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Thread: Anyone running out of nose up trim on final?

  1. #1

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    Default Anyone running out of nose up trim on final?

    Hey guys. I have a new (to me) Model 4 with an electric trim tab.

    I find myself running out of nose up trim with higher flap settings on final. Seems to be more than normal back pressure on final to maintain slope with full up trim. Seems to happen with all load configurations.

    Anyone else have this issue? Any fixes?

    thanks!
    Last edited by SwiftFox; 05-26-2017 at 10:18 AM.

  2. #2
    Administrator DesertFox4's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    Try your approach with less or no flaps. The flaps give you a nose down pitch result with little drag increase so if you don't need that to clear obsticles on the approach end of your runway, try it without the flaps. Should leave you ample trim. I seldom use flaps on my model four. Slips I use frequently.
    Flaps usually used for a shorter take offs.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  3. #3

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    Default Re: Anyone running out of nose up trim on final?

    Thanks for the reply DesertFox!

    You're absolutely right. I've been experimenting with flapless landings and it is much better. No trim issues. Also much more efficient!

    I've been wanting to use the flaps for the additional lift for increased short field (hopefully off airport) performance. From what I've seen so far, at the same touchdown attitude, I can get 20kts slower with near full flaps and relatively high power. Just a lot more stick pressure.

    Also, I'll be getting soft bush wheels and want to minimize touchdown wear on paved strips with the lower landing speeds. Might just have to deal with it then..

    I was curious if a trim tab extension would help a bit in this scenario? Has that been done?

    Thanks again
    Jeremy
    Calgary, AB
    Kitfox 4
    912ULS
    GT constant speed comp prop
    Tailwheel

  4. #4
    Senior Member HighWing's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    Elevator Authority has been an often talked about issue with the Model IV and earlier. Most have used a gap seal between the Horizontal Stabilizer and Elevator. Your post suggests you have adequate elevator authority, but lose trim ability. I suspect it is elevator authority that is the real problem. I seem to recall at one of the Desert Fox Fly-ins in the old days seeing Steve's (Desert Fox 4's) trim tab was about half the length - along the trailing edge - of the factory Speedster tab and he mentioned it was adequate. Am I correct on this one?
    Lowell Fitt
    Goodyear, AZ


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  5. #5
    Jch's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    I can fully trim one notch of flaps, but I can't trim for full flaps on my SS7. I wanted to ask the same question.
    Flying SS7
    Rotax 912 ULS
    Whirlwind 3-Blade

  6. #6
    Administrator DesertFox4's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    Lowell, my trim tab is about half regular size.
    Another point I forgot to mention was I have the larger elevator also.


    DesertFox4
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  7. #7
    Senior Member jiott's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    I reset my electric trim range a little different than the manual states. I set it so I get full nose up trim at the very bottom of the slots at the leading edge of the horizontal stab. This gives me full trim at half flaps, but almost but not quite full trim at full flaps. Full flaps still requires stick back pressure but the force is reduced. I have never come close to running out of nose down trim. I have toyed with the idea of cutting the slots to get even more nose up trim-has anyone done this?
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #8
    Senior Member HighWing's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    Quote Originally Posted by DesertFox4 View Post
    Lowell, my trim tab is about half regular size.
    Another point I forgot to mention was I have the larger elevator also.
    I guess that validates my theory that it is elevator authority rather than trim authority. Thanks for validating at least part of this old guys memory. On my IV, I spent a lot of time closing the hinge gap with fiberglass fairings and have had no issues with trim - factory elevator.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  9. #9

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    Default Re: Anyone running out of nose up trim on final?

    Quote Originally Posted by jiott View Post
    I reset my electric trim range a little different than the manual states. I set it so I get full nose up trim at the very bottom of the slots at the leading edge of the horizontal stab. This gives me full trim at half flaps, but almost but not quite full trim at full flaps. Full flaps still requires stick back pressure but the force is reduced. I have never come close to running out of nose down trim. I have toyed with the idea of cutting the slots to get even more nose up trim-has anyone done this?
    I think I might try this. I've never used more that 3/4 nose down trim. Even in a high power decent. Whatever helps right?
    Jeremy
    Calgary, AB
    Kitfox 4
    912ULS
    GT constant speed comp prop
    Tailwheel

  10. #10
    Senior Member cubtractor's Avatar
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    Default Re: Anyone running out of nose up trim on final?

    I don't use any more than about 12 or 15 degrees flaps. On mine, there is no change in stall speed between that and full 25 degrees of flaps, and very little increase in drag with full flaps, and it alleviates the need for all the trim. I have installed gap seals on the elevator and VG's on the underside of the horizontal stab. The combination of the seals and VG's made a world of difference. I use a pressure relief type of trim vs. a trim tab and can relieve all the control pressure. At 50-55 mph it sinks like a rock.
    Mike Bentley
    Model IV-1200
    Jabiru 2200A #438
    Rotec Aerosport LCH Heads
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