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Aviation History
1910
1910 - 0536.PDF
-angle, and the use of a considerable angle implies that the aero dynamic resistance is proportionately great as compared with the skin friction. This Langley observed to be the case ; indeed, he speaks of the skin friction as being negligible. Langley dtove his models through the air at high speeds, but he was appa rently unable to go fast enough to bring the skin friction within the realm of appreciable magnitude, let alone into the position of equality with the aerodynamic resistance which would have represented a condition of minimum resistance and the limit of his observation of diminishing power. If Langley had employed very light planes sach as would have been supported at very small angles at com paratively low speeds, he would have observed that his higher velocities made a considerable difference in the relative value of the skin friction, and even had he not been able to actually attain the speed of minimum total resistance, his scientific mind would certainly have seen the necessity of taking account of skin friction in the application of his experiments to theoretical deductions. Langley's error consisted of overlooking the consequences of the law of skin friction, with which he was in all probability familiar, but the import of which he had apparently allowed to be obscured in his mind by the insignificance of the skin friction values that his experi ments provided. CORRESPONDENCE:. The name and address of the writer (not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. WING WARPING. NOTB.—Owing to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter will appear practically in sequence and at the earliest possible moment. BLERIOT FRAMEWORK. [594] Several correspondents lately have asked for details ot Bleriot framework for models; I hope the attached sketch will interest them. No wire strainers are necessary, as the nails hold the wire firm at each joint. Twist wire round the French nail at A, and then drive nail home (B). This makes a very substantial joint. Brockley, S.E. " KXARK." BAMBOO JOINTS. 15951 I" a recent issue of your valuable paper, some questions were asked about bamboo ; I therefore send you a sketch of a joint which does not require crossed wires to strengthen it. The patent claims this to be, weight for weight, the strongest, lightest, and neatest way of making joints and framework for aeroplanes and dirigibles. By treating the inside and outside of the spars with glue and varnish, and binding when wet with cotton tape and silk, very greatly increased strength and reliability is obtained, and the thin strips of spring steel and the binding prevent a broken sp^r from dividing and doing further damage to the aviator or his machine. Joints and crossings can be made at any angle, and a broken spar neatly spliced, and, if necessary, made stronger than before by -inserting a thin steel plate and binding. For dirigibles, this framework will not interfere with wireless telegraphy as metal does, and it may perhaps be of practical service >to the new science of aviation. Barnes. PAM DALTON. [596] Would you kindly inform me through the medium of your valuable paper of what movement '' warping the wings " consists of, and how this movement is generally controlled. I might mention that I am particularly interested in the control of the " Macfie " monoplane. Thanking you in anticipation, Sparkhill. L. T. M. [The accompanying sketch illustrates diagramatically the warping control on the Macfie monoplane, and serves to illustrate the general principle. Warping consists of deflecting the trailing edge of one wing while the trailing edge of the other wing is simultaneously flexed upwards. An actual reversal of the camber seldom takes place Rear Spar ~—— (TiexiM?) ^ /Lyienifq if ,V««4. 7 in the latter case. The wing that has its trailing edge deflected downwards exercises a relatively greater lifting effect than the opposite wing, and consequently raises its own side of the machine if both wings are forced to proceed through the air at the same speed. A disturbing influence is introduced by the fact that the deflected wing offers a greater resistance to motion through the air, and therefore tends to slew the machine from its true path. This is why the rudder has to be used in conjunction with wing warping, in order to keep the machine straight. If the slewing effect is allowed to take place, the increased lift of the depressed wing will be lost and the machine will capsize.—ED.] THE NEGATIVE ANGLE AND AN APPARENT PARADOX. [597] With reference to the discussion on the practicability or flight with planes set at a negative angle, it strikes me as impossible for the reason following :— The inventor claims that planes set at a negative angle support the machine. A support implies an upward thrust. If, therefore, two planes be made up into a propeller it would work effectively, giving a thrust in the same direction whichever way it was rotated. A. H. HORN. [It is a clever deduction that has been made by our correspondent in the above letter, that the combination of an aeroplane with a negative angle and another with a positive angle of incidence (chord the wind) would form the elements of a propeller theoretically capable of exercising a uni-directional thrust, irrespective of the direction of rotation. Mr. Horn evidently concludes that this is a reductio ad absurdum, and, therefore, a logical reason why an aerofoil with a negative angle should not exert a lift. With this conclusion we are by no means in agreement, although we admit that the problem is in the nature of a paradox. A little investigation will show that the suggested arrangement of aeroplanes is aerodynamically similar to Sir Hiram Maxim's "paradox" aero plane, which he describes on page 87 of his "Artificial and Natural Flight." Reference is also made to this device in FLIGHT, Vol. I, page 75, where Sir Hiram Maxim's early lift and drift experiments formed a subject of a special article. Incidentally, this subject is allied to two other aspects of the aero plane that are attracting the attention of readers, one being the phenomenon of " upper surface lift," and the other being the question of the relative importance of the angle of incidence, and the angle that we have decided to call the " angle of deflection." 534
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