Yeah, let's not miss a chance to trash Merlins, even if the figures don't exactly prove the point.
Basic weights (includes radios and 6 guns, but no ammo, pilot, fuel and oil), 'clean' A/C, data from 'America's hundred thousand', lbs:
-P-40F: 7089
-P-40K: 6880;
So the -F is ~3% heavier empty.
Engine power at 20000 ft, no ram: 840 HP for the -K, 1060 for the -F. The -F has ~25% more power there, it's power is better from 6000 ft above.
Cram 180 gals of fuel on the P-39N and P-40N, full ammo, additional oil, and then see how good they will climb. The engine installed on the P-51A, P-39N and P-40N will have power deficit of 150 HP at 20000 ft vs. Merlin 20/28/V-1650-1, and was running late vs. V-1650 by almost a year. Any vs. Merlin XX by two and half years.
Merlin 45 for the Americans is the moot point - they don't have it in production.
The decison to use Merlin 45 on Spitfires have had much to do with realities of war-time production (Merlin 20 series went to bombers in huge quantities, plus at the Hurricane), as well as timing, since Hurricane needed any help it can get to cancel the performance gap vs Bf 109E in 1940. Thus Spitfire got Merlin XII, and later 40 series.
The Merlin Mustangs need to be deployed in Britain. Allison Mustangs don't have the altitude performance to challenge Luftwaffe avbove 15000 ft, until the 2-stage engine is available.
added:
Merlin 45: 1385 lbs,
V-1650-1 (= Merlin 28): 1520 lbs
Re: Rolls Royce Merlin XX / Merlin 45 / Packard V-1650-1 / Allison V-1710-81/85
A P-40F with a Packard Merlin XX engine was heavy, at about 8,500 lbs. for take-off. The Kittyhawk II with British spec changes weighed about 9,000 lbs. with a normal service load. Either way the rate of climb was poor and service ceiling was below 35,000 feet during U.S. and U.K. government trials.
Basic weights (includes radios and 6 guns, but no ammo, pilot, fuel and oil), 'clean' A/C, data from 'America's hundred thousand', lbs:
-P-40F: 7089
-P-40K: 6880;
So the -F is ~3% heavier empty.
Engine power at 20000 ft, no ram: 840 HP for the -K, 1060 for the -F. The -F has ~25% more power there, it's power is better from 6000 ft above.
That does not read like a missed opportunity.
In any case a Mustang with a Merlin XX would have been heavier still, and would not have climbed higher than a P-39N, P-40N or P-51A.
Cram 180 gals of fuel on the P-39N and P-40N, full ammo, additional oil, and then see how good they will climb. The engine installed on the P-51A, P-39N and P-40N will have power deficit of 150 HP at 20000 ft vs. Merlin 20/28/V-1650-1, and was running late vs. V-1650 by almost a year. Any vs. Merlin XX by two and half years.
The supposed performance gain of the Merlin XX was brought into question after the A&AEE used a Hurricane for trial installation with the Merlin 45 engine. This airplane easily out-climbed a standard production model with a Merlin XX. Hurricane P3157 (Merlin 45) climbed to 20,000 feet in 7.1 minutes, compared to a best time of 8.5 minutes by Hurricane Z3564 (Merlin XX). The take-off weights were 6,685 lbs. (P3157) and 7,397 lbs. (Z3564).
The Merlin 45 weighed less, consumed less fuel, had fewer moving parts, and returned a lower build and maintenance cost than the Merlin XX. It's no surprise that the RAF made the Merlin 40 series standard for Spitfires until the 60 series was available.
Merlin 45 for the Americans is the moot point - they don't have it in production.
The decison to use Merlin 45 on Spitfires have had much to do with realities of war-time production (Merlin 20 series went to bombers in huge quantities, plus at the Hurricane), as well as timing, since Hurricane needed any help it can get to cancel the performance gap vs Bf 109E in 1940. Thus Spitfire got Merlin XII, and later 40 series.
The Allison engine held a big advantage at forward airstrips because of the down draft carburetor, with the air scoop being on top of the engine nacelle. The RAF Desert Air Force and USAAF reported that the V-1710 ran dependably with the air cleaner removed, for the purpose of increasing power.
The Merlin used an updraft carburetor setup that ingested dirt and sand like a vacuum cleaner. Taking out the air cleaner was attempted, but doing so ruined the Merlin quickly. The engine nacelles of many RAF planes were retrofitted with tropical air intakes but the Kittyhawk II was not one of them.
The Merlin Mustangs need to be deployed in Britain. Allison Mustangs don't have the altitude performance to challenge Luftwaffe avbove 15000 ft, until the 2-stage engine is available.
added:
Merlin 45: 1385 lbs,
V-1650-1 (= Merlin 28): 1520 lbs
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