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  • TST Elevator trim

    My TST seems to need alot of elevator trim or bungee tension to stop it from going nose down and gathering speed in the cruise, lots of tension is needed to keep it in the 45-50 knot range, enough to hold the elevator in the full up position when parked on the ground, with the bungee slack it just goes into a dive and keeps accelerating without holding back pressure on the stick. I am flying it solo with half fuel and the seat well forward due to my short legs. Was wondering if it was a nose heavy Cof G that could be causing this. does anybody else have any experience or advice on this that they may have found on there own machines.

    cheers Jonathan.

  • #2
    TST Elevator trim

    You have tried the stick central/elevator level check. If that's ok then you are probably nose heavy, bear in mind that most Thrusters will trim nose down if the fuel tank is less than half full. With a full tank the trim cord on our TST is completly slack, but we retain the orignal lighter mainwheel springs. We have a T300 pod and although these are normally heavier than the standard TST pod ours was made by Thruster at Wickenby and turned out lighter that the original (thanks Mark). We also refused to have the T300 top panel fitted as this was more weight forward, another means of adding weight forward that I've come up against is a screen made of thicker material than design, it should be 2mm.

    Good Luck

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    • #3
      TST Elevator trim

      I recall being surprised by the amount of trim needed the first time I took up a small lady student who needed to sit well forward of the normal position, so it may just be that. I sometimes demonstrate to students the effect of shifting CG by simply trimming out for straight and level, and then loosening my shoulder straps and leaning forwards. It makes quite a few knots difference.

      As Ginge points out, the fuel tank is behind the CG so filling that might help - you may need to fly more often though to ensure that you continue to use fresh fuel :-)

      I trust that you have checked the CG is within bounds (The W&B calculations from the latest weighing should be in your aircraft's paperwork).

      I'd reckon that as long as you can control it into a full three-point landing then it's probably OK. Oh, and if you try (at altitude) a gently-entered full stall at idle you may find that you need to move the stick forward manually from fully back to achieve the recovery; that disconcerted me a little the first time I discovered that I could let go of the stick and it stayed back!

      Fun little machines the TSTs, eh?

      Joan

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      • #4
        TST Elevator trim

        Thanks for all your help, it seems likely that my issue is simply a slightly nose heavy situation, will check the weight and balance calculation again.

        Many Thanks
        Jonathan.

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        • #5
          TST Elevator trim

          I think that you are probably right, I spoke to Brian who has flown that aircraft a few times. He is a very experianced TST pilot and says that with a full tank and the seat right back he pulled a small amount of trim on take off and left it there for a nicely trimmed flight.

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          • #6
            TST Elevator trim

            Thanks again for your help Ginge, when it is flyable again I will try it with the tank full and the seat further back, my legs are bent more than I realised so should still be ok reaching the rudder pedals.

            Another gentleman on the yahoo group today suggested that trim can go a little wayward if the elevator covering becomes slack with age and time, and starts to billow. Anybody else heard of that happening? sounds quite possible to me, my elevator covers dont seem overly taught, they are tensioned through the eyelets with cable ties, is this normal? would have thought they would be done up like a corset with cord then tied off.

            Cheers Jonathan.

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            • #7
              TST Elevator trim

              Yes that is the normal way to tension the tail skins and it works pretty well.

              This time of year as you pull and gain a bit with every tug it helps to gently warm the skins, keep working your way back and forth until there is nothing more to gain. If however the edges are touching and you are unable to gain any more the normal trick is to remove the skins,a quick and simple job, to add gaffer tape or similar to the leading edge to take up the slack, it's worked for me in the past

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              • #8
                TST Elevator trim

                Back in the day when the Thruster Bulletin was active, although not legal here, Tony Hayes produced 'Former kits' for the Tailplane and Rudder. They were rib-lets that fitted between the steel tubes, and by all accounts, they transformed the controlability of the Thruster.

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                • #9
                  TST Elevator trim

                  Aways wondered about those, for me though the thing that transformed the handling was learning that apart from the grosser landing movements and the most violent thermic activity a Thruster is flown by the fingertips.

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                  • #10
                    TST Elevator trim

                    Skin tension makes a massive difference to handling. I have flown lots of different thrusters over the years as check pilot and instructor and the handling can vary considerably between different examples - and it's almost entirely due to differing skin age and tensions. The biggest difference is on the control surfaces - rudder, elevators and ailerons.

                    Loose skins make the controls heavier and can upset the trim. What happens is that if the control surface is presented at an angle of attack the skin balloons - concave on the 'windward side' and convex on the 'downwind side'. This then forms an aerofoil shape that opposes the movement. Around neutral angle of at attack the skin can balloon either way making for a wandering neutral. In the case of the elevator which is generally loaded a little from above the skin balloons downwards trying to suck the elevator downwards leading to nose heavy trim.

                    Shimming the frames leading and trailing edges as Ginge says can help to increase tension and alleviate the nose down trim and control forces. They need to be drum tight on all the control surfaces if possible. Try and use smooth faced tape with a slippery surface so the skins can be slid back on easily and tensioned.

                    If the skins are too tired though it's worth replacing them.

                    Paul

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                    • #11
                      TST Elevator trim

                      Totally agree with everythhing Paul wrote in his last Post.

                      It exactly what I was going to type as I two have had the same experiences as Paul what with having flown 34 different TST's, 5 T300's and about 16 T600's too.

                      All the Best Mark
                      Galaxy Microlights.

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