FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1947
1947 - 0625.PDF
24 - cylinder Sleeve - valve Unit of 3,500 BMP. ' ITH what may well prove to be the last of the very high-powered piston engines Rolls-Royce have resurrected one of their most famous type names—Eagle—and on examination there is no reason to believe that this latest Derby creation will not carry to new heights the lustre bequeathed by its famous namesake. The new Eagle is a twin-crank flat-H sleeve-valve engine aspirated with a two-stage two-speed supercharger, and, in Mk 22 form, is equipped to drive an eight-blade contra- rotating airscrew. It is the first Rolls-Royce production sleeve-valve engine, although the company extensively investigated the potentials of sleeve valves as a part of their normal research programme in the early 1930s. In point of fact, although it is not generally known, Rolls produced an air-cooled 22-litre sleeve-valve 24-cylinder engine of X-form which, called the "Exe," first flew in September, 1938, in a Fairey Battle. This was a quite successful engine, but it was dropped in order that full effort could be concentrated on Merlin production in view of the gathering war clouds. In addition to being the first R-R sleeve engine, the Exe was also the first air- cooled engine produced by the company since the 1914-18 war. Before going on to consider the Eagle in detail we might briefly run over the design factors that decided its form: the initial design project was conceived toward the end of 1942 as the necessity for a higher-powered engine was foreseen. Considerations of aspiration and flame travel set a more or less effective limit of about 6 inches to bore size, and with cylinders of this order it has been estab- lished that 12 pistons per crankshaft is about the practical limit. Thus a twin-crankshaft engine was necessary, and the disposition of the cylinders in a flat-H followed naturally, since far and away the best installation case is met by this layout. Sleeve valves were decided upon in view of the fact that they undoubtedly offer advantages over poppet valves from the aspect of maintenance and obviation of adjust- ment ; and whilst no one would be so reckless as to sug- gest that the poppet valve has reached the ultimate peak of development, it is not far short of the summit and its limitations are very well known. These factors were the underlying fundamentals which •led to the Eagle. As to its use, we are permitted at present to say no more than that it is to be the power unit of the Westland Wyvern T.F.i naval aircraft, but for the future it is, perhaps, more than likely that the Eagle may serve to power more than one civil aircraft—particularly in view of the airscrew-turbineposition. In general terms composition of the Eagle may be sum-marized as consisting of twelve cylinders on each side formed in monobloc castings, through-bolted with thevertically split crankcase. Each row of six cylinders is served by its own induction manifold which, in turn, isfed from an individual aftercooler. Exhaust is through paired ejector stacks mounted in a • central row betweenthe upper and lower banks of cylinders. The reduc- tion gearing is powered equally by both crankshafts, andwith it is incorporated the contra-rotation gear for airscrew drive. In this particular instance—i.e., the Mk 22—thenose-length requirements of the aircraft in which the engine is first to be installed have called for an extendedsnout bousing forward of the reduction gear, but for other installations this might not apply, and the overall lengthof the engine would thus be reduced by perhaps as much as 15 inches^. Detail Analysis Now to consider.the make-up of the engine in detail:we will start with the crankcase and work systematically from that foundation. The case is split vertically intoport and starboard halves of cast light alloy—and a beautiful piece of work it is—with seven bearings for eachcrankshaft carried in lateral webs axially stiffened by integral intercostal bracing in each half. Lightening andpressure-balancing holes are formed in each web, and each crank chamber has two drain holes into the sump. Thefront end of the crankcase is double-walled with approxi- mately a 2in cavity, the inner wall housing the No. 1main bearings of each crankshaft, and the front wall carry- ing the tail bearings for the timing gears uniting thecrankshafts. Cylinder blocks are also very fine examples of sand-casting technique in light alloy, the upper and lower row* of cylinders on each side being formed in one casting.Each cylinder is ventilated with three inlet and two exhaust ports, the latter ports of each vertical pair ofcylinders discharging to a common pair Of ejector stacks. Sleeve drive is by a worm shaft on each side commonlyserving top and bottom rows of sleeves, each shaft run- ning in six split plain bearings. The bearing castings alsDincorporate the split plain bearings for the worm wheel spindles. Theworm shafts are drivenfrom their rear endsthrough
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
