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  • mad max
    started a topic Vertical stabilisers

    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, 09:07 PM.

  • Tim
    replied
    Yes Ross, I took another look at my first diagram and thought I must have been drunk (even though I don't drink).

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  • RossM
    commented on 's reply
    OCD coming out in you Tim
    (obsessive compulsive disorder, everything has to be spot on)
    [cannot use smiley symbol in a comment post]
    The pod will make a lot of turbulence in front of the pod, (maybe not for a Newo or some of the euro's)
    Last edited by RossM; 10-30-2017, 05:23 PM.

  • Tim
    replied
    I'll try to improve on my propeller slipstream diagram (and my posting ability)

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  • Tim
    replied
    The only hummingbird I ever flew had the worst rudder response of any tail design I've flown. Very poor in X wind take offs and negligible response when landing correctly. You always had to land into wind unless you touched down at Euro tub speeds, which can always be iffy with a short wheelbase and foot steering.
    Waddles is right, the prop slipstream converges behind the prop simply because the low pressure created ahead of the prop draws air in from all directions including outside the prop tip arc and squeezes it towards the centre (high pressure) as it exits the prop. This is most pronounced at low speeds and high throttle settings.
    Technically the most efficient rudder is a symmetrical airfoil which is aligned with the airflow (least drag) and has enough "volume" to effect adequate yaw control, even in a power off situation. With the varying rudder designs and being so close to the prop, there is no such thing as one design that suits all conditions and configurations.
    Please excuse my rough 5 minute sketch.
    NB, I wonder why Beechcraft discontinued the V tail?
    Click image for larger version  Name:	image.jpeg Views:	1 Size:	22.3 KB ID:	36647

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  • aussie_paul
    replied
    My first two seater frame was made by Hummingbird with their V tail. Terrible thing. I had to immediately replace it with fin and rudder larger than the standard Bensen.

    Aussie Paul.

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  • Sean
    replied
    I think I posted in the incorrect spot new to posting

    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.

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  • Sean
    replied
    Pic 1 Hummingbird gyro. Pic 2 Hummingbird hybrid direct drive turbo ea81 with 100kg pilot flew 2 hour to Watt Bridge can't remember from were thinking Maryborough pic 3 Kerry Keys machine work was done by me but was changed soon after for the reasons stated in previous post.

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  • Sean
    commented on 's reply
    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, 02:01 PM.

  • Waddles
    replied
    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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  • aussie_paul
    replied
    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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  • Waddles
    replied
    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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  • aussie_paul
    replied
    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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  • Waddles
    replied
    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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  • aussie_paul
    replied
    There we go Max

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