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Thread: Clark Y 20%/9% airfoil data needed.

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    Clark Y 20%/9% airfoil data needed.

    Hi.

    I'm new at the board and I,m needing the X,Y coordinates for a Clark Y airfoil with the following dimensions.

    Wingspan = 10 meters
    Center chord = 2102 mm. with a Clark Y 20% thickness at 30% of chord.
    Wingtip chord = 1002mm. with a Clark Y 9% thickness at 30% of chord.

    The rounded wingtips will be added on the wingtip chord.

    I need the information to plot in the X,Y coordinates into my CAD system, and I have had no luck using some of the free download softwares.

    I hope someone can help me here and thank you in adwance.

    Regards.

    Orla

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    Registered User Himat's Avatar
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    Re: Clark Y 20%/9% airfoil data needed.

    Quote Originally Posted by orla View Post
    Hi.

    I'm new at the board and I,m needing the X,Y coordinates for a Clark Y airfoil with the following dimensions.

    Wingspan = 10 meters
    Center chord = 2102 mm. with a Clark Y 20% thickness at 30% of chord.
    Wingtip chord = 1002mm. with a Clark Y 9% thickness at 30% of chord.

    The rounded wingtips will be added on the wingtip chord.

    I need the information to plot in the X,Y coordinates into my CAD system, and I have had no luck using some of the free download softwares.

    I hope someone can help me here and thank you in adwance.

    Regards.

    Orla
    The coordinates for the Clark Y and some others can be found at UIUC Airfoil Data Site
    This coordinates are in a "standard" format to be scaled to the requried size.

    One thing about the Clark Y and a lot of other airfoils. They have a spesified thickness. The Clark Y is something like 13% thick. Scale it to a different thickness and it's no longer a Clark Y airfoil and might have different properties than the original airfoil.

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    Re: Clark Y 20%/9% airfoil data needed.

    Hello Himat.

    I see your point, but at the same time I can find a ClarkYM15 and 18 airfoil where my guess is that 15 and 18 = % thickness. So I was looking for an Clark Y airfoil with a 20% thiskness at eh center and a 9% thickness at the wingtips.

    Orla

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    Registered User SVSUSteve's Avatar
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    Re: Clark Y 20%/9% airfoil data needed.

    I see your point, but at the same time I can find a ClarkYM15 and 18 airfoil where my guess is that 15 and 18 = % thickness. So I was looking for an Clark Y airfoil with a 20% thiskness at eh center and a 9% thickness at the wingtips.
    The point is just don't expect it to act like a Clark Y. Also, 20% is a damn thick wing. What would you need it to be so thick (and likely high drag) for?
    "Unfortunately in science what you believe is irrelevant."- Orion

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    Re: Clark Y 20%/9% airfoil data needed.

    Well, it's the specs. for a Fokker D.XXI 1938 fighter main wing, and yes it was that thick at the center of the wing (positioner under a very wide fuselage at approx 100mm.) as it was supposed to carry 20mm. canons and 12,5Kg. bombs under the wings.

    Orla

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    Registered User Mac790's Avatar
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    Re: Clark Y 20%/9% airfoil data needed.

    Orla, download a free demo version of DesignFoil here DreeseCODE Software, LLC I've just checked mine, and you can modify it to whatever thickness you need. With this software you can directly transfer your foil into Solidworks or Rhino (Personally, I've never tried with Rhino, but with Solidworks it works perfect).

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    Re: Clark Y 20%/9% airfoil data needed.

    Quote Originally Posted by orla View Post
    Well, it's the specs. for a Fokker D.XXI 1938 fighter main wing, and yes it was that thick at the center of the wing (positioner under a very wide fuselage at approx 100mm.) as it was supposed to carry 20mm. canons and 12,5Kg. bombs under the wings.

    Orla
    Ah. That explains it. I figured either you were new to aerodynamics or you were dealing with a design from before they figured out a lot about the structural design of wings and aerodynamics.
    "Unfortunately in science what you believe is irrelevant."- Orion

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    Re: Clark Y 20%/9% airfoil data needed.

    Thanks Seb, that was quite easy, and I can modify the Clark Y airfoil to 20% and 9% thickness. I'm using Cadam so I have to see if I can export/import the airfoil as a DXF file.

