FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 0761.PDF
SI JULY 29, 1932 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT It will, of course, be necessary to modify these KL curves as fresh data becomes available, but in the mean time they provide a fairly reliable guido upon which estimates can be based. For a biplane (in the absence of tests showing the effect of aspect ratio) the maximum lift may be taken as about 90 per cent, of that for a monoplane, Fig. 13. Using the foregoing data, it is now possible to esti mate the complete profile drag curve for any normal wing. This has been done for the sections given in Ref 7. The agreement is in most cases too close to show on a graph, so the results have been tabulated as follow: — Section Camber Ratio, Km() Thickness Ratio, t \ Section TABLE 3 Gott 398 0-0477 -0041 0-1385 0-786 KL Obs. 0-2245 0-3725 0-516 Calc. 0-00551 0-00591 0-00686 0-6515 0-00996 KDp Obs. 0-00555 0 0063 0-00795 0-01135 0-757 ;0-01516 0-01965 0-786 0-018710-0319 1 ! TABLE 4 B106 Camber Ratio 0 0327 Km0 Thickness Ratio Klmax Section -00260 0-1306 0-7675 KL ! KDj) KUp Obs. i Calc. : Obs. i 0110 IO-00496!0-00485 0-185 !o-00501000490 0-258 jO-00516 0-00530 0-406 j0-00596 0 00635 0-547 10- 008710 -0085 0-676 1001121 0-0128 0-7675 0-01796 0-02665 TABLE 5 N. 60 Camber Ratio 0-0385 Km0 Thickness Ratio Kl-max -0-0400 \\ 0-1245 0-808 KL Obs. KDp 1 KDp Calc. | Obs. 0-1335'0-0050 0-212 10-0051 0-289 10-0052 0-365 0-0055 0-513 0-650 0-771 0-808 0-0069 0-0096 0-0157 0-0200 0-00505 0-00495 0-0052E 0-0056 0-0069 0-0100 0-0156 0-0246 Gott 398.R 0-0325 Reflexed -0-0035 0 1385 0-6845 KL Obs. 0-084 0-236 0-386 0-5295 0-655 KDp Calc. K»P Obs. 0 • 00513J0-00495 0-00533 0-00545 0-00643 0 0065 0-00838 0-00875 0-01518 0-01425 0-6845 0-02013 0-02775 B 106.R 0 0241 Refiexed -0-0005 0 1306 0-6930 £L Kl>" KDP Obs. Calc. Obs. 0-041 0-193 0-341 0-0048 !0-00465 0-0050 jO-0050 0 0058 10-00595 0-490 0 0089 10-0079 0-623 |0-0125 00121 0-678 0-0182 0-01675 0-691 0 0192 0 0352 N. 60.R 0 0295 Reflexed -0-0005 0 1245 0-7035 KL j KDp KDp Obs. ; calc. Obs. 1 I 0-056 0-0048 ;0-00465 0 132 0 0048 10-00460 0-2095 0-00492 0 00495 0-364 10-0058 0-0058 0-514 0-00805 0-00715 0-05250-0134 0-0122 i0-703510-0198 0-0193 1 ~—" ~—"" The observed values have not been faired in any way but are taken direct from Reference 7, after correction to British notation. The agreement between the experimental and calcu lated values of KD given above might be considered satisfactory, except perhaps for Gott 398 at the higher values of Kt and at the stall for some of the other sections. The disagreement in the case of Gott 398 would cause a slight over-estimate in the rate of climb, but at top speed the estimated drag would be correct. The reflexed sections Gott 398.R, etc., have been designed to give no-moment at no-lift in each case. From these results it is apparent that the drag of such reflexed sections is the same as that for non- reflexed sections of the same maximum camber. The maximum lift coefficient for the reflexed section is less than that for the non-reflexed of same camber. This is allowed for in Figs. 11, 12 and 13 by plotting Kt max against Km . From this it is suggested that a reflexed section has the same maximum lift as a symmetrical section of the same thickness to chord ratio, the profile drag and KL , corresponding to the maximum camber. opt r ° The tests on the symmetrical sections show that in many eases the flow is very unstable at maximum lift. The stall takes place very suddenly and a reduction of angle, once the stall has taken place, results in a much lower lift coefficient at the original stalling angle. This effect seems to be worst round about 12 per cent, thickness ratio There is no evidence to show whether or not this effect is present with small cambers, or at what mini mum camber it vanishes. There is no evidence of it with the reflexed sections nor with the sections of cambers of 0.04 c, but such cambers are somewhat higher than the average used in biplane work. Further tests are, therefore, necessary before it can be stated what is the lowest camber for a non-reflexed section which can be used with any thickness ratio to avoid a sudden stall. The question of no-lift characteristics is under investi gation by the writer, but certain difficulties have presented themselves. It may be necessary to await further tests before any generalised curves or empirical correction to the method of R. & M. 910 (Reference 10) can be developed. It is suggested, therefore, to leave this section of the problem of the prediction of aerofoil characteristics to be dealt with in a later article. 10 R. & M. 910. A Theory of Thin Aerofoils. H. Glauert, B.A. STRIP MANIPULATION. By W. S. HOLLYHOCK, THE most common methods of forming lengths of corru gated or augulated sections for use in aircraft structural members are the manipulation of comparatively thin strip by " rolling " or " drawing," and the process known as extrusion. The latter is not greatly used, partly because the resulting sections are not economical from the point of view of weight for most aircraft work, and partly because aircraft manufacturers have not usually the facilities or plant for carrying out such work themselves. The process of rolling consists of forming the required section by bending flat strip between pairs of rolls. The strip is carried along by the rolls, which are themselves 710 c
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
