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Old Oct 14, 2012, 03:58 AM
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Are you hot wire cutting the wings?.. If not then realistically you will be limited on what airfoils you can use. Also most high performance sailplane airfoils have razor this trailing edges that couldn't be done, or at least wouldn't last long in 'plain' foam.
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Old Oct 14, 2012, 04:11 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by HELModels View Post
I was hoping one of you might be able to run a sequence on 4 different airfoils, RAF32, Clark Y, Selig 4061, NACA 4508. The version of Clark Y I have gives crazy results and Xfoil's pplot isnt as good as profili.
Sorry, I forgot about this. here's the runs. At this low re number there is some 'funny stuff' going on.
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Old Oct 14, 2012, 09:23 AM
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Can somebody show me what a NACA 3306 looks like?
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Old Oct 14, 2012, 09:46 AM
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Jetplane thanks for running those! The Clark Y was giving me trouble.

Here's a NACA 3306. Xfoil is free and will give you any NACA 4 digit you can imagine. You just type "naca 3306" and you get a perfect version of it. To see what it looks like, you then type "gdes" and from there you can run polars. If you download it, download the manual too and it will show you all the different commands. It will do stuff that I'll never understand like using the lift distribution to shape an airfoil, pretty amazing.
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Old Oct 14, 2012, 11:30 AM
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I see a real move to the 2400 series of NACA airfoils in models.
2414 seems to be the most common.

In model building, I think that the 2414 is the new Clark Y.
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Old Oct 14, 2012, 11:45 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by wuest3141 View Post
I see a real move to the 2400 series of NACA airfoils in models.
2414 seems to be the most common.

In model building, I think that the 2414 is the new Clark Y.
Maybe for sport power models but you wont find them on small sailplanes like the OP wants to build.
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Old Oct 14, 2012, 03:23 PM
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Quote:
Originally Posted by sraden View Post
Full info:
-Roughly 4 foot wingspan
-constructed of foam (simple insulation board foam)
-not sure about weight, probably 250 grams or so
-mostly looking for smooth, steady, long flight with low stall speed

just looking for 3 different airfoils that i could compare
If you want good performance I think you are going to have to change your construction method - there's a reason foamboard sailplanes aren't common! Of the sections mentioned so far most are just too thin to be constructed this way without reinforcement (carbon strip or balsa spars and sub spars), and getting an accurate profile using this method will be tricky.
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Old Oct 14, 2012, 05:34 PM
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Ok... I will rethink my method.

Xfoil isn't working for me, can someone show me a Clark y, ag 14, and naca 3306 together?
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Old Oct 14, 2012, 06:03 PM
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I just did a comparsion of 4 common airfoils and found one I think would do well, provided it could be built accurately. The parameters defined so far describe a very light and low reynolds glider. If it were my choice, I'd try the S9037.
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Old Oct 14, 2012, 06:17 PM
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Here's Clark Y, AG14 and NACA3306.
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Old Oct 14, 2012, 08:58 PM
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Stupid newbie question here...
in this picture does camber = 3.43% for the Clark Y and camber = 3.00% for the NACA 3306 mean that they have a "greater" camber than the AG 14 (camber =2.10)?
Quote:
Originally Posted by whitecrest View Post
Here's Clark Y, AG14 and NACA3306.
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Old Oct 14, 2012, 09:01 PM
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If Xfoil isnt working, I just found this really cool javafoil that will run in a browser.

http://www.mh-aerotools.de/airfoils/javafoil.htm
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Old Oct 15, 2012, 03:00 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by sraden View Post
Stupid newbie question here...
in this picture does camber = 3.43% for the Clark Y and camber = 3.00% for the NACA 3306 mean that they have a "greater" camber than the AG 14 (camber =2.10)?
Yep, at very low Re you can't use much camber because the slow moving air wont follow the curve and you get separation which leads to loss of lift and lots of drag.
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Old Oct 15, 2012, 05:09 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
Yep, at very low Re you can't use much camber because the slow moving air wont follow the curve and you get separation which leads to loss of lift and lots of drag.
Do these have low Re?
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Old Oct 15, 2012, 09:15 PM
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Re = Reynolds number and that depends on chord of the wing, density of the air, speed. Consider it an effect, with low speed, small model having a low Re and a full scale having a much higher Re.

Like JetPlaneFlyer said, at low Re the effect is the air doesnt want to follow the shape and drag goes way up. The plots that have been posted are at low Reynolds and if you wanted to see what the effect is, you could plot the same airfoil at different Re and see the change in the lift/drag.
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