Reducing Induced Drag...A French Approach By G. Limbach, EAA 6911 56 E. Oaks Rd., St. Paul, Minn.

W enough to translate verbatim a letter to the editor of Inter-Aero No. HILE MY French is not good

3, September, 1963, by Mr. G. C.

Richard, I do think many homebuilders will appreciate his ideas. By now, all pilots should be familiar with the phenomenon of wake turbulence. It results from the vortex created at the wing tips by the air curling around the tip from the bottom to the top and trailing off. The generation of this vortex at high angles of attack especially accounts for a good percentage of the total aircraft drag. Different attempts at wing-tip design to decrease this drag have been made with varying success. Notably the studies of Dr. S. F. Hoerner have been used by many to increase aircraft performance. Mr. Richard made studies of a novel wing-tip design. His photos in the French journal, which I hope can be reprcducsd legibly, are very interesting. Fig. 1 shows the tip vortex, which is visual evidence of the induced drag at the wing tip. The airfoil is at 11 deg. angle of attack. Fig. 2 shows the same airfoil at 11 deg. angle of attack with the Richard tip configuration. It can be seen that

you sailplane builders . . . this design or a variation of it might be very beneficial. If any of you builders do try your hand at this approach, how about letting us know what you did and what you found. Perhaps a word

from some of our professional designers would be interesting in regard to this tip design. I guess the only question left is to ask who will be the first to build a wing tip for the

birds?

®

Fig. 1

the vortex is broken up and, appar-

ently from his studies, the induced drag was decreased considerably. Fig. 3 shows the design principles of Mr. Richard's tip. Unfortunately, he provided no data on the airfoil section used in his prototypes as shown in the drawings. Mr. Richard

Fig. 2 FIGURE

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said, however, that in principal he was attempting to create for an airplane cr sailplane wing the same effect that he believes mother nature has provided to the birds as a result of their wing-tip feathers. Mr. Richard made his studies in

the early fifties and the illustrations shown were taken at his initiative at

the O.N.E.R.A., the official French testing center. The pictures and data were published in "Les Ailes", a

French publication, in October of 1955 and again in August of 1960. As of his letter to Inter-Aero in 1963,

to Mr. Richard's knowledge, no one had used his data to create a better wing tip. How about you T-18 builders? Your

design is a natural to use as a test bed for the new tip experiments. And

TOP VIEW OF WING TIP SPORT AVIATION

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