Engine balancing, crankshaft stresses, steering issues, and the choice of a 12-cylinder engine for high speeds.
| Identifier | ExFiles\Box 5a\1\ 01-page060 | |
| Date | 29th January 1931 guessed | |
| (3) (i) Less overhanging weight, but this is less important than at first appeared (because not pure whirl.) (ii) Less weight remote from the centre of oscillation more important, but takes away our flywheel effect. (iii) Stiffen up back plate and crank pins: this may shift the speed up 10 to 20%. This is what we have done to 'China(Experimental Engine)' There are many other things as stated in Memos, but they are more difficult and I fear less effective, but will help in other ways. For instance half balance the couples - our high engine revs. though they ask for this, also prevent its being done except for this half amount. We have some time ago agreed that this is best carried out by the four balance weight scheme. Counterbalancing the couples reduces the loads on the bearings proportionally but the increase in engine revs. increases it as the square of the speed, (i.e. 42% increase in revs. doubles the crankchamber stresses and bearing loads.). It will be understood that even if we could make a crankchamber stiff enough we could not provide in the space satisfactory bearings for extremely high speeds: our 3000 revs. = 1/100 sec. per stroke or 5.5" starting and stopping. You will see now that double top is very much needed at the very first possible moment because I understand we now run too fast for maximum HP. at maximum road speeds; as well as the very high engine revs. being bad for maintenance, cost, fuel, oil, and wear. This letter only points out that steering troubles also come from high road wheel revs. and gyrostatic effects, somewhat reduced by independently sprung front road wheels. I cannot recommend "Reversible steering" unless we find complete satisfaction in some other specimen. After about 65/70 MPH. the front axle goes steady again: racing cars may pass this quickly. The 12 cyl. engine was started because it could be super-charged for the speed merchant: a 6 cyl. is quite unsuitable in our 'P. 2. size. If this letter contains any errors will someone kindly point them out to me. R. {Sir Henry Royce} | ||
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).