Clark-Y

The Clark-Y profile is probably the best-known and most frequently used wing profile in history. Only profiles from the four-digit NACA series z. B. in aircraft made by Cessna (e.g. NACA 4412) or the NACA 23 series (e.g. NACA 23015). However, the Clark-Y has much better all-round properties, especially with low Re numbers .

history

Spirit of St. Louis with Clark-Y

Virginius E. Clark, Colonel in the US Army , developed a series of wing profiles from Clark-A to Clark-Z in the early 1920s. The Clark-Y is a profile originally developed by Ludwig Prandtl in Göttingen in 1918 , which Clark converted to a straight underside of the profile in 1922. The purpose of this change was to make it easier to put on a protractor to make it easier to carry out investigations into the pitch of propellers . The end result of this modification was a profile which achieved very favorable values for almost all areas of aviation and model making at the time. This fact has not changed to this day and the profile is still up to date despite its hundred-year history.

use

Charles Lindbergh flew across the Atlantic in 1927 with his Clark-Y equipped Spirit of St. Louis . The Lo 100 uses it to do glider aerobatics, including a variety of light aircraft such as B. the Aeronca C-2 used the Clark-Y. It was also used as the outer profile of many gliders from the 1930s. Other known types of aircraft were:

Two Lo 100 in mirror flight

From today's point of view, the profile is a bit out of date, but at the same time very good-natured in the stall, so that it z. B. can be used in trainer models to this day. In addition, the straight underside makes it easier to build up rib surfaces . A version diluted to 10% is still a good choice for everyday use in electric model flying.

Clark-YH

The Clark-YH is a variant with a slight S-beat . The profile (also NACA CYH) was published in June 1926 by George J. Higgins at the NACA. The aim was probably to reduce the zero torque. The profile is identical to the Clark-Y up to 60% of the depth. However, the zero moment is still negative. This profile was used on many combat aircraft of the Second World War, such as:

Clark-YH on a Jak-18T

Clark-YS

There is another dubious variant in which the S-impact has been reinforced so that the moment coefficient is positive. This change, which presumably came from early model circles, can be used in board-only wings, but it does not perform particularly well and, in contrast to the initial profile, is very sensitive to changes in the Reynolds number . The S-beat is quite inharmonious as if the profile had been constructed from a Clark-YH with a negative valve deflection without smoothing the coordinates.

Coordinates from 1928

Clark-Y, 11.7%

Clark-YH, 11.7%

The coordinates refer to the underside of the profile. This system is no longer in use today. Coordinates for the system commonly used today, which is based on a profile chord through the profile nose , can be called up in almost all profile databases. These are mostly "smoothed" variants with more support points. The old coordinates, however, clearly show the straight underside of the profile.

     X        Yo        Yu
     0       3.50      3.50
     1.25    5.45      1.93
     2.5     6.50      1.47
     5       7.90      0.93
     7.5     8.85      0.63
    10       9.60      0.42
    15      10.69      0.15
    20      11.36      0.03
    30      11.70      0.00
    40      11.40      0.00
    50      10.52      0.00
    60       9.15      0.00
    70       7.35      0.00
    80       5.22      0.00
    90       2.80      0.00
    95       1.49      0.00
   100       0.12      0.00

literature

Ira H. Abbott: Airfoils: Significance and Early Development. Air Force Museum Dayton, Ohio, March 1980.
James M. Shoemaker: Air Force Tests of Sperry Messenger Model With Six Sets of Wings. Report No. 269, NACA, Langley Memorial Aeronautical Laboratory, Washington 1928.