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).
Analysis of spring periodicity and mean radius, comparing single, double, and Curtiss D.12 valve springs.
| Identifier | ExFiles\Box 56\2\ Scan066 | |
| Date | 20th February 1929 guessed | |
| (3) The single spring No.(3) although very nearly the same periodicity as the double spring No.(4) appears to be satisfactory where the latter is not. This is difficult to explain. To shew however that a high F.O.M. does not necessarily go with a low periodicity we quote the Curtiss D.12. These Curtiss springs have very small Mean Radii and in consequence high stress range, though the max. stress is very low. In passing it should be noted that there is a useful difference between the periodicities of the inner and outer Curtiss springs. We were unfortunate in the SS.{S. Smith} double springs having periodicities less than 2% different between inner and outer. PERIODICITY & MEAN RADIUS. So far as we have gone the obvious inference is that it is good practice to proportion valve springs to obtain the highest possible natural frequency. Selecting a known spring - e.g. Phantom E70442. we will take the same quantity of wire but wind it to a mean radius .1" smaller. The results are as follows: | SPRING. | LOADS. | STRESSES. | F.M. 90,000 Max:+Range. | Periodicity per min. | | :--- | :--- | :--- | :--- | :--- | | | Min: | Max: | Min: | Max: | Range. | | | | Phantom E70442 7 coils of 8 SWG .64 mean radius. | 60 | 89.5 | 47,650 | 71,000 | 23,350 | .95 | 10,780. | | 8.3 coils of 8 SWG. .54 mean radius. | 55.8 | 97.3 | 37,400 | 65,250 | 27,850 | .96 | 12,870. | The spring-loads are based upon arriving at the same pressure at one third valve lift. [A graph shows two ascending lines. The lower line starts at a point labelled 55.8 and ends at a point labelled 97.3. The upper line starts at a point labelled 60 and ends at a point labelled 89.5] It will be observed that the periodicity has been substantially raised with no alteration to the FOM., the maximum stress having decreased and the range increased. | ||