Clark-Y airfoil

Flat bottom, blunt nose, high lift, easy to build as the ribs lay flat on the table.

Don

The Clark Y, while being mostly flatbottomed, does have a somewhat rounded entry...

The story goes, Clark drew it up when he had a few too many.... The next day, he didn't know when or Y. The airfoil tested in the wind-tunnel to be about the cleanest in 1928, giving the best lift-to-drag ratio for wings of aspect ratio = 6, and having a very forgiving stall. Not only that, it was very simple to construct.

Many airfoils were designed to capture its characteristics, notebly the NACA 4412 and I think the Goettingen 385.

-Fritz

Whoops, I meant 1922, not 1928, A second source said that the Goettengen airfoil was invented during the same period as the Clark, so it isn't clear whotook it from who.

-Fritz

Thanks to you all for gettig back to me. Interesting stuff. Jeff

Also, maybe you have already [or maybe it is what the Waco used but I wouldn't know] but I would verify that it really does have a true Clark Y airfoil. A real Clark Y is only flat from the 25% chord point rearwards. There is a specific set of coordinates for it like any other airfoil. So many times I have seen people refer to an airfoil as a Clark Y when it looks more like it was created by drawing a straight line, a LE radius and some french curve profile on the top. I've even heard the Gentle Lady airfoil referred to as a Clark Y before as an example. Not quite.

I have built a few sport sailplanes and power models using a properly designed Clark Y and it is truly a very well mannered airfoil with a gentle stall. I don't mean to suggest that there are not better airfoils in existence now for many/most applications but the Clark Y is still a good choice for many sport aircraft. Plus it sits nicely on the building board. Dave Thornburg endorses its use for sport sailplanes in his book.

Mike D.

--------------------------------------------------------------------- "Are you still wasting your time with spam?... There is a solution!"

Protected by GIANT Company's Spam Inspector The most powerful anti-spam software available.

That big leading edge radius is what tames the stall. Sharpnosed airfoils, whatever the rest of the airfoil looks like, will have abrupt and unforgiving stall behaviors. Cessna started using "drooped" leading edges around 1973 or 1974 on their light airplanes; the droop was necessary to increase the radius and improve low-speed performance. We have both the old-style and new 172s, and there is considerable difference in handling. Makers of STOL kits for various airplanes use the same trick. Some of the models I've seen have really ragged or pointy leading edges, and they must be a stinker to fly. Increasing radius does wonders, and doesn't increase drag noticeably.

Dan

Just think....... that's the typical airfoil on nearly every 'basic trainer' offered today !

David

Actually, such flatbottomed airfoils are rarely seen anymore. They're too slow, and people want to go fast. The Maule has a relatively highly cambered airfoil, IIRC, as does the Citabria and a few homebuilts, but most, like the 172's, are nothing like the Clark Y. It really isn't necessary to use a fat, flatbottomed wing to get low stall speeds if flaps are available. Those old airfoils were more popular before more powerful engines were widely available to haul around the extra weight of flap mechanisms.

Dan

How many basic trainers really use a Clark Y airfoil, versus a straight line with an LE radius and some curve on top? The Clark Y is only flat from 25% back and is not really overly thick at 11.72%. The Kadet airfoil for example sure ain't a Clark Y. The Clark Y is, in colloquial terminology, a "semi symettrical" airfoil with 3.56% camber.

Mike D.

I'll add a little more specificity here and say that my favorite airfoils for virtually anything I design are the NACA2412 and NACA2415. The 2415, especially, is a real floater. And with flaps, I personally think it's a much better airfoil than the Clark Y.

MJC

Ok, guys. Go to

and click on Clark Y to see what it looks like. Not a true flatbottom. Compare that with the Clark Z or the USA 35B to see what a more flatbottomed foil looks like. Check out, too, the difference between the P-51's root foil compared to its tip foil. FS light airplanes often use foils like the NACA23012. Lots of interesting stuff on this site.

Dan

IINM, the J3 Cub uses the USA 35B and not a Clark Y as most everyone thinks.

Dan Thompson (AMA 32873, EAA 60974, WB4GUK, GROL) remove POST in address for email

Boy are they ever close! I just overlayed the two. Thickness almost identical, slghtly more camber in the USA35B. I should try adding a hair of camber to the Clark-Y and see how tightly they match...

Interesting.

Mike D.

I found this on the Taylorcraft.org site while searching for "Piper Cub airfoil".:

"What airfoil did Taylorcraft use that has less drag than the Piper Cub? The Taylorcraft uses the NACA 23012 airfoil, it is a semi-symmetrical airfoil. The Taylor Cub wing had a flat bottom surface, which continued to be used by Piper for the J-3."

Another site mentions that the Piper Cub used "NACA designed airfoils". I realize that the above sentence does not say that the Piper Cub used the

23012 airfoil.

What is odd to me though is that if I ring up a NACA 23012 on Compufoil it looks nothing like a light plane airfoil, but a 28012 is not too different from the Clark-Y or USA35B. Is the NACA airfoil generator out of whack or was it not a 23012?

Not that I will lay awake at night about this or anything..

Mike D.

I found a couple of references that confirm the USA35 B comment of yours, Dan.

Mike D.

Seems everyone had a hand in it:

the Cub has also performed duties with the U.S. military. Airfoil designs created by NACA were used for the wing.

Most of the Maule models, including the MT-7-235, use a slightly modified version of the Piper Super Cub airfoil. However, the wing used by Piper had a one-eighth-inch concave lower surface while the Maule wing is flat on the bottom. The North Star's airfoil is the same as the Piper's USA 35B (not the Clark Y I had always supposed it to be),

The USA35B is slightly concave on the lower rear surface. A Piper Cub wing chord with that airfoil seems like it would have a bit more than 1/8" or so, maybe 3/16"-ish.

MD

Hi guys,

I have designed a foam profile parkflyer (a stand-way-far-of Spitfire) from 3-view drawings and used templates from CompuFoil? Clark Y for hot-wire cut foam wings. The plane flies reasonably wel (even inverted) but, I have been thinking of trying a semi-symmetrica airfoil. On the off-chance that you guys are still being notified o new posts and with the expertise I see in this thread, I would like t solicit some recommendations. Only criterion is a thick (slow) airfoi ? the foam also gets some of its strength from the cross-section. The plane is electric. It uses a Hacker B20S with a 4:1 gearbox

3-cell Li-Poly battery pack, a 10 X4.7 propeller and the all-up weigh is 13.8 oz. and the wingspan is 34? Any ideas? Thanks, Jac

- Jack Gros

---------------------------------------------------------------------------------- Posted from the RCGroups.com Discussion Forums Visit us at