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 design of 14-inch diameter Bentley front brake drums, aiming for minimum weight, maximum rigidity, and cooling area.
| Identifier | ExFiles\Box 84\2\ scan0294 | |
| Date | 5th February 1935 | |
| Hs{Lord Ernest Hives - Chair}/AFM.{Anthony F. Martindale}25/KW.5.2.35. Report on Design of 14" dia. Bentley Front Brake Drums, having minimum weight, and maximum rigidity and cooling area. It is proposed to make 14" dia. brake drums for Bentley front axles for experimental purposes. The advantages for braking purposes are considerable, but other things being equal the larger drum means more weight and more distortion under the load of the shoes. It is known, however, that the present standard drum is not as rigid as a drum of its weight should be, and by improving the design it is hoped to produce a 14" dia. drum that is more rigid than standard and very little heavier. The brake drums fitted to Bentley 5-B-IV, detailed on drawing No. EX.16384, have been chosen as the criterion. The 14" dia. drum is not to exceed them in weight, and is to be at least as rigid without sacrificing any of the cooling area. We have accordingly made measurements on standard 'C' series drums and 5-B-IV drums, the results being attached hereto in graph form. A word of explanation is necessary to understand them. When the brakes are applied on a stationary car, the shoes press outwards that section of the drum with which they are in contact, and to compensate for this the "free" portion of the drum is drawn inwards. It is much easier to make calculations with regard to this free portion, and so we have obtained an empirical connection between the outward and inward deflections. Graphs (1) and (2) show this connection for the two drums under test, graph (3) shows the strengthening effect the hub plate has on the drum at its centre, and graph (4) shows the effect of using shoes having a smaller angle of embrace. It will be noticed that the deflection produced by maximum normal load is the same in each case, but that under lighter brake applications a bigger proportional deflection takes place with the shorter shoes. A higher degree of rigidity will be required if the latter shoes are used. | ||