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).
Chassis stiffness, engine mounting schemes, and improvements for future designs, comparing with Bentley and Hispano.
| Identifier | ExFiles\Box 12\6\ 06-page042 | |
| Date | 8th April 1931 guessed | |
| (2) Bentley is now, I firmly believe, trusting to the body to help the stiffness and using our old 3 point mounting (P. 1. scheme.) I have for some time thought that without the assistance of the engine we are somewhat at a disadvantage with P. 2. because we have a combination gearbox which prevents our fitting a substantial cross member between engine and gearbox - i.e. we have a larger bay for the engine. I have for a long time thought that the engine feet near the dash are very likely to transmit vibrations to the dashboard and decided that the torque arms forward would be better. This was at the time we schemed torque reaction dampers as a temporary improvement to P. 1. and 20HP. Now we come to a further idea of using 2 front arms and 2 arms from the gearbox to the cross member behind the gearbox to get the most efficient torsional stiffness from a soft mounting. Such a scheme should be tested: it may be hardly good enough vibration insulator for a big 6 but might be good for the 25HP. I want to impress upon all concerned that we have always suffered (with others) from want of torsional stiffness of the chassis (formerly we thought it was want of lateral stiffness) but I am convinced that the latter does not worry us at present. Bonnet wear and knocks, radiator, wings, and lamp unsteadiness all come from this trouble and front axle excess movement etc. and since we now have the knowledge we must on our next designs profit by it. I also want everyone to realise that after we have done all we can even with the assistance of the engine we shall still be too flexible torsionally so we must in our improved designs be able to take full advantage of the engine. It must be interesting to find how bad the Hispano is which we believe is still firmly bolted into one with the frame. It will be understood that Bentley cannot have solved this unsolvable problem but must like ourselves have made some more or less imperfect compromise. Balloon tyres and more vigorous shock dampers are asking for greater stiffness in the frame which naturally will enable us to get better steering and road riding qualities because of the more effective front damping. Increase in road speeds have demanded these more effective dampers. | ||