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 effects of wheel discs and wheel cowls on brake drum cooling rates at different speeds.
| Identifier | ExFiles\Box 120\1\ scan0303 | |
| Date | 1st January 1928 | |
| Bm/MHR.{M. H. Rigby}4/ET.28. - 3 - disc on the outside, and more curves obtained using this wheel on front and rear. The curves got successively worse with each step. Results are shown in Figure 1 in the form of cooling rate speed curves, obtained from a series of cooling curves. Since there were only three points for each condition, we have not attempted to draw true curves, but have merely joined the points. It will be seen that the discs reduce the cooling rate to a greater extent at the higher speeds, giving an earlier flattening out of the curve since it is the air flow that they restrict. The use of both discs reduces the cooling rate at 60 m.p.h. by 25% on the front and by 33% on the rear. WHEEL COWLS. The wheel cowls were not available for the Coupe, but tests were started on the Comet while it was here, and completed on the Cresta. Results obtained with the latter car are given in Figure 2. These also include figures for front drums, and the effect on the rear drum cooling of various shoe adjustments, and of an air deflector which will be discussed later. The difference in cooling caused by the fitting of the wheel cowl is observed by comparing curves 4 and 5, and it can be seen that, at 60 m.p.h., the cooling rate at 150° C. fell 40.7%, although at 40 m.p.h. the change was only 21.9%. A complete set of figures was not obtained for the Comet, but at 60 m.p.h. the difference amounted to 38.2%, thus agreeing fairly closely with the Cresta. From its shape, we suspect curve 1, and prefer the dotted curve obtained on the Comet. By comparing this curve with No.6, it is clear that, at their worst, the rear drums cool at little more than one third the speed of the fronts. With regard to curves 2, 3 & 4, for every two notches variation in shoe adjustment, the air gap changes by 0.00875". POSITION OF DRUM RELATIVE TO WHEEL. We have no direct comparison on this subject, but some idea of the importance of the distance between a given drum and wheel can be obtained by comparing the curves in Figure 3, all taken from Figures 1 & 2. Now curve 4 in Figure 2 was obtained with an air-deflector fitted. Since the effect of this air-deflector only amounted to 2° C./minute (from curves 5 & 6), we have subtracted 2° C/minute from the 60 m.p.h. point on curve 4 figure 2 to obtain curve 4 on figure 3. | ||