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  • #46
    Originally posted by Vance View Post
    ... In either case, the blade is not reusable and I have not seen a benefit from the blade staying in one piece.
    Rotor systems failing in flight does not seem to be a significant issue.
    In my opinion, The Sport Copter blades have many nice features so there is no reason to make up imaginary features that have no benefit.
    ... It appears that AutoGyro and Magni are doing a good job of design and they are marketing their features and benefits well...
    +1 to Vance!

    This is like arguing about Glass vs Polycarbonate Car Headlight outer shells.
    The glass Headlights do not frost over with age.
    The Polycarb lights are lighter and less expensive to produce.
    They both can last for the life of the car and light up the road just as well.
    They both have their own Pros and Cons but perform their job acceptably.
    No matter which type you have, they will need to be replaced if you hit a tree.

    If you do not like the Headlight analogy, then let's argue about what brand of paint on a car hold up better in a crash.


    Comment


    • #47
      That's a good one Bill.But how blades bend or break in a crash is really important,I know I sleep better now that I
      have been enlightened.
      What a great subject of discussion,WOW.
      Best Regards,
      Eddie Sigman,Polvadera,nm
      (575) 835-4921

      Comment


      • #48
        Originally posted by C. Beaty View Post
        Jake, your Skywheels rotor solves the 2/rev vibration problem by not copying Bensen and necking the rotor down to 2 ½ inches at the hub.

        You may remember a gyro flier that used the name; “Madman Mike” from, I think, Arizona.

        Mike crashed and smashed his Skywheels and then started using extruded 8H12 rotor blades with a 2 ½” hub, bitching continuously about the shake. Following my suggestion, Mike installed external drag struts and like magic, 2/rev vibration vanished.

        On second thought, Mike might have been using extruded blades on a Skywheels hub and smashed the hub when he crashed.

        In any case, stiffening the rotor inplane raised its resonant frequency above the aerodynamic excitation frequency and solved the problem.
        Chuck:
        Have you ever recorded the values for 2/rev with actual equipment accelerometers etc. with a 3 inch hub bar versus a hub bar with rod ends like Ernie did or with McCutchen's composite wide hub bar on the same exact rotors and machine?
        I'd like to know because I suspect that you have never done that and are stating this out of theoretical analysis only. Not a bad theory mind you but I don't think it works. If you have done this work then I'd really like to know and see what you exactly did to get better results because that would be a great advance and I would be happy to use it. So far from what I have seen this wide hub bar theory does not actually reduce 2/rev.
        Last edited by fara; 08-12-2018, 03:24 PM.

        Comment


        • #49
          Arthur Young, designer of the Bell-47 helicopter and inventor of the underslung teetering rotor, might have known something about underslung teetering rotors. He realized 2/rev rotor shake was caused by inplane resonance and temporarily solved the problem by the use of external bracing, using an arrangement called the “Swedish yoke” to honor his test pilot, Floyd Carlson, who had suggested it.
          Arthur Young did all this without the use of a vibration analyzer.
          Watch this film clip from: “Birth of the Bell Helicopter” starting at ~3 minutes into the film.

          https://www.youtube.com/watch?v=JOh09JJwoWM

          Comment


          • #50
            Originally posted by C. Beaty View Post
            Arthur Young, designer of the Bell-47 helicopter and inventor of the underslung teetering rotor, might have known something about underslung teetering rotors. He realized 2/rev rotor shake was caused by inplane resonance and temporarily solved the problem by the use of external bracing, using an arrangement called the “Swedish yoke” to honor his test pilot, Floyd Carlson, who had suggested it.
            Arthur Young did all this without the use of a vibration analyzer.
            Watch this film clip from: “Birth of the Bell Helicopter” starting at ~3 minutes into the film.

            https://www.youtube.com/watch?v=JOh09JJwoWM
            I know that quite well what he did. He could not go even 20 mph without being afraid of shaking. I don't think that was just 2/rev that did that. We obviously reach in excess of 100 knots for long periods of time without experiencing that.
            I am asking for a direct answer to if you have done it and recorded data to see if this really works. Lots of smart people have tried to find n per rev solution in rotor dynamics field and have no answer to eliminate it. I think they know about Arthur Young as well. If this solves the problem and you have data recorded to show that, I am very interested in seeing it and am interested in implementing the solution but I did not see a solution neither from wide hub bar nor from rod cage like Ernie did. In the end the result properly recorded shows the difference. I am not trying to argue. I don't have any solution either but just letting you know this doesn't work at all. And if it did work for you and you have more than an anecdote here and there (actual test results with accelerators on a balancer recording 2/rev significant reduction) please let me know. I am very interested in what exactly was done to get that.

