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).
Vibration tests on a Steel Panelled Bentley Saloon, model B-56-BN.
| Identifier | ExFiles\Box 90\5\ scan0072 | |
| Date | 13th September 1935 | |
| To Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}25/KW.13.9.35. Vibration Tests on Steel Panelled Bentley Saloon, B-56-BN.{W.O. Bentley / Mr Barrington} The attached diagram Hs.{Lord Ernest Hives - Chair}2121 shows the results of the above tests in the form of response curves. The range of frequencies covered was from 500/min. to 760/min. Lower frequencies would have been interesting when the Bumper Bar was fitted, but were not used as it would have necessitated increasing the out of balance of the machine and there was not sufficient time for this. At frequencies higher than 760/min. the vibrations were of smaller magnitude. The torsional frame frequency without the bumper bar is 690/min. With the bumper this frequency is reduced to about 450/min. It is very doubtful whether the present standard bumper bar acts as a true harmonic stabiliser as its natural frequency is certainly below 690/min. and it probably operates purely as a dumb bell. It was found that the car had a period of transverse vibration at approx. 630 cycles/min. with two nodes, one just behind the front axle and the other just in front of the rear axle. This transverse vibration is the cause of the sideways vibration of the steering wheel which is noticeable on the road. The amplitude of the steering wheel vibration is greater than that of the chassis in line with the driving seat, the amounts being 0.30 and 0.18 respectively with the bumper bar fitted. With the bumper bar removed the transverse vibration is increased in front of the forward node and reduced at all points behind it, and in this case the steering wheel movement is 0.22 and chassis movement 0.14. The effect of one piece wings and rigid scuttle and dash connection was tried, and the results are shown below. | ||