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).
Analyzing the effect of various dampers on crankshaft critical speed and natural frequency.
| Identifier | ExFiles\Box 132\2\ scan0209 | |
| Date | 30th April 1941 | |
| To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} 11.6 Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}4/ET.30.4.41. 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 (from Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}1/ET.9.12.40). 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. 14,100 vib/min. Natural frequency of crankshaft after fitting Studebaker type damper. 14,150 vib/min. Thus, when a damper is fitted, the natural frequency drops 5 1/4% in the case of the Wraith type 7 1/4% in the case of the Humber type and 7% in the case of the Studebaker type. DIRECT REPLY - When the Humber damper is fitted, we may expect the critical speed to be about 100 R.P.M. lower than with a Wraith type damper. With the Studebaker damper, the critical speed should be about 80 R.P.M. lower than with a Wraith type damper. APPENDIX. In making the above calculations, the drop in frequency when a damper is fitted is dependent on empirical formulae for the length of a piece of crankshaft, and is therefore open to doubt. The difference in the frequencies with the different types of damper, however, is almost directly dependent on their respective hub weights, and may therefore be taken as correct. | ||