1944: the best fighter under 15000 ft?

[tomo pauk]

Hi, Bill,
US 100K has something lacking for the Allison Mustangs. Ie. there is no graph depicting plane's performance on WER. The climb rates, on WER, are above 3000 ft/min from SL until 9500 ft. The WER was 1480 HP, from SL to ~9000 ft, as one can read on Williams' site.
Interestingly enough, the US 100K gives RoC of under 3000 ft/min, WER, between SL and 15000 ft. Those are in agreement with values where engine was operating on 60-61" (so, military, not WER), on Williams' site.

 

[Timppa]

Goodson's book is btw. one of the best I have read. It really has literary value, like the Clostermanns book.
4th FG Reunion Debrief

 

[Aozora]

"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,

I stand corrected - I shoulda looked before I lept. One advantage the Allison did have over the Merlin was that it ran smoother at low revs and could be leaned out to provide greater range at low altitudes; one reason 2 TAF Tac Recon squadrons hung onto their Mustang Is and IIs for so long was that they couldn't find anything to match their combination of high speed and range.

 

[drgondog]

I stand corrected - I shoulda looked before I lept. One advantage the Allison did have over the Merlin was that it ran smoother at low revs and could be leaned out to provide greater range at low altitudes; one reason 2 TAF Tac Recon squadrons hung onto their Mustang Is and IIs for so long was that they couldn't find anything to match their combination of high speed and range.

I agree but the RAF late version of low altitude merlin was an excellent performer...

With the F.4R version of the Allison, it would perform very well against the P-51B/C/D but peaked IIRC around 10K. perfect for Tactical/Recce

 

[drgondog]

Hi, Bill,
US 100K has something lacking for the Allison Mustangs. Ie. there is no graph depicting plane's performance on WER. The climb rates, on WER, are above 3000 ft/min from SL until 9500 ft. The WER was 1480 HP, from SL to ~9000 ft, as one can read on Williams' site.

I referenced that flight test on Mike's Site (by link above) report on the P-51A simply to illustrate the 'best it could be' with the -81 but also highlighting the difference between that Flight test with 400 grit sandpaper polish, and 1/2 load of fuel to compare against the production P-51B-1 and -5 and -7 reports.

Interestingly enough, the US 100K gives RoC of under 3000 ft/min, WER, between SL and 15000 ft. Those are in agreement with values where engine was operating on 60-61" (so, military, not WER), on Williams' site.

I don't recall the sub 3000 fpm on anything but the -39 at 52", but maybe they ran it at 57"?

The 100K plots for climb included only the 'ruptured duck 1710-39 IIRC. Tomo I don't recall that the -81 was documented beyond 57" - which is where the P-51 Mustang Performance report is found

More discussion is referenced for the 56.8" WEP run - which was at 396Mph, with racks, and no special surface prep at 9700 feet, and 409mph after pumice and water finish.
The Report
http://www.wwiiaircraftperformance.org/mustang/P-51-A_43-6007_Flight_Tests.pdf including plots for 52 and 57"
The dashed line represents 56.8" dash and climb runs with ~3750 fpm at 9700 feet 7600 pounds

 

[CobberKane]

Tests comparing the Tempest V to the Mustang III demonstrated that while the Mustang was generally outperformed by the Tempest up to 20,000ft it was certainly not embarrassed, whereas above 25000ft the Mustang was all over the Tempest like a cheap suit. So, if I wanted an aircraft for low to medium altitude work, including a bit of ground attack, the Tempest is certainly the better option. But if I wanted one aircraft to do it all at any altitude it would be the Mustang any day. All fighters were compromises, but the P-51 was probably the closest anyone came to building a fighter that was all things to all men. It just wasn't the BEST fighter below 15000ft.

 

[tomo pauk]

[tomo pauk:] Interestingly enough, the US 100K gives RoC of under 3000 ft/min, WER, between SL and 15000 ft. Those are in agreement with values where engine was operating on 60-61" (so, military, not WER), on Williams' site.[/tomo pauk]

I don't recall the sub 3000 fpm on anything but the -39 at 52", but maybe they ran it at 57"?

Sorry for not performing a more complete analysis, in a timely manner.
The plane from the quoted part of may post refers to the P-51B, and the RoC ar in range between 3100-3500 fpm, from deck to 15000 ft, 1650-3 engine. So I've compared those values with ones at Williams' site, where we can read the values of 4000 fps, +-, from various tests. Ie. my point was to underline that values from the US 100K are not the last say on P-51 performance, I was not saying that P-51A was a better performer than P-51B (it was not). Especially with advent of the 1650-7 engine.

The 100K plots for climb included only the 'ruptured duck 1710-39 IIRC. Tomo I don't recall that the -81 was documented beyond 57" - which is where the P-51 Mustang Performance report is found

The 1710-81 (ie. P-51A) is also in the chart, but chart lacks the values when engine is run on WER. The MAP value, power and altitude, as represented in the US 100K again do not match what can be read in manuals for the 1710-81 - manuals flight tests say 57in (=1420 HP, manuals, or 1480, flight tests)was obtainable above 10000 ft only with ram, the US 100K says 57in was obtainable at 11800, no ram, but gives only 1330 HP for the stated altitude MAP.

More discussion is referenced for the 56.8" WEP run - which was at 396Mph, with racks, and no special surface prep at 9700 feet, and 409mph after pumice and water finish.
The Report
http://www.wwiiaircraftperformance.org/mustang/P-51-A_43-6007_Flight_Tests.pdf including plots for 52 and 57"
The dashed line represents 56.8" dash and climb runs with ~3750 fpm at 9700 feet 7600 pounds

Thanks.