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  • Vertical stabilisers

    I have twin Vertical/stabilisers and when manufacturing the profile of one I seemed to make it more like an airfoil
    with lower pressure on one side so I made the other the same but opposite and assembled them so that there was a bit of 'pull in' towards the centre when wizzing through the air, thinking that it may have a more stabilising effect and it worked well. The next day I observe a photo of a Russian helicopter with twin rotors and low and behold I observed they had turned the stabilisers slightly inward at the front for extra stability I assume. (us Vikings must think alike)
    Last edited by mad max; 10-18-2017, 10:07 PM.

  • #2
    The only reason I could think of to not shape vertical stabilisers, on gyros, like aerofoils is that the resultant lift in the horizontal axis brings with it an increase in drag, though as I think about it, it is that drag that provides the additional stability that you’ve gained in calm conditions(?). Extra drag though brings with it a higher power requirement for a given airspeed. Have you noticed a decrease in airspeed for a given throttle setting? The other issue I think could impact on stability in yaw is - in gusty conditions the relative airflow over the vertical stab could potentially change due to the lateral component introduced by the gust. The change in lift of the vertical stab (increase in lift on the vertical stab on the side the gust has come from) would not act in opposition to the yawing moment created by the gust and could result in some instability in yaw in gusty conditions. Now having said all that, my knowledge of gyrocopter aerodynamics is completely theoretical and I only comment here as I know you (Max) invite technical debate. Happy to hear other’s thoughts and be corrected if I’m way off the mark.

    Fly safe.

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    • #3
      V tails leads me back to the V tail Bonanza, Remember when they first came out .....nearly & was taken by the V tail. Rumors I heard were that the V tail were a bit more twitchy than conventional & if memory serves me correct a few of them crashed but have no idea why that so. Was one in Mildura that crashed after takeoff at Robinvale nearly wiping out a Mildura firm of accountants coming back from Melbourne. Guess its the disasters that we remember first.

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      • Sean
        Sean commented
        Editing a comment
        I see several comment regarding v tails so I thought.... Probably my first mistake!
        You mentioned the v tail and how they perform from a gyro prospective
        I to remember the bonanza tails and wanted to know more myself.
        Many years ago if my memory serves me correctly, the early hummingbird gyros had a v tail and after speaking with one of the early creator who flew these aircraft, raved about how well they flew
        Curiosity got the better of me so I manufactured one identically from the original drawings and these are my conclusions.
        Firstly the tail was mounted low similarly like the early Benson designs.
        It was a 90 degrees design with a 6" flat section joining the v shape.
        This design is both horizontal and vertical stabilisation in one with the control surfaces being two rudderons to control pitch and yaw.
        Basically there is no horizontal stabilisation because there is nothing in the propellor wash at low speed as air speed increases the control surfaces take effect and work exceptional well. Now saying that!
        The down site to this is when taxing with rotor spinning at flight speed is that if you unload the front wheel before reaching enough forward velocity for the v tail design to take effect aerodynamically the gyro will yaw dramatically possible causing a rollover.
        I managed to avoid this purely by fluke and not good management but I did manage to scare myself shirtless several times.
        If you pin the front wheel with this design when pre rotating and during your take off roll at all time when there isn't sufficient rudder response dew to low air flow over the tail all will be good.
        I found from memory with regards to the design I tried you needed at least 30 knots IAS for this design to have any rudder effect. HS on tall tail and Benson design tails both have better yaw effect at lower speed due to being in the direct propellor air stream in my experience
        The problem only becomes a issue if airspeed decays below the aerodynamically effectiveness of this design
        I abandoned this design as this could catch you out very easily if you were not aware of these pitfalls.
        I later re-bent the tail section to 20 degrees. 10 degrees each side from vertical effectively creating a twin vertical stabiliser which put it into the propeller wash, making it much more responsive to rudder at low speed.
        later I installed a horizontal stabiliser to the top of the twin vertical stabilisers which later stiffened up the tail section and made a convenient place to install a HS and into the propeller wash to boot. How's that for good management. Well it did repurpose the materials which was a bonus.
        Last edited by Sean; 10-24-2017, 03:01 PM.

