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).
Temperature tests and cooling rate analysis of brake drums on the Comet and Cresta models.
| Identifier | ExFiles\Box 120\1\ scan0305 | |
| Date | 28th February 1941 | |
| Results obtained on the Comet are given in Figure 4, and show clearly an improvement in the cooling rate, at 60 m.p.h., of over 50%. As has already been seen in Figure 2 curves 5 & 6, however, the same air deflectors fitted on the Cresta gave only a small improvement in cooling rate, and that only at 60 m.p.h. Evidently, on this case, it was not in the best position to catch the air flow due to peculiarities of the body. Experiment would no doubt produce a better position for this car and probably a compro-mise suitable for any car. TEMPERATURE TESTS ON THE RED GATE ROAD. On the Red Gate Road we heated the rear drums to 300° C. on the Comet, and higher temperatures of the order of 350° C. must have been obtained on several occasions when the linings were burned out. Later, on the Cresta, keeping inside the safe lining temperature margin, we found that when driven hard so as to obtain high temperatures, we obtained nearly equal temperatures front and rear. For slower driving, however, a rear temperature of 197° C. was accompanied by a front temperature of 175° C., and when travelling still more gently, the temperatures were 180° C. and 115° C. respectively. For the Cresta, these figures appear to depend largely on the speed of the car, as the curves on Figure 2 show that, whereas the cooling rate of the fronts does not increase much between 40 and 60 m.p.h., yet the difference on the rears is considerable; in other words, for a given front drum temperature the rears will be much cooler at 60 m.p.h. than at 40 m.p.h. A rough check was made on the above figures by means of the cooling curves at 60 m.p.h. and 40 m.p.h. shown in Figures 5 & 6 respectively. Using the 60 m.p.h. curves, we find that the cooling rate of the offside rear drum at 197° C. is 25.6° C/minute. Now the front/rear braking ratio of this car was 1.54 x 25.6 = 39.4° C/minute. The offside front drum curve has this gradient at 169° C., the actual reading on the road being 175° C. If we apply the same process on the 60 m.p.h. curves to a rear temperature of 180° C., however, we get a theoretical value of 146° C. for the front drum, when it should be 115° C. But we know that these figures were obtained at lower speeds, so using the 40 m.p.h. curves, we get a cooling rate of 15.75° C/minute on the rear at 180° C. and the required 24.2° C/minute occurs on the offside front drum at 116° C. It may be argued from these results that if at high temperatures, the front drums are as hot as the rears, then why were we not always relining the fronts on the Comet? But as has already been pointed out, there is a difference in the cooling curves for the Comet and Cresta respectively, the front drums on the Comet continuing to improve their rate of cooling above 40 m.p.h. when those on the Cresta had stopped. Thus the difference between | ||