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 letter discussing modifications for an order of springs with increased camber and deflection.
| Identifier | ExFiles\Box 52\2\ Scan251 | |
| Date | 15th October 1930 | |
| GS/DME. Mr. J. {Mr Johnson W.M.} Wortley Fawcett, Tinsley. 15th. October, 1930. Rolls Royce Order for Springs - October 11th. This order calls for springs which include modifications from existing designs, in the direction of very much increased camber and deflection under load. Item 1. This asks for a pair of 1100 lbs. springs 66" span, to have a free camber of 9.75" instead of 8¼". The existing design employs a main plate thickness of .28". The range of stress in the main plate, from free to loaded position, is at present 27.6 tons/sq.in. In order to increase the deflection under load from 8¼ to 9¾", it will be necessary either to increase the stressing in the main plate in the same proportion, or to decrease the thickness of the main plate in that proportion, or to compromise by partially increasing the stress and partially reducing the thickness. The stress mentioned has hitherto been proved to be satisfactory range, but I do not consider we have much margin. On the other hand, I do not think that Messrs. Rolls Royce would care to have the thickness of the main plate for these springs, appreciably reduced below .28". Before putting the work on these springs in hand, it is desirable to obtain from Messrs. Rolls Royce, what is the lowest thickness to which they would be willing to have the main plate reduced. It might, for example, be reduced to .25", but in order to give the deflection required, this would still leave us with the necessity for increasing the working stress by 5½ per cent. If this is acceptable to them, the necessary accommodation in the thickness of the remaining plates in order to give the required stiffness, could be arranged. At the same time, the effect on working life due to the increase in working stress, should naturally be the responsibility of Messrs. Rolls Royce. Incidentally, on the order it is suggested that this modified design can be obtained with alterations to existing springs made to the previous conditions. It would probably be more economical to start afresh and make up entirely new springs. Item 2. This calls for a pair of springs of the same span but to be made with a higher load, 1300 lbs., and to give 12" deflection. The increase in stressing on the main plate due to this increased deflection, corresponds to the ratio of 8¼" to 12", i.e. an increase of nearly 46 per cent. This is such a drastic increase, that it is doubtful if even the springs would stand up to the conditions under dead loading. To reduce the stress by reducing the thickness, as mentioned above, would give such a thin main plate that it is scarcely practicable. However, this might be reconsidered when Messrs. Rolls Royce give us a statement of the minimum thickness which they would 1. | ||