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Aviation History
1932
1932 - 0166.PDF
FLIGHT, FEBRUARY 19, 1932 TESTING A FRAME: The FLYING principle BOAT of this iivr\i»"^ . * iiv p; iTli-jpic Ul Kills testing machine is generally similar to that of the wing-testing machine. (R.A.F. Official, Crown Copyright.) distribution of load, and these levers are connected to the wing by means of short horizontal beams E-F and G-H, parallel to the spars, and by vertical struts E-J, F-K, etc. Between each of the transverse beams and their respective jacks near the trailing edge a hydraulic ram N is inserted. These rams are all fed from a common source, and for the loading case representing a CP co-efficient of 0.25 all rams are of equal diameter, and therefore carry equal loads. In carrying out a wing test, the loading gear was first balanced by means of suitable bob weights on the various levers and beams, and by the application of a suitable initial hydraulic pressure under the rams. Increments of load were applied by increasing the hydraulic pressure on the rams. Vertical scales, fixed relative to the wing, were attached at 18 different points, and vertical movement of the scales was read by using a Dumpy level mounted some distance away from the wing. In the early tests the load could be applied at the rate of 20,000 lb. per hour, in five increments. This rate was subsequently doubled. The advantages of this method of strength testing were summed up by the lecturer as follows: The loads applied are always under complete control. Application and release of loads are safe. Any appreciable yield results in auto matic and instantaneous reduction of the load. Total collapse of structure is impossible. The structure being tested may be safely and easily observed through out the tests. The economy in time spent in testing, and the con venience of being able to release the load quickly so as to observe how much distortion is permanent more than counterbalance the apparently high initial cost of providing the test apparatus. Mr. Gerard concluded by ex plaining testing machines based on a similar principle, but in tended for testing flying boat hull frames and monocoque fuselages. These are shown in illustrations. TESTING PORTION OF MO N OCOQUE FUSELAGE : This testing machine induces combined shear, bending and torsion stresses. R. A . F. Official, Crown Copyright.) Points from the Discussion Major Barlow, in asking Mr. Langley to open the discussion, said that he thought the lecturer deserved much credit for his research work. He personally would like some more information about fatigue stresses. Mr. M. Langley wished to know something more about the corrosion problem and which metals gave most trouble. Also what was the effect in a spar of many corrugations of small and large radii coming together. Major Wylie referred to the use of eccentric end loading for imitating exactly the actual conditions of load in a wing spar. By supplying the end load with considerable eccentricity (8-9 inches) a bending movement was produced. Mr. Hollis Williams referred to the two difierent methods in force in this country and on the Continent. Here we used calculations based upon theory, and backed them by mechanical tests of components, etc. On the Continent they used mechanical tests only. One result was that " on paper " the I.C.A.N. load factors appeared twice as high as ours. Mr. W. O. Manning thought that if the variation in I (moment of inertia) of a spar section was large enough to cause any appreciable difference, then it ought to be large enough to be measured during flight. Dr. G. Lachmann was interested in the small curved test pieces, and thought possibly the same principle could be applied on a larger scale, for example to parts of monocoque fuselages. He would like more information about complete wings. In Germany the DVL had done a good deal of work on this subject, and they had found that the stress developed was less than that of small parts of the materials themselves. Mr. H. J. Pollard thought that in making mechanical tests the loads were applied too slowly, and that conditions more representative of actual ones would be attained by a more rapid application of the loads.
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