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 using a Cambridge Vibrograph and considerations for its future use and adaptation.
| Identifier | ExFiles\Box 138\2\ scan0171 | |
| Date | 13th September 1938 guessed | |
| - 5 - (4) THE TESTS PERFORMED WITH THE CAMBRIDGE VIBROGRAPH DURING THE DEMONSTRATION. In view of our interest in cylinder block vibration on the aero side some tests were made upon Merlin G.19, readings being taken concurrently with Askania instrument for the purposes of comparison. Owing to the proximity of the exhaust pipes and the arrangement of the Cambridge vibrograph it was not possible to apply this directly to the block in order to observe the transverse vibration at the head of the cylinder, so that diagrams had perforce to be taken from the panel of the valve cover. We had already has some experience that this location was unsatisfactory for studying the general vibration of the block owing to the introduction of a panel vibration which completely blurred the Askania diagrams. However the Cambridge instrument produced a clear diagram with the fundamental at crankshaft frequency together with a very pronounced harmonic content. Further diagrams were taken from the mounting feet of the engine, and portrayed a vibration with the fundamental at airscrew shaft frequency. It was found however that certain other points in the engines which have been of interest, e.g. various portions of the control mechanism of the carburetters and electrical auxiliaries were inaccessible to the Cambridge vibrograph in its present form. Proceeding to the car engine beds diagrams were taken in connection with a transverse vibration of the crankcase walls of the 4¼ litre engine. Here the shape of the instrument proved to be more convenient although the stylus could not be applied directly at the forward end. A set of enlargements of these records have been forwarded to RM{William Robotham - Chief Engineer}/GRYLLS with the measured results. (5) CONCLUSIONS : THE POSSIBILITIES FOR ADAPTATION OF THIS INSTRUMENT. In considering the general usefulness of this vibrograph in our works, a point which affects us is the question of film speed and the time available for making the record on a 16 cm. strip. From our experience with the Askania instrument we expect that a large number of the records will have fundamental frequencies of the engine first order which may extend to 70 cycles per second and over in the near future. Consequently in order to resolve the individual cycles it becomes necessary to use the highest film speeds, and in the drum pattern vibrograph the reading is restricted to less than eight seconds. It has already been mentioned that an alternative type of vibrograph for continuous recording on a film some 600 cms long giving four minutes duration is available. This would undeniably serve our purpose much more conveniently, especially under flight conditions, but attention must be drawn to the difference in the estimate for the two froms :- (i) Portable vibrograph - standard (drum) pattern £52.5.0. (ii) " " - continuous film pattern £121.0.0 The other question which has to be raised is concerned with difficulties arising out of the general size and contour of the instrument, and the demonstrated fact that in its present form the application to an engine on the test-bed was much limited by these considerations. In the instance of air frame measurements and in flight it is also to be expected that its use will be restricted | ||