P-39 vs P-40

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Actually the leading cause of fighter losses in 1944 is 'other causes' = 637.
MAW II, III, and IV together cover 1943, but I predict that crunching the numbers in these volumes won't get you a match with the figures from the document, which is from this:
USAAF Statistical Digest .
 
The P-40E's main problem was it's combat ceiling was under 20000'. It was at a disadvantage against almost all other first line combat planes due to it's extremely heavy weight compared to it's engine power.

The mechanical two stage Allison was in production from May '43 and would have made both the P-40 and P-39 (and the P-51A) into great high altitude fighters. This engine eventually went into the P-63, a bigger and heavier version of the P-39 from late '43.
 

The LF versions of the IX and VIII used the Merlin 66, which had the same ratings as the V-1650-7 used in later P-51Bs and P-51Ds. Low altitude was a relative term.

The LF.Vs were, as I understand it, retrospectively given the the LF designation. They were not designed as low altitude fighters, but were modified to be - specifically to combat the Fw 190A.

The XII was a low altitude fighter because it used a single stage Griffon, as those were the only ones available at the time.
 
The P-40E's main problem was it's combat ceiling was under 20000'. It was at a disadvantage against almost all other first line combat planes due to it's extremely heavy weight compared to it's engine power.

But that isn't actually true. You didn't understand what you have been reading. Performance, especially climb, fell off starting at 12,000 ' and climb rate was no doubt very bad by 20,000', but that was not the ceiling. They routinely intercepted enemy bombers flying much higher than that. You should read this article which I posted previously, about the use of P-40s in the defense of Darwin. From March to September 1942, Japanese records confirm that novice P-40E pilots from the 49th FG were able to shoot down 12 "Betty" bombers flying at 27,000' in spite of a heavy escort of A6M2s so not only were they able to fly that high, they were fairly effective in combat (albeit with heavy losses of their own) .

Quote from the article:

"Darwin's 3.7-inch anti-aircraft artillery forced the G4Ms to ingress at high levels—generally between 25,000 to 27,000 feet. Such a high ingress altitude sorely tested the P-40E fighters as their Allison V-1710 engines suffered from an inadequate mechanically driven supercharger. The Allison, while rugged and reliable, lost considerable power at the higher altitudes, with the operational ceiling of the P-40E limited to around 27,000 to 28,000 feet."

In fact the only US fighters I'm aware of which were literally unable to attack high flying bombers during the war were P-39s / P-400s' over Guadalcanal and that was apparently due to a lack of suitable oxygen equipment. P-39s were also active at Darwin but I don't know of any stats on their use there, do you?

The Darwin campaign was an early experiment, efficiency got much better. AVG and later 23rd FG etc. were routinely shooting down high flying Japanese bombers all through the war with P-40E, K and later N with minimal and diminishing losses.

S
 

Yes but lets be real the LF Spit Mk V, many regular Spit V, recon Spit IV and various others were using other specifically low altitude optimized Merlin engines like the Merlin 45, 45M, 50, 50M etc. some of which had cropped impellers specifically for low altitude power. For example Merlin 45M had a critical altitude of 2,750 ft (838 m) where it gave 1585 hp. Interestingly this is about the equivalent of the P-40K (which the English liked quite a bit) at normal / sanctioned WEP settings.

The short version of this is that they did perceive a need for low altitude fighters optimized to perform down where the Stukas were dropping their bombs.

I'm not an expert on the Rolls Royce engines, the Merlin or the Spitfire so I'm going mainly off of this:

List of Rolls-Royce Merlin variants - Wikipedia

S
 

Why would you predict that? Are you suggesting Shores numbers are off?

I will do some number crunching on one of the months, maybe July or June 1943 and we can see how it adds up. I'll post it in the P-40 vs 109 thread and then link back to here.
 
There were no P-39s at Darwin. While oxygen was a problem with P-400s at Guadalcanal, P-39s did not have that problem. The record of P-400s and P-39s attempting to intercept bombers in New Guinea was poor at best. They were constantly bounced from above by escorting A6Ms. They did not have enough early warning time to get to altitude. AVG and 23rd FG P-40s benefited from adequate early warning as did Darwin P-40s, though perhaps to a lesser extant. P-40s in Java had no such luxury. The use of the P-39 and P-40 is a lesson in how US fighters were thrust into jobs that they were not intended for. They were not interceptors. The P-38 was an interceptor but forced into the high altitude escort role, among others where it did not excel.
 
Why would you predict that? Are you suggesting Shores numbers are off?

I will do some number crunching on one of the months, maybe July or June 1943 and we can see how it adds up. I'll post it in the P-40 vs 109 thread and then link back to here.

The USAAF stats certainly seem to portray a different picture than MAW does, for 1943 at any rate; with some 75% of USAAF fighter losses attributed to enemy aircraft according to the stats, just 11% to flak. As you yourself have remarked, in MAW fighter losses to flak are higher than that. Which numbers are off, I don't know, and I much prefer to think that there is a plausible explanation for why there is such a difference.

I agree on taking a single month or two and comparing the numbers, it's the way to go ; it will be interesting to see how it turns out.
 

By the time the 'cropped' superchargers were in use, the threat of Stukas was not present. Main threat/target were Fw 190s now (ie. early 1942 on).
The Merlin 45 and 50 were 'normal' versions, with impeller diameter of 10.25 in. The 45M and 50M were the ones with cropped S/C (dia of 9.50 in - same as 'ordinary' V-1710s), so gains in low altitude were traded for loss of hi-alt power.



