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).
Phantom model springing, discussing stiffness, rating calculations, and manufacturing limits.
| Identifier | ExFiles\Box 67a\1\ scan0054 | |
| Date | 6th January 1926 | |
| +8410 BMR GWB. C. Hs.{Lord Ernest Hives - Chair} M.{Mr Moon / Mr Moore} BY2/H.{Arthur M. Hanbury - Head Complaints} 6.1.26. **************** PHANTOM SPRINGING. ***************** Further to BY11/H.31.12.25. and in reply to CWBL/EP.{G. Eric Platford - Chief Quality Engineer}5.1.26, dealing with paragraphs by number, our remarks are:- 1. In CWBL/EP.{G. Eric Platford - Chief Quality Engineer}11.12.25. the statement was made that there was an impression at your end that "springs had got stiffer and stiffer". This could only occur by a modification to the method of calculating springs. The information given you re rating has misled you. The rating of the rear spring is arrived at by treating the cantilever spring as a semi-elliptic, which means actual rating in relation to load on axle is 300 lbs. per inch. The reason for using a 600 lbs. rating is that this covers the method of testing spring when it is treated as a semi-elliptic. The limits in the rear spring are plus or minus .250 at 8" deflection. We have tried to reduce this limit as SP{Mr Spinney} knows, and failed, as when we tried to work closer to plus or minus .125, we found that due to limits necessary on camber, a lighter spring by poundage actually raised chassis higher and increased the variation from standard position instead of decreasing it, as it should have done. This was due to the fact that the manufacturing limits in the camber "masked" the correction, and resulted in increased error. The limit of plus or minus .250 cannot be reduced at present, due to this position, but the plus or minus .250 only means we can be that amount away from the theoretical loaded position. It never means a spring is 150 lighter or heavier than the one specified by Drawing Office. By our methods we specify a spring as say:- "2000 lbs." "2000 lbs. plus". or "2000 plus wide". and similarly:- "2000 lbs. minus" or "2000 lbs. minus wide". Contd. | ||