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Clark Y is the name of a particular airfoil profile, widely used in general purpose aircraft designs, and much studied in aerodynamics over the years. The profile was designed in 1922 by Virginius E. Clark using thickness distribution of the German-developed Goettingen 398 airfoil. The airfoil has a thickness of 11.7 percent and is flat on the lower surface aft of 30 percent of chord. The flat bottom simplifies angle measurements on propellers, and makes for easy construction of wings.
For many applications the Clark Y has been an adequate airfoil section; it gives reasonable overall performance in respect of its lift-to-drag ratio, and has gentle and relatively benign stall characteristics. The flat lower surface is not optimal from an aerodynamic perspective, and it is rarely used in modern designs.
thumb|right|200px|Clark YH wingroot of a [[Yakovlev Yak-18T|Yak-18T]]
The Clark YH airfoil is similar but with a reflexed (turned up) trailing edge producing a more positive pitching moment reducing the horizontal tail load required to trim an aircraft.
Applications
Aircraft
The Lockheed Vega and Spirit of St. Louis are two of the better known aircraft using the Clark Y profile, while the Ilyushin Il-2 and Hawker Hurricane are examples of mass-produced users of the Clark YH.
The Northrop Tacit Blue stealth technology demonstrator aircraft also used a Clark Y.
Cars
An inverted Clark Y airfoil was used on the spoilers of the Dodge Charger Daytona and Plymouth Superbird.
Aircraft
Some of the better-known aircraft that use the Clark Y and YH:
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