WW2 Aircraft more successful in secondary role

mongrel, forget gis. Hang on to Scarlett Johansson.

The Merlin you list certainly was a different animal. a Two stage supercharger unless I am very much mistaken.

Critical altitude for the early Allisons vary up or down about 1200ft. It may depend on exact manifold and type of backfire screens fitted (or even if fitted). And just like the Merlin III can be found with 3-4 different critical altitudes max power is very dependent on altitude.
1030hp at 16250ft at 6lbs, 1310hp at 9000ft at 12lbs boost and 1440hp at 5500ft with 16lbs boost.

Something about the power levels you quote for the Allison doesn't add up. 4 extra inches of boost (2lbs) shouldn't equal 210 more horsepower. I would also note that one source claims 1470hp for the Allison 39 at sea level using 56in of boost. Another gives 1490hp at 4600ft at 56in of boost. Getting 66in of boost out of an Allison using 8.80 supercharger gears may involve a lot of ram and running the engine at over 3000rpm.

Edit: I would also note that the power levels described required fuel that was not available in 1940 and for any hope of engine longevity (engine doesn't fail in the next two flights after pulling that kind of pressure) crankshafts that were not available in 1940. 1940 Allison crankshafts being pretty much plain alloy steel. By Jan/Feb of 1942 they were not only allow steel but both shot peened and nitrited which increase their fatigue life tremendously.

I was quoting exact figures from the Allison Division, General Motors Corp.
letter dated December 12, 1942 sent to the Commanding General, Army
Air Forces, Materiel Center in Washington, D.C. If there is a problem with
the horse power figures I have posted.....well, you're going to have to take
it up with them.

gjs238 said:

I took you for a Keira Knightley kinda guy

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Naah be like sharing my bed with a Broom handle

CORSNING said:

GrauGeist,
I agree 100% that the British didn't ask for a low-level ground support aircraft, but they new
that was exactly what they were ordering from North American when they stipulated the Allison
engine. That was their call and like it or not the Mustang was designed and accepted as a low-
level air superiority fighter. I also agree that they were hoping to get something along the lines
of the Spitfire. So was every other nation in 1940.

I still stand by my original post, probably dumber than squat, Jeff.

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Problem is, the BPC order with North American was signed before the Battle of Britain - up to that point, the air war over Europe and the Med was happening at low to moderate altitudes.

This could go all the way back to the Spanish Civil war, the invasion of Poland, the Battle of France and North Africa. All of these actions generally did not see high altidude bomber missions and/or fighter engagements.

I might also point out that Castle Bromwich hadn't assembled their first Spitfire by the date of North American's order, either.

So based on the fact the Britain was anxious to get more fighters into service AND the nature of the air war hadn't evolved into a high altitude contest yet, the performance of the P-40 (and subsequently the Mustang I) hadn't been an issue.

And like I posted earlier, it wouldn't be until the Mustang I/IA had been tried in the new combat conditions that it's shortcomings at higher elevations would become aparent. Leading the British to conclude in 1942, that the Mustang was not suitable for higher altitude combat, but was more than capable at lower altitudes.

But NOBODY knew beforehand, that the airwar would evolve into higher altitudes as the airwar shifted to a trans-channel contest...

CORSNING said:

I was quoting exact figures from the Allison Division, General Motors Corp.
letter dated December 12, 1942 sent to the Commanding General, Army
Air Forces, Materiel Center in Washington, D.C. If there is a problem with
the horse power figures I have posted.....well, you're going to have to take
it up with them.

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and

Allison V-1710-39 (-F3R): Critical altitude is 10,800 ft. (3.292 m./1,150 hp. @ 43.9"Hg).
That does not mean a whole lot though. The Middle East pilots were pushing that engine
to 66"Hg/3,000 rpm (1,570 hp.), Australian pilots pushing theirs to 70"Hg (1,780 hp.)

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Allison approved a WEP rating of 1490hp at 56in MAP at 4300ft for the -39 engine.
They approved a WEP rating of 1580hp at 60in MAP at 2500ft for the -73 engine in the P-40K
The -73 engine had a few of it's components strengthened and also use 30% gylcol/70% water cooling.

Now maybe the Mid east pilots were pushing the engine to 66" on their gauges but they had no torque meters installed on the engine and I doubt the Mid east temperatures were corrected to the standard 59 degrees Fahrenheit which makes actual power output more than a bit doubtful.
Since the only production Allison engines to get to 1700hp were either turbo charged engines in the P-38 or the two stage mechanical supercharged engines in the P-63. The P-38L engines needed 150 PN fuel to reach 1700hp (70")and the P-63 engines needed water injection to go past 1500hp and 60-61" of manifold pressure and 100/130 fuel. They could hit 1850hp at sea level using 75"

And yet somehow in the field squadron pilots pulled 1780hp (measured how?) out of a -39 engine in a P-40E using 70" of MAP using a single stage supercharger, 100/130 fuel and no water injection.
Two stage superchargers as a general rule heat the intake charge less and require less power to drive.

