Sir, While appreciating the amplitude of Mr. I. G. Macleod’s reply, I feel that he has ranged over a somewhat wider field than was contained in the scope of my
letter—viz., the sleeve valve. I will, therefore, arrange my comments in two groups, (/) Points pertaining directly to the sleeve valve and (2) others arising from his more general remarks.
Mr. Macleod alleges that the only respect in which the sleeve valve is superior is in the elimination of the hot spot caused by the exhaust valve. But this, surely, is the primary object of all the many valves devised to take the place of the poppet. The other advantages I mentioned, which may possibly not apply directly to the racing-car, are of real value since they would be of first importance when the ultimate production stage was reached.
Recent developments have been in the direction of higher speeds and smaller pistons. Our unit, some few years ago, with 67 m.m. bore, straight fuel and unsupercharged, ran for twenty-five hours continuously between 3,500 and 5,000 r.p.m. (B.M.E.P. 165 to 140 lb. per square inch). No trouble was experienced with detonation, sparking plugs or vibration. Moreover it was stated at the time that, with a unit of this size, considerably higher speeds could be obtained without recourse to balancing gear. Since then, Ricardo has demonstrated the possibility of running an engine over long periods, with B.M.E.P. between 400 and 500 lb. per square inch (depending on fuel). Once again I should like to emphasise the practical side of the situation If an engine can pass the Air Ministry’s type
test, undoubtedly the hardest test of its kind in the world, then the practicability of that engine is indisputably proved.
I may assure Mr. Macleod that 1, too, am most interested in the Rotary valve. The controlled valve loading as applied to the Cross engine, certainly appears to have overcome one of the greatest of the previous difficulties experienced with this type. I was very sorry that the Halford-Cross-Rotary was unable to perform on Whit-Monday. Regarding Mr. Macleod’s suggestions for the future racing-car engine, I feel compelled to make these comments. Simplicity has always been the key note of success, but surely Mr. Macleod’s pet is rather an unnecessarily complicated piece of mechanism. Firstly, as no engine could be of the C.I. type (i.e. no spark and run on petrol, I am left with fuel oil as the alternative. Or can it be that ” direct ” petrol injection with sparking plug is suggested ? I should have thought that a two stroke with petrol injection into blower or manifold would have been more in line with his other suggestions. Incidentally engines were running daily In America, three years ago, with injection into the manifold—to avoid the never absent fear of a frozen carburetter in some of the northern states. I can only imagine that the similarity to the Jumo refers to the free air scavenging effect which of course is common to nearly all two-cycle H.S.C.I. engines. Figures for the P.N. and Bristol engines were for maximum output. Maximum r.p.m. on all aircraft should not be held for more than five minutes under normal service
conditions. As to the Shelsley—I do not feel that it is quite fitting for us to eulogise the products of Messrs. A. F. N.
Ltd. lest it seem presumptuous ; but I am indeed sorry that Mr. Macleod has, quite evidently, not made the acquaintance of one of the finest of our too few remaining sports-cars.
Thanking you for the courtesy of your valued columns. I am, Yours etc.,
R. P. G. JoNEs.