The Merlin 30, 32 and 34 were also low-level engines, sporting small impeller (9.75 in diameter) and other modifications:

 

There is the "book" ceiling (service ceiling) at which a plane can still climb at 100ft per minute ( or a metric equivalent). rarely quoted is an operational ceiling, figured by the British for example as 500fpm of climb which allows a formation of aircraft to maneuver and maintain formation (assume worst plane in the squadron is on the outside of a turn) and there is the COMBAT ceiling, generally around 1000fpm of climb which allows the plane to perform combat maneuvers without excessive loss of altitude. Obviously the last is the most subjective and nobodies aircraft could perform hard turns or part loops or other high energy consuming maneuvers in succession without losing altitude.

Given enough time/warning a formation of P-40s could climb to intercept height and execute an attack run (or more than one) on a formation of bombers. Dog fighting the escorting Zeros was pretty much out of the question. Shoot at them if they were in front of you but otherwise, get in/get out turn around at a safe distance and repeat. trying to do much more than roll the P-40 form one side to the other and gentile snake turns was going to result in a large loss of altitude that would take minutes to recover from. A P-40 might take 6 minutes or more to climb from 24,000ft to 28,000ft depending on weight or air temp/pressure and that is at best climb speed, once at desired altitude it still has to accelerate to combat speed.

Depending on such a fighter to intercept attacking bombers is not a good choice if other fighters are available.


The Darwin campaign was an early experiment, efficiency got much better. AVG and later 23rd FG etc. were routinely shooting down high flying Japanese bombers all through the war with P-40E, K and later N with minimal and diminishing losses.

The P-40N had the later engine and all ceilings are raised by 3-4000 ft.
Stripping weight (pretty much guns, ammo and fuel) could also improve the performance of fighters in the field.


The P-40E was overweight, there is no" if, and or but" about it. The six .50 cal weapons installation was simply too heavy for the engine available. about 900lbs of guns and ammo which is several hundreds more than guns/ammo in a Spitfire V/IX or most of the the 1941-42 single engine fighters. It may be more than the FW 190. it may be triple what some of the Italian and Japanese fighters were carrying for armament.

Unfortunately once you design the plane around such a weapons load you can't go back to "zero" by simply taking out a pair of guns in the field and not filling up the ammo bins.
The P-40 gained around 300lbs of weight in the wing structure from the initial P-36 wing to the late model P-40 wings. If you want to keep the 8 "G" service rating (12 "G" ultimate load) you have to beef up the structure as the gross weight increases. Likewise weight of the landing gear/tires and even the fuselage may have to increase slightly to handle the higher weights. You are stuck with those wight increases in the field no matter what you do with the guns/ammo/armor.

Lets also remember that the P40D/E was ordered in the spring-summer of 1940, before the Battle of Britain.



Design and performance estimates have to looked at in that light and not as much what it was faced with in combat in late 1941 (British and Soviet ? use) and 1942 against the Japanese. Please note the P-40F prototype flew in the summer of 1941 around 6 months before Pearl Harbor so the US was not ignoring the lack of altitude capability of the P-40.

I would also note that the P-40D/E was initially rated with a combat load of 120 US gallons of gas. You could put an additional 28 US gallons in the rear fuselage tank but you basically had a 8100lb airplane with just that 120 US gallons of fuel and 1150hp engine (the WEP ratings are totally irrelevant at this point as at the time of the order/s and finish design work the older Hawk 81s {tomahawks and P-40B/C} had not entered active service let alone combat so there was NO unofficial combat boosting going on of the older engine let alone anything base overboosting of the new -39 engine on.)

It shouldn't have taken a degree in astrophysics to figure out the power to weight ratio wasn't going to be good to good. In defence in the summer of 1940 nobody else (except the the British ) had supercharger much better than the one on the Allison in service.

Back to the weight thing. As a very rough estimate you can figure that the payload of plane (for a fighter guns/ammo/fuel/pilot etc) as 30% (or somewhere between 25-35% ) of the gross weight of plane in the initial design stage. You want to add 20-30% to the payload you need a plane that grosses 20-30% more to keep everything else (field length, stalling speed/turn etc) the same. But once you make the wings/fuselage/landing gear bigger and heavier to handle the higher payload you don't get all the performance back by not putting the full the payload into the larger aircraft.

 


we have several confusing things going on here. we are also using the retrospectroscope to a fair degree.

That 1585hp figure for the Merlin is at 18lbs boost and yet the Standard Merlin 45/50 was good for 1470 to 1515hp at much higher altitudes using 16lbs boost.
better comparison is that at 3000rpm and 12lbs boost the cropped impeller engines were good for 1230hp for take-off and the uncropped engines were good for 1185hp.
Please note that again these were the ultimate ratings as finally decided in time. At some points in service the cropped impeller engines may have been allowed to use higher boost than the uncropped engines at certain altitudes.
Like in Jan of 1942 the uncropped engines were limited to about 15lbs of boost by the end of 1942 this had changed 16lbs (not a big deal) but climb ratings were now being done at this power level and not restricted to 2850rpm an 9lbs of boost.

The cropped impeller engines may have been rated at higher boost sooner (Jan 1942 saw the low geared Merlin 30 rated at 1lb more boost than any other Merlin) and again the fuel situation was in a state of flux. there was no 100/130 fuel in 1941 or the start of 1942. The cropped impeller engines may have been a way around the fuel limit until the supply of 100/130 fuel was a given.
The Merlin 45 was limited to 9lbs (48in?) when first introduced and then changed to 12lbs (54in) and finally to 16lb ( 62in?)

we have the luxury of knowing what fuels were to become available