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Thread: V.G.'s and stall fences.

  1. #11
    N82HB's Avatar
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    Default Re: V.G.'s and stall fences.

    I am not very happy with the high approach speed of the Kitfox and would love to try and find a solution; it is the only thing less than great about the airplane.
    I have a Model 4 w/ a 912s now, but I previously had a 3 with a 582. I did install VG's on the 3. I used the ones from Landshorter.com and located them a 10% of the chord which is known as a common success point on most airfoils. I did not see anything noticable after the installation. But remember that is a totally different airfoil. I also did not put any on the horizontal and I think that could help.
    On the 4, I tend to run out of elevator at slow speeds. I did try taping the gap as suggested by many forums about many different airplanes, but the problem persisted. I then removed the tape.
    I am very interested in trying a few more things to get this solved. 4 mph would be a great win in my opinion.
    I am once again thinking about snow falling and installing my skis. It could be a good winter for that up here.
    Just letting you know people are reading and listening,
    Kelly

  2. #12
    Senior Member HighWing's Avatar
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    Default Re: V.G.'s and stall fences.

    Kelly,

    I just helped a neighbor attach the empenage on his RV10 before his inspection. He had spacers on the forward attach point of the horizontal stabilizer to srt the incidence and I asked him how he determined the thickness of the spacers. He said it was a factory thing. The factory recommends a starting point, then during the test phase, he is to observe the elevator's relative position to the stabilizer in cruise and if it was not nearly parallel, to change the thickness of the shim to correct the relationship.

    This is rarely if ever discussed on Kitfox so I wonder how many of us are flying and living with horizontal stabilizer issues. I wonder if dropping the leading edge a bit might help in the flare.

    Lowell

  3. #13
    N82HB's Avatar
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    Default Re: V.G.'s and stall fences.

    I'll look at that the next time I am standing at the Kitfox. I hadn' thought about that being adjustable. It was on my Tailwind and I took advantage of that.
    Thanks,
    Kelly

  4. #14
    Senior Member War Eagle's Avatar
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    Default Re: V.G.'s and stall fences.

    I'm not much of a KF historian but I believe that over time, design changes increased the size of the tail feathers (rudder and horizontal) to improve some of the flying characteristics (which included flair behavior etc). I believe that between the model 1 and the model 4 each model saw larger tail feathers. When the model 5 was introduced then it's tail feathers were again modified to help provide improved control. The model 6 has the same set of tail feathers as the 5 but when the model 7 was introduced the motor mounts were lengthened (4 inches I think) to move the cg forward (this allowed higher baggage compartment capability and I guess potentially lighter tail loading) and a larger elavator was added to again improve the flair control. The horizontal on the 7 is the same as on the 5 and 6 (I believe).

    So in theory you can add the larger horizontal from the 7 to the model 5 and 6 and get more elavator authority. The elavator from the 7 does not fit the 4 or earlier models.

    Vg's added to the underside of the horizontal are supposed to to have the effect of increasing the flair authority. I have several model 7s (in tail dragger configuration)that I fly with that have installed vg's on the underside of their horizontal and they reported an improvement in elevator authority.

    I don't personally know anyone that has added vg's to the underside of their model 4 horizontal so I can't say anything about any improvement in their elavator authority but that might be one thing to try and see if it provides more control for you.

  5. #15
    Administrator DesertFox4's Avatar
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    Default Re: V.G.'s and stall fences.

    Kitfox Aircraft LLC has had an enlarged elevator for sale for some time now that fits the 3,4 and Lite Squared models.
    Page 31 of their online parts catalog.
    Part #51018.201 (with out electric trim)

    Part # 51018.301 for those using electric trim.

    Powder coating is optional on both versions.
    I run the last version on my Classic 4 and it has all the flair authority i'll ever need.


    DesertFox4
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    912 ULS Tri-gear


  6. #16
    BigJohn's Avatar
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    Default Re: V.G.'s and stall fences.

    I did more flight testing with the VG's and found that at Gross weight I was unable to fully trim with full Flaperons on, I again listed below along with the Gross Weight #'s. I have since installed the VG's to the underside of the Horizontal Stabalizer as in Pacific NW Aero plans and saw improvement in more rapid recovery at Stall and slightly lower speeds, very solid 1mph with 2mph at times but not consistant, I still have to test at Gross Weight with the Horiz Stab VG's installed. Thus far all the findings are very favorable, I did loose approx 50rpm at max speed that is I am flying at max speed now at what was the same speed at about 50rpm less, not much of a loss at top speed 2-4mph but at normal Cruise speed I lost nothing measurable.

