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Thread: XL trim speed

  1. #1
    Co-Pilot Wexfordair's Avatar
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    XL trim speed

    A friend fitted a new (yes brand new) sail a while ago and now has 10 hours on it. The trim speed was 55mph indicated and is now 45mph indicated. Without wing tip adjusters, is there an easy way to increase trim speed back near the book figure?
    There's already a lot of tension on the wing so nothing to gain there.


  2. #2
    Co-Pilot Arielarts's Avatar
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    Might be worth looking to see if the Battens have lost any profile.

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    Co-Pilot BobH's Avatar
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    Sorry to say this, but all XL wings cruise at around 45mph after a few hours use. Don't forget, it's a 17 sqmtr wing with only half the number of battens that later wings had, so any stretch of the fabric will change the trim speed. I once had an XL with a sail that had only 7 hours on it from new. For the first few hours it flew at over 50mph, but it soon began to slow down, and by the time I sold it, it was cruising at 45mph, even on the front hang point hole.

    As Arielarts has said, examine the battens against the profile sheet (that your friend should have got when he bought the plane) to see if there has been any flattening. On the XL the front centre batten is important for climb performance. When that one goes flat you'll find that the plane won't climb as readily. After ten hours of use your friend will probably find that the front centre batten has lost some of its profile. There's not much you can do about this other than reprofiling it every 5 hours or so, but if I remember there might just be enough room in the batten pocket to sneak in another batten. If your friend can get hold of another front centre batten then try to fit both of them into the pocket. If there's enough room then the extra strength of having two battens in there will help to keep the profile correct.

    If your friend's XL is SSDR then he could get a much stronger front centre batten made up out of thicker walled ally tubing. Also, I was told a long time ago, by someone who knew much more about XL's than me, that at one time Pegasus (as they were then) made thicker battens for the export version of the XL wing than were used on the domestic ones. So see if you can contact the P+M factory to find out if they've still got any lying around on a shelf somewhere. You never know, there might be a pristine set of them just waiting to be bought and used.

    Best of luck!


  5. #4
    Captain Randombloke's Avatar
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    I'm with Aerialarts on this, pay special attention to the outboard battens, when they flatten, they adversely affect trim speed IMV.
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"


  6. #5
    Co-Pilot BobH's Avatar
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    Randombloke,

    I agree, but you have to be very careful about the outboard battens. By all means make sure they are correctly profiled, but don't be tempted to add any more camber than shown on the sheet. I was told about this as a tuning trick, and I was tempted to do that with my wing, and as I still have an XL I could do it even now, but when profiled to the batten sheet the wing is well balanced, and I was told by my old inspector not to mess with the profile to try and get more speed out of it.

    It would be better to replace the wing with a Q wing, as this fits straight on to the XL trike anyway, and is designed for a 55mph cruise speed. The only modification needed on the monopole is to drill out the hang bolt hole from 3/8" to 10mm. The difference between the sizes is almost negligable, but necessary for the Q hang bolt. I did that on mine, then in order to be able to fly it with the XL wing as well, I drilled the holes on the hang bracket of the XL wing out to 10mm, and use a 10mm bolt for both wings. Alternatively the bloke with the XL could replace the standard XL monopole with a Q monopole. It's 1" longer than the standard XL monopole, but has a better bearing at the top, and then just drill out the hang bracket holes on the XL wing to 10mm.

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  8. #6
    Co-Pilot Wexfordair's Avatar
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    Maybe the battens have lost some shape but the wing has only just been assembled and the sail is brand new.
    I did wonder about using the trimming technique of adding reflex into the 3rd batten but do it to both wings?


  9. #7
    Captain Randombloke's Avatar
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    Quote Originally Posted by Wexfordair View Post
    Maybe the battens have lost some shape but the wing has only just been assembled and the sail is brand new.
    I did wonder about using the trimming technique of adding reflex into the 3rd batten but do it to both wings?
    Despite what other posters have said I am only advocating making the battens reflect the supplied profile accurately. Do not step outside this unless you are an expert, in which case you would not need my advice and could therefore ignore me.

    The other thing to check is that the hose supplying the ASI has not split, and that nothing in the ASI chain is leading to an incorrectly measured air speed?
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"


  10. #8
    Co-Pilot BobH's Avatar
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    Good points Randombloke. As for the third batten, adding or removing reflex to that one is normally the way to tune out a turn in an XL wing, and they are prone to turning a different way every time you rig the wing. I know I nearly always had to make some slight adjustment to the outer battens in order to get the wing to fly straight every time I flew the thing.


  11. #9
    Co-Pilot Wexfordair's Avatar
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    Good points all!
    He is grounded at the moment with a bad shoulder so we have some time to give it plenty of looking at!
    I had heard of the heavier battens and they seem to be a great idea, but never approved as a mod


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