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Aviation History
1926
1926 - 0208.PDF
SUPPLEMENT TO FLIGHT MARCH 25, 1926 THE AIRCRAFT ENGINEER The handling chassis can be used with a considerable saving in personnel and time, and its operation can be made much more of a routine job. Accessibility of Hull. When a flying-boat is resting on a beach cradle, a large portion of the bottom of the hull is not available for inspec- tion, repair, painting, etc. To carry out these operations the machine has to be removed from its cradle by jacking up or lifting, a very tedious and precarious job. Furthermore, this portion of the hull is in more or less constant contact with the padding of the cradle, which is soaked with sea water. This is a matter of vital importance when duralumin hulls are considered as the portion of the hull in contact with the sea water soaked cradle is seriously liable to corrosion, and is not even available for inspection •without considerable work. The handling chassis eliminates all these disadvantages, and leaves all parts of the hull quite accessible. Transportation. Beach cradles for large flying-boats are necessarily heavy and cumbersome, and difficulty is experienced in transporting them by rail or boat. A handling chassis is light and comparatively small, and can be transported without difficulty. Sphere of Operation. In spite of its name, the beach cradle can only be used successfully on a slipway, and considerable difficulty would be experienced on the average type of natural beach. The handling chassis has a much larger sphere of operation, and can be used quite efficiently under these circumstances. The use of the handling chassis for flying-boats may be described as a recent development, and the experience available is not very extensive. There is little doubt that considerable improvement can still be made as our experience increases. There is every indication, however, that the use of the handling chassis will prove a very important step in the efficient and economical operation of flying-boats. TECHNICAL LITERATURE. A.R.C. REPORTS. HIGH-FREQUENCY FATIGUE TESTS By PROFESSOR C. F. JENKIN, C.B.E. Work performed for the Engineering Research Board of the Department of Scientific and Industrial Research. R. and M., No. 982 (M. 30). October, 1925. Price ; 9d. net. The experiments on high-frequency fatigue in copper, Armco iron, and mild steel described in the following paper were carried out in the Engineering Laboratory, Oxford, at the suggestion of the Elasticity and Fatigue Panel of the Aeronautical Research Committee. The question is of importance to the users of high-speed machinery. In 1911 Professor B. Hopkinson* called attention to the importance of ascertaining whether the fatigue limit of metals was dependent on the rate of alternation of stress. He designed and made an electric alternating direct-stress machine, and published the results of tests on mild steel carried out at about 7,000 periods per minute (116 per sec), which was more than three times as fast as any tests made up to that time. The results at this speed were compared with those made by Dr. Stanton at the National Physical Laboratory on the same material at 2,000 periods per minute (33 per sec). Professor Hopkinson considered that the results showed that speed had a marked effect, but he did not consider that his tests were conclusive. In the light of the knowledge gained on fatigue testing since that date neither set of tests can be considered satisfactorv. After a large number of tests using the apparatus rotating aAi a iteo^v\etvcy oi \VW ^erio&s -^es seconsi, ANVACVV -was later, increased for tests with torsional vibrations at large ampli- tudes to 5,000 periods, the experiments were ultimately * Boy. Hoc. Proc, A. Vol. 86. November, 1911. abandoned. The apparatus was found not to be powerful enough to overcome the large hysteresis which appeared as the fatigue limit was closely approached, the power being apparently limited by the magnetic saturation of the iron in the armature. The amount of the strains actually attained in typical experiments were as follows :— Test piece made of copper tubes or copper rods, of diameter about -J- in., and the effective length 3 in. ; approximate stress was between 3 -3 and 3 • 7 tons per square inch and the strain 0-0012. The specimens remained unbroken after upwards of 10' periods. SOME EXPERIMENTS ON A MODEL OF A B.A.T. •-••"' BANTAM " AEROPLANE WITH SPECIAL REFER- ENCE TO SPINNING ACCIDENTS. PART I.—LONGITUDINAL CONTROL AND ROLLING EXPERIMENTS. By H. B. IRVING, B.SC, and A. S. BATSON, B.SC. PART II.—EXPERIMENTS ON FORCES AND MOMENTS (INCLUDING RUDDER CONTROL). By H. C. H. TOWNEND, B.Sc., and T. A. KIRKUP. R. & M. No. 976 (Ae. 190). November, 1925. Price Is. '3d. net. The spinning of aeroplanes is a problem which has engaged the attention of the Aeronautical Research Committee on several occasions, and the first report dealing with the subject in much detail is R. & M. 618.* The experiments described in the present paper relate to difficulties experienced in coming out of a spin by a certain type of aeroplane which was in other respects a very nice machine to handle. Non-Rotational Experiments.—Measurement of pitching moment (including elevator control) over a large range of incidence and for angles of yaw up to 40° on the model with standard wing gap (0-81 X chord) and model with gap increased to 1-03 X chord. Rotational Experiments.—Measurements of auto-rotational speeds and couples were made for the complete model with standard and increased gaps (no yaw), and the auto-rotation of the yawed model measured about an axis through the centre of gravity of the aeroplane (angle of yaw 30° ; original gap) ; pitching and yawing moments due to rolling were also observed (wings only). Is on-Rotational Experiments.—The pitching moments and longitudinal control of the " Bantam " do not appear to possess any unusual features. Sideslip (or yaw) produces a pitching moment tending to increase the angle of incidence ; the magnitude of the moment is similar to that observed in the case of the S.E.5A model. The longitudinal control is practic- ally unaffected by sideslip. Increasing the wing gap by raising the upper plane had very little effect on either pitching moment or longitudinal control. Rotational Experiments.—The "Bantam" has an abnor- mally high speed and large range of auto-rotation. Sideslip corresponding to 30° yaw completely stopped auto- rotation at any angle of incidence, the ailerons being set so as to balance the rolling moment due to sideslip ; raising the upper plane of the model reduced the range and maximum speed of auto-rotation. Pitching moment due to rolling was found to become positive at large angles of incidence, but its magnitude was always small compared with the control available. The high speed and large range of auto-rotation of the " Bantam " are shown to be easily explainable by the absence of stagger and by the small wing gap of this aeroplane. The results are then discussed with special reference to the problem of difficulty in recovery from a spin, attention being chiefly directed to the various factors affecting the longitudinal trim during a spin. Effect of Inertia Term.—Attention is drawn to the import- ance of the inertia term in the equation of pitching moments iox t\\e conditions oi a spin, particularly -when, the char acter- istics of a biplane, e.g., small wing gap combined with zei' * R. & M. 618. " The Investigation of the Spin of an Aeroplane'H. Gilauert. June, 1919. 178;
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