            Comment


            • #51
              Inplane stiffness of the rotor is only ½ of the story; the other half is mast stiffness. The mast supplies a spring restraint at the center of the rotor, lowering the resonant frequency of the system.
              The use of square tubing as a mast is part of the problem.
              Bensen selected square tubing as an aid for home builders; bolt holes could be drilled so that bolts ran tangentially to inside walls, eliminating the need for internal spacers. Square tube is much too stiff.
              Then along came the designers of Euro Bensens with welded airframes of square steel tubing: Young’s modulus for steel is ~3x as great as aluminum. With a welded airframe, there is no need for square tube.
              My first gyro, long before I understood the nature of rotor vibrations used a mast of round, 2024 aluminum tube and never had a 2/rev problem, no matter which rotor. One of my early rotors used Hughes 269 rotor blades which the previous owner had tapered the root ends to mimic Bensen blades. I, not believing there was enough inplane strength remaining for a Young rotor, built an articulated rotor with a coning hinge at its center and outboard drag hinges without undersling. Smooth as silk but a real eye opener when I tried the same scheme on a gyro with stiff rotor pylon. A long, slow learning process.
              A vibration analyzer mounted at the rotorhead must show 2/rev motion; otherwise, something will break. That’s another reason for a soft mast.
              I’ve never needed a vibration analyzer.
              Last edited by C. Beaty; 08-12-2018, 07:33 PM.

              Comment


              • #52
                Originally posted by C. Beaty View Post
                Inplane stiffness of the rotor is only ½ of the story; the other half is mast stiffness. The mast supplies a spring restraint at the center of the rotor, lowering the resonant frequency of the system.
                The use of square tubing as a mast is part of the problem.
                Bensen selected square tubing as an aid for home builders; bolt holes could be drilled so that bolts ran tangentially to inside walls, eliminating the need for internal spacers. Square tube is much too stiff.
                Then along came the designers of Euro Bensens with welded airframes of square steel tubing: Young’s modulus for steel is ~3x as great as aluminum. With a welded airframe, there is no need for square tube.
                My first gyro, long before I understood the nature of rotor vibrations used a mast of round, 2024 aluminum tube and never had a 2/rev problem, no matter which rotor. One of my early rotors used Hughes 269 rotor blades which the previous owner had tapered the root ends to mimic Bensen blades. I, not believing there wasn't enough inplane strength remaining for a Young rotor, built an articulated rotor with a coning hinge at its center and outboard drag hinges without undersling. Smooth as silk but a real eye opener when I tried the same scheme on a gyro with stiff rotor pylon. A long, slow learning process.
                A vibration analyzer mounted at the rotorhead must show 2/rev motion; otherwise, something will break. That’s another reason for a soft mast.
                I’ve never needed a vibration analyzer.
                Hi Chuck:
                Do you suggest mounting accelerometers past the mast, perhaps in the cockpit or on the keel tube to take some measurements of 2/rev there with a spectrum analyzer? Would that in your opinion give a better picture of the 2/rev effect on the system.
                I agree that a soft mast can curtail the passage of 2/rev down into the cockpit. As such an Aluminum mast should in theory do a better job everything else being equal compared to a chromoly welded mast or a stainless steel mast.
                Even the active vibration mechanisms that are used in today's advanced helicopters simply act to re-distribute vibration from the cockpit to other areas.
                Sikorsky seems to have developed a new system in 2015 working with Lord Mount company to actually create a true choke point system where vibrations are eliminated. They call it HMVS ad they tested it on an Army Black Hawk. It uses 4 brush-less electrical ring motors with a center Tungsten mass to counter actively the frequencies creating the vibration. Two motors turn in the same sense as the rotor and the other 2 turn counter to it but at 4 times the speed. Obviously a bit rich and complex for a simple gyroplane but a clever idea.

