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).
Copy of a letter discussing P.2 engine vibrations, periods, and mounting.
| Identifier | ExFiles\Box 137\4\ scan0298 | |
| Date | 31th March 1931 | |
| COPY OF LETTER RECEIVED FROM R.{Sir Henry Royce} 8634 Le CanadelHenry Royce's French residence. 31.3.31. x3993 P.2 VIBRATIONS. Thank Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} for his very complete report of the work done on the above. I am not, however, quite in agreement with the conclusions or the policy for the future. Though we know for certain that the 6 cylinder engine has imperfections such as torque reactions and overrunning vibrations I think we are worried with something else because the worst of our troubles are at certain periods. Take our 18-EX. although one feels that most people even like myself would think this to be as good all round as one could hope for, when critically observed there seems two distinct periods which it seems possible to alter. After passing the torque reactions at 25 m.p.h. these are very manifest on corners which generally reduces the speed to 18 m.p.h. we pass from 25 to 35 through a very smooth time when at 37 we can detect a slight but definite period at about 1200 engine revs. and this adds up to an octave vibration of the one at 65/75 which is very manifest and since it begins to show itself on a bad body earlier than on 18-EX. may well be the one LHS.{Lord Herbert Scott} mentioned at 60. Now Hs.{Lord Ernest Hives - Chair} and Rm.{William Robotham - Chief Engineer} do not believe this is flywheel, I think it is because I cannot see there is anything else to give us a period except the torsional vibration of the crankshaft, which I understand Derby is quite satisfied that it is not an octave or harmonic of the master period. Being a period it must depend on the elasticity of something in the engine, its mounting including the chassis frame or the body synchronism, which suggested to me that the power unit should be put upon the test plate with something to replace the frame and our experts should tell us if any of these three periods are still there in periods at the same engine revs. (1) Torque reactions 3 per rev at 800 engine revs (vigorous).(2) Something at 35 m.p.h. probably 2 per rev, very slight like an harmonic or octave. (3) The bad one at 65/75 probably 1 per rev. If the engine shews these periods at the same engine revs on the test bed with an entirely different mounting, then the engine is at fault and can be improved. If not then it may be impossible to mount the engine in the chassis satisfactorily so that we get the combination of isolation from vibration with torsional support to the frame. Engine Mounting. I assume that Hs.{Lord Ernest Hives - Chair} would choose for future work the | ||