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  • QUANTUM FLYIN TO FAST

    HI ALL I FIND MY Q2 WING ON MY QUANTUM FLYS TO FAST EVEN WITH FULL TRIM ON

    60MPH VERY HARD WORK ON THE ARMS ANYBODY GOT AN IDEAS HOW TO SLOW IT DOWN TO 50 WITHOUT ARMS OF STEEL

  • #2
    QUANTUM FLYIN TO FAST

    Hi,

    I have always found on my Quantum that the trim control makes hardly any difference... well maybe 2 or 3 mph.

    It'll cruise about 55 full trim and 58-60 with it wound off.

    It's always loosened off while in the hanger....

    Andy

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    • #3
      QUANTUM FLYIN TO FAST

      hi brian
      i always take the trim off when i land your right 60 is a good cruise speed but i like to slow down a bit when the air is lively and that takes a good bit of preasure on the bar my plane is a 582 4300rpm to achive that cruise i will try setting it up again thanks for your help
      gary

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      • #4
        QUANTUM FLYIN TO FAST

        Gary

        It sounds like your battens may have flattened off.

        This happens to all wings, left rigged or stored in the bag. Reset each batten to the batten plan and make sure that they are identical pairs each side.

        I do mine as part of my 50 hour service.

        As Brian said, winding on trimmer increases the stall speed and you can get in slower if the wing is clean. The trimmer is using the trailing edge to create drag, hence the wing flying slower. In doing so, it also reduces the chord length, reducing the lift and moving the centre of lift forwards. The trailing edge will sit up slightly in normal flight and the trimmer needs to be adjusted so that it works when this edge is raised.

        Wind the trimmer on (in flight) until it starts to move the bar forward. This is the starting point and the cable length should be adjusted so that there is a small amount of slack beyond this point.

        Pete

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        • #5
          QUANTUM FLYIN TO FAST

          . The trimmer is using the trailing edge to create drag, hence the wing flying slower. In doing so, it also reduces the chord length, reducing the lift and moving the centre of lift forwards. The trailing edge will sit up slightly in normal flight and the trimmer needs to be adjusted so that it works when this edge is raised.

          [/quote]
          The trim wires pull on the luff lines and pull up the trailing edge of the wing and increase the reflex. This increases the angle of attack at which the "Centre of Pressure" is co-incident with the hang point. That is to say it increases the angle of attack at which the wing is pitch neutral about that point.
          Our wings are designed so that when we push the bar we increase the angle of attack which moves the "Centre of Pressure" backward and produces a pitch down moment on the wing and pushes back against us on the bar (and vise versa for pulling on the bar). The "centre of Pressure" is exactly on the hang point at one particular angle of attack. increasing the reflex changes this one particular angle of attack. The increased angle of attack leads to a lower speed (for the required amount of lift) in level flight.

          Laurie (2)

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          • #6
            QUANTUM FLYIN TO FAST

            Laurie

            You are correct, I was just trying to keep it simple and understandable.

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            • #7
              QUANTUM FLYIN TO FAST

              Much confusion it seems on how the aerodynamics of the Rogello wing functions. How about this. Reflex is set and maintained to create a pitch up moment, ie, dive recovery. The pitch trimmer pulls in extra reflex (works the same as an elevator on 3 axis by primarily creating a down force to rotate the wing about the hang point, extra drag is created but only as a secoundary effect) thus increasing the angle of attack, increasing the lift, moves the centre of pressure FORWARDS, and has negligable effect on stall speed. If power is the same the aircraft will climb, if power is reduced the aircraft is able to fly straight and level but at a slower airspeed. Forget the trimmer for now. We have established that pitch up moments (dive recovery, bar pulling out of your hand) are mostly a function of reflex. So now what causes pitch down moments, ie, when the bar wants to push back into your chest. The clue is in the planform shape of the delta wing, as it rotates in pitch about its lateral axis through the hang point. Thus when you push the bar out all of the above occurs, but notice that the wing tips are now decending into the airstream further than the middle of the sail and will act as horizontal stabilizers trying to level the wing out again. The tips do a similar but reduced and reversed function when diving, backed up by reflex. Roll control, well thats another story.

              Geoff

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              • #8
                QUANTUM FLYIN TO FAST

                Allow me to put forward another point of view;

                The wing of a 3-axis plane is unstable in pitch - that is to say an increase in angle of attack produces an increased pitch up moment (the "centre of pressure" moves forward) and visa versa. The 3-axis plane has a tail, the horizontal stabiliser, which counteracts the pitch moment of the wing and taken as a whole the plane is stable in pitch.

                Our flexwings do not have a tail and so the wing itself must be stable in pitch. This is achieved either with reflex or with fixed washout. In older wings like my Mainair the trailing edge of the centre section of the wing is curved up by the battens and by the luff lines. The wing tips are free to rotate upwards to negative angles of attack but are not held up mechanically and in practice always run a zero lift AoA (in straight flight).

                On more modern wings like the BB Tria the wing tips are mechanically held at a negative lift angle of attack (-21 degs, but I donít know what datum that is measured from) and the centre of the wing has no reflex.

