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Help- mathematical results for a banked turn

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  • #16
    Help- mathematical results for a banked turn

    Paul Dewhurst wrote: Of course you can be at 90 degrees or greater with any g load. It's only if you start in level flight and increase bank whilst maintaining level flight that G will rise according to the hard relationship law.

    With aerodynamic pitch control you can be at 90 degrees and have negative G if you wish.
    On a PG with no rigid structure we can be above the wing in an asymmetric spiral or even a tumble. On a flex wing with a wingover we can go beyond 90 degrees of bank. Agreed.

    But it's instantaneous, and not something you can adjust or control slowly whilst watching a G meter or ASI.

    Just warning of the dangers, as the pilot in my previous link found out when he peloyed his reserve....

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    • #17
      Help- mathematical results for a banked turn

      Not really Steve, with a trike you can quite precisely control the G applied. It's all directly down to bar position. Not difficult at all really. Done lots of it for test flying for sectionS approval, where we measure control force against G - usually In a continuous spiral turn, but applies to any turn, - the G is directly proportional to bar position - not bank angle.

      Of course I am not advocating we all go flying 90 degree turns ( although we have an exemption from the 60 degree bank limit from CAA for the WAG team). Just pointing out that it's not the bank angle that applies the G in itself - its all down to bar position. It's also not particularly useful Mick to try and calibrate a G meter form flying bank angles - it's not so easy to precisely measure the bank angle, and just a tiny bit of climb or descent varies the G considerably.

      Paul

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      • #18
        Help- mathematical results for a banked turn

        Paul Dewhurst wrote: Not really Steve, with a trike you can quite precisely control the G applied. It's all directly down to bar position. Not difficult at all really.
        I was talking about wing overs or asymmetric spirals. Input has to be precise and correctly timed or the pilot is in the sail. The video link demonstrates my point...

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        • #19
          Help- mathematical results for a banked turn

          Hi Steve,

          We are obviously talking about a different form of flying which we would not want to go near.

          Exploring the loads and limits in the aircraft with words are something which will bring knowledge and appreciation of the complexity of problems and the reason for limits in our flying and with a better understanding of what the plane will do and what effects it must make you a better pilot in my personal opinion.

          Paul,

          The angle concerns came from the discussion, it was the G loads which interested me , mainly because given the accepted formula it appeared to be completely wrong when calculating the steeper turns , Steve appears to be working along these lines of using the formula which predicted G loads which obviously were not happening so the question had to be asked why. I now understand the reasons but still have not got a mathematical conclusion or crossover point even after simplifying it to a flat constant speed turn. I will work on it some more.

          Its obviously difficult but would be nice so we could move on to predicted stall speeds but the main motivation was to check out the data logger I am working on which in theory at least gives all the angles, accelerations and GPS positioning to maybe get enough information to start monitoring changes.

          I know from my work on the bikes that information is key and a good logger when understood is very useful.

          Thanks for the contributions
          Mick Broom
          Member 909
          Shadow G-MWTN

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          • #20
            Help- mathematical results for a banked turn

            Not sure why it's difficult? g is just produced by lift. The bank angle is irrelevant - unless you want to maintain level flight. Of course that's impossible to sustain for high bank angles - which is why the maths ramps the G up almost infinitely.

            It seems like you are struggling with trying to relate what you have observed / experienced with the math? Seems to me it's the level flight bit that is the trouble. The boys in the last WAG were banking 90 degrees but only pulling 4g - but that's because they weren't increasing lift enough to support level flight - but it didn't matter becuase the time scale was very short, so there was no noticeable height loss.

            Paul

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            • #21
              Help- mathematical results for a banked turn

              Your correct Paul,

              I am struggling to relate the maths with the facts but I now think I see what you are saying is the maths is correct but it takes the plane into a place which is impossible to do.

              I understand the G is produced by the lift but if the forces are of a greater magnitude than the static 1G downwards which can be produced by the centrifugal effect ( speed / radius ) then it acts through the mass/lift axis which could be at any angle, even upside down???

              I am afraid what my head says is that when its at 90 degrees the dominant force is due to the centrifugal load which is dependent on the speed and radius of the turn , push out more G. Obviously too stay level you would need to fly at less than 90 degrees to offset the gravity.

              Not enough brain cells left , more drink needed

              :burger:
              Mick Broom
              Member 909
              Shadow G-MWTN

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              • #22
                Help- mathematical results for a banked turn

                its still all down to lift - even at 90 degrees of bank - it's the lift that is producing the turn radius and the G. And in this context lift is the force the wing is making - not the vertical component - which at 90 degrees can only be zero!

                There was some weird stuff earlier in the thread about not being able to roll out of the turn at 90 degrees due to gravity pulling the trike / hanglider pilot out of Perpendicularity with the wing. That's not really relevant and the angle the trike adopts has no effect on the wing - it's roll torque applied by the pilot through his / her arms to the bar that produces roll force to the wing.

                Paul

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                • #23
                  Help- mathematical results for a banked turn

                  Wasn't it you Paul (could have been BB) who worked out it was impossible to load a flexwing beyond 4G because of unloading due to airframe distortion?
                  Dave

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                  • #24
                    Help- mathematical results for a banked turn

                    Depends on the individual machine and its aeroelastic coefficient. We plotted the curves from flight testing stall speed against g for the kiss 400 and Va ( the speed where you ca get 4g without stalling first) was above Vne.

                    But types with a higher sail tension don't twist off so much under load and can pull more g.

                    Paul

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                    • #25
                      Help- mathematical results for a banked turn

                      Found this on my quest

                      Web page of bank/loads

                      Stall speed doubles at just over 70 degrees and trebles at just over 80 degrees which probably explains why we cannot pull High loads.

                      We just cannot go fast enough
                      Mick Broom
                      Member 909
                      Shadow G-MWTN

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                      • #26
                        Help- mathematical results for a banked turn

                        Dave Smith wrote: Wasn't it you Paul (could have been BB) who worked out it was impossible to load a flexwing beyond 4G because of unloading due to airframe distortion?
                        Dave
                        The BHPA test rig has managed to produce figures well above 4G on some wings, but others shed load. It's not flight though as the ability of the rig to load the wing is limited mostly by engine power overcoming the drag at those high lift values.

                        Think the highest figures ever sustained without failure on a test rig are close to 7G. Think this was on the US test rig in the late 1990s.

                        Mark Dale ran the rig most of the time but current Tech Officer Ian Currer also has some experience on it, and used to be a flex wing manufacturer.

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