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).
The investigation and analysis of high-frequency vibration in Vulture II engines during test bed trials.
| Identifier | ExFiles\Box 142\1\ scan0277 | |
| Date | 20th October 1938 | |
| (3) Early investigation showed the presence of a high-frequency vibration component which could not be resolved on the normal Askania diagram, the order being at least the sixth. However, following a suggestion by Lr{Mr Ellor}/SGL. this instrument was adapted to increase the film speed by some 2 1/2 times which allowed the necessary resolution to be obtained. Under these conditions whilst the frequency indication is considered to be correct, we are less certain about the amplitude accuracy owing to the difficulty experienced by the recording mechanism in following the higher accelerations. The final tests were made - Vul. II - 4 ... Test bed 22 .... 19-20/10/38. Vul. II - 2 ... " " 7 .... 18/10/38. 3. RESULTS. - The measured results from the two engines are given in the accompanying print V.M.I. for various/engine conditions. In general, the conclusion to be arrived at is that no special vibration conditions mark out the engine II - 4 with the revised gear drive. We must be prepared to accept certain discrepancies arising from the fact that the tests were actually made on different beds and for this reason we do not wish to stress the fact that in many of the measured results the vibration recorded on II - 4 is lower than that on II - 2 at similar speeds. Investigations have revealed that under test bed conditions the vibration sustained by the four distributor units is approximately similar, with some slight reduction on "D" bank. The records from the lower pair are more irregular in character but this may be attributed to the increased difficulty in holding the vibrograph. In any case from the preponderance of failures on the lower banks during the airscrew period it would appear that some modification of conditions must be imposed by the hangar mounting. In general the longitudinal vibrations are less marked than those occurring in the vertical and transverse directions. 4. TECHNICAL CONSIDERATIONS FROM THE DIAGRAMS.- An examination of the waveforms has shown that the frequencies present are sixth and first order (except in certain instances where the airscrew frequency is present, this being attributed to the effect of some degree of misalignment on the bed). However, the structure of the waveform is of interest in that the effect is not entirely one of straight forward addition but that the normal sixth order vibrations may actually be modulated in amplitude at first order frequency. Furthermore, in some cases, notably the vertical and transverse vibrations in engine II - 2 at 2400 r.p.m., both the effects of addition and modulation can be detected. At higher speeds the modulation effect only is discernable. | ||