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).
Technical letter discussing minimum flywheel inertia, damper design, and braking performance.
| Identifier | ExFiles\Box 127\1\ scan0223 | |
| Date | 21th May 1935 | |
| Mr. W. A.{Mr Adams} Robotham. 5-21-35 - Page 2. As to the minimum flywheel inertia, I have always worked on the basis that this should not be less than approximately one-eighth of the total flywheel effect of the engine. This is just a rough rule and there has been no point to determine what the minimum flywheel effect can be. I do know, however, that it is more difficult to make small dampers operate properly than ones which have a fairly large flywheel inertia. In connection with dampers, our rubber enclosed friction and elastic type damper has not only proven to be very effective - in fact much more effective than a straight Lanchester type - but it is better adapted to damp the different orders of critical speeds. In other words, the damper characteristic is more nearly like the amplitude characteristic of different orders of vibration at the different critical speeds. What I am trying to say is that some years ago we used a lead ring in our Lanchester type damper, the centrifugal force of which tended to increase the damping actions with high speed which was necessary to get good characteristics. Our combination of friction and elastic damping does this job very much better and with a more foolproof construction. In the five years in which we have been building this damper in our various Packard lines, including the twelve, I don't know of a single damper that has been returned for any cause other than a loose fit of the hub on the shaft. All of its predecessors have been subject to conditions of the atmosphere and were very susceptible to water around the engine, especially water pump leaks, etc. It was also very difficult to maintain them in adjustment, for if the periods in the lower speed range were taken care of, the ones in the top range would be bound to stick out like a sore thumb. If the opposite adjustments were made, the reverse was true. I am enclosing a construction drawing of this damper which you may find of interest. I was much interested in what you said of Girling brakes and the inadequacy of Bendix productions. You certainly must use your brakes much oftener and far more viciously than we do. In my personal driving I have reached approximately 10,000 miles between adjustment of the brakes and better than 30,000 miles for brake lining replacements. I am speaking now of driving I do in town and cross-country work with the family, considering that we make 500-mile runs between breakfast and dinner with plenty of time out for lunch and sometimes sightseeing, you can see that we have to maintain a high average speed, which, I would say from my own impressions, is accompanied by considerable use of brakes. | ||