Allison service reps did note instances of up to 66in used on the -73 engine and the Service reps in Australia did note use of 70" with the -73 engines. But power was not noted in the book I read.
Factory power graphs show the basic Allison with 8.80 gears just running out of the ability to flow enough air to get much past 61-62"mpa without either large amounts of ram (high speed level flight) or over revving the engine at sea level.

Edit. The change from 15 degrees C to 38 degrees C (59F to just over 100F) lowers the actual air density (weight of air per cubic_____) to 92.57%. Taking in the same cubic feet (or meters) of air per second or minute at the higher temperature will result in 92.57% of the power (in theory) of the "standard" temperature of 59F or 15C that most nations used as a standard. This is if the air pressure is standard.
This also means that a pilot could (boost control permitting and some US aircraft didn't have a automatic boost limiter) use 7-8% more absolute manifold pressure than "book figures" and yet only being making the "book" power numbers. Trying to get too tricking in gimmicking the boost control could land the pilot in trouble as the temperature at altitude (even 15-20,000ft) doesn't vary as much
as the temperature at ground/sea level around the world. Yes the temperature at 15,000 is higher in the tropics (or NA desert) than in England (or Ohio) but not the same difference you sea at ground level. Setting the engine up to "over" boost at sea level could very well result in too much over boost at an altitude of 9-10,000ft.
Now perhaps the North African and Australian figures were taken in their "winters" or cold snaps but pressure readings ( or max pressure seen by pilot while doing ?????) don't really translate into reliable power figures.

I have a couple of suggestions for contenders:

The Kawasaki Ki 45. In many ways it can be called the Japanese Bf 110, with the reservations that it was later, slower and build in fewer numbers. It never served in it's intended role as long range escort but did fly as a bomber interceptor. It did see much service (and improvements to enhance capability) in the roles of night fighter, ground and sea attack.

Another would be the Commonwealth CA Boomerang (I've come across several alternative ways of designation, I hope this covers the whole series in general). Build and employed as a fighter, to my knowledge it never shot down an aircraft. Making it likely it did better iwhen assigned to ground attack and miscellaneous other kinds of army support.

I mean, occasionally it should at least have succeeded in hitting the ground.

I must emphasize I don't intend to say the Boomerang was a bad aircraft/design. Even though it from the right angle can look a little like a Buffalo, I have no strong opinions about its good and bad qualities, except that its performance dosn't seem impressive for a fighter entering service in late 42.

Schmidt, the Ki.45 is a great example of an aircraft that excelled (to a degree) outside of its
original designation.

Oh, and everyone else, I am going to digress now. From what I can tell the majority
is considering the Allison and the Merlin as just fighters that were considered just fighters
in the same classification that could do different things.

I know, I have the right to remain silent...I know it...yes, I know it.................................

..... I'm sorry, I just don't have the ability. I agree with everyone that the UK believed they
were getting a better fighter than the P-40D, and they were. I agree that they believed they
were getting a fighter that could do what they wanted it to do, and it could. I also agree that
the rules of the game change by the time the NA-73 and P-51 came along,...and they did.
That brought about the classifications of fighter aircraft. With that came the classification of low level
army co-op....The NA-73 and P-51 filled this bill better than the Spitfire or Hurricane. BUT THAT
BECAME ITS CLASSIFICATION! The Merlin (second generation if you will) was a totally different animal
PERIOD!

Since the consensus does not seem to agree, I am bowing out.

My original stance (in my own mind) has not wavered. I still believe that the change from
Allison to Merlin in the Mustang brought one of the best 'long-range, high-speed Army ground
support fighters' of the late-early war to the best 'long-range, high-speed Army Air Force
escort fighter' of late-mid to late war.

I know, ' Mamma always said, stupid is as stupid does'. For a while there I was beginning
to think she was probably talking about me...again.

But then, I don't think so this time.

But you keep missing the point:
The Mustang was designed, engineered and built as a fighter.

The British Purchasing Commission purchased it with the intention of using it as a fighter.

It first saw combat as a fighter.

All of it's variants, with the exception of the A-36, were primarily used as a fighter. The A-36 proved itself to be formidible as a fighter, even though the A-36 was the ONLY variant of the Mustang series to be a dedicated ground attack type.

Even after the RAF determined that the Mustang I/IA was not suitable for higher altitudes, it was still used as a fighter at lower levels, where it excelled.

P-51A/B/C/D/K was intended to be, and was used as, a fighter in it's primary, designed and built role. The fact that it could carry bombs and shoot up targets on the ground does not change it's intended and primary function. It simply means it could multi-task, just like the Spitfire, F6F, YaK-9, Bf109 or any other fighter. Add to that, the role of long range escort also changes nothing. It simply meant that this fighter had a longer range than other fighters, and when it encountered enemy interceptors, it shot them down.

How does P-51A compare to P-51B at low altitude?

