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).
Engine vibration tests, focusing on airscrew shaft frequency and the effects of master rod positioning.
| Identifier | ExFiles\Box 138\2\ scan0160 | |
| Date | 18th July 1938 | |
| - 5 - Measurements taken at various points along the top water pipe and connections however revealed that the high-frequency vibration amplitude was considerable and that no improvement had been effected since Series II. It is necessary to find an explanation for the disappearance of the airscrew shaft frequency from the vibration spectra of the upper blocks. (i) Misalignment of engine on test bed during Series II. This must be checked, but it should be noted that the same test bed was employed for Series II and V.{VIENNA} Consequently, we are led to the consideration of :- (ii) Some unsuspected effects associated with the fitting of the reduction gear unit. SERIES VII. These tests were carried out on Vulture I No.3. on 18.7.38 in accordance with the schedule issued 16.7.38. This engine had been specially refitted with the master rod transferred to 'C' bank, as this arrangement had been calculated to reduce the fluctuations in the side thrust summed over the blocks 'A' and 'B' and 'C' and 'D' respectively, - these combinations being regarded as tied by their joint induction systems. (The effect of changing the position of the master rod is to alter the phase in which the piston side thrust forces for the "tied" blocks must be summed. It has been shown that the maximum fluctuation in the summed side thrusts was reduced from 1700 lbs. to 900 lbs. following the adoption of the new arrangement). Vibrograph records were made for the following conditions in comparison with the results of Series II. (i) Readings taken on 'A' block (now opposite the master rod) with the engine running at the climbing boost of 5½ lb/sq.in. at speeds of 3000, 2800, 2600, 2400 and 2200 r.p.m. (ii) At the "worst speed" as determined from the foregoing, further readings were taken on 'A' block at boost pressures of 6, 4, 2 and -2 lb/sq.in. (iii) With the engine running at 4 lb/sq.in. and at the "worst speed" as above comparative readings were taken on all four blocks. The standard vibrograph position was employed with the instrument held in the horizontal plane. It was found that, in accordance with the theoretical considerations the vibration amplitudes were considerably reduced, and that the fundamental frequency now corresponded with crank-shaft frequency. Personal judgement on the test bed confirmed the reduction in the magnitude of the vibrations. The reason for the disappearance of any vibrations excited at the airscrew shaft frequency is presumably accounted for by some variation in | ||