                Both of these methods produce pitch stability. When I push the bar I increase the angle of attack and the "centre of pressure" moves backwards behind the hangpoint thus producing a force pitching the wing nose down. I feel this as the bar pushing back at me. Conversely when I pull the bar to reduce the angle of attack the "centre of pressure" moves ahead of the hangpoint and the bar tries to pull away from me towards the centre position.

                Notice that equilibrium is when the "centre of pressure" of the wing is coincident with the hangpoint so moving the hangpoint from the back hole to the front hole produces a new equilibrium with the "centre of pressure" further forward and thus at a lower angle of attack. The same amount of lift (same weight) from a lower angle of attack means faster hands-off cruise, which is what you expect when you move the hangpoint forward.

                Laurie (2)

                Comment


                • #9
                  QUANTUM FLYIN TO FAST

                  Excellent discussion so far, thank you.
                  Laurie, I think the point we disagree on is the assumption that a 3 axis wing when subjected to an increased of AoA will exhibit a more forward centre of pressure (this I agree with) but the same increased AoA on a flex wing produces a rearward centre of pressure shift (here we disagree, how can a wing section act in both ways??). We seem to agree that the tips produce pitch stability for the reasons I 've already stated, also worth mentioning is the prime reason for washout (tips at reduced or even negative AoA) is the prevention of tip stalls at very high AoA's.

                  Over to you

                  Geoff

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                  • #10
                    QUANTUM FLYIN TO FAST

                    Iíve had a look in my textbooks and I cannot find a proper analysis of a reflexed wing. The best I can find is in "Tailless Aircraft", (Nickel and Wohlfart). It contains a long quote from a paper, "Lets consider airfoils for flying wings", Barnaby Wainfan, 1989, which contains the following passage;

                    "There are two ways to create a positive pitching moment wing. The first is to use a combination of sweepback and washout so that at zero total wing lift, the tips are pushing down and the root is lifted up. The second is to use an airfoil that has a positive Cm0. The use of sweep and twist is limited by several factors and cannot produce a very large pitching moment. It can be enough to trim the aircraft only if the airfoil has little or no negative pitching moment."

                    However it can be observed that the BB Tria wing is 100% double surface with no reflex and it relies on sweep and washout for its pitch stability.

                    There are rigid winged tailless aircraft which are not sweptback. Thereís one in the Shuttleworth collection but I donít remember its name.

                    Laurie (2)

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                    • #11
                      QUANTUM FLYIN TO FAST

                      Finally, Iíve figured it out.

                      I need to talk in terms of the force which is the resultant of the pressure distribution over the upper surface of the wing separately from that of the lower surface, in order to explain my thinking.

                      Firstly - you are right. The resultant force of the summation of the reduced pressure over the upper surface of the wing moves forward as the angle of attack increases (regardless of reflex).

                      Start with the wing at a zero lift AoA. We know that the resultant force of the pressure on the upper surface is equal in magnitude and in the opposite direction to the resultant force of the pressure on the lower surface - hence zero lift. But these two resultants are not in the same place along the cord. The upper surface resultant is somewhere between quarter and half cord and the lower surface resultant is near the front of the wing. So even though there is no lift there is a couple which tries to rotate the wing nose down.

                      Now suppose the trailing edge of the wing is turned up to produce reflex and the effect of this is to produce a reduced pressure under the trailing edge and hence a force downwards on the wing at the trailing edge.

                      Now zero lift will occur at a greater AoA than before and the resultant force on the upper surface will be larger having, as it does, to balance both the resultant under the front of the lower surface and also the new downforce at the trailing edge.

                      If the resultant of the pressure on the upper surface occurs ahead of the half cord position - as seems likely - then this new situation will result in a nose up moment regardless of the point about which we calculate the moments.

                      Now go to the other extreme, the AoA just before the stall. The resultant force of the pressure distribution over the upper surface of the wing is at itís furthest forward position. So long as the hang point of our Flexwing or the CofG of our tailless 3-axis is ahead of this point on the cord of the wing then we must have a nose down pitch moment. At this AoA the Cl is maximum and this resultant force is much greater than any other resultant acting on the wing. We might also expect the downforce at the trailing edge as a result of the reflex to reduce with increasing AoA (I think so long as it doesnít actually increase we are OK).

                      So now we have a situation where at minimum AoA we have a pitch up moment regardless of where we put the hangpoint and at stalling AoA we have a pitch down moment so long as the hangpoint is ahead of the upper surface resultant. Hoorah! A stable wing without a tail or sweepback.

                      The action of reflex therefore is to produce a pitch up moment at minimum AoA and have less and less effect as the AoA increases. So long as the resultant force of the upper surface never moves ahead of the hangpoint then the wing will be stable and a pleasure to fly.

                      Laurie (2)

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                      • #12
                        QUANTUM FLYIN TO FAST

                        Laurie (2)

                        Nice explanation, I concur.

                        Cheers Geoff

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                        • #13
                          QUANTUM FLYIN TO FAST

                          Jeremy

                          I have always assumed that luff lines are pulled out by the airflow and this raises the trailing edge. It is this action that applies reflex as the speed increases. Is this correct?

                          Laurie, even I followed that

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