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Aviation History
1913
1913 - 1206.PDF
\fiwr NOVEMBER 8, 1913. Edited by V. E. The Problem of the Ornithopter. A Model Ornithopter. The ornithopter drawings which we give this week are taken from a French model which can be obtained commercially. The drawings show the wing flapping mechanism quite clearly, and need no further explanation. The model is constructed of aluminium and steel wire. The motor rod being a piece of aluminium tubing with a steel spring shock absorber in front. The leading edges of the planes are aluminium tubing, and the ribs and rear edges steel wire, the wing has thus a (comparatively speaking) rigid leading and flexible trailing edge, for reasons stated in last week's issue. As most of the readers of FLIGHT are aware, French model aviation construction is far behind the British. The aluminium motor rod soon collapsed, and other minor breakages occurred, and but little success was obtained with the model as first purchased. A hollow spar (of greater length) was substituted for the aluminium JOHNSON. M.A. but little resemblance to a bird, but that has nothing to do with the matter. We want first of all a model which (from our past knowledge of aviation model work), appears most likely to fly. The machine is essentially designed as a flying-stick of the flapping wing type. When we have obtained some success with such a type, then we can proceed to elaborate. It is the crudest form of flapping flight, but I am quite sure of one thing, and that is that in the first instance success will not be obtained by attempting to build a model entirely on bird-like lines. Valvular Wings. It has often been asserted that the wings of birds are so con structed that the air on the down stroke canaot pass through the feathers, whereas on the upstroke it can. If this were so the wing would obviously act as if it were fitted with valves. The chief and only evidence that we know of to support this theory is that whereas Q) BELL CRANKS FASTENED FIRMLY TO THE WIMGS (b) WINDIN6 HANDLE. CO ELASTIC WHICH CAUSES DOWNSTROKES OF VVIM6S TO BE MORE POWERFUL THAN THE UPSTROKES 1 SIDE VIEW OF MECHANISM 2 PERSPECTIVE VIEW 3 THE COMPLETE MODEL A French ornithopter model. tubing, and a few minor alterations were made, and in the end a flight of some 40 ft. was obtained hand launched. Unfortunately these experiments were made some time ago, and I can only remember some of the chief deductions I arrived at ; they were that the gearing should be done away with, since it appeared to absorb at least 50 per cent, of the energy, that two pairs of wings should be used instead of one, and that the rubber springs for accelerating the down stroke were a great mechanical disadvantage and that some other means should be devised of obtaining the same result. All attempts without the use of such were, however, an absolute failure, and it appeared an absolute essential feature of successful ornithopter flight that something in the nature of astioke-accelerator was absolutely neces?ary. The model was also tried with the rubber springs accelerating the up stroke, but with what result I cannot now remember, but I seem to have some kind of recollection that it was rather successful, although on the face of it, this appears to be a somewhat ab.urd conclusion. I should strongly recommend anyone about to try any experi ments with such models to proceed on the following lines: For the motor rod or backbone use a very light hollow spar some 3 ft. long, tapering, of course, towards both ends. This should be built up of two half u shaped sections joined centrally and not one complete u section with a piece along the top; it can be of either a square or oval section. Use no gear but two rubber motors, extending nearly the full length of Hat fuselage, employ two pairs of wings, one at each end of the motor rod. The length of the rubber motor will thus be the length of the motor rod minus about half the wing breadth. Balance with a horizontal and vertical fin (position alterable), placed somewhere between the wings, say about midway. Mount the model on wheels, say one in front and two behind, using featherweight wheels, and the lightest steel wire chassis that will support the weight of the model. Experiment with it on the smoothest surfaces obtainable. Such a model bears it is quite easy to thrust one's finger through the wing from the upper side, it is quite a different matter to do this from the lower. In the case of bats, flying foxes, &c, it is self evident that no such theory can be applied. The natural curvature of the wing of a bird naturally renders it easier to move it upwards than downwards. A valvular wing containing a sufficient number of valves would tend to reduce, or even counterbalance any support during the up-stroke, and the bird would be compelled to rely solely on its momentum for the maintenance of its altitude during each upstroke of the wing. Valvular wings have been a pet subject with aviation inventors of a certain type, as long as the writer can remember, but no practical results have ever followed from such. Not only do they introduce many additional mechanical complications, but they set up all kinds of irregular air flows, which not only greatly augment the head resistance but skin friction as well. Moreover we have no real evidence of any such in the world of flying creatures. Wing Flexure. If the flight of a flapping bird be observed directly from under neath—the movement of the wings appears to be an alternating extension and flexure ; being spread out to its full extent one instant and contracted the next. From this it would appear that during the down stroke the wing is spread out to take full advantage of the maximum area of sustentation and flexed or contracted during the up stroke in order to have minimum resistance to upward vertical motion. Major Baden-Powell constructed a paper cylinder, of a diameter approximately equal to the spread of a certain bird's wing. The interior of the tube was smoked, and the bird being put in at one end, flew through the tube, the tips of his wings scratching off the smoke as he flew. The cylinder was then opened, and a very clear diagram obtained. In another experiment two pieces of smoked paper were hung parallel face to face at a distance apart approxi- 1232
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