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 frequency and amplitude measurements on Vulture engine blocks under varying boost pressures.
| Identifier | ExFiles\Box 138\2\ scan0158 | |
| Date | 11th July 1938 | |
| - 3 - The fundamental frequency in the vibration spectra of 'B' block is seen to correspond with the airscrew shaft frequency. At this stage it was difficult to ascribe any definite reason to excitation at this frequency, but possible causes were considered (i) Misalignment of the engine on the test bed. (ii) Some effect unspecified but associated with the layshafts etc. in the reduction gear housing. It will be appreciated that the fundamental frequency of the forces due to the piston side-thrust will be at 3 x crankshaft frequency. The above tests having been carried out on 'B' bank only, a further series of runs was performed on all blocks to determine whether 'C' and 'D' were affected to the same extent whether the bottom assembly containing the master-rod was more satisfactory, as had been indicated by the record of failures. These runs were performed at the speeds where the vibration was most marked, i.e. at 2700 and 2800 r.p.m. with a boost of 4 lb/sq.in. It was found that both 'A' and 'B' banks were exhibiting vibrations at the airscrew-shaft frequency, as might have been expected in view of the tying action of the induction pipe. However in the case of the lower pair it was evident that the fundamental occurred at a considerably higher frequency although the amplitude of the vibrations was relatively smaller. Owing to the character of the diagrams it was not possible to determine the frequency accurately, but it was estimated to lie in the region of 45 cycles, i.e. at crankshaft frequency. The final set of measurements under Series II were carried out to determine the effects of boost pressure on vibration amplitude, and were run at the previously determined "worst speed" of 2700 r.p.m. The measured amplitudes on 'B' block with the vibrograph held in the horizontal plane were as follows :- TABLE II. CYLINDER VIBRATION AND BOOST PRESSURE. 2700 RPM. 'B' BLOCK. VULTURE I NO.1. (MASTER ROD IN 'D' BLOCK). Boost lbs/sq.in. Amplitude. Airscrew Shaft Frequency. Recorded Frequency. 6 0.013" 18.0 17 4 0.013" 18.0 17 2 0.010" 18.0 14.5 -2 0.007" 18.0 16 These results agree with the theoretical considerations that an increase in boost pressure will result in an increase of the loading producing vibration. SERIES IV. This series was carried out on 11.7.38 upon Vulture II No.2. The tests were made during a 5 hour run as part of the type test and were consequently limited to 3000 r.p.m. and the maximum climbing boost of 5½ lb/sq.in. | ||