Rolls-Royce Eagle II / H-24
This was the last of the line of reciprocating, liquid-cooled units. The initial design project was conceived toward the end of 1942 as the necessity for a higher-powered engine was foreseen. The Rolls-Royce design team realised that producing a scaled-up version of their Griffon V-12 engine would lead to excessively large combustion chambers and problems with detonation.
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 established that 12 pistons per crankshaft is about the practical limit and considered an X-24 design. This layout had previously caused unreliability with the Rolls-Royce Vulture due to the need to fasten four connecting rods in a complicated arrangement to a common big end bearing.
The designers finally settled on an 'H' layout with two crankshafts and 'blade and fork' connecting rod attachments, the crankshafts being connected through the propeller speed reduction unit. Sleeve valves were decided upon in view of the fact that they offer advantages over poppet valves from the aspect of maintenance and obviation of adjustment.
The case is split vertically into port and starboard halves of cast light alloy, the front wall carrying the tail bearings for the timing gears uniting the crankshafts. Cylinder blocks are also examples of sandcasting technique in light alloy, the upper and lower rows 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 of cylinders discharging to a common pair of ejector stacks.
Sleeve drive is by a worm shaft on each side commonly serving top and bottom rows of sleeves, each shaft running in six split plain bearings.
A two-speed, two-stage supercharger and intercooler were used to compress then cool the air-fuel mixture, following Griffon and Merlin practice. Starting was by Coffman starter. An auxiliary shaft driven by the lower crankshaft operated the main coolant pump, intercooler coolant pump, pressure and scavenge oil pumps and a fuel injection pump. Piston ring failures and cylinder head sealing problems were experienced during early flight testing.
It was designed and built in the early-1940s and first ran in March 1944. The Eagle was never fitted to a production front-line fighter, as it was overshadowed by a new wave of turbojet engines, such as the Rolls-Royce Derwent and turboprops such as the Dart and Armstrong Siddeley Python. Fifteen Eagle 22s were produced to power the prototypes of the Westland Wyvern fighter / torpedo bomber as its intended powerplant, the AS Python was late in development.
46H Eagle II
46H Eagle (20 srs) 22