibri View Post
                                Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.
                                What I'm wondering here in relation to N198LT was if they had descended from 900 feet to about 150 feet and then found themselves over the trailer park.
                                Chris may have been naturally reluctant to then add power with such strong nose-down pitch. As you explained, "
                                any small lapse or relaxation on the stick will see the aircraft bunt."
                                This trepidation could have allowed his airspeed to decrease, thus decaying RRPM and resulting in that plummet.
                                Regards,
                                Kolibri
                                I have read about the need to maintain airspeed to maintain flight rotor rpm in several of your posts in various threads Kolibri.

                                What indicated airspeed do you feel needs to be maintained in a Cavalon to maintain flight rotor rpm and avoid the plummet?

                                What indicated airspeed do you feel needs to be maintained in your RAF to maintain rotor RPM and avoid the plummet?
                                Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                                Comment

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