                Comment


                • #53
                  A soft mast is an essential part of a Young rotor system, performing both tuning and isolation.

                  Bolt an anvil to the top of the mast and 2/rev vibration will be eliminated but the blades will develop trailing edge cracks within a short time. A number of years ago, some Australians were using heavy starter motors for prerotators and stumbled across this. This also happens when trying crisscrossed seesaw rotors.

                  The RAF magic rubber bushing provides an excellent solution to 2/rev vibration although it should act laterally as well as longitudinally.

                  Accelerometers should be mounted down on the airframe; there will always be 2/rev motion at the rotorhead unless an anvil is bolted to the top of the mast.

                  Comment


                  • #54
                    Chuck you can also make an absorber with a (compression) spring and a mass. The stiffer the spring, the higher the frequency and the lighter the mass on top of this spring the higher the frequency. We can mount it and tune it to the 2/rev frequency and it will start absorbing it while the mounting surface will become smoother. Anyway, multiple ways to do this. Your limber mast with rotor system mass on top is one.

                    Bottom line that I have been able to gather is N-per-Rev is intrinsic and comes from various factors including shadow of the passing rotor over the fuselage and root shears given by the rotor to the rotor-head/hub. These root shears are both horizontal and vertical and they combine at the rotor-head to make 2 per rev. Increasing the number of blades to be 5 or so reduces this to a very low level and that seems to be the current consensus in the industry. N+1 per rev and N-1 per rev are actually produced but their addition and combination comes across through transmission down as N per rev. Rigid blades would help but then Kolibiri would be all pissed because rigid blades will break and not bend I think. Sorry couldn't resist :).
                    From all the study I have done it seems as though if you get 1 per rev too good in both X and Y, you will notice 2 per rev pretty badly and thus some 1 per rev is many times re-introduced in the system deliberately.

                    Comment


                    • #55
                      Chuck, Abid,

                      It's not often an off-topic debate classes up a thread, but yours has. Thanks!

                      Back on topic for a second, It might be possible to make rotor blades so stiff that they didn't deform at all in a ground strike. The downside would be redirecting all that energy into repeated body-slamming of the fuselage into the ground, or failures in masts, etc. I'll take rotor deformation.

                      The fact that Sport Rotors usually keep their skins together, to me, says more about the quality of the adhesive and the bonding process than it does about their stiffness.

                      I've had great respect for Sport Copter products over the years. It's discouraging to see the new marketing direction demonstrated in this thread.
                      Paul W. Plack
                      Private ASEL, SP Gyroplane
                      Secretary, URA & PRA2
                      Editor, Western Rotorcraft

                      Comment


                      • #56
                        1/rev and 2/rev vibration of the rotor are 2 entirely different and unrelated matters.

                        1/rev is always track and balance, 2/rev is the result of aerodynamic input and the oscillating mass above and below the teeter bolt of a coned rotor.

                        1/rev vibration is easily solved; balancing a rotor is no different from balancing a bicycle wheel and out of track is obvious to anyone who looks.

                        2/rev is far more difficult and is often exacerbated by the inplane resonance of the rotor/mast combination falling too near to 1/rev (rotation of the rotor produces frequency doubling).

                        Comment


                        • #57
                          Originally posted by PW_Plack View Post
                          Chuck, Abid,

                          It's not often an off-topic debate classes up a thread, but yours has. Thanks!
                          I agree. This is some good stuff.
                          Mike Gaspard
                          Forum Administrator
                          Kaplan, Louisiana
                          Bensen B8MG, NX36MG

                          Comment


                          • #58
                            The round mast vs square mast design has been posted before. I wonder why at least one modern factory built design hasn't gone back to the round mast? Didn't someone build an entire frame out of round tubing way back when? It strikes me as a KISS (keep it simple stupid) solution vs adding dampers or magic bushings.

                            Comment


                            • #59
                              gyrojake, unless completely solid with material (foam, aluminum, glass -- none of which has been alleged of SC rotors), all blades have some hollow sections.
                              How stringently do you intend to use the word "hollow"? Would a solid blade with some inherent bubbles be "hollow"?

