From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Introduction to the use of a recording accelerometer, with typical records shown.
| Identifier | ExFiles\Box 138\2\ scan0181 | |
| Date | 1st June 1926 guessed | |
| INTRODUCTION MEASUREMENTS of the accelerations of moving objects are of value, not only in giving information regarding the changes in the rate at which they move and the effect of obstructions, springing devices, etc., but in securing data whereby the forces acting upon the moving body can be calculated. Since every force can be equated to mass multiplied by acceleration, it follows that a record of the accelerations of a body also forms a record of the forces causing such accelerations. A recording accelerometer is, therefore, an instrument of considerable usefulness, and provides a wide variety of data of practical value to engineers. For example, it is frequently of importance to record the vertical accelerations of an aeroplane, not because the actual accelerations are of much value in themselves, but because from such records the forces due to air pressure on the wings, and hence the maximum strains in the struts and tension wires of the aeroplane, can be calculated, and the factors of safety determined. Further, an accelerometer is of value in recording vibrations, particularly when these are of high frequency. Other applications include the physiological and psychological study of the effect of vibrations upon the human system, and the characteristics of the movements of the human body in walking. The accelerometer has also many applications in the direct measurement of the accelerations of moving objects such as trains, electric tramcars, motor cars, or lifts, thus determining, for example, the maximum acceleration or deceleration that can be obtained, or is consistent with other conditions, such as the comfort of passengers or the safe limits of the stress—due to acceleration—to which the materials of the moving object or its structural supports can be subjected. It has been found to be of much value in connection with investigations regarding the springing of vehicles and the effect produced upon them by various road surfaces, and in comparing the “comfort” of different types of tyres, springs, shock absorbers, etc., when fitted to cars. The Recording Accelerometers described in this catalogue are light, robust instruments, by means of which permanent records can be obtained of accelerations in either vertical or horizontal directions. The principal novel feature in their design lies in the method of recording, which does not depend upon optical or photographic methods, and yet is capable of great accuracy even when recording rapidly changing accelerations. The records are obtained by the action of a moving stylus upon transparent celluloid film. The pressure upon the stylus is extremely light and the celluloid flows plastically under the rounded point of the stylus, the line produced having such optical characteristics as to render any point on an enlarged image of the diagram readable to a high order of accuracy. A wide range of accelerations can thus be successfully recorded. The moving parts of the instrument are made small and arranged to move through small distances, so that accelerations of considerable magnitude, or vibrations of high frequency, are recorded accurately and undisturbed by instrumental inertia effects. The stylus-on-celluloid method of recording has also the advantage of durability, in that the record cannot fade, and is impervious to oil or water. Other instruments utilising this method of recording include Stress Recorders, Vibrographs, Bridge Deflectometers, Chronographs, Draught Recorders and Micro-Indicators for High Speed Engines. Information regarding these instruments will be forwarded on request. TYPICAL RECORDS. Photographically Enlarged. Fig. 12. Fig. 13. 3550 Records showing the vertical (Fig. 12) and horizontal (Fig. 13) accelerations of a normal pedestrian. (Magnification 12 linear). Fig. 14. Fig. 15. 3551 Records showing the vertical (Fig. 14) and horizontal (Fig. 15) accelerations of a pedestrian with an artificial leg. (Magnification 12 linear). Fig. 16. 3546 Record showing the vertical accelerations measured on an Armstrong-Siddeley motor car (18 h.p. mark I) travelling at 15 m.p.h. The tyres of the car were purposely blown up too hard in order to give a severe test to the springing on a particularly bad piece of road. (Magnification 10 linear). Fig. 17. 3547 Record taken on the same car, and under the same conditions as Fig. 16, but with the car travelling at 25 miles per hour. (Magnification 10 linear). 7 | ||