BLine22,
In 1942 and early/mid1943 there was no Merlin P-51B. By the time the P-51B-1 became operational
in December of 1943 it had to contend with the Allison V-1710-81 engine in the P-51A. At low levels
the P-51A was faster, faster climbing and could out maneuver the P-51B using 67"Hg boost if the P-51A kept its speed up.

GrauGeist, I agree with you completely. In 1940 before everyone knew what was actually
going to happen for the rest of the war, your statements are dead on. But situations changed,
by the time the Mustang came on board, classifications were drawn.

BLine, here is a little data on the two on how they matched up in December 1943.
North American P-51A (Mk.II) and P-51B (Mk.III) Mustangs - World War II

CORSNING said:

My original stance (in my own mind) has not wavered. I still believe that the change from
Allison to Merlin in the Mustang brought one of the best 'long-range, high-speed Army ground
support fighters' of the late-early war to the best 'long-range, high-speed Army Air Force
escort fighter' of late-mid to late war.

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I would really like to see where the Allison Mustangs in either British or American service were categorized or labeled as
'long-range, high-speed Army ground support fighters'

All except the A-36 did not carry bombs, making them strafers only. The need for long-range Army ground support fighters would be minuscule at best, regardless of speed. Army Ground support planes usually attacking either front line troops or areas/supply points/supply line in close proximity to the front lines. Long range not needed.

Ground support being a bit different than even tactical bombing or strikes although they can cross over or be performed by the same units/aircraft on different missions.

Tactical or general reconnaissance is a different mission that "Army ground support" and may well require high speed and long range even if done at low altitude. Allison Mustangs did perform, many many low altitude photo-recon missions for both the British and Americans but that was not Army ground support.

Shortround6 said:

I would really like to see where the Allison Mustangs in either British or American service were categorized or labeled as
'long-range, high-speed Army ground support fighters'
.

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There really wasn't any such thing at the time. Much later, after the invasion the two principle mission types were, in British terms, Close Air Support and Armed Reconnaissance.
Both the British 2nd TAF and the US 9th AF carried out substantially more of the latter, and it was much more dangerous. The MAAF used different terms, but most of its missions would also fall into an armed reconnaissance rather than close air support category.
Helpfully, in early 1945 the 2nd TAF's No.83 Group started to divide its armed reconnaissance missions into two categories, 'shallow' and 'deep', which gives us an idea of the sort of missions they were flying.
A 'deep' sortie passed over a line running through Hamm-Munster-Rheine-Almelo-Zwolle, at that time about 60 miles behind the German front line. A 'shallow' sortie obviously operated in the area between the front line and this line.
Even in 1945 I think it debatable that a long range ground support fighter was required. These aircraft operated from airfields close to the front lines and penetrated 60-100 miles behind the lines at most. They were barely flying further than the Luftwaffe's Bf 109s in the BoB, though they did enjoy rather more loiter time.
Cheers
Steve

My wording may be off some. I apologize if it was misleading. The term used is Close Air Support.
The NA-73 interred service with the RAF Army Cooperation Command on 10 May 1942 with No.26
Squadron.
RAF Army Cooperation Command - Wikipedia, the free encyclopedia

Army Cooperation Command was a bit of a non event. Remnants of it, along with substantial units from Fighter Command and the often forgotten Bomber Command, eventually morphed into 2nd TAF (it was a bit more complicated than that, but that's a simplified version).
Cheers
Steve

For it's success in not one, but multiple secondary roles, it's hard to beat the P-38. While designed as an "interceptor" it performed a wide variety of roles.
Long range escort fighter
Ground support/fighter bomber role
Dive bomber
Skip bomber
4000 lb bomb load capability
Tested as a torpedo bomber, carrying (2) 2000 lb torpedos
Photo-recon aircraft-one of the most successful of the war
High altitude level bomber with "droop snoot" variants equipped with Norden bombsites
Radar equipped Pathfinder
Night fighter

Idaho,
I will agree 100% that the P-38 was an extremely versatile aircraft. The original
question was asking," What aircraft was (became) more successful in a secondary
roll?"
I will have to do some research here, but I believe the P-38F entered service as
an interceptor/air superiority fighter. I believe that is were it excelled in the Pacific
late in the war as the P-38L.
The P-51 (NA-73) interred service as an Army coop (close air support) low altitude fighter. It
later became what is now arguably the best high altitude, long range escort fighter.

"The P-51 (NA-73) interred service as an Army coop (close air support) low altitude fighter."

You keep repeating this but it is highly debatable.
It was not designed as such, and while to was assigned to Army co-operation squadrons (at least they were named that) it did a lot more recon/photo recon in it's early operational deployments. Due to a rather notable lack of boots on the ground (Dieppe being a major exception) there was a distinct lack of actual Army Co-operation missions in Europe until 1944.
There were a lot of "tactical" or low altitude strikes against railroads, barges and airfields during 1942 and 1943 but there were no Army ground troops to support no matter what the squadrons were named.
If you are not actually supporting the Army and the majority of planes have 1-3 cameras fitted is the plane really a close air support fighter?