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 tests conducted on Vulture and other engines using an Askania vibrograph.
| Identifier | ExFiles\Box 138\2\ scan0156 | |
| Date | 5th July 1938 | |
| VIBRATION TESTS ON VULTURE AND OTHER ENGINES - EMPLOYING THE 'ASKANIA' VIBROGRAPH. The Askania instrument was originally applied to the Vulture engine in connection with a cylinder block vibration which was considered abnormal and held to be responsible for the repeated failures experienced with such items as water-connections etc. In the Vulture engine with four cylinder banks at 90° spacing, the connecting rod assembly follows the usual articulated arrangement with the master rod normally located in 'D' bank. (Bottom left hand as viewed from airscrew end). Consequently the maximum angularity and the maximum side thrust occur on the articulated rods in 'B' bank, and it was suggested that the effects of this arrangement were responsible for the abnormal conditions. In support of this argument it was found that the upper blocks 'A' and 'B' exhibited the greatest amount of vibration, and experience had shown that the majority of failures were confined to these banks. It will be noted that the induction system on the engine is located between banks 'A' and 'B' on the top and 'C' and 'D' on the bottom and consists of a massive pipe assembly which may be regarded as tying together the respective members of the top and bottom pairs. SERIES I. A series of vibrograph readings had been taken on Vulture I prior to 3.7.38, records being available for speeds of 3000, 2850 and 2600 r.p.m. for the several cylinder banks. The vibrograph had apparently been actuated from various points on the valve-cover casting which provided a suitable section for the generation of spurious 'panel' vibrations. These were present on the diagrams as a high-frequency component which interfered with the normal waveform and produced a 'blurred' appearance that rendered an estimation of the vibration frequencies impracticable. However, it was clear that the vibration amplitude was considerable and most marked on the upper pair. It might reasonably be assumed that any excessive vibration originating in 'B' bank with the greatest angularity would have been transmitted via the induction pipe to 'A' bank. SERIES II. An extended series of vibration tests was carried out on Vulture I No.1. on 5.7.38, in order to gain further information, the routine being covered by the schedule of that date. The engine was first checked for performance at 3 points on the constant boost curve and then a diagram was taken off the valve cover on 'B' block to ensure the similarity of test conditions with those of the previous series. The next run was intended to demonstrate the effect of vibrograph location on the diagrams obtained for block vibration and in particular the high-frequency vibrations induced in the panels of the valve cover. The engine was run under the maximum climbing conditions of 5½ lb/sq.in. boost at 2850 r.p.m. and the vibrograph positions on 'B' bank included the following :- | ||