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).
Comparison of intermediate bearing loads in Wraith III and Bentley 111 crankshafts.
| Identifier | ExFiles\Box 115\2\ scan0371 | |
| Date | 5th December 1938 | |
| SWDL{Len H. Swindell} (crossed out) (Horsfall) SP.{Mr Spinney}.. (crossed out) Bearing General File BY (crossed out) C. Rm{William Robotham - Chief Engineer} BY/E.G/G.5.12.38. 102 D COMPARISON OF INTERMEDIATE BEARING LOADS IN WRAITH 111 AND BENTLEY 111 CRANKSHAFTS. At the outset it should be explained that the calculations were made for a Wraith connecting rod which is not now standard, and is rather lighter than the present production rod, thus :- Rod taken in Production rod. calculations. Weight of small end .406 lb. .3905 lb. Weight of big end 1.0312 lbs. 1.1405 lbs. 1.4372 lbs. 1.531 lbs. The Bentley connecting rod taken, also, is not the production model, but is rather heavier, being the rod with which a 15,000 miles trial was run. Thus, when comparing production models of each engine, the Bentley bearing loads will exceed the Wraith bearing loads by a rather less amount than that given by the calculations. This calculated excess load itself is only small, amounting to less than 240 lbs. in a total of about 3000 lbs. i.e. about 8%. The balance weights used on the Bentley are about .87 of the corresponding weights on the Wraith, a reduction of 13%. The outer intermediate bearings B and F are the most severely loaded bearings in relation to their length, when either inertia loading or explosion loading is considered. In the Wraith, due to rotating masses only, the absolute loading of F, (i.e. total load, and not per unit area), is practically equal to that of the centre bearing, which is so much longer. This is because of the large balance masses directly helping the centre bearing, which would otherwise suffer from the combined loading of cranks 3 and 4 in line. The outer bearings, A and G are very lightly loaded because of the large balance weights adjacent to them, which could be more usefully employed elsewhere. It seems possible that smoother running, by non-disturbance of the flywheel, could be obtained by thickening the webs of Crank 6 in an axial direction, and balancing locally. The bearings would be improved by increasing the total balancing weight, if this is possible without undue lowering of the critical speed. The moments of inertia (which affect | ||