P-51's vs. Me-109's and Fw-190's

Milosh - the P-51B-1-NA and all the early P-51B-5 and C-1 had no internal fuselage tank at the factory - just the 92 gallon wing tanks (each wing). The Field mods performed all the way through 43-7112 and 42-103778 were to install the 85 gallon fuselage tank on a modified lower radio shelf floor. After that all the P-51's headed for PTO/MTO and ETO (not including US Training Command) had the 85 gallon tank installed on all subsequent P-51B/C/D/K at the factories.

SOP because of the stability issues for the full 85 gallons creating and aft CG issue - was to attempt to drain down to 25 gallons in the 85 gallon tank. It was not always done based on range considerations.

I noticed that you were correct to highlight my misprint of "drain 85 gallons to 85 gallons"

Milosh,
I did not read your post carefully. My mistake.

On the Mustang fuselage tank, I once read (somewhere) that the early versions had no baffle system so the fuel would slosh around dangerously. Is this true or just another myth. Thanks.

The fuselage tank with baffle was introduced with P-51H, so the rumor might be true.

The first 85 gallon tank(s) (quantity not known by me) did not have baffles. Somewhere I have a AAF Flight test report dated February 1944 that indicated satisfaction with the applied mods to prevent/diminish 'sloshing' as the fuel drained down.

Since the P-51H was mentioned, it's top speed was really 787km/h (about 489mph) as some sources state or it was less as other sources show?

The post-war data sheets note 410-412 kt max speed - 472-474 mph, with water injection used (90 in Hg = 1800 HP at 26000 ft, with ram). Without water injection, one test shows 450 mph (67 in Hg = ~1300 HP at 30750 ft, with ram).
Onthe other hand, there is a test where only 451 mph is attained with water injection.

The 487 mph. maximum speed published by many authors comes from an estimated North American report. You can strip down any WW2 fighter and make it go faster. As a fighting vehicle even in clean condition using water injection and 90"Hg manifold pressure the maximum speed of the P-51H was 'officially' listed as 473 mph./22,705 ft., to the best of my knowledge at this time.

Two points to be noted - the first is that the 1650-9 as delivered in 1945 experienced issues related to the operation of the Simmonds manifold pressure boost control unit and the Bendix-Stromberg updraft injection carburetor. The flight tests mentioned above (July, 1945) were disappointing relative to the expected Perfomance estimates by NAA, indicating significant reduction in power delivered compared to Bench specs.

As a result of the July 1945 tests the P-51H NAA 8284-A of November 1945 Analysis re-examined the NAA 8284 September, 1944 report. It was calculated to account for the reduction in HP due to replacing the Bendix-Stromberg with the standard carburetor. The result which was validated in flight tests was 471mph at 90"-WI at 22000 feet FTH and 447mph with 67" at 29000 feet at combat gross weight with racks, but no external stores.

As an aside, the Parasite drag of the P-51H was nearly 10% less, despite greater surface area of wing, fuselage and empennage. Had a 1650-7 been flight tested with 72" Boost with 150 Octane fuel, it probably would have achieved in the 460+ mph range - clean.

By the time Packard sorted out the -9 (mid 1946), the 150 octane fuel necessity had dwindled to zero and AAF went back to 130. The result IIRC is that the engine was limited to 80", down from 90", with WI which delivered closer to 1800 Hp at FTH. The subsequent 1947 and beyond ops were restricted to 80" with WI and never achieved 487mph (clean, no racks) but did consistently achieve 470+mph at FTH

The P-82 had the same basic engine, 1650-11/21 and the 465mph flight speed in 1945 was afflicted with the same performance issue in the Simmonds boost control. By the time that was sorted out the future production versions were saddled with the two speed/two stage Allisons that never achieved consistent reliability, even at 67", forever emasculating the P-82 from potential Merlin performance levels.