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75 complete plus 26 engine-less airframes is an awful lots of prototypes.
The Peregrine engine wasn't all that small. Most aircraft have some growth potential. I suspect the Whirlwind could handle an additional 83kg per wing for the more powerful Merlin engine. In fact the two engines are so close together in weight that I wonder why RR developed the Peregrine engine at all.
517kg. Peregrine I V12 engine. Liquid cooled.
590kg. DB601A V12 engine. Liquid cooled.
600kg. Merlin I engine.
For me the key question is whether the Whirlwind could take on German daytime fighters. To give that concept some serious consideration one would have to allow for normal stretching of the design before large scale squadron introduction. Mosquitoes entered service with a top speed of 360 mph and ended the war with a top speed of around 420mph. Is it unreasonable to extrapolate the whirlwind to a similar extent?
Mosquitoes could take on LW SE fighters with at least some hope of success, but it was a tough ask, and ..... basically, would whirlwind escorted daylight raids in late '41 have been less expensive than unescorted nightime raids
134 gallons. Whirlwind internal fuel capacity.
194 gallons. Fuel capacity of proposed Whirlwind II. This version also had Merlin engines.
As to why the Peregrine was developed:
The Peregrine was an outgrowth of the very successful Kestrel engine. In the mid-1930s, Rolls-Royce felt that the engine would be its major powerplant for fighters and in an X configuration as a bomber powerplant, along with another engine based on the 36 litre type R (which ended up as the Griffon) for bombers. It was a proven, reliable design that offered very good power to weight for the time.
The project the Merlin grew from was initiated later, when it was realised that there was a substantial gap between the power produced by the Peregrine (initially around 700-800 hp) and the planned 1500 hp type R derivative.
It was also felt that PV-12 (the Merlin project) was a bit of a risk. The Peregrine was initially very promising - 885 hp from 21 liters is nothing to sniff at - but it turned out that the basic Kestrel design had been taken about as far as it could be. A higher power version promising 1010 hp at +12 lbs boost with 100 octane was in development, but the engine was really too small for and the Merlin was clearly more promising. By the time the Peregrine was hitting 1000 hp, the Merlin was pushing 1450 hp.
Four Kestrel/Peregrine cylinder banks attached to a single crankcase and driving a single common crankshaft would produce the contemporary Rolls-Royce Vulture, a 1,700-horsepower (1,300 kW) X-24 which would be used for bombers.
For me the key question is whether the Whirlwind could take on German daytime fighters. To give that concept some serious consideration one would have to allow for normal stretching of the design before large scale squadron introduction. Mosquitoes entered service with a top speed of 360 mph and ended the war with a top speed of around 420mph. Is it unreasonable to extrapolate the whirlwind to a similar extent?
Victor Binghams book on the Whirlwind has several reports of the Whirlwind shooting down Me109's, oddly though there are also a number of reports of inconclusive combats with FW190, where both sides have disengaged?
most people tend to use the channel dash debacle as indication that the Whirlwind was not up to the job of engaging enemy S?E fighters, but that ignores the Me109's shot down prior to this engagement, which was decided by the numbers of 109's involved!