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).
And comparing vibration amplitudes and frequencies between 6-cylinder and flat-12 cylinder engines.
| Identifier | ExFiles\Box 159\5\ scan0073 | |
| Date | 26th October 1940 | |
| Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} from Rm.{William Robotham - Chief Engineer} 1373 Thermostatic Shop (handwritten) Rm.{William Robotham - Chief Engineer}8/ML.26.10.40. The information contained inRm/TAS.{T. Allan Swinden}8/JH. 24.10.40. is not quite what I wanted. I am interested to know what amplitude one might expect the 6/rev period on a flat-6 12-cylinder engine to attain. When talking of amplitudes, it is easier to give their magnitude relative to the half-speed period on a 6-cylinder engine, because we are familiar with this particular period and know what it feels like on the road. As you know, the 3/rev period on our present rationalised 6-cylinder engines, attains a maximum at somewhere about 5,100 revs and yet starts breaking the timing gears as low as 4,000 revs. It will certainly break a crankshaft in a very short space of time at 5,000 revs. We are not clear how much of this period is due to inertia and how much gas pressure. We do know that at 5,000 revs gas pressure is almost negligible but if maximum M.E.P. could be maintained at this speed, would inertia still be a predominating factor? The reason the half-speed or 6/rev period on a 6-cylinder engine is not more violent, as we understand it, is because the crankshaft only gets a kick from the cylinder every other cycle of it's natural vibration. On a "12" on the other hand, it gets a kick every cycle. We should have thought this would have the 6/rev period on the "12" much more than twice the amplitude of the 6/rev period on the "6". Normally, the shaft of a 12-cylinder engine is stiffer than the shaft of the corresponding "6" of half it's displacement. On the other hand, it usually has twice the big end inertia with corresponding increase in balance weights, so that the fundamental frequency remains the same as that of the 6-cylinder shaft. Will you correct me if I have made any fundamental mistakes in this picture of the flat-12 and, at the same time, give me approximately :- - Continued - | ||