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).
From R. on new aero engine designs, comparing 12-cylinder and 16-cylinder models and recommending an alternative engine.
| Identifier | ExFiles\Box 43\1\ Scan064 | |
| Date | 11th May 1924 | |
| To CJ. from R.{Sir Henry Royce} c. to BJ. RG.{Mr Rowledge} c. to BY.{R.W. Bailey - Chief Engineer} HS.{Lord Ernest Hives - Chair} MR. Claremont. X3989 R1/M5.11.24. RE. NEW AERO ENGINE DESIGNS. X.3989 X.4827 RE. 500 HP. SUPER EAGLE. The 12-cylinder model of this engine is progressing side by side with the 16-cylinder, as very much of the design is in common. Though I suggested making both these engines so as to be sure that we are not making a mistake I believe it would reduce the work and expenditure if we were to first make the 16-cyl. engine, and if this is as good as I anticipate we shall not want to make the 12-cyl. engine. You will remember that 10 years ago I pressed for the 12-cyl. engine, and when we produced the Eagle, there were few, if any, engines of that type that had been successfully made. One remembers that nearly all the successful severe work upto the present has been done by this type of engine. The reason that I favoured the 12-cyl. V.{VIENNA} was due to its smooth turning and perfect balance, but naturally we knew it had a long and flexible crankshaft and very severe interval stresses in the crankchamber, especially at the very high speeds that have lately been adopted, to obtain a better H.P. weight performance. I now believe that we and others cannot do much to improve the best performance of this type of engine, and owing to its internal stresses above mentioned its reliability at these high speeds cannot be all that is desired. I am therefore at this moment recommending an alternative engine. Of all the possibilities I have examined in numbers and arrangement of cylinders I find there is nothing to my mind of sufficient perfection until we arrive at the 16-cyl. 4 row engine with certain special features I believe will prove so nearer perfection in running, that for HPs.{Horace Percy Smith - Experimental Factory Mgr} of 500 and more, the number of cylinders will soon be forgotten. This engine appears to work out lighter and smaller with the short stiff crankshaft, which can by our schemes, be arranged to have practically no crankchamber stresses due to inertia, and will prove the solution of the difficulties which manifestly contribute to that want of reliability which has been so apparent in the engines undertaking long journeys with heavy loads. You will remember that earlier I proposed an engine of 3 blocks of 4 cyls. radial, with our special crankshaft arranged, but on examination i found this engine might be a disappointment owing to its want of perfect balance. I therefore increased the blocks to four which not only gives perfect balance and a smaller head resistance, but has a number of practical advantages in its construction. This engineis the one we are working on vigorously. contd :- | ||