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 analysis comparing the strength and deflection of different brake drum designs.
| Identifier | ExFiles\Box 84\2\ scan0295 | |
| Date | 5th February 1935 | |
| -2- This brings us to graph (5), which is obtained from graphs (1) and (2). This graph shows the deflection of the drum at all points in its cross section. It will be noticed that the curves do not converge on a point in the hub plate, but on some point approximately 0.3" outside it. This is taken to mean that this plate bends due to the cylindrical surface of the drum assuming an approximately conical shape. The cure does not lie in strengthening this plate, but in placing a rib of sufficient strength on the inside of the drum to prevent this change of shape. If the 14" brake drum is not to exceed the weight of 5-B-IV's 12" drum, it is imperative to reduce the thickness of the drum proper. If then the rib mentioned in the preceding paragraph is of great enough strength to keep the inner and outer radii of the drum equal, the weakened section will assume the shape of a barrel. To reduce this tendency the single deep section rib has been split, which also has the effect of returning the cooling surface to normal, or rather better than normal. Referring to the drawing of the suggested brake drums attached hereto, scheme (1) has the same weight as the 5-B-IV drums. Scheme (2) has the same weight except for the small rib, which rib, however, weighs less than that section of the hub plate with which we have dispensed. Scheme (2) seems preferable if the design is acceptable. The plate should be fixed outside the drum. To give a comparison of the strength of these drums and 5-B-IV drums is not very easy, but it seems that the second moment of area of the inner half of the cross section of these two types of drum affords a good comparison. These figures are :- 5-B-IV 0.0132 ins. 4 14" dia. 0.0473 " It will be seen that the new drums are very much stronger in this respect, but against this the bending moment movement increases with the size of the drum, and the rigidity also decreases with the size. It is hoped that this drum will be rather stiffer than the 5-B-IV drum. Hs{Lord Ernest Hives - Chair}/A.F.Martindale. | ||