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).
The demonstration of a Cambridge Portable Vibrograph used to measure transverse vibrations on a 'Wraith' car engine crankcase.
| Identifier | ExFiles\Box 138\2\ scan0163 | |
| Date | 13th September 1938 | |
| RM{William Robotham - Chief Engineer}/GRYLLS. Pilee 1163 DEMONSTRATION OF CAMBRIDGE PORTABLE VIBROGRAPH. 13.9.1938. We are enclosing a series of photographic enlargements of the records taken from the crankcase of the 'Wraith' car engine with this instrument. A separate report on the performance of the vibrograph will be issued very shortly. Readings were taken of the transverse vibration of the crankcase walls at the level of the sump joint. The vibrograph stylus was applied at three points : - (1) Rear end, about 3" forward of the clutch-housing. (2) Centre - in line with centre main bearing. (3) Forward end. In this instance the form of the vibrograph made it impossible to apply it directly to the crankcase and the stylus was actually placed on the flange of the timing-cover. The timing-marks on the records are at 1/10 second intervals, with every tenth mark suppressed. The multiplication of the recording mechanism was given as 7x and the photographic enlargement is approximately 8.5x, corresponding to an overall linear magnification of the vibration of approximately 60. The salient features of the record are analysed below:- | Diagram. | Position. | Engine R.P.M. | Frequency P.P.M. | Total range of movement. | Remarks. | |----------|------------------------|---------------|------------------|--------------------------|----------------------------------------| | 1. | In line with centre main. | 2500 | 2570 | 0.021 | Very pronounced 2nd harmonic. | | 2. | In line with centre main. | 3000 | 2960 | 0.016 | Harmonic content much reduced compared with (1). | | 3. | Rear of crankcase | 3000 | 3000 | 0.017 | Harmonic content low. | | 4. | Front cover | 3000 | 3050 | 0.010 | 2nd harmonic. | | 5. | Rear of C'case | 2500 | 2520 | 0.017 | Pronounced 2nd hc. | | 6. | Front cover | 2500 | 5040 | 0.020 | Twice engine frequency. | | ||