                              I'm looking at a cross-section photo of an SC blade with an AG blade. The SC blade is substantially more solid than the AG.


                              Click image for larger version  Name:	Sport Copter vs. extruded blade.png Views:	1 Size:	140.5 KB ID:	1136677



                              Both blades have some hollow portions, but the AG's degree of hollowness is much greater.
                              Thus, by your notion, the more solid SC blades should be breaking. But they're not, QED.


                              Me and Jim are like oil and water, his words mean less to me than yours.
                              And it seems Jim gave you false info . . .
                              Ah, that helps to explain your attitude.
                              Have you more experience in flying and designing gyros than Jim Vanek? I doubt it.



                              ___________
                              The RAF magic rubber bushing provides an excellent solution to 2/rev vibration although it should act laterally as well as longitudinally.
                              Chuck, RAF copied that from Jim Vanek, who recalls the airshow when Dan Haseloh was snooping around and taking notes. fyi . . .



                              Rigid blades would help but then Kolibiri would be all pissed because rigid blades will break and not bend I think. Sorry couldn't resist :).
                              fara, why would I be pissed? Sport Copter makes probably the most rigid aluminum blades in the industry, and they've no history of breaking at all.


                              ___________
                              Back on topic for a second, It might be possible to make rotor blades so stiff that they didn't deform at all in a ground strike. The downside would be redirecting all that energy into repeated body-slamming of the fuselage into the ground, or failures in masts, etc. I'll take rotor deformation.
                              PW_Plack, SC rotors do deform and absorb impact energy. However, they do not break and thus endangers others. To me, that is the ideal.

                              The fact that Sport Rotors usually keep their skins together, to me, says more about the quality of the adhesive and the bonding process than it does about their stiffness.
                              Keeping their skins together is a related but separate issue.
                              SC rotors don't break off from the hub bar. There's more going on with that than just the bonding process.


                              I've had great respect for Sport Copter products over the years. It's discouraging to see the new marketing direction demonstrated in this thread.
                              My Kolibri posts are published solely in my personal capacity, and not to represent any company or other individual.



                              ___________
                              A gyroplane rotor near flight rpm has a lot of stored kinetic energy.

                              A soft rotor blade has a longer time to dissipate the energy as it deforms with a sudden stoppage.

                              A stiff rotor blade has a shorter time frame to dissipate the energy and is more likely to break in a tip over.
                              Then, Vance, since AutoGyro blades consistently break that means they are stiffer than Sport Copter blades?
                              That seems a difficult notion to posit.


                              In either case the blade is not reusable and I have not seen a benefit from the blade staying in one piece.
                              It seems quite axiomatic that blades which won't break up upon impact at full flight RRPM have an excess of strength in the air.
                              And, during impact, I think it obviously more preferable that the gyro does not throw a blade with "
                              a lot of stored kinetic energy."
                              But, since you're flying your second set SC rotors, you've never had to wonder or worry.


                              _____________
                              I'll wade through the other new posts and reply later today.

                              Meanwhile, some new photos.
                              First, two of Trixy. The stainless steel mast has folded up in both cases.


                              Click image for larger version  Name:	Trixy post-crash damage.png Views:	1 Size:	434.2 KB ID:	1136663

                              Last edited by Kolibri; 08-13-2018, 02:00 PM.
                              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


                              • #60
                                The last American Ranger I flew and the last Titanium explorer I flew were both so smooth rotor vibration was not an issue Tim.

                                I doubt if I could tell the difference if someone substituted a round mast on either aircraft.

                                The Predator has too stiff a mast and will never be smooth. I had a lovely flight to Camarillo Sunday and the rotor vibration was not a bother to me.

                                In my opinion the production numbers of gyroplanes are too small to invest heavily in research and development. Why reinvent something that is acceptable?

                                In my opinion based primarily on my experience with designing motorcycle frames; managing perceived vibration is more of an art than actual engineering.

                                A Robinson 44 and a Bell 206 manage two blade teeter rotor vibration very well with elastomeric isolators.
                                Last edited by Vance; 08-13-2018, 06:30 AM.
                                Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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