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).
Design rationale and modifications for a new ultra-high-speed engine.
| Identifier | ExFiles\Box 43\1\ Scan065 | |
| Date | 20th January 1925 guessed | |
| contd :- -2- As an ultra high speed engine which this one is capable of, I have decided that it is desirous to go back to the overhead camshaft and use twin valves per cylinder. We shall then be sure that neither the heating of the valves or their leaving the cams will cause us any trouble because such valves can easily be made to follow their cams up to and above 3000 r.p.m. (and the valve sizes in this case will be about 1¼") so that we are pretty certain to have no valve or valve spring troubles. One beauty of this engine is that it is a better manufacturing proposition, being made of a larger number of small parts which are interchangeable, and therefore facilitates the mass production of the parts, and as this is one of the difficulties with aero engines, we think that although the engine may sound rather formidable owing to the larger number of cylinders, I believe that both in appearance and with experience of making, it will cost less as a tested finished engine than would be the 12-cyl. V type engine of the same H.P., and that it will beat this latter in weight and reliability. We have lately discovered that the last item of perfect balance, owing to the staggering of the big ends, can be cured by re-arranging the order of the con. rods on the crankpins, and making the lower or upper cylinder blocks longer. The total length of the engine however will only be increased ¾", but this disadvantage is only partial, as we then get extra bearing or crank web dimensions. The sketchs sent to Mr. Claremont from a patent point of view shew this last modification to give perfection of balance. You will remember that in an earlier memo. I suggested firing this engine in pairs, and can fire the whole engine with 2 double spark 8 cyl. magnetos. If however we wish to render the turning moment still more smooth, as may be necessary for gearing, we can get 16 equally spaced impulses by modifying the design of the crankshaft and camshaft, and fitting four 8 cyl. single spark magnetos. The sketch of this modification is also included. We may find however that four impulses per rev. as originally arranged gives sufficiently smooth turning moment, considering all the other good qualities that the engine has. These we described in a recent letter. These are again summarised here, with some additions. The estimated weight etc. we are not in a position to give at present. R.{Sir Henry Royce} | ||