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Thread: junkers flaps info after 1930's?

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    junkers flaps info after 1930's?

    I've been looking around for info on Junkers flaps, but everything I've found so far is from the 1930's and isn't necessarily all that precise. Plus I'm thinking with CFD and all, there might be foils especially designed for it. For Part 103, they are flaps that the will be recognised as such, maybe making things look a bit less high tech. And if I read, was it Hoerner's?, correctly, less drag for the additional lift than some other types. Seems like they might be simpler to build than some of the other flaps that can get the same sort of high Cl, plus allow a bit of negative when trying to escape sink.

    Anyway, anyone seen more recent info about them.

    BTW, has anyone seen info about two part symmetrical airfoils, which are sometimes used for sailboats. One of my persistent fantasies is to build the highest pointing, fastest Footie. http://www.sailfootyuk.com/

    Thanks,

    Lincoln

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by lr27 View Post
    BTW, has anyone seen info about two part symmetrical airfoils, which are sometimes used for sailboats. One of my persistent fantasies is to build the highest pointing, fastest Footie. http://www.sailfootyuk.com/

    Thanks,

    Lincoln
    This wing sail did well:

    http://ultraviolet.org/scottmetze/Ru...088/index.html


    BJC

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by lr27 View Post
    I've been looking around for info on Junkers flaps, but everything I've found so far is from the 1930's and isn't necessarily all that precise.
    Lincoln
    I gather you've already looked at the NACA archive... you're right, from the 1930s -- see reports #541, #614, #573, #604 and #603 if you haven't already... mostly build around the 23012 wing as I recall. Old, but plenty precise enough for anything I'd be able to build... I'd have to dig out my Hoerners, don't recall what he might have said about non-attached flaps...

    See: http://naca.central.cranfield.ac.uk/

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by lr27 View Post
    I've been looking around for info on Junkers flaps, but everything I've found so far is from the 1930's and isn't necessarily all that precise. Plus I'm thinking with CFD and all, there might be foils especially designed for it. For Part 103, they are flaps that the will be recognised as such, maybe making things look a bit less high tech. And if I read, was it Hoerner's?, correctly, less drag for the additional lift than some other types. Seems like they might be simpler to build than some of the other flaps that can get the same sort of high Cl, plus allow a bit of negative when trying to escape sink.

    Anyway, anyone seen more recent info about them.

    BTW, has anyone seen info about two part symmetrical airfoils, which are sometimes used for sailboats. One of my persistent fantasies is to build the highest pointing, fastest Footie. http://www.sailfootyuk.com/

    Thanks,

    Lincoln
    Possibly because external airfoil flaps -- like Junkers and Youngman flaps -- are not seen to be sufficiently superior to Fowler flaps. Of course, there is a lot of information on multi-element airfoils, with cascades being the most extreme type.

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by Swampyankee View Post
    Possibly because external airfoil flaps -- like Junkers and Youngman flaps -- are not seen to be sufficiently superior to Fowler flaps.
    But Fowler flaps make really lousy ailerons! For ultralights and flying wings the Junkers are a pretty good trade.
    Conventional wisdom and practices yield conventional results. If that is good enough for you:
    Problem solved.

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by lr27 View Post
    BTW, has anyone seen info about two part symmetrical airfoils, which are sometimes used for sailboats. One of my persistent fantasies is to build the highest pointing, fastest Footie. http://www.sailfootyuk.com/

    Thanks,

    Lincoln
    This may help with the Footie. http://www.sailwings.net/article.html

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    Re: junkers flaps info after 1930's?

    Thanks. I've seen various sailing things with self-trimming wing sails like that, but what I had in mind was keeping the two parts very close and using the rear part like a slotted flap which could be put on one side or the other depending on whether it was port or starboard. This would provide a much higher lift coefficient.

    Here's a rig using both ideas:
    http://www.lusas.com/case/composite/...sail_yacht.jpg

    Of course, on a footie the Reynolds numbers would be just a bit lower.

    Anyway, someone somewhere knows a lot about this stuff.
    Last edited by lr27; January 1st, 2017 at 09:33 PM.

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    Re: junkers flaps info after 1930's?

    Found a list of references in a paper. The paper itself wasn't so hot.
    NASA:
    CR-198580
    CP-2487
    TM-85788
    CP-2413
    TP-1865
    ---------
    Multiple Element Airfoil Optimized for Maximum Lift Coefficient, AIAA Journal Vol 10, December 1972

    High Lift Aerodynamics, Journal of Aircraft Vol 2 No 6 1975

    However, I suspect most of these will be only tangentially related.

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    Re: junkers flaps info after 1930's?

    For sailing, have you discovered the Amateur Yacht Research Society? http://ayrs.org They've had numerous unusual sails over the years.

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    Re: junkers flaps info after 1930's?

    Quote Originally Posted by Hot Wings View Post
    But Fowler flaps make really lousy ailerons! For ultralights and flying wings the Junkers are a pretty good trade.
    Well, there is that.

    If I remember, one of the problems with external airfoil flaps (Junkers are one variety) is that there is a lot of adverse yaw. The other problems, such as high drag and ice accumulation aren't problems for low-speed, fair-weather only aircraft.

    Look up information on multi-element airfoils. Junkers (and Fairey-Youngman) flaps are a special case of those.

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    Re: junkers flaps info after 1930's?

    High drag is a problem in the case I'm looking at. However, the numbers I've seen from the thirties don't look so bad. I think the drag coefficient with a slightly negative flap was something like 0.01, but the chart was hard to read.

    However, I ran into a paper* on a two element laminar flow setup with fixed positions. I'm not sure I believe the polar, but it maxed out at a Cl of something like 2.7, as I recall, and had Cd in the neighborhood of 0.01 between Cl of less than zero up to about 1!

    Oops, that was the CFD result, experiment was somewhat lower. Haven't pored over it enough to figure out if it's really better, and not sure I can trust it anyway.

    *A thesis by a Mr. Steen at Texas A&M called A TWO ELEMENT LAMINAR FLOW AIRFOIL
    OPTIMIZED FOR CRUISE

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