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).
Explaining the operation of a pendulum type vibration damper.
| Identifier | ExFiles\Box 132\1\ scan0158 | |
| Date | 29th April 1940 | |
| Ev.{Ivan Evernden - coachwork} from Rm{William Robotham - Chief Engineer}/JRS. c. JNR.{Charles L. Jenner} 1073 Rm{William Robotham - Chief Engineer}/JRS.3/JS.{Mr Johnson's Secretary}29.4.40. 1116 PENDULUM TYPE VIBRATION DAMPER. The S.A.E. preprint "Geared Engines for light air planes" by C.H.Wiegman of the Lycoming Division of the Aviation Manufacturing Corporation attached to OY.11/D/Mar.26.40. contains a section on Crankshaft Dampers. It shows amplitude-speed curves for an undamped engine and for engines fitted with Lanchester type and Pendulum type dampers. In his letter OY states that the Lanchester type did not work and that it suppressed the fourth harmonic, but made the second harmonic worse. This is not true. The fact is that the mass of the damper lowered the critical speed of both harmonics and, while it did actually increase the amplitudes at certain speeds, it was because the peaks of the damped curve were at a lower speed than those for the undamped curve. In order to explain the operation of the Pendulum type of damper, it is simpler to start with the undamped harmonic damper. This is shown diagrammatically in Fig.1. The addition of a small mass 'm' connected to the main mass 'M' by a spring of stiffness 'K' results in a complete change in the resonance curve, Fig.2. There are now two frequencies at which resonance occurs, but there is one frequency at which there is no vibration. This frequency is the natural frequency of the damper and in this condition the main mass 'M' is held stationary and the disturbing force is balanced by the force supplied by the vibration of the absorber mass 'm'. The pendulum type of damper is an absorber whose frequency is always equal to the frequency of one harmonic of the disturbing force. This is arranged for as follows: The disturbing frequency of any particular harmonic Continued... | ||