    Short Field Takeoff's and Landing tests at 3800 Density Altitude showed consistant improvements of approx 50-70'. This was accomplished by comparing landing and takeoff distances with two other aircraft (Avid B & Remos) prior to VG's and After wing VG's were Installed. Prior to wing VG's both the Avid and Remos were able to takeoff slightly shorter and land as short or shorter. After the Installation of VG's I was able to consistantly out perform both aircraft on Takeoff and Landing and this was with between 100 & 250lbs more gross weight than the other two. We were seeing consistant takeoff and landing sub 200' at 3800' density altitude at 1100lbs and sub 300' at 1300lbs.

    Gross Weight 1100lbs Stall (Indicated)
    Prior to VG's / After Wing Vg's / Wing & Horiz Vg's
    No Flapperons 46 41 40
    Full Flapperons 42 37 36
    Full flight control with flapperons on at 40mph

    Gross Weight at 1300lb Stall (Indicated)
    No Flapperons 49 45 Still Testing
    Full Flapperons 45 42 With 1st Notch only on, With full flapperons on at this loading full trip could not be achieved.
    Still testing with wing and Horiz vg's at 1300lbs and full flapperons.

    The 1300lb testing was done with very little loading in the baggage area mostly accomplished by Pilot, Co-Pilot weights, fuel and only about 30lbs of weight in the cargo area.

    The 1100 lb testing was done with Pilot, Fuel and about 30lbs in the cargo area.

    Aft loading of CG certianly would change things and allow for more successful trimming, i.e. not running out as soon.

    I know that all of these findings are some what Subjective based on Pilot skill weather variances etc but this is as accurate as I am able to get and I am very happy with the overall results.
    BigJohn
    Kitfox 5 Outback
    Rotax 912ULS With 1622cc Big Torque Zipper Conversion

    Youtube BigJohn655
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  7. #17
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    Default Re: V.G.'s and stall fences.

    Completed the flight testing with Wing and Horiz Stab VG's at 1300lbs with the following results.

    No Flapperons 45mph
    1st Notch 41mph
    Full Flapperons 38mph
    BigJohn
    Kitfox 5 Outback
    Rotax 912ULS With 1622cc Big Torque Zipper Conversion

    Youtube BigJohn655
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  8. #18
    BigJohn's Avatar
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    Default Re: V.G.'s and stall fences.

    Forgot to add photo's to the above posts, So here you go.
    Attached Images Attached Images
    BigJohn
    Kitfox 5 Outback
    Rotax 912ULS With 1622cc Big Torque Zipper Conversion

    Youtube BigJohn655
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  9. #19
    N82HB's Avatar
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    Default Re: V.G.'s and stall fences.

    Using your photos as a guide I installed a set of VG's on a Kitfox IV. The VG's I received from Landshorter.com had a template, but only a suggestion of the fore/aft placement. I placed these like yours and am very happy. This was on a friend's airplane, but I will be doing exactly the same on mine soon.

    I did make one other change. I did not put any VG's on the wing inboard of the fuel caps. This area will typically be boosted by prop blast so the loss should be minimal. My thought was that I did not want to have them in the way while fueling, with cans especially.

    I have not done any full on flight test yet, but I will say I was flying final at speeds I had not seen before. I would guess a solid 5 mph change.

    Thanks for the quality info!
    Kelly

  10. #20
    BigJohn's Avatar
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    Default Re: V.G.'s and stall fences.

    Kelly,

    Glad to hear that you have innitially found some good reduction in approach speeds, I have seen significant improvement in the STOL performance with the VG's and have been able to get full touch to stop landings on dirt in 150' now at DA of 3400' at 1100lbs. also on the measurement on the VG placement I am curious if you are about 5" from the leading edge to the front of the VG on your placement or where they ended up?
    BigJohn
    Kitfox 5 Outback
    Rotax 912ULS With 1622cc Big Torque Zipper Conversion

    Youtube BigJohn655
    https://www.youtube.com/user/BigJohn655

    SPOT LINK:
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