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Thread: 7ss vs 7 Speedster differences

  1. #11
    Senior Member HighWing's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    Quote Originally Posted by Dusty View Post
    The speedster appears to have no dihedral which would be hard to change.I'm curious to why the difference and if anyone has flown with both options good or bad or indifferent?
    I have a buddy that used to have a Model IV with dihedral that he said reminded him of a diving pigeon. He hated the look. When I was building my first IV I asked the factory the difference in performance since the early IV Speedster also had no dihedral. I was told - no difference. I reduced the dihedral, but did not eliminate it. Then recently I read an article in Kitplanes Magazine discussing "Dihedral Effect". Essentially, Wing dihedral is critical in low wing airplanes, but not so much in high wing airplanes. With a high wing a side slip will create high pressure under the up-wind wing due to the fuselage being below the wing and low pressure under the down-wind wing for the same reason resulting in a favorable roll tendency. This effect is missing (actually potentially reversed) with a low wing airplane. This necessitating dihedral on low wing airplanes. My first IV had minimal dihedral as I built it from day one. The one I fly now had the wings installed by the first builder and somewhat resembles the diving pigeon. With my two Model IVs, I perceive no difference in handling.
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    Lowell Fitt
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  2. #12
    Super Moderator Av8r3400's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    Lowell, what about speed?

    Was the plane with minimal dihedral any faster?
    Av8r3400
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  3. #13
    Senior Member HighWing's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    The speed of the second airplane even with more fairings, is a bit slower than the first. Not sure the specific reason as there so many factors to consider. I sort of feel, though, it is because of the empty CG first vs. second - explained in the "Zipper Big Bore" thread. I should mention that the second airplane is lighter than t he first by 35 lbs.
    Last edited by HighWing; 12-07-2017 at 02:41 PM.
    Lowell Fitt
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  4. #14
    Senior Member jrevens's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    Quote Originally Posted by HighWing View Post
    The speed of the second airplane even with more fairings, is a bit slower than the first. Not sure the specific reason as there so many factors to consider. ...
    Do you think it might be largely attributable to the landing gear, Lowell?
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  5. #15
    Senior Member HighWing's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    That is a reasonable thought. The cabane gear is dirty despite the gear legs being faired. By coincidence, I am working on the feasibility of wheel pants, or rather the half wheel pants as seen on some Aircoupes. Along with that, a fairing around the brake calipers and gear leg to wheel pant with fairings on all cabane and spring strut tubing. We'll see. Last fall I faired a friend's cabane gear. No word on that because the Avid Mk4 has yet to fly.
    Lowell Fitt
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  6. #16
    Super Moderator Av8r3400's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    My old Kitfox had the faring on the radiator. The Mangy does not. I believe this to be an area of increased drag, too.
    Av8r3400
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  7. #17
    Senior Member av8rps's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    So...if Lowell's old faster airplane weighed 35 lbs more but had a spring gear and no dihedral, verses the slower, later but lighter and better faired out airplane with a cabane gear and dihedral, unless the CG difference is substantial, it's reasonable to think that it is either the gear or the dihedral making it faster. I personally think the no dihedral is more of an advantage for speed.

    I believe the dihedral is the bigger factor because my 912ul Kitfox 4 on amphib floats is faster than many Kitfoxes on wheels. And those 14 ft long 230 lb floats have got to be draggier than any landing gear, right?

    With that said, I still am a firm believer that having more wing underside false ribs is a big factor in whether or not you will have a fast Kitfox or not. Without the extra false ribs at higher speeds the airfoil tries to revert back to the older undercambered airfoil, which is a significantly slower wing than the riblett airfoil.

    I'm pretty confident if you put 4 underside false ribs between each rib, removed the dihedral, and then faired out everything you reasonably could, the landing gear wouldn't have a huge impact unless you went with large bush wheels.

  8. #18
    Senior Member HighWing's Avatar
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    Default Re: 7ss vs 7 Speedster differences

    Lots of good thoughts and good ideas. Yes, Larry, I do think the fairing around the radiator helps. I think of that a lot as well. Another thing not yet mentioned is prop pitch. That is one thing I have not played with with the new airplane. A local guy with the in flight adjustable IVO claims speed performance that I will only be able to match with a significant compromise in climb. Right now I am still in the fairing mode with lots planned. The pictures are early in the half wheel pant project. Right now it is to just see if it is feasible. The mounting will be the real test -- but fun.

    What I call the fairing Liner
    Wheel Pant Liner.jpg
    The original Wheel Pant stretched to fit the larger tire diameter
    Wheel Pant Stretch.jpg
    Lowell Fitt
    Goodyear, AZ


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