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).
Analysis of clutch-burning and moderate speed drive failures, focusing on grinding cracks and pinion misalignment.
| Identifier | ExFiles\Box 143\2\ scan0189 | |
| Date | 24th June 1941 | |
| - 4 - BY/HB.{C. E. Harcombe}5/EIM.24.6.41. Continued: of aircraft controls could produce this condition. As a result of this steps are being taken to hasten the standardisation of a more positive change-over mechanism which will ensure that no neutral period can be found. Pilots must put the change right over and not use the clutch as a slipping member under any circumstances. 2. The clutch-burning epidemic, however, proved to be only a percentage of the trouble and further engines showed breakup of the moderate speed drive in some way. The types of failure being as follows:- (a). Failure due to grinding cracks in the rim of the M.S. wheel. An examination of the defective parts showed cracks in the side of the rim of the wheel remote from the web, these cracks starting from both the inside edge running to the roots of the teeth and from the roots of the teeth inwards. Only one or two of these cracks developed seriously but this was sufficient to allow the rim of the wheel to expand loading up one side of the pinion and causing it to tilt. This would cause a fatigue crack to start from the side of the web of the pinion which was in tension, no doubt aggravated by the poor finish of the web which was noted in each case, further running causing failure. (b). Failure of the moderate speed pinion due to it being out of alignment with the wheel. The majority of failures have undoubtedly been due to this cause, the defective parts showing that bedding had not been taking place across the whole width of the M.S. pinion thus one side would be carrying more load than the other. This again would have the effect of tilting the pinion over and placing the side of the web remote from the overhang of the wheel in tension resulting in fatigue cracks starting from machining marks in the web and consequent failure. To overcome these defects the following alterations have been made. The question of grinding cracks in the rim of the M.S. wheel was most fully discussed at Crewe and it was made clear that work of this nature could not be tolerated. In addition a radius has been specified at the roots of the teeth and an alteration has been introduced continuing the chamfer on the ends of the teeth so that it does not run out co-incident with the roots of the teeth thus removing the possibility of a series of sharp edges running into a sharp corner. A .025" chamfer at 30° on the outside corner of the stiffened section rim has been specified to produce two obtuse angles instead of one acute and thus make it more difficult for cracks to occur. The possibilities of dry grinding have also been discussed and the need for getting the coolant jet on the correct - continued - | ||