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The P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe. If ultimate performance was the aim then the P51 would have been fitted with a Griffon, as later racers were. However a Griffon engine P51 wouldn't have reached Berlin and returned to base. The US air force could have coped with a lower top speed rate of climb etc on the P51 they could not have coped with a reduced range.
M opinion was based on the Griffon being bigger and heavier and having a larger swept volume. All of these tend to increase fuel consumption. It may be true that a Griffon engine P 51 would consume approximately the same while cruising to rendezvous. Personally I doubt it. However much of a P51s mission was on escort where consumption was in gallons per hour and the speed dictated by the bomber formation. On this part of a mission and in combat it would definitely consume more.Not sure about the range.
Certainly the endurance would be reduced, but the cruise with the Griffon should be faster, which would offset the time factor to some degree.
Rolls-Royce were keen to put the 2-stage Griffon in the Mustang, but NAA said there would be too much rework involved (at that stage of the war - 1942).
It shouldn't consume a lot more while cruising. Power required it pretty much dependent on drag. Yes the extra weight will cause a bit of extra drag ( higher angle of attack for wing at same speed) but that is going to be rather small. Larger radiator scoop? but airflow through the radiator will be in proportion to the power being made.
That leaves the actual fuel economy of the engine. The Griffon is 36% bigger in swept volume to be sure but it runs approximately 10% slower. It also has about 22% more scrubbed area of cylinder wall and pistons scrubbing cylinder walls are roughly 75-80% of the friction in an engine. Fiction goes up with the square of the speed soooo.......
Running an engine even 200rpm slower can make a difference in friction losses (one big reason for dropping the revs and using high boost (relatively) for cruising.
A clean Mustang (tanks gone) can cruise at over 300mph true at 1850, boost not given, at 25,000ft using 59 gallons an hour. I don't know what the power is but is seems to be well under 700hp. (2400rpm and 36in/3lb is 775hp at 22,500ft)
I have no idea what settings are needed to get 5-600hp out of a Griffon at 22-25,000ft.
Not sure about the range.
Certainly the endurance would be reduced, but the cruise with the Griffon should be faster, which would offset the time factor to some degree.
Rolls-Royce were keen to put the 2-stage Griffon in the Mustang, but NAA said there would be too much rework involved (at that stage of the war - 1942).
If North American said the P-51 required too much modification to take the Griffon they meant it would be better and faster to start an all new aircraft. The P-51B had vast amounts of panel changes over the P-51A while the P-51H was new again.
Of course North American could have built a Griffon powered P-51H given the effort involved in the H but would that have yielded a better aircraft? Larger certainly but faster than 487 mph?
The reason Supermarine shoe horned the Griffon into a hybrid of the Spitfire IV and Spitfire VIII is because brute power was the only way to overcome the limitations of the early 1930s airframe and aerodynamic technology. A Merlin Mustang was as fast if not faster than Griffon Spitfire. A Griffon mustang may not be much faster.
Agree. This reminds me of the B-29 "Battle of Kansas" situation.From what I have seen of the P51 production line it was true mass production, you cannot make small changes to such a system, any modification means in effect a new aircraft.
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The reason Supermarine shoe horned the Griffon into a hybrid of the Spitfire IV and Spitfire VIII is because brute power was the only way to overcome the limitations of the early 1930s airframe and aerodynamic technology. A Merlin Mustang was as fast if not faster than Griffon Spitfire. A Griffon mustang may not be much faster.
Simply re write history. Give the plans for the Griffon to Napier and tell them to make it instead of the Sabre.. Give the plans to the P51 to Hawkers and say make it with a Griffon. No more Typhoons or Tempests but a lot of different P1s and Mustang XIVs for a variety of roles.Another problem was the Griffon itself, where were hundreds or thousands of 2 stage Griffons going to come from in 1942?
I mean this form a planning perspective. First squadron with Spitfire MK XIVs didn't become operational until Dec of 1943.
To build Griffon powered Mustangs instead of Merlin Mustangs in 1943 (and Packard couldn't build Merlins fast enough in the Spring/summer of 1943) you need a source of 2 stage Griffons at a rate of hundreds per month by the middle of 1943.
? From mid 44, to the end of the war the P-51D with high octane fuel, was a class A fighter easily contesting the skies over Germany and Japan. Not until late 1944 did Germany generate any aircraft that could challenge the Mustang but never had the quantity to do it.he P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe.
It's a bit of a myth that the Mustang was significantly faster than a Spitfire with the same engine. The oft-quoted statement that the Mustang was '20-30 mph faster' applied to an early Spitfire IX with the Merlin 61 (nominally capable of 403 mph). By contrast the Spitfire HFIX with normal wing-tips and the Merlin 70 could do 419 mph, which suggests that a P51B would be ~10 mph faster if both aircraft were in pristine condition.
The top speed of about 430 mph for the P51 is also quoted in Bowyer and Sharp's Mosquito.
Of course, the Mustang's wing was much more sensitive to dirt and dents and after a few missions the speeds would probably be more-or-less identical.