I couldn't follow that data sheet very well.
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Externally carried stores like bombs create drag which reduce speed. I think the maximum speed for the Sea Hurricane (Merlin III) in your data sheet is the speed with no bombs carried.
The speed is for the mean weight, ie. no external loads indeed.
AFAIK the Hawker P.4/34 (better known as the Henley) and its rival the Fairey P.4/34 (which was modified to become the Fulmar) carried their bombs internally. That's why I think either of them would have been a better choice. IIRC it has been mentioned in other threads that the Fulmar was stressed for dive bombing, so presumably the Fairey P.4/34 was too and possibly the Henley.
As we want to use either P.4/34 as a CAS aircraft rather than as a true light bomber I think we don't need the second crew member and we might less fuel because a shorter range is required. Both measures would reduce weight which might make both P.4/34s faster and more agile.
The Fairey's proposal carried bombs externally, thus it will be less attarctive than either of the Hawkers. Hurricane with external bombs will not be any bit slower than Henley with or without bombs, and once bombs are gone it is a certified fighter. Meaning that pilot(s) can choose whether to fight or to run away. Hurricane is also a smaller target, might come in handy when a perspective enemy has AAA and aircraft that number in thousands.
There is one feature that I'd 'transplant' from Henley to Hurricane, namely the layout of the radiator - less plumbing around for lower chance to be punctured, less drag, will not be destroyed in forced landing, less weight.
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What was the performance of the early Hercules engines at higher altitudes. Because...
Imagine a Hercules powered Fulmar entering service in 1940 with a 1,350-1,400hp engine. Actually they might have been able to get it in 1939 by ordering more of them from Blackburn and Boulton Paul instead of the Skua and Roc.
Substituting the Merlin for the Hercules on the Boulton Paul Defiant and Hawer Hotspur would have improved their performance. Boulton Paul did propose night fighter versions of the Defiant using more powerful engines like the Griffon with up to 12 machine guns or six 20mm cannon in the wings while keeping the turret or replacing it with an observer.
The 'normal' fighters need good power at altitude, that was one of the Merlin's strong suites. There was, however, the Hercules III from 1939, that gave 1210-1270 HP at 15000 ft (different sources state different HP figures), or some 15-20% more than Merlin III/X. Having the 2-speed S/C gear, it also provided 1400 at low level, vs. ~1100 for the Merlin X (and Merlin VIII from 1940), and ~900 for the Merlin III.
All figures for 87 oct fuel.
I'm all for Hercules-powered 1-engined stuff in 1939/40. That would've especially come handy for the aricraft that were not that sleek (Defiant, Fulmar, Henley, even Battle) and/or sport lousy radiator set-up (Hurricane, again Defiant), and less handy for sleek A/C (Spitfire).
The earlier RAF/AM forgets about turret fighters, the better
As the Hercules you're proposing for the CAS Hurricane produced 1,350-1,400hp compared to 1,030hp fitted to the Hurricanes that took part in the Battles of France and Britain and the later marks of Hurricane had Merlins producing 1,280hp it looks as if we could have had a Hercules powered Hurricane in 1940 with the Hurricane Mk IIB and IIC performance and armament.
Stick the tail on that plan and call it a weasel
