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).
Vibration analysis report detailing tests on engine banks, component frequencies, and asymmetric forces.
| Identifier | ExFiles\Box 138\2\ scan0159 | |
| Date | 14th July 1938 | |
| - 4 - The diagrams were taken at the standard position on each of the four banks in turn with the vibrograph in the horizontal plane. It was found, as might have been expected from the tying action of the induction systems that similar diagrams were obtained from the members of the upper and lower banks respectively. An estimation of the frequency showed that the upper pair were moving with a frequency equal to the airscrew shaft frequency, but no such frequency could be observed in the lower pair. Unlike those of Series II however, the diagrams from 'C' and 'D' banks were well defined and a reliable estimate of the frequency gave 50 cycles per second, to correspond with the crankshaft speed. Examination of the diagrams from 'A' and 'B' banks revealed the presence of a component superimposed upon the basic diagram at approximately 3 x airscrew shaft frequency and it may reasonably be held that this corresponded to the exciting frequency in the two lower banks. (It must be pointed out that a similar superimposed component was found on the corresponding diagrams at 2900 and 3000 r.p.m. in Series II, although it was not apparent at the lower speeds investigated.) This test afforded clear evidence that an unspecified set of asymmetric forces were acting in the engine to produce vibrations at different frequencies in the upper and lower banks. It is difficult to ascribe the exciting force at airscrew frequency to misalignment between engine and brake on the test bed, as this affects only 'A' and 'B' banks although the geometry of the engine mounting is perfectly symmetrical and the vibration is consequently to be expected equally on every bank. Alternatively, there may be an unsuspected effect associated with the reduction mechanism, but here again difficulty is introduced by the symmetrical arrangement of the gearing with four layshafts. SERIES V.{VIENNA} No.1. This series was performed on 14.7.38 with Vulture I This engine had been rebuilt since its employment for Series II on 5.7.38. and had been reassembled with reduced backlash in the timing and camshaft gears. The tests were made at 3000 r.p.m. and 5 lb/sq.in. boost. The results so obtained are of interest because it was found that the fundamental frequency of vibration had become the same for all four blocks and occurred at crankshaft frequency with a trace of a superimposed component which may correspond to the third harmonic or piston side thrust frequency. The amplitudes on the various blocks were measured as follows :- (based upon the static calibration). 'A' ........ 0.006" 'B' ........ 0.006" 'C' ........ 0.008" 'D' ........ 0.007" Comparing these figures with those obtained in Series II, it will be noted that the amplitudes of 'C' and 'D' remained at the same order, but that some improvement had been effected in 'A' and 'B'. | ||