Had this sent to me a while back,
With the P24 design - there was no "coupling" of its two component halves - They were two entirely separate engines - one of which drove its propeller through the hollow driveshaft of the other. Other than that there was absolutely no mechanical linkage between the two "halves" at all – So very little to go wrong.
The P24 Monarch was a very advanced engine if the surviving details are true...
Compressed Glycol /Water Cooling - As first used in Rolls Royce production engines (Merlin XII) from the end of 1940. RPM of 3,000 (same as wartime Merlins) 2 Stage, 4 Speed supercharger (Rolls Royce only ever managed a 2 speed Supercharger on the Merlin and only managed a 3-speed supercharger on post-war Griffons).
With a 2-stage, 4 speed supercharger you would expect the Monarch to have had a very impressive performance at height.
There were two designs - The 16 Cylinder H-16 "Prince" of 1.540 hp and the 24 cylinder P-24 "Monarch" of 2,240hp (perhaps more).
The H-16 had only a two-speed single stage supercharger.
The H-16 could well have boosted a Battle Bomber to close to 300 mph - who knows with a Monarch - 350 mph +???
The Fulmar and Barracuda could have had similar boosts in performance – along with "Twin-engine" reliability.
Both the H-16 and P-24 used essentially the same cylinders as the earlier P12 Prince - Which had first flown in 1934, and it used poppet-valves, and so would have had none of the problems Bristol + Napier had with sleeve-Valves, so it is by no means unreasonable to think that with a bit of government backing the H-16 and P-24 could have been in production as early as 1938, and certainly by 1940. As it was CR Fairey said to have spent at least 1 million pounds (at today’s prices) out of his own pocket on the project.
The information on the Fairey family of engines is somewhat fragmentary...
The Prince 1 and II were just normal liquid-cooled "V" engines - very close in performance to the very late R-Royce Kestrel and the Peregrine.
The Prince H-16 was essentially two lots of 8 cylinders from Prince 2 engines each rearranged into a "U" shape - one on top of the other to form a "H" (but not a true "H" engine - two separate halves) - This is the only one we have firm data for weight on ... 2,180 Lb - a bit heavier than the weight of a Griffon (1,980 lb)- in it's prototype form it was not as powerful as a Griffon - giving only 1,600 hp - but this is not far off the 1,720 hp of the very early Griffons (although they were later developed to 2,500 hp). Because of it's layout the Prince H-16 would have had a bigger frontal area - leading to a somewhat "blunt" nose on any aircraft it was fitted to - unless a particularly large spinner or extension shaft was used (both these methods would add weight). -
The Monarch prototype was rated at 2,400 hp - but it was considered capable of development to 3,000 hp - no figures survive for its weight. The extra eight cylinders would have made the engine longer - but the frontal area would have been the same as the Prince H-16. I think it's fair to approximate this engine to a Bristol Centaurus in terms of weight.
I think most aircraft designers would have used the more powerful Monarch engine if given the choice - But there might have been some designs (the Fairey Fulmar and Barracuda spring to mind) where the Prince H-16 would have been a handy stop-gap to avoid major redesign for the extra weight of the Monarch.
As a general rule I think it's fair to say any aircraft with a late model Hercules or a Griffon engine could probably have used the Prince H-16 instead.
Similarly any aircraft designed with the RR Vulture or Centaurus could have taken a Monarch without too much redesign.
