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 engine unit pressures, bearings, and weight-saving measures for the Wraith engine.
| Identifier | ExFiles\Box 114\2\ scan0076 | |
| Date | 1st October 1934 guessed | |
| -4- The unit pressures are much below the big-end figures. Comparing the Wraith with the Bentley we are providing more balance, but at the same time we are providing larger main bearings. It appears that we could reduce these in length is we wished, saving length on the engine. Supposing in the limit we were to make all cylinder centres the minimum value we should save a total of 1.45" on the length of the engine, a considerable amount in weight. The journals would then be .950 long and the main bearings would still be 79% of the area of each big-end, whereas they only need to be about 75%. The above table would then be as follows:- End. Inter. Centre. Areas. 2.375 2.375 2.375 sq.ins. Average inertia press: 480 680 960 lbs/sq.in. Max.gas unit pressure. 1580 1580 1580 lbs/sq.in. These figures still compare favourably with the big-ends. Since we fit fairly large balance weights there is no longer any reason to make the centre bearing any longer than the others. The saving in weight would more than justify the extra weight on the balance weights, in other words we should save more than the added weight of the balance weights. Before the adoption of counter weights on the six cylinder engine the average unit pressures on the intermediate and centre main bearings were respectively 30% and 80% greater than on the big ends. I also suggest that instead of having a groove all round the bearings and one oil hole in the journal as in the Bentley we should have grooves in the top shells only or on the sides as in the Phantom and aero. engines, with two or three oil holes in the journals. The Bentley intermediate bearings are 1.15" wide and having grooves .15" wide they are hardly longer than the .95" suggested for the Wraith if ungrooved. Contd: | ||