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).
Connecting rod length and engine vibration for the improved 25HP model.
| Identifier | ExFiles\Box 137\4\ scan0165 | |
| Date | 11th January 1931 | |
| R.{Sir Henry Royce} FROM E.{Mr Elliott - Chief Engineer} C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} C. to HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} X634 E1/11.1.31. CONNECTING ROD LENGTH IMPROVED 25HP. X. 5030. X. 634. Referring to HS{Lord Ernest Hives - Chair}/RM{William Robotham - Chief Engineer}1/MJ9131., we have always had the impression that the 25HP. manifested over-run vibration which could be felt to a greater degree than on Phantom 2., and it was for this reason that it was desired to bring the improved 25HP. connecting rod crank ratio into line with the big car. The evidence of flywheel vibration so far exibited in the case of each engine does not yet, we think, entirely clear up the question of con. rod length. We cannot believe that other constructors have blindly copied Phantom 2. since they shew enough enterprise in other directions. All American six cylinder engines are consistent in using a ratio of con. rod to stroke of two or greater than two. Shorter ratios are in use in Europe. The 20HP. Sports Lorraine for example is 1.77 similar to our China. It is true that the curve of influence on the inertia of one piston does not shew much change in the range of ratio under consideration - Graph text: Y-axis: DIFFERENCE BETWEEN PISTON INERTIAS AT TOP & BOTTOM OF STROKE X-axis: CON ROD LENGTH / STROKE Curve labels: 25HP, L. COTTAGE, IMPROVED 25HP but on the other hand Sharp gives an expression for six cylinder inertia torque involving the expression r/l. We suggest that a dress rehearsal of the longer rods on an existing 25HP. chassis would be worth while, and that we should proceed with our new design unaltered for the present. (1) | ||