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 principles of dampers, referencing Frahm anti-rolling tanks and suggesting adjustments for crank frequency.
| Identifier | ExFiles\Box 170\2\ img091 | |
| Date | 21th July 1931 guessed | |
| The principle is exactly the same as the Frahm anti-rolling tanks, namely that at the critical speed the damper (or water in the tanks) is 90° out of phase with the motion of the object. It tends to produce two secondary peaks, the first of which (damper and shaft in phase) is the worse, and the second (damper and shaft in opposition) is the better. Both of these peaks are less than the original peak (with a reasonable mass of damper) and they are largely "smeared out" by damping. Timoshenko on p 198 has something to say on the mass (or inertia) of the applied damping weight, from which it appears that in theory any weight can be used, but in practice the small weight gives an impossible spring and there is an optimum condition to be calculated (by trial) between inertia and spring stress. You may recall I suggested some time ago that by simply adjusting the circumferential springs on the PII & 25hp dampers to give a natural frequency equal to the crank frequency and perhaps reducing the friction and a little, you will have all you want without change in design, and probably in the best although not the simplest form. | ||