    • #4
      In my case Brian it's two vertical stabilisers. Not V tail. my theory was if two stabilisers are slightly pulling in towards each other then there maybe more stability than two equally profiled on both sides. My airspeed seems the same however I may of not noticed a slight loss due to a bit of extra drag.

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      • #5
        I'm currently knee deep in flight and gyro theory as I prepare to start lessons soon, so I have a question about the theory of a V tail. I have read a thread on the rotary forum that sings the virtue of V tail based on wind tunnel tests - but as I understand the horizontal stabiliser is the important element in the tail for safety to dampen any tendency for pitch oscillation. So surely a V tail is a poor match for a gyro? Assuming a v-tail doesn't use a horizontal stabiliser (would look weird) and the horizontal vector forces on the V tail wouldn't be as effective as the typically sized horizontal stabilisers I see on most gyros (about the size of writing desk).

        Let me know if I'm off beam in this thinking.

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        • #6
          I didnt read your post properly Max but stabilizers are a interesting topic.

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          • #7
            I just love the freedom to experiment a little and flight test ones ideas. My wife once sugested we lash out and purchase a good second hand European bathtub but I supprised myself and said I'd rather stick to my homemade flying machine as it's an engineering challenge as well as pilot skill challenge.
            Last edited by mad max; 10-20-2017, 11:43 AM.

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            • #8
              Hey Max. Are your VSs in or out of the propeller slipstream and do you also have a fixed VS with the rudder attached? i.e. A tri-tail.

              Waddles.

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              • #9
                G'Day Waddles. I have a tall tail with a horisontal stabiliser back in the slip stream on the keel with one large vertical stabiliser on each end. There's a photo of it on my Facebook front page that anyone who has facebook can access I think. I'm not nerdy enough to put a photo on the forum.

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                • #10
                  There we go Max

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                  • #11
                    Thanks Max; thanks Paul,

                    I tend to think that the HS is far enough aft that is not fully in the slipstream, as in general, the slipstream waists in after the prop but by how much I'm not sure. It's the effect of the airflow due to forward airspeed that causes this, I believe.

                    That aside, if the fixed vertical Stabilisers (VS) are fitted such that the leading edges are inboard of the trailing edges, then it should enhance the yawing stability as follows:

                    Consider an atmospheric upset that causes the gyro to yaw to the left. This would result in the left hand VS presenting an angle of attack to the relative airflow which, for arguments sake, is now zero. Where there was an angle of attack to the relative airflow before, it is now zero and therefore creates less "lift". Now consider the right hand VS in the same situation. It has presented an increased angle of attack to the relative airflow and therefore more "lift" towards the centreline of the gyro. The now unbalanced forces acting on opposing VSs generate a force that tends to push the TAIL feathers back to the left thus countering the atmospheric upset resulting in a stabilising effect.

                    So, according to my theory Max, you should expect more yawing stability with your setup.

                    Let the critics step in!!!

                    Regards,

                    Waddles

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                    • #12
                      Yes Allan, but there has to be a speed penalty, minute but still there. I would think the theoretical answer would be to have them parallel and larger, or parallel and further back.

                      Aussie Paul.

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                      • #13
                        Agreed Paul,

                        I'm not advocating the use of VSs like Max has, just trying to explain why that setup might provide a more stabilising effect in the yawing plane.

                        Waddles.

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                        • #14
                          Originally posted by Waddles View Post
                          Agreed Paul,

                          I'm not advocating the use of VSs like Max has, just trying to explain why that setup might provide a more stabilising effect in the yawing plane.

                          Waddles.
                          Max's set up will not provide more yaw stability than when both are parallel. I went through this with Chuck Beatty 15 years ago.

                          Aussie Paul.

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                          • #15
                            OK Paul. I think it MIGHT depend on whether or not the VSs are symmetrical section, flat plate or semi-symmetrical depending on which side the curved surface lies. Either way, the difference from one to the other is, in my opinion, negligible.

                            Waddles

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