Clark Y

This airfoil dates back to 1924 and in QFI 28 (August/September 1997) Martin Simons wrote about a comparison with the E 193 and concluded that Clark Y was a bit better at floating than the E 193 but not quite as fast due to the thickness, and that nothing much had happened for modeling airfoils between 1924 and 1975. If you compare Michael Selig's polar of Clark Y to the Aquila's polar, the Clark Y polar shows a fraction less of the Aquila's lifting capabilities at low speed but it is far superior at higher speeds. What does this mean in practice? It means that an Aquilla equipped glider and an Clark Y equipped glider can fly at about the same slow speed with the same sinking speed (= same dead air time), and that the Clark Y equipped glider will out glide the Aquila glider when speeded up. None of them will ever be sprinters; for real sprint you need thinner and less cambered airfoils (and tons of lead) but if the choice is between Aquilla and Clark Y, I wouldn’t hesitate to go for the Clark Y. Neither did the Ryan factory that produced “Spirit of St. Louis” with which Charles Lindberg made the first ever solo non stop transatlantic flight in 1927 – this modified “Ryan NYP” had the airfoil Clark Y in the wing! Beware that it wasn’t the airfoil that was the modification; it was the extra gallons of fuel.

And remember: This is the real Clark Y – Clark Y for men. There is no such thing as a “flat-bottomed Clark-Y”. If you ever hear anybody say “flat-bottomed Clark-Y”, you now know they are pufters and that they are talking of a home made Aquila type airfoil – i.e. a flat bottom and a curved top – you instantly know that they are aerodynamic ignorants compared to yourself and their aerodynamic wisdom is what you read on a box of cereals every morning. The Clark Y is a real airfoil with curves like a lady and just straight enough to be a joy to handle on a flat table.

Imagine if the Dassel had been build with the Clark Y instead of E 193 and still won numerous contests around 1980? Martin Simons wrote about a comparison between E 193 and Clark Y here in QFI and surprisingly they both have low drag at the same lifting coefficient but the Clark Y had lower drag at Cl=1,0, a better Cl-max = better high lift capability (around 1,25) and a bit higher drag at low Ca.-values. This means that a Clark Y equipped Dassel could have been flown almost as fast in straight line and that the turning and launching would have been better.

Clark Y is a whole lot faster than the Aquila and with the same dead air time and at the same time the Clark Y just as almost as fast as an Eppler 193 but with better launch and better hang time / dead air time.

Here you can find more about this wonderfull airfoil: http://www.aerodesign.de/profile/profile_n.htm

Hartmut Siegmann's advice is to thin the Clark Y to 10 or 9% to get rid of some of the drag, but without sacrificing too much lift. Also see my 2-meter beginners glider with a potential - Simplex 2M.