BMatthews
Posts: 8943
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline
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Dick, I have no doubt at all that many airfoils came off a set of ships curves. But I suspect that like the ones I used to make up either freehand or with french curves to achieve TLAR that some background on shape was also behind the fellow's design. And of course of full sized stuff that airfoil would then be stuck into a wind tunnel to test it. And that testing is the key.
NACA 4 digit series airfoils all come from the misguided idea that math can form a shape that the air likes. The "envelope" they finally came up with in the 00xx shape finally produced a shape that the air happened to like. From there they added camber to get all the various airfoils to suit the tasks and performance was confirmed in the wind tunnels.
Back in your early pattern days the designers did much the same thing. High points and thickness and leading edge radii were adjusted without a care for the air other than in COMPARISON TO THE LAST MODEL in order to enhance one aspect or another. Now there's certainly nothing wrong with iterative research. Mother nature has done it for millenia and we are the result. And as the flight task changed we found the airfoils needed to change along with them. Hence we find that, like a butterfly or bumble bee, we are down to the flat foamies now where the reynolds number. wing loading, and thus lift requirement, and, just as importantly, the flight tasks are such that flat plate airfoils work very well. More interative research that finally produced a model that flies in a particular manner the way the designer wants.
But I would never think of putting a flat plate on a pylon racer and I'm sure neither would you. In the straights it would work nice with a little leading edge shaping and trailing edge taper but in the high G turns the extra shape of the more typical airfoil for that style of plane will result in the higher lift with reasonable drag for that task.
Note I didn't say "proper airfoil". As you've pointed out flat foils are valid and quite proper. It's just that for so long a flat plate has been used to demonstrate all the "bad" things that "proper" airfoils can avoid. The difference now being that the flat foamies are putting those "bad" charactaristics to use and turning "problems" into "advantages". It's funny but a perfect example of this same iterative development. Look at the stick style fun fly models of some 10 to 15 years ago that invariably had those really thick 25 to 20% airfoils. Somewhere along the way along the way some designers went with ever thinner airfoils until someone decided "we may as well just make it a flat plate". Either that or someone out there that was REALLY lazy side stepped the process and produced a mutant that jumped directly to the flat plate. I would not be surprised if the introduction of Depron had a lot to do with that possible mutant formation. A mutant that obviously survived and flourished as it does just what so many flyers want it to do.
The funny thing is that if you think about it the flat plates are not really flat plates. With the size of the control surface portions they are actually more of a "very thin variable camber" airfoil with a V shaped camber line. Only at specific moments do they happen by accident to be running with a 0% camber.
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Bruce-
Proudly wasting balsa since 1965.
Free Flighters go that extra mile........
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My knowledge of airfoils. - 
