NACA airfoils

Tantalum

Tantalum

Final Approach
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Why does just about every GA plane use a NACA airfoil?

Seems every "airfoil" entry on Wikipedia, or any other research you do into a plane, is a NACA number

Free? Someone else did the work for you?

The dumb question.. if people always talk about "THAT MOONEY WING :drool:" then why doesn't everyone use NACA 63-215?

Educate me.
 
A few counterexamples: Piper J-3, Waco, Cirrus SR20/SR22, Diamond DA20/DA40/DA62, Christen Eagle, Extra 300, An-2...

But beyond that, I suppose NACA did a really good job.

Edit: Forgot about Maule
 
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Tantalum said:
Why does just about every GA plane use a NACA airfoil?

Seems every "airfoil" entry on Wikipedia, or any other research you do into a plane, is a NACA number
Click to expand...

Guilty! NACA 64.415 ...
 
Tantalum said:
Someone else did the work for you?
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That. Starting in the 1930s NACA set out to do a systematic survey of airfoil shapes on the tax payer's dime, so they developed a huge catalog of airfoils and wind tunnel data. Easy Peasy.
Now days, however, with all the computational fluid dynamics software it is easy to customize an airfoil for a particular application so they are less popular than they used to be.
skier said:
Roncz, Gottingen, Clark Y.
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Gottingen airfoils date back to WW-1. Clark was 1920's IIRC - some of those foils were the "base" designs that NACA worked with. Roncz is pretty modern.
 
If you are seriously interested in airfoils you should read Harry Riblett's book on GA airfoils. Here is a link to an article about him in Kitplanes. https://www.kitplanes.com/the-airfoil-adventures-of-harry-riblett/ it has been several years since I studied his work, so I am commenting based on my memory. Harry concluded the NACA airfoils were never intended to be used as is on flying aircraft, but instead were intended to give performace guidance so that aircraft designers could roll their own airfoils from scratch for each application. He found certain flaws in the various series of airfoils that could be corrected, and set out to correct these flaws and create a true catalog of practical airfoils that can be used in GA aircraft designs. The Ribblet airfoils are supposed to have gentle stall characteristics and maintain all of the pros of the NACA airfoils they are based on. I have often wondered if existing designs could benefit from the reapplication of Riblett airfoils, but this is best applied to a new aircraft built from scratch instead of an existing airplane.
Hope this helps.
 
William Pete Hodges said:
If you are seriously interested in airfoils you should read Harry Riblett's book on GA airfoils. Here is a link to an article about him in Kitplanes. https://www.kitplanes.com/the-airfoil-adventures-of-harry-riblett/ it has been several years since I studied his work, so I am commenting based on my memory. Harry concluded the NACA airfoils were never intended to be used as is on flying aircraft, but instead were intended to give performace guidance so that aircraft designers could roll their own airfoils from scratch for each application. He found certain flaws in the various series of airfoils that could be corrected, and set out to correct these flaws and create a true catalog of practical airfoils that can be used in GA aircraft designs. The Ribblet airfoils are supposed to have gentle stall characteristics and maintain all of the pros of the NACA airfoils they are based on. I have often wondered if existing designs could benefit from the reapplication of Riblett airfoils, but this is best applied to a new aircraft built from scratch instead of an existing airplane.
Hope this helps.
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Hey, this is a great, thanks!
 
William Pete Hodges said:
If you are seriously interested in airfoils you should read Harry Riblett's book on GA airfoils. Here is a link to an article about him in Kitplanes. https://www.kitplanes.com/the-airfoil-adventures-of-harry-riblett/ it has been several years since I studied his work, so I am commenting based on my memory. Harry concluded the NACA airfoils were never intended to be used as is on flying aircraft, but instead were intended to give performace guidance so that aircraft designers could roll their own airfoils from scratch for each application. He found certain flaws in the various series of airfoils that could be corrected, and set out to correct these flaws and create a true catalog of practical airfoils that can be used in GA aircraft designs. The Ribblet airfoils are supposed to have gentle stall characteristics and maintain all of the pros of the NACA airfoils they are based on. I have often wondered if existing designs could benefit from the reapplication of Riblett airfoils, but this is best applied to a new aircraft built from scratch instead of an existing airplane.
Hope this helps.
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Thanks for the recommendation, I will check it out.. was just something I noticed that so many airplanes seem to use a common theme of airfoils.
 
Capt. Geoffrey Thorpe said:
Gottingen airfoils date back to WW-1. Clark was 1920's IIRC - some of those foils were the "base" designs that NACA worked with.
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Right. The NACA engineers observed that the Clark Y and Gottingen 398 (IIRC) performed better than many other airfoils. They created a mathematical model for the thickness distribution of those airfoils, then created a whole series of other airfoils by using that thickness distribution with other thicknesses and camber shapes. They became the NACA 4-digit airfoils. The NACA 2412 is almost exactly the same as the Clark Y.

Later, the 5-digit series was created from mathematical analysis. The 6-series so-called "laminar flow" sections took it even further, with airfoils very high lift/drag ratios, but only in a narrow AOA range.

NACA tested a wide range sections in each series, from razor thin to absurdly thick, with varying cambers. They were not necessarily intended as airfoils for an actual aircraft, they weren't striving to create airfoils with any specific characteristics, instead they were testing a wide range of shapes to expand the general understanding of aerodynamics. But while many of the shapes would perform horribly as an airplane wing, some of them turned out to be pretty good indeed.

People use them because they're "good enough" for most applications and well documented; build an airplane with, say, a 23012 airfoil and you'll be able to predict the flight characteristics with reasonable accuracy even with today's computational capabilities.
 
Dana said:
They created a mathematical model for the thickness distribution of those airfoils
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Which, if you look at the equation, and think about having to come up with it using tables of logarithms (too many digits for a slide rule), it's pretty effing impressive.
 
Capt. Geoffrey Thorpe said:
Which, if you look at the equation, and think about having to come up with it using tables of logarithms (too many digits for a slide rule), it's pretty effing impressive.
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They had computers... in the original meaning of the word, a person whose job it was to do computations.

But yeah, pretty impressive.

Thickness-distribution-equation.png
 
As in all things related to aviation, everything is a compromise. The airfoils and high aspect ratio wings of the Diamond DA20-C1 (airfoil: Wortmann FX 63-137/20 HOAC) and DA40 airplanes are optimized for high lift, low drag and gentle stall characteristics at the cost of top speed. They show a clear lineage to their sailplanes ancestry.

http://airfoiltools.com/airfoil/details?airfoil=fx63137-il
 
For typical low speed aircraft, the precise airfoil shape is surprisingly uncritical. When asked what airfoils were used on his designs, Homer Kolb would give a number... the size of the car tire he used to bend the wing ribs around.
 
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