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).
Comparing the effect of a Humber type damper versus a Wraith type damper on crankshaft critical speed.
| Identifier | ExFiles\Box 132\2\ scan0208 | |
| Date | 28th April 1941 | |
| 1116(?) To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}16/ET.28.4.41. EFFECT OF HUMBER TYPE DAMPER ON CRANKSHAFT CRITICAL SPEED. --------------------------------- With reference to your memo Rm.{William Robotham - Chief Engineer}2/ML.20.4.41 to Jnr.{Charles L. Jenner}, here is the answer to Item 5., which was the effect of the inertia lowering the critical speed using the Humber Damper. Natural frequency of B.60 crankshaft, with no damper fitted. 15,200 vib/min. Natural frequency of crankshaft after fitting R.R. Wraith type damper. 14,400 vib/min. Natural frequency of crankshaft after fitting Humber type damper. 13,750 vib/min. Thus the damper causes a 9½% drop in frequency on that for an undamped crankshaft, 4½% more that a Wraith type damper. DIRECT REPLY - In other words, when the Humber damper is fitted, we may expect the critical speed to be about 220 R.P.M. lower than with a Wraith type damper. In making these calculations, the 9½% drop is dependent on empirical formulae for the length of a piece of crankshaft, and is therefore open to doubt. The difference in frequencies with the two types of damper, however, is almost directly dependent on their respective hub weights, and may therefore be taken as correct. APPENDIX. --------- Weight of the damper parts attached solidly to the crankshaft on: A.{Mr Adams} R.R. Wraith type damper. Friction disc. 1.69 lbs. B. Humber type damper. Driving flange, flange plate, pins etc. 2.66 lbs. Camshaft gear. .58 " Pulley, etc.. 2.66 " Friction washer, ferodo bush and springs. .17 " ---------- Total...... 6.05 lbs. Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} | ||