I once wrote quite a detailed 'what-if' about the potential outcome of the Hawk 75 replacing the Hawker Hurricane as one of the two mainstays of the RAF from 1937 onwards. Unfortunately, my laptop harddrive died last year, taking the piece with it (all 50-odd pages of it), as well as all the supporting data I'd collected, including original French and UK performance tests for Hawk 75s and Mohawks and manuals.
Procurement and production:
I'd posited that Hawker goes bust in 1935 or 1936, leaving the Hurricane stillborn and the RAF casting about for a new fighter. It decides to purchase several hundred Hawk 75s – under the name Mohawk - from the US and also acquires licences to produce the aircraft and the R-1830 engine (probably fanciful, I know).
Imported Mohawk I/II are broadly similar to the Hawk A-1/A-2: 950-1050 hp R-1830-SC-G engine, 6 x .303, top speed of around 300-310 mph at 12,000 ft, climb of 5.8-7 minutes to 15,000 ft.
My alternative history would have Mowhawk II production in the UK commencing in late 1937, with about 400 aircraft delivered by the outbreak of war and production at a rate of around 1.2 per day over the first five months of 1940.
This is about 50% down on Hurricane production, as I'd imagined problems with R-1830 production in the UK. This is somewhat made up for by direct imports of aircraft from the US. Production would match UK historical Hurricane production by around April/May 1940 and then actually exceed historical production – albeit only minimally – during the Battle of Britain period.
By early 1940, the UK secures a licence for the up-rated SC3-G with 1200 hp, beginning production around June-July at a rate of 2-3 per day, creating a situation broadly analogous to the introduction of the Hurricane Mk II, albeit without the larger increase in altitude performance.
Performance vs Hurricane
From reading the various evaluations and looking at the comparative performance data, my conclusion was that the Hawk 75 was more nimble and a better dog fighter than the Hurricane but maybe would not have made as good an interceptor or bomber destroyer.
The Hawk 75 was more pleasant to fly through the entire speed range – particularly at higher speeds. It had better lateral control and could even turn inside the famously nimble Hurricane. The aircraft would have been very good at high speed slashing attacks and its controllability was much superior to the Hurricane above 350 mph.
The Hawk 75A/A-1/A-2 were notably inferior to the Hurricane I in terms of speed at most altitudes. The Hawk 75A-2 was around 10-15 mph slower below 10,000 ft, becoming roughly equal around 12-16000 ft and then increasingly inferior above that. By 20,000 ft the Hawk 75A-2 is 30 mph slower than the Hurricane I and almost 45 mph slower at 26,000 ft.
Climb performance is also down on the Hurricane. The Hawk 75 was reportedly nicer in the climb and also climbed at a faster speed (by about 20 mph). However, time to climb is about 7 ½ minutes to 15,000 ft, about 1 ½ to 2 minutes slower for the A-2 than the Hurricane I with a constant speed prop. The A-2 was about 5 ½ minutes slower to 20,000 ft.
Additionally, the gun package is not as tight as that of the Hurricane I, as well as being a third lighter.
The more powerful A-3 and the R-1820 powered A-4 – both with 1,200 hp - were a match for the Hurricane I in speed until about 12-15,000 ft, but the Merlin-powered Hurricane proved increasingly superior as altitude increased. The A-4 was superior to the Hurricane I in the climb until 12,000 ft.
Other factors:
The R-1830 didn't suffer from negative G cut-out the same way the Hurricane did, so there is a plus. Unfortunately, the Hawk 75 is still outpaced in terms of acceleration in a dive by the 109E.
R-1830 was very reliable and quite mature by the late 1930s and I'd expect the engine to be overall more reliable than the Merlin. The Hawk 75 was quite accessible as far a maintenance went, so it would probably be easier on ground crews than the Hurricane.
Both the Hurricane and Hawk 75 were notoriously rugged. Both had good ground characteristics and the Hawk 75 was rated as even easier to take-off in than the Hurricane, something of a positive for training.