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 steering box rocker shaft failure on a Phantom III Paris demonstration car.
| Identifier | ExFiles\Box 153\1\ scan0253 | |
| Date | 14th April 1939 | |
| Sg.{Arthur F. Sidgreaves - MD} Hs.{Lord Ernest Hives - Chair} C. Rm.{William Robotham - Chief Engineer} PHANTOM 111. RE: FAILURE OF STEERING BOX ROCKER SHAFT ON PARIS DEMONSTRATION CAR. I have been dealing with this matter personally from the time of receiving the report of the failure. Its seriousness was, and is, appreciated. Having now had an opportunity of examining the fractured rocker shaft I can say without fear of contradiction that the failure of the shaft was due to what occurred at the time the accident occurred. The material itself was in excellent condition, its tensile strength being as high as 64 tons per square inch, with a high ductility, as evidenced by the twist on the shaft which occurred before fracture took place. By calculation, the load on the ball end of the pendulum lever necessary to break the rocker shaft is 14 tons. In addition, the roller race at the opposite end of the shaft was indented as a result of the impact by the rollers forming the bearing being forced into the hardened race, a fact which confirms the intensity of the blow which caused the failure. The remarks attributed to Mr. Faroux in Sr.7/ET. 5.4.39. are quite fair and impartial. You will notice that he remarks that he is incapable of stating whether the fracture of the rocker shaft took place prior to the car over-turning or at the moment of impact or at the moment when he felt the lack of control. What I would consider to be a reasonable explanation of the accident, and how so heavy a blow could be transmitted to the steering, is that a loose heap of dirt, such as described in the report, into which the right hand front wheel of the car was driven would not lift the wheel off the road like a heap of closely packed sand or a similar heap of small stones, the effect of the impact of the wheel into the loose earth would be to press the earth down at first, and then built it up in front of the wheel, and I consider that the offside or R.H. wheel was forced through the mass of earth by the energy of the car, the earth acting practically as a solid chock in front of the wheel. Under these circumstances, a heavy blow which would persist in the sense of following up the first attack steadily would be imparted to the road wheel, and through the wheel to the levers and rocker shaft, and I can imagine the blow being of a sufficient intensity to shear the rocker shaft. It is rather interesting that in following the description in Sr.7/ET.5.4.39. I remarked that a heap of sand or stones would be quite innocuous, but that a heap of loose | ||