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).
Investigation into engine vibration failures, torsional resonance, and experimental testing on various engine models.
| Identifier | ExFiles\Box 142\1\ scan0276 | |
| Date | 4th October 1938 | |
| (2) All these types of failure have been recorded separately on past occasions and a consideration of the conditions points to the fact that they are in general the resultant of excessive vibration, similar units having achieved a satisfactory degree of reliability on other types of engine. However, in view of the above record which was less satisfactory than those obtained on previous development runs, a feeling was expressed that these failures might be attributable to increased vibration associated with the revisions of design incorporated in engine II - 4. On the other hand, it was also suggested that severe vibrations might be induced from the interference effects experienced when running a 16 ft. airscrew at Sinfin Hangar. It is clear that due to the asymmetric conditions a considerable forcing torque would be experienced at 3x airscrew frequency, which might conceivably induce a torsional resonance in the airframe. No definite figures are available from Hucknall as yet for the natural torsional frequencies of the Vulture engine in its mounting but by analogy with the Merlin Whitley mounting (*) the figure for this resonance is scarcely expected to be above the first order airscrew frequency, thus ruling out the possibility of any mounting resonance excited by the interference frequency. However, in this connection it must be pointed out that on one previous occasion a 16 ft. airscrew was employed successfully on the hangar mounting, when Vulture II - 6 ran 22 hours including 2 hours climbing without ignition failure, the test being terminated by a definite lubrication failure. 2. EXPERIMENTAL WORK.- The Askania vibrograph was used for an investigation into the vibration of the units contained in the normal type of shroud following the return of engine II - 4 to the bed for the final 30 hours. A similar investigation has also been made on the engine II - 2 for the purposes of comparison in order to ascertain whether any special vibration conditions existed on account of the drive and reduction-gear modifications in II-4. It is pointed out that engine II - 2, which was standard in respect of the drive, etc. has completed 85 hours out of 100 hours development running, including 40 hours hangar running with 20 hours at 2850 r.p.m., without sustaining vibration failures on the ignition. It is, therefore, assumed that the vibration conditions obtaining are satisfactory. (This test was also run with a 16 foot airscrew). For the purposes of the tests readings were taken of the vibration components in the vertical, longitudinal and transverse directions from the top of the screening cover. (The lower banks were not accessible for the vibrograph to record longitudinal vibrations). (*) See "Static Testing of Merlin Whitley Mounting"...Dor{Mr Dorey}/Hks.2/FEB. 4.10.38. | ||