    Thanks

    Orla

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    Re: Clark Y 20%/9% airfoil data needed.

    You are right on both accounts SVSUSteve

    Orla

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    Re: Clark Y 20%/9% airfoil data needed.

    Even without software, you can just take the standard Clark Y coordinates and multiply the v-coordinates by the thickness proportion (20/12 and 9/12 or whatever the exact Clark Y thickness is... it's close to 12).

    A close approximation would also be to use the NACA 2409 and 2420 as the NACA 4 digit airfoils were based on the Clark Y thickness distribution (the 2412 is very close to the Clark Y). I don't know if the camber line is the same, though.

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    Re: Clark Y 20%/9% airfoil data needed.

    Okay, if it is 5 meters half span : how many ribs do you need on it?
    "Do what you can, with what you have, where you are"

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    Re: Clark Y 20%/9% airfoil data needed.

    Rib spacing depends upon wing loading, dive speed, and what the skins are. The higher the wing loading and dive speed, the closer they gotta be. And the stiffer the wing skin, the further apart the ribs can be. And then you have not even said what the skins are. Options range from all fabric to plywood D-cell plus fabric, to all plywood, to metal, to fiberglass/foam sandwich, which can actually get to zero internal ribs.

    Then after you tell us all of this stuff, you have to hope either there is someone who knows this or is willing to give away design services for free...

    Billski

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    Re: Clark Y 20%/9% airfoil data needed.

    Quote Originally Posted by SVSUSteve View Post
    The point is just don't expect it to act like a Clark Y. Also, 20% is a damn thick wing. What would you need it to be so thick (and likely high drag) for?
    To get a nice, deep root section to minimize spar weight. For instance, Miles used an NACA 23024 root section tapering to an NACA 23009 tip section on several aircraft, including the Miles M.25 Martinet. Check out The Incomplete Guide to Airfoil Usage to see that 18% thick root sections, just a tad shy of the damn thick 20%, are rather popular for cantilever wings.

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    Re: Clark Y 20%/9% airfoil data needed.

    The B 29 root profile must be over 20% going on photos and likewise many other big aircraft have surprisingly thick wing roots . Which Fokker was it that collapsed the wings in negative bending in a dive (the sesquiplane wing comes dimly to mind ) -at that time the very thin but highly cambered airfoils had at least as much drag as the thick airfoils and cantilever wings that Fokker introduced -in cruise condition . The Fokker trimotor used to first fly the Pacific is being displayed this weekend at Melbourne's Moorrabbin airport in full size replica --it might be one we built in 1982 for a film about Charles Kingsford Smith ("A thousand skies") at Essendon airport --it was a taxying film prop but non flying and used one old radial and two electric motors --anyway the wing was very thick and pretty much a flat bottomed airfoil like clark y (the figures for the Ckark y are in Rice's book on airfoils also )

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    A cautionary note on Clark Y sections

    Scaling the ordinates of the original Clark Y will yield sections which are flat on the bottom from 20% of the chord to the TE. The convenience of the flat bottom is purchased at a price: the thicker the section, the greater the value of the maximum camber (as a percent of chord) occurring at 40% of the chord.

    A wing tapering from a 20% flat-bottomed Clark Y at the root to a 9% flat-bottomed Clark Y at the tip will have camber that is markedly decreasing toward the tip. Skipping a lot of hand waving about aerodynamics, this is not always desirable, which may be the reason for NACA devising a scheme whereby the basic thickness distribution of the Clark Y can be scaled to an arbitrary thickness and combined with a camber line which has been derived by scaling the basic Clark Y camber line to obtain the desired maximum camber percentage. By this process, you can generate Clark Y sections that are not flat on the bottom, and the deviation could go either way (convex along the entire bottom, or concave on the bottom, i.e. "undercambered") at any thickness. The details are given in NACA TN-1016, but suffice it to say here that the Clark YM15 and YM18 in the UIUC database are convex along the entire bottom.

    So the critical question is whether the Fokker D.XXI wing was flat on the bottom at every rib position. If it was, then all sections should be obtained by scaling the original Clark Y.

    However, if the wing was in fact not flat on the bottom at every rib position, then the next critical question becomes: Exactly how does the maximum camber percentage vary along the span? The precise answer will determine whether or not the YM15 and YM18 occur along the span, but finding that answer might present a rather sticky wicket....

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