FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 0574.PDF
44 SUPPLEMENT TO FLIGHT JUNE 17, 1982 THE AIRCRAFT ENGINEER A much better agreement seems possible by expressing the " extra " drag as A K» --= f "opt K>. K L "opt (7) The results using this procedure are shown in Figs. 6 and 7. Very close agreement is obtained for the Symmetrical Sections, but here the thinnest section No. 0006 is not included, as in this instance the drag rose rapidly pre ceding the stall. As such a thin symmetrical section is probably only of interest for completing the series tested, there is no loss of generality by neglecting this result. ni4 * ' 012 •010 008 006 004 002 0 ( JoMlN SYMMETRICAL SECTIONS 0009 TO 0021 • < o • * r. FIG.6. ) -1 -2 3 -4 5 .6 -7 -8 -9 1-0 - KLMAX „ « «NDR£M " Extra " profile drag curves. Referring to Fig. 7 it will be noticed that there is no change in AKD with camber for the 43 and 63 Series. The two sets of results lie on the same curve. This is not so with the 45 and 65 Series. Here only Section 4509 agrees with the results obtained from the 43 and 63 Series. Why the sections having the maximum camber at 0.5 of the chord should show this marked increase in " extra " profile drag with increasing thickness and aamber is not apparent. It is conceivable that the minimum value for this " extra " drag is given by the symmetrical aerofoils. Those sections having their maximum camber at 0.3 of the chord have an " extra " profile drag curve almost identical with that of the Symmetrical Sections as shown by Fig. 8. 014 012 010 008 006 004 •002 0 D MIN. FIG.6 SEC noNS 0009 00I2 00I5 00I8 002I SECT IONS 4309 43I8 6309 63I8 4509 J 1 -2 3 A S "6 7 8 8 ID + K.u-KLopt K, MAX-Ki opt-. With constant camber and increasing thickness, or constant thickness and increasing camber, some com bination of camber and thickness is reached above which this " extra " drag breaks away from the minimum given by the Symmetrical Sections. The present tests indicate that for sections having the maximum camber at 0.5 c. the point is reached earlier than with sections having the maximum at 0.3 c. So far as these tests go, they suggest that for most practical aerofoils with maximum camber at 0.3 c. there is no breakaway of the " extra " drag from the minimum. This does not mean that the sections with the maxi- •045 •04 •035 •03 •025 K.D-* o •02 •015 •0 •005 0 O MIN. SYMBOLS O 4309 V 6509 + 4318 x 6518 ta 4509 <•> 6309 A 4518 T3 6318 ^-^" FIG .7. / *• K i j A J1 /] / • 1 ' " 2 -3 4 5 6 7 8 -9 I- + KL - KL opl- l\L MAX- KL Opt". w R ANDREWS < > 0 Meaned *' Extra " profile drag curves. mum camber at 0.3 c. are more efficient than those with the maximum at 0.5, since the maximum lift of the latter is generally greater than that of the former. The tests are not sufficiently comprehensive to give the exact combination of camber and thickness at which the breakaway of the " extra " drag occurs. As, however, the majority of aerofoils have their maximum camber at 0.3 of the chord or thereabouts, the minimum value for the " extra " drag will apply in most cases and will be at the most only a few per cent, out at climbing speed for the worst cases. At top speed the effect of the " extra " drag is not appreciable, and the accuracy of the profile drag at this point is almost wholly dependent upon the estimated minimum profile drag. Fig. 8 may then be used for obtaining the drag curve between KL . and KL for all practical aerofoils. opt max r Once the maximum lift coefficient has been deter mined, the drag curve can be completely defined. (To oe concluded) REFERENCES 1 N.A.C.A. Report No. 312. "The Prediction of Aerofoil Characteristics." George J. Higgins. 2 The Estimation of No-lift Characteristics. W. R. Andrews. FLIGHT, December 27, 1929. 5 N.A.C.A. Report No. 221. Model Tests with a Systematic Series of 27 Wine Sections at Full Reynolds Number. Max. M. Munk and Elton •W. Miller. 4 N.A.C.A. Technical Note No. 385. Characteristics of Symmetrical Aero foils. E. N. Jacobs. 5 N.A.O.A. Technical Note No. 391. Characteristics of Aerofoils. E. N. Jacobs and R. M. Pinkerton. 6 N.A.C.A. Technical Note No. 392. Aerofoils. Tests in V.D. Channel. E. N. Jacobs and R. M. Pinkerton. 7 N.A.C.A. Technical Note No. 388. Wind Tunnel Comparison of Three Normal and Three Reflexed Aerofoils. G. L. Defoe. 8 N.A.C.A. Technical Note No. 397. The Aerodynamic Characteristics of Six Commonly used Aerofoils over Large Range of Positive and Negative Angles of Attack. Raymond F. Anderson. 9 R. & M. 946. The Theory and Design of Aerofoils. H. Glauert, M.A. 530 d
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
