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).
Comparison of observed and calculated critical speeds for various engines using different calculation methods.
| Identifier | ExFiles\Box 137\4\ scan0002 | |
| Date | 8th April 1929 guessed | |
| Contd. -2- This gives much closer agreement with your formula, as shown. The test on 15 C was done before my time, and I should not be perturbed over the large error - 19%. We have had plenty of shafts since whose errors have not exceeded ± 6% twisted in bearings. The other two prints show estimated and observed critical speeds. Table 2. is obtained by the brief method of considering 1/3rd of the distributed inertia as concentrated on the nose, plus any inertia there already (e.g. spring drive hub, etc.) Agreement is pretty close. Table 3. shows the results using the "system of flywheels" method, i.e. considering the crankshaft as a row of similar flywheels connected by shafts of equal stiffness. The error is as follows: Engine. Critical speed. Ratio: Observed. Calculated. Calc./Observed. 1-G-1 3850 4300 1.12 Std. 20 H.P. 3300 4180 1.27 Std. Phantom. 3250 3260 1.00 Lorraine. 3800 3280 .86 Stutz -8. 3800 2710 .71 Results are not so good as with the simple method. I regret we have no aero-engine figures to send you, but hope to be able to some day. Please let me know if you would like further enlightenment. Yours faithfully, For ROLLS-ROYCE LIMITED. | ||