As Shortround says, it is unlikely that the P.24 had a 4 speed two stage supercharger. As it was basically two engines on a single crankcase it is most likely that each half had a single stage two speed supercharger.
Having just read your thread, it has just occurred to me that you and shortround6 might be right.
I did at one stage have a USAAF report on the P.24, which evidently didn't like some of the features of the engine - like the cranks not having counterweights.
That would be an interesting read. Regarding the Fairey fan's claim, unless he's able to produce concrete evidence, I would be tempted to believe Mr Lumsden's account, as this book is quite a hefty tome. Lumsden trawled through the archives to produce the info contained within.
Here's a bit more from the book:
"If there was any confusion (conceivably intentional on the part of the company) about the V-12 engine, this was nothing by comparison with that which surrounded the second and radically new type of Fairey Prince; the 'double engine'. Pursuing the Prince theme has been an intriguing exercise. Grham Forsyth [Chief engine designer for Fairey] had very ingenious ideas about a double engine in the shape of a vertical 'H'. His idea was that each vertically-opposed half should operate quite independently, each driving a separate unit of a pair of co-axial counter rotatingand constant speed feathering propellers, with independent reduction gears on a commom crank case. For long economic overseas patrols, this is an interesting solution, offering twin twin-engine reliability from a 'single-engine' installation without inconvenient assymetric characteristics.The Royal Navy was known to be interested and Fairey himself was well known in the Admiralty. The idea of an H shaped engine was of course not new at the time. Frank Halford's air cooled 16-cylinder Napier Rapier and 24-cylinder Dagger, both of which had twin crankshafts geared together were in RAF use and widely advertised.
Complete official company records have been hard to discover but thanks to the researches and personal recollections of Sir Peter Masefield (a redoubtable historian, who, in his early years worked at Fairey's 'Great West Aerodrome' headquarters at Hayes}, some most revealing facts have emerged. Indeed, he himself made a number of flights in a Fairey Battle test bed, behind a 24 cylinder Fairey P-24 Double Prince.
Almost at the end of frustrating searches into these little known engines, an unpublished series of engine data sheets, dated 5 March 1941 from Sir Roy Fedden's Bristol archives came to light and included some unexpected information on the Fairey engines. As with so many long lost sources of information, total reliance on its accuracy at first seemed unwise, although the source of it was as impeccable as it could be. And then, at the very last minute, some long lost details of the Fairey P-24 Monarch were, thankfully made available to the author.
The unique new layout, in accordance with the novel ideas of Graham Forsyth, was intended to appear in two versions with 16 and 24 cylinders and used the same bore and stroke as the earlier Prince. In the Fairey system, the H-16 was to be a 16 cylinder engine, retaining the name 'Prince'. However, the name 'Monarch' was adopted for the 24 cylinder H-shaped P-24 engine in the first drawing, dated 29 August 1932.
Exactly what was the eventual outcome of the proposed 16-cylinder engine was still unclear at the time of writing, but happily, an engine called a Fairey Prince is carefully preserved at the FAA Museum at Yeovilton. The engine was originally rescued from a scrap yard in Kingston-upon-Thames after WW2. This unique engine is believed to be a P-24 Monarch. All the surviving Fairey drawings and data, signed out and authorised by A.G. Forsyth call it so. It is a vertical, H-shaped engine with side mounted superchargers. Therefore it is a rare, if not the uniquely surviving Fairey four speed, two stage engine. The photograph of a Prince engined Battle, having one engine run up also show four exhaust stubs top and bottom, suggesting H-16. The drawings show, however that the six exhausts in each bank were combined in four outlets, an arrangement also adopted by RR in certain instances.
The first Monarch to be built was installed in Fairey Battle K9370 in October 1938 and had a civil type test in May and June 1939. It achieved 50 hours without incident with fixed pitch contra-rotating propellers, being first flown by Chris Staniland in June. Tests went so well that it was cleared for flight trials of 120 hours and it was delivered to RAE Farnborough on 12 July 1941, having completed a 50-hour bench test and 87-hours flying in the Battle. While there it was installed in the large wind-tunnel for the study of contra-rotating propeller effects, together with thrust and propeller blade strain gauge tests. It was submitted to 15 hours testing at take-off power without trouble."
More soon