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).
Continuation of a letter to W. A. Robotham regarding piston and connecting rod design, materials, and stress analysis.
| Identifier | ExFiles\Box 170\1\ img054 | |
| Date | 18th January 1939 | |
| Continuation of letter to :- Page 2, W. A.{Mr Adams} Robotham, Esq. 18/1/39. diameter of the cutter which can be got in to take metal out of the inside of the heads, enabling weight saving in the piston. One extra machining operation is introduced, that of taking away the forged bosses which extend from the gudgeon pin bosses to the crown. We have arranged this to leave you with two ribs extending from the bosses, up to the crown, and cross the top, on both the pistons which we have designed for you. The material will be the new cerium alloy which has been developed for pistons. The pistons are produced by pressing, not forging. We suggest that since the weight saving in the piston is approximately 29%, it should be possible to design a larger diameter gudgeon pin of no greater weight than your present one, if not lighter. We also think that you will find it lighter to use circlips instead of gudgeon pin end-caps, but we have not allowed for these in our drawings attached. [Handwritten note] Circlips work loose at high speed With regard to the connecting rod, we do not pretend this is as strong as your present steel one, which I take it is your intention. The neck stress due to inertia at 5,000 R.P.M. is only 8,460 lbs. per sq.in., whereas the neck stress in the Lagonda rod at 6,000 R.P.M. was 9,300 lbs. per sq.in. We have done our stress comparisons on the two engines at these speeds which we think favours your engine, in that the margin is greater. Lagondas have never had a straight breakage on any of their rods. The only rod they have broken was through seizure, before the lubrication of the big end was understood. The engine has done quite a lot of running at 5,750, and has been run up to 6,400 R.P.M. on the road. Cont'd ... ... ... - 2 - | ||