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 discussion on brake drum design, materials, and cooling improvements.
| Identifier | ExFiles\Box 120\1\ scan0309 | |
| Date | 28th February 1941 | |
| Rm{William Robotham - Chief Engineer}/MHR.{M. H. Rigby}4/LT.28.2.41. - 8 - From these figures it is evident that, since we cannot make our drums of larger diameter with 16" wheels, we must have them wider than the present type, with more ribs and a larger cooling area more in the air flow, and of a material having a high specific heat. We are now getting some aluminium drums cast round cast iron liners, these drums being of roughly the same dimensions as the present cast iron type. When we have developed a light alloy drum which does not crackle when hot, we shall know something of its heat dissipating qualities and shall be able to design a wider drum and hub combined. With regard to the wider drums and shoes, Figure D, shews in sketch 1 the present type of drum, and in sketch 2 a scheme using shoes 3 1/4" wide and two more ribs on the drum, giving a 2" wider track to the car. The cooling area of the drum is 40% up, and since a large portion is now away from the wheel, the improvement in cooling due to these causes combined will be perhaps 60%. In addition, the heat capacity of the new drum would be about 20% greater than for the existing type of drum, giving a further improvement. We do not know how effective are the ribs nearest to the wheel, but we could find out by taking cooling curves of 2 rib drums EAS.1755 as used on 12-B-V chassis. We could then decide whether the scheme in Sketch 3 on Figure D.{John DeLooze - Company Secretary} would be much less effective than that shewn in Sketch 2. A conclusion drawn from these tests has been that the more one covers up the wheel and drum and restricts air flow, the less is the cooling of the drums affected by the speed of the car. The ideal condition for rationalisation would be to produce a drum having a cooling curve so steep that the faster cars automatically cooled themselves as efficiently as the slow models. Whatever the final scheme adopted, we feel that the air flow should somehow be improved. Taking the drums out of the wheels comes under this heading, as do air-deflectors. If driven to it, we can always use ventilated pressed steel wheels on the rear since they will be hidden by the cowls. The spare wheel aspect is not considered to be serious. Rm{William Robotham - Chief Engineer}/MHR.{M. H. Rigby} | ||