24 - cylinder Sleeve - valve Unit of 3,500 BMP.

' ITH what may well prove to be the last of the civil aircraft—particularly in view of the airscrew-turbine very high-powered piston engines Rolls-Royce position. have resurrected one of their most famous type In general terms composition of the Eagle may be sum- names—Eagle—and on examination there is no marized as consisting of twelve cylinders on each side reason to believe that this latest Derby creation formed in monobloc castings, through-bolted with the will not carry to new heights the lustre vertically split crankcase. Each row of six cylinders is bequeathed by its famous namesake. served by its own induction manifold which, in turn, is The new Eagle is a twin-crank flat-H sleeve-valve engine fed from an individual aftercooler. Exhaust is through aspirated with a two-stage two-speed supercharger, and, paired ejector stacks mounted in a • central row between in Mk 22 form, is equipped to drive an eight-blade contra- the upper and lower banks of cylinders. The reduc- rotating airscrew. It is the first Rolls-Royce production tion gearing is powered equally by both crankshafts, and sleeve-valve engine, although the company extensively with it is incorporated the contra-rotation gear for airscrew investigated the potentials of sleeve valves as a part of drive. In this particular instance—i.e., the Mk 22—the their normal research programme in the early 1930s. In nose-length requirements of the aircraft in which the point of fact, although it is not generally known, Rolls engine is first to be installed have called for an extended produced an air-cooled 22-litre sleeve-valve 24-cylinder snout bousing forward of the reduction gear, but for other engine of X-form which, called the "Exe," first flew in installations this might not apply, and the overall length September, 1938, in a Fairey Battle. This was a quite of the engine would thus be reduced by perhaps as much successful engine, but it was dropped in order that full as 15 inches^. effort could be concentrated on Merlin production in view of the gathering war clouds. In addition to being the Detail Analysis first R-R sleeve engine, the Exe was also the first air- Now to consider.the make-up of the engine in detail: cooled engine produced by the company since the 1914-18 we will start with the crankcase and work systematically war. from that foundation. The case is split vertically into Before going on to consider the Eagle in detail we might port and starboard halves of cast light alloy—and a briefly run over the design factors that decided its form: beautiful piece of work it is—with seven bearings for each the initial design project was conceived toward the end crankshaft carried in lateral webs axially stiffened by of 1942 as the necessity for a higher-powered engine was integral intercostal bracing in each half. Lightening and foreseen. Considerations of aspiration and flame travel pressure-balancing holes are formed in each web, and each set a more or less effective limit of about 6 inches to bore crank chamber has two drain holes into the sump. The size, and with cylinders of this order it has been estab- front end of the crankcase is double-walled with approxi- lished that 12 pistons per crankshaft is about the practical mately a 2in cavity, the inner wall housing the No. 1 limit. Thus a twin-crankshaft engine was necessary, and main bearings of each crankshaft, and the front wall carry- the disposition of the cylinders in a flat-H followed ing the tail bearings for the timing gears uniting the naturally, since far and away the best installation case is crankshafts. met by this layout. Cylinder blocks are also very fine examples of sand- Sleeve valves were decided upon in view of the fact casting technique in light alloy, the upper and lower row* that they undoubtedly offer advantages over poppet valves of cylinders on each side being formed in one casting. from the aspect of maintenance and obviation of adjust- Each cylinder is ventilated with three inlet and two ment ; and whilst no one would be so reckless as to sug- exhaust ports, the latter ports of each vertical pair of gest that the poppet valve has reached the ultimate peak cylinders discharging to a common pair Of ejector stacks. of development, it is not far short of the summit and its Sleeve drive is by a worm shaft on each side commonly limitations are very well known. serving top and bottom rows of sleeves, each shaft run- These factors were the underlying fundamentals which ning in six split plain bearings. The bearing castings alsD •led to the Eagle. As to its use, we are permitted at incorporate the split plain bearings for the worm wheel present to say no more than that it is to spindles. The be the power unit of the Westland worm shafts are driven Wyvern T.F.i naval aircraft, but from their for the future it is, perhaps, more rear ends than likely that the Eagle may through serve to power more than one