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).
Series of fan failure tests caused by deliberate imbalance.
| Identifier | ExFiles\Box 86\5\ scan0047 | |
| Date | 29th May 1935 | |
| -2- (4) The fan used in (3) was deliberately put 3 1/2 oz. ins. out of balance and run for 15 minutes at a speed corresponding to 4,850 engine r.p.m. After 15 minutes the fan broke up. Examination showed that the trunnion housing (E.52864) on the fan spindle arm had broken at the point where it is spigotted into the arm, see fig. This had permitted the arm to be pulled back against its stop, which was broken. The spindle was undamaged. The main cause of the fatigue failure of the trunnion appeared to be the sharp corner shown in diagram (1). (5) Test (4) was repeated with spindles with strengthened trunnions (nickel steel with corners radiussed), using both a standard fan bracket and a strengthened phosphor bronze bracket. In the first case the spindle was cracked and the bracket twisted, while a blade was torn off by the guard. In the second, the spindle fatigued and broke at the section shown in diagram (1), a blade also being torn off. These failures took place after approximately 15 - 17 minutes' running. In the case of the phosphor bronze bracket it was found that if the adjusting trunnion was locked with a nut either side (see diagram 2), no breakage occurred in 40 minutes' running. (6) To establish the fact that the failures were not being caused by fan blades flying off, a test was run with a fan flange with no blades fitted - conditions as in last test (standard fan bracket). After 10 minutes' running the fan spindle fatigued and failed as in (5). (7) The above test was then repeated with the out of balance reduced to 2 oz. ins. (the figure for the production fan which we checked after failure). The spindle failed after approx. 30 minutes' running, the failure being a fatigue one of precisely similar type to the previous ones. (8) A 10 hour endurance test on a Bentley fan fitted with Dural blades was run (speed = 5,000 engine r.p.m.). No trouble occurred. | ||