"Originally Posted by CobberKane
It's hard to argue against the P-51 as the best overall fighter in WWII, because even if it may have been outperformed by other aircraft in specific roles, it was at the least competitive with any of them and it had that ace in the hole - range. But this thread poses a specific question - best fighter below 15000 feet - and within those parmeters there are aircraft that were somewhat superior to the mighty 'stang.
I wonder what your thoughts are on this comparison? The V-1710-81 was outperformed by both the V-1650-3 and 1650-7 for the P-51B, ditto V-1650-7 in the D.
The two airframes, P-51A and P-51B, when loaded to same fuel loading had about 450+ pounds (engine weight plus extra 50 cal ammo) difference. Reference NAA specs and Dean's America's Hundred Thousand and Gruenhagen's Mustang.
From Mike Williams April 1943 tests of sanded down, light loaded P-51A with water injected V-1710-81.
This P-51A with sanded surfaces, GW at TO of 8200 (100 of 180 gallons of fuel for this test) pounds and WEP did achieve 374mp on the deck. AFAIK the performance dropped considerably with standard camo and full fuel load, but this is only placeholder for a speed advantage over the B and only against the P-51B-1 with the Merlin 1650-3 at MP/61". The comparable top speed of the B-7 was 371mph BUT at 500 extra pounds of fuel and no special surface treatment and had external racks!! Additionally reference the P-51A and B-5 flight tests in the Mike Williams link below,
P-51A Climb rate was ~ SL = 2200 fpm, MP/52" at 8600 pounds GW at TO:
At WEP/57" the climb rates were = 3000, 3140, 3260 and 3400 at Sl, 5, 10 and 15K for V-1710-81 sanded and test weights at ~7800 pounds (which is 900 pounds below TO GW Combat load without drop tanks). This ship was tested with only 100 gallons of fuel.
Contrast the test results of the P-51B-1 with full internal wing tank fuel (no fuse tank) with Merlin 1650-1 engine, no surface prep, racks, per link below
At MP (not WEP) 61" the P-51-1 ROC at 8430 pounds was 3600, 3570, 3540, 3520 at SL, 5, 10 and 13K - full wing but no internal fuel..all Low Blower MP to 14000 feet - this is closest comparative test with the aforementioned P-51A w/-81 and WEP
P-51B-7 Climb rate was for 9200 pound GW at TO, at WEP/67" ~ 4400, 4300, 3800, 3450fpm at SL, 5, 10 and 15K for 1650-7 standard production ship with 80 gallons of fuel more (180) on take off - but fuselage tank empty.
You probably should infer that the P-51B was not only faster with an equivalent load, but proved it climbed a great deal faster despite carrying 500 extra pounds of fuel. Both Gruenhagen's Mustang and Dean's America's Hundred Thousand will supply an excellent cross section of data to use with
P-51 Mustang Performance.
Additionally the P-51A Roll rate was substantially below the P-51B by ~ 15 degrees per second at 200mph, 20 dps at 300mph then closing gap at 390. Curiously the XP-51 had much better roll rates than both, peaking at 130 dps at 235mph with beveled trailing edges on ailerons (pg 328 and 329 "America's Hundred Thousand").
So, the P-51B-1 through -15 with the high and 'medium' altitude Merlins with equivalent combat loading were faster, climbed much faster, rolled better until 400 mph (which was about as fast as the 51A could go, while the P-51B continued to roll responsively through 500 mph. The only possible advantage for the 51A is initial turns.
I suspect at equal loading WEP to WEP on the deck that the P-51A might slightly out turn the 51 because of slightly lower WL - but Certainly not at MP where the decided extra muscle of the Merlin will pull the 51B with more authority as energy bleeds speed in high AoA flight.
Where do you 'feel' the P-51A was better?
The 1710-81 had a better supercharger than the 1710-39 which gave it 1200 hp at TO, 1330 Bhp at WEP w/57" at 14,000ft.max continuous.
The weaker of the Merlins for low altitude is the -3 which 1380 bhp at TO, 1600 hp at WEP for 11,800 ft at 67" and 1480 bhp WEP at 13,750 ft for Low Blower Critical Altitude at 61"
The 1650-7 produced 1490 bhp at TO power/61", 1720 at CA of 6200 feet WEP/67", 1590 hp MP at CA 8500 feet
The best single source for performance in which the side by side
So - same aerodynamics and drag, 300+ pounds heavier but Hp differences of ~ 300 Hp at SL,