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 a fractured fan spindle from chassis B-34-AH, attributing the failure to imbalance and comparing it with other cases.
| Identifier | ExFiles\Box 88\1\ scan0190 | |
| Date | 24th May 1935 | |
| To Wor.{Arthur Wormald - General Works Manager} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to Hy.{Tom Haldenby - Plant Engineer} c. to Sft.{Mr Swift} c. to Hd.{Mr Hayward/Mr Huddy} X261 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}2/KW.24.5.35. Chassis B-34-AH. Philipson. We have examined this fan, which was removed from a customer's car with the spindle fractured. Fortunately in this case the failure was discovered before the fan smashed itself up against the radiator. We find that the fan is 7 1/2 grams out of balance. This amount of out of balance represents an alternating load on the spindle of 63 lbs., the engine revs at 4,500. This load, coupled with that of the belt tension, would in our opinion be sufficient to cause a fatigue failure of the spindle. The failure we recently had in France on 5-B-IV was due to the bracket failure. In this case the fan was probably slightly out of balance and the fan bracket, having been made in magnesium for experimental purposes, soon gave way from fatigue. Owing to the low geared axle, this engine was of course running faster than standard. We have since these failures done a great deal of running on the test bed at high speeds with fans, and have never yet succeeded in getting a fan blade to fly off unless the fan has been out of balance. We therefore conclude that even though fan blades have been found which did not appear to be damaged and which were detached from the fan hub, they must actually have struck something after the spindle failed which caused them to break off. Therefore, summarising our conclusions :- (1) The fan spindle and bracket on the Bentley are essentially the same as on the 20/25. The fan blades, however, are considerably heavier; they are therefore likely to be more out of balance than those of the 20/25. We understand that a number of these fans may have got through on production without being balanced; i.e. similar to the one which we have tested. If this has happened it would account for the failures which have occurred. It is evident that particular care must be taken to balance these fans in the future, and Hy.{Tom Haldenby - Plant Engineer} has issued the necessary instructions. Experimentally we are running aluminium fan blades, which are used on the Cadillac and which, being less than half the weight of the steel, will be easier to manufacture in balance. | ||