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Published online by Cambridge University Press: 28 July 2016
The problem of the maximum lift of airfoils has concerned the authors greatly since there were first discovered in the spring of 1932 serious discrepancies in this characteristic between results obtained in the wind tunnel of the Guggenheim Aeronautics Laboratory at the California Institute of Technology (GALCIT) and those reported from certain other wind tunnels. An elaborate experimental investigation by the junior author and A. L. Klein indicated that the value of CLmax for a given airfoil was strongly affected both by Reynolds number and by the degree of turbulence in the tunnel wind stream.
Reprinted by courteous permission from the Transactions of the American Society of Mechanical Engineers, Vol. II, No. 1, March, 1935.
Note on page 619 3 “The Effect of Turbulence: An Investigation of Maximum-Lift Coefficient and Turbulence in Wind Tunnels and in Flight,” by C. B. Millikan and A. L. Klein, Aircraft Engineering, August, 1933 (London).
Note on page 620 4 “On the Theory of Laminar Boundary Layers Involving Separation,” by Th. von Kármán and C. B. Millikan, N.A.C.A. Technical Report No. 504.
5 Condensed accounts of portions of the discussion of this section have already been presented by the authors; cf. “ Quelques Problemes Actuels de l'Aerodynamique,” by Th. von Karman, Journees Techniques Internationales de l'Aeronautique, Paris (1932). “The Effect of Turbulence: An Investigation of Maximum—Lift Coeiiicient and Turbulence in Wind Tunnels and in Flight,” by C. B. Millikan and A. L. Klein, loc. cit. “The Use of the Wind Tunnel in Connection with Aircraft—Design Problems,” by Th. von Kármán and C. B. Millikan, Trans. A.S.M.E., 1934, pp. 151-166, paper AER-56-4.
Note on page 628 6. “Tests of N.A.C.A. Airfoils in the Variable Density Wind Tunnel, Series 24,” by E. N. Jacobs and K. E. Ward. N.A.C.A. Technical Note No. 404, January, 1932.
7 “Theory of Wing Sections of Arbitrary Shape,” by Theodore Theodorsen. N.A.C.A.Technical Report No. 411 (1932).
Note on page 630 8 “Effect of Turbulence in Wind Tunnel Measurements,” by H. L. Dryden and A. M. Kuethe.N.A.C.A. Technical Report No. 342, 1929.
Note on page 631 9 It might be mentioned that, since the present paper was written, additional experiments have been made and reported by one of the present authors (“Further Experiments on the Variation of the Maximum-Lift Coefficient with Turbulence and Reynolds Number,” by Clark B. Millikan, A.S.M.E. Transactions, November, 1934.) These experiments were made with rather unconventional airfoil profiles, whose lift curves had considerable curvature below the stall. As might have been expected, the dependence of CLmax on Reynolds number and turbulence was quite different from that for conventional airfoils like the 2412. The desirability of an extension of the present theory in order to explain the maximum-lift phenomenon for some unconventional profiles has, therefore, been experimentally demonstrated.