The Fairey P.24 Monarch or Prince 4 was a British experimental 2,000 hp (1,490 kW) class H-24 aircraft engine designed and built by Fairey in the late 1930s.
The P.24 Monarch was an enlarged development of the Prince, designed by chief engine designer Captain A.G. Forsyth. Similar in layout to the Napier Dagger the cylinders were arranged vertically in two separate blocks, driving contra-rotating propellers via separate shafts and gears. Like the smaller Prince engine each bank of cylinders could be shut down in flight to drive only one propeller, an idea that was reused much later in the Armstrong Siddeley Double Mamba turboprop. The engine was test flown in a Fairey Battle, serial K9370, with its first flight taking place on 30 June 1939.
The engine was considered for use in the Hawker Tornado and K9370 was later shipped to Wright Field in the US, where testing (Project MX-229) was carried out in 1942 with a view to using the potentially 3,000 hp of the P .24 in the Republic P-47 Thunderbolt, a total of around 250 hours of test flying in the Battle being completed at Wright Field before the idea was abandoned. Following cancellation, the engine provided three trouble-free years of service in K9370.
P.24 Monarch
Type: Liquid-cooled H24 engine
Bore: 5.25 in (133.35 mm)
Stroke: 6.0 in (152.4 mm)
Displacement: 3,117 in³ (51.08 L)
Length: 86.25 in (2191 mm)
Width: 43 in (1092 mm)
Height: 52.5 in (1333.5 mm)
Dry weight: 2,180 lb
Valvetrain: 2 intake, 1 exhaust valve per cylinder
Supercharger: Four-speed, two stage
Cooling system: Liquid-cooled
Reduction gear: Spur gear, 0.543:1
Power output: 2,240 hp (1,670 kW) at 3,000 rpm at 9,000 ft
All Aero 