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Thread: Drag reduction

  1. #1
    Senior Member Delta Whisky's Avatar
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    Default Drag reduction

    It has been said that more speed is available by more power or less drag, or both. I'm intrigued with the drag part of the equation and and am currently at phase II of the process (see my jury strut posting). Phase I was elevator strut fairings and they yielded about 1.5 knots.

    Of course phase II leads to phase III - finding out if a significant drag reduction might be had by fairing the Monster shocks and a bit of the associated bracing. (The unknown: can it offset the interference drag from the close quarters of the undercarriage?) So far I've laid out a 2D concept, Joe kindly created the 3D models and those were shipped off to printing this evening. A public thank you to Joe. Basically I'm planning on mounting ribs to the shocks and skinning with aluminum. The test fit unit makes it appear as if there is at least a small chance of some success.
    Shock aero fairing test fit rib.jpg

    Ain't experimental aircraft more fun?

  2. #2

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    Default Re: Drag reduction

    (Without citing a reference) if I remember correctly from my sailplane days, one of the greatest areas of drag was a 90 degree angle between two planes parallel to the air stream. Think h-stab to v-stab. I donít know exactly how this applies to junctions of tubes but on the gliders it meant a fillet area about as thick as the airfoil at any intersection. All that nonsense is to say that since your fairing ends more than a tube width from the next intersecting tube I donít think the interference drag (if any) will be more than the drag reduction of the fairing. Hiding those struts has to be a good thing. I like it.

  3. #3

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    Default Re: Drag reduction

    Since these gear struts are in the prop circle they see a higher airspeed due to the prop blast. So anything you can do to reduce drag here will pay off.

    A way to spot high drag areas are smashed bugs!

    Building a KF IV Classic

  4. #4
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    Default Re: Drag reduction

    Darrel , I look forward to your drag reduction projects so keep us posted as you proceed. While I realize the kitfox is not made primarily for speed (the Mcbeans kitfox motto "its not how fast, its how fun " comes to mind) there is no reason to not make attempts to make my plane as efficient as possible with some aerodynamic improvements . I started this endeavor during my Series build many years ago with a few mods. Never liked the unfinished look of the grove gear hanging below the fuselage, so I built a one off foam mold and made a fiberglass fairing for this area, for looks and less turbulent airflow ( see pic 1). Next I used airfoil shapes on the lift , jury, and stab struts . I think gap seals are important and the speedster option on the verticle solves this for the rudder and I fabricated a foam one for the horizontal. I also used Jim Ott's idea (great idea Jim) to use brushes to seal the stab trim slot , 2 things accomplished with this mod-clean up the airflow a bit and reduces the cold air on the neck syndrome that the kitfox is noted for in cold climates. Future ideas include fairing the strut to wing intersection- started with the jury struts (pic 2) and the lift struts are next. Found the perfect start for molding this area when I bought a new pair of shoes recently, and when I pulled the cardboard inserts out of them , the homebuilder wheels started turning...... With a little scribing and fitting I should have a nice mold for fiberglass (pic 3). I enjoy these projects on the plane and if I gain a few MPH and a cleaner looking Kitfox I've achieved my goal. Bruce N199CL
    Attached Images Attached Images

  5. #5
    Senior Member Delta Whisky's Avatar
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    Default Re: Drag reduction

    We are thinking alike Bruce. Did you take data and come up with measurable speed improvements that you're willing to share?

  6. #6
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    Default Re: Drag reduction

    Hi Darrel, since most of the stuff I have done was accomplished during my build , I had no baseline to go by. From what I have read , the biggest improvements come from turning round tubes into airfoils, like you are doing with you gearlegs. I suspect that will yield measureable results for sure. Lift struts, jury struts and stab struts are also a great area to streamline. My cruise TAS is 120 MPH at 65 % power on my IO-240 and that seems to be the sweet spot even with my 22" tires. Bruce N199CL
    Last edited by airlina; 01-21-2022 at 03:41 AM.

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