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).
The investigation of friction losses in 3.5 litre and 4.25 litre Bentley engines.
| Identifier | ExFiles\Box 133\1\ scan0200 | |
| Date | 13th May 1937 | |
| To E.{Mr Elliott - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards} c. to Hs.{Lord Ernest Hives - Chair} c. By.{R.W. Bailey - Chief Engineer} c. Da.{Bernard Day - Chassis Design} 112-97 Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards}8/AP.13.5.37 BENTLEY FRICTION LOSSES. A considerable amount of work has been done recently in a detailed investigation of the friction losses in the 3 1/2 litre and 4 1/4 litre Bentley. The results fall into two sections:- (1) Measure of I.H.P. by the two methods of first cutting out cylinders, and second, measuring the power absorbed in motoring the engine. (2) Measurement of the power absorbed by the friction of the various components of the engine, and by breathing. SECTION I. It was found that of the two methods of finding the I.H.P., the second was easily the most accurate and the simplest, it being possible to repeat results at quite long intervals between runs to within half an m.e.p. With the other method viz:- cutting out the cylinders, however, a very slight error in the brake power readings was magnified six times in the indicated power readings, and to repeat curves accurately was found to be both long and tedious, as well as requiring accuracy almost outside experimental limits. Accordingly, while it is appreciated that for normal test bed work, this method is the most suitable, accurate results appear very difficult to get and the method should be used with discretion. Indicated and brake powers are given on Figs. I and II., where it will be seen that the method of cutting out the cylinders gives a somewhat lower result than the direct method. This is probably due to the action of the petrol in diluting the oil on the cylinder walls, and hence lowering its viscosity, a theory borne out by direct tests with the petrol on and off, the petrol on giving slightly lower results than when it is off. Considering now curves of mechanical efficiency on Figs. IV. and V.{VIENNA}, we see that the 4 1/4 litre unit compares unfavourably with the 3 1/2 litre, figures being as under:- continued | ||