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The Craziest airfoil shapes!

Old 03-21-2015, 03:49 AM
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theapplepi3.14
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Default The Craziest airfoil shapes!

Okay. So there I was harmlessly looking through the airfoil database. Then I started increasing the minimum required L/D ratio for the results. I started with a reasonable 60. Then 70. Then 90. Then 100. Then 130. Then 200. Then 300. Then 400. Then 500!!!!!!!! That is right! the GOE 462 AIRFOIL has a max L/D of 596!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Not only that, it also has crazy characteristics like multiple stall and stall recovery points on the Cl/theta curve! It stalls at 3,5, and 9 degrees and I assume it has another stall point beyond the graph! That means that if you ever stall the plane you could either try to level the plane out, OR you could pull back on the stick!
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Old 03-21-2015, 04:57 AM
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Wildflyer
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Sounds like a strange airfoil. Yet it looks like a real bird so it might work ok. but I would hate to build a wing with it.
http://airfoiltools.com/airfoil/deta...foil=goe462-il
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Old 03-21-2015, 05:42 AM
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Looks a lot like an airfoil used in FF models back in the 1930's
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Old 03-21-2015, 06:01 AM
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All I know is it would make an awesome glider!

How do you create your own airfoil from data points in XFOIL?
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Old 03-21-2015, 11:50 AM
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JetPlaneFlyer
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Originally Posted by theapplepi3.14 View Post
All I know is it would make an awesome glider!
It would actually make a trully terrible glider, you would be lucky if it flew at all.

If you are getting unbelievable numbers out of any calculation then the calculation is usually wrong. The GEO 462 is a VERY high camber airfoil that might work over a very limited speed range for full size planes but would be hopeless for any model. it actually has an appallingly bad l/d ratio and due to the extreme camber it stalls at about 2.5 degree AoA, even at Re=100k .


I couldn't get it to converge on low Re numbers like you would see in typical model gliders so i had to use some smoothing and increase Re to 100k to get it to run at all. Results are attached (it sucks!). I've used a genuine sailplane airfoil for comparison. GEO is black line, Drella sailplane airfoil is red line. I've also put in a Andrukov (blue line) which is an airfoil from a freeflight duration model, which is great but has limited speed range so not so good for multi task RC use.
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Old 03-21-2015, 03:16 PM
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theapplepi3.14
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I said it would make an awesome glider under the assumption that it has a 596 L/D airfoil. Now that it is up for debate I retract my statement.

I am really bad at using XFoil. Anyone interested in giving me any tips? particularly on how to create my own airfoils for XFoil...

Thanks
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Old 03-21-2015, 03:18 PM
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This one is fun,,,,
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Old 03-21-2015, 03:19 PM
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Is that the viewing angle or is the wing quite curved?
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Old 03-21-2015, 03:54 PM
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fhhuber
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Amazing how an airfoil that couldn't work for models is in the group (variations on the large under-chamber with thick section forward and thin aft of the 30% chord line) that was winning all the FF contests for many years.
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Old 03-21-2015, 04:03 PM
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Looks a lot like the Jedelski airfoils tried and tested in the 70's and prior. The Southwestern Honker series out of New Mexico used it as did the kit designed by Joe Wagner of VECO, the Dakota bipe. (Plans for each are on Outerzone)

Here is link to an article discussing and a diagram of how to build one from balsa:

http://www.djaerotech.com/dj_askjd/d.../jedelsky.html
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Old 03-21-2015, 04:54 PM
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"Don't drink and derive. Alcohol and calculus don't mix."

Oh my god you are a GOD! That has been one of my favorite puns of all time(The second part of it is new to me though. Nice job man!)!
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Old 03-21-2015, 05:58 PM
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Originally Posted by theapplepi3.14 View Post
Is that the viewing angle or is the wing quite curved?
its complicated and fun,, bubsteve
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Old 03-21-2015, 06:49 PM
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Why isn't there a pitching moment upwards? All flying wings I know of have to have a special shape to prevent a moment force, but it looks like yours doesn't have one. Is the plane unstable?
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Old 03-21-2015, 07:10 PM
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Take a look at this site. http://www.mh-aerotools.de/airfoils/flywing1.htm
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Old 03-21-2015, 07:17 PM
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Originally Posted by theapplepi3.14 View Post
All I know is it would make an awesome glider!

How do you create your own airfoil from data points in XFOIL?

Most CAD programs have a Script function...take that data, put it the correct script format and it'll draw the airfoil right into your CAD program....


or...you can just trace it out using those data points in any CAD program....hard way but it does work...

Last edited by Brner; 03-21-2015 at 07:19 PM. Reason: added info
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Old 03-21-2015, 07:30 PM
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Originally Posted by stevecooper View Post
its complicated and fun,, bubsteve
Unless the photo is deceptive that thing wouldnt fly without the elevons being trimmed upward (reflexed)... If they were reflexed then it would fly fine i'm sure but the photo makes it look like they are slightly down following the camber of the airfoil.
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Old 03-21-2015, 07:37 PM
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Originally Posted by fhhuber View Post
Amazing how an airfoil that couldn't work for models is in the group (variations on the large under-chamber with thick section forward and thin aft of the 30% chord line) that was winning all the FF contests for many years.
Aerodynamically those airfoil are nothing like the GOE 462... The freeflight airfoils you refer to have a camber around 6% or so, the Andrukov I did the simulation on is an example of one such freeflight airfoil taken from a rubber power duration model. The GOE has a camber of over 13% !.. there is no comparison.

The 'problem' is that at low Reynolds numbers the airflow cant stay attached to the excessively curved upper surface of very highly cambered airfoils. Anything much over 6 or 7% and the performance starts to deteriorate. By 13% camber the airfoil will be stalled all the time at low Re which is why this airfoil would be hopeless.
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Old 03-21-2015, 09:06 PM
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But on a large aircraft...
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Old 03-21-2015, 09:11 PM
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Originally Posted by theapplepi3.14 View Post
But on a large aircraft...
Yep on a full size airplane it would work much better but only over a very limited operating envelope. That's why you don't find this type of airfoil actually in use on full size (or any other) airplane, except maybe one designed for a very sharply focussed and unusual task.

l/d isn't where it would excell anyway. If you look at the planes that have the very lest l/d ratios of all (high performance sailplanes) they have airfoils that have no resemblance at all to the GOE 462.
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Old 03-21-2015, 10:52 PM
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The wing is unusual because very close to the max lift on the l/theta curve drag drops like crazy for a short time so it reaches the high L/D but other than it is just a bad high lifting type wing. Maybe a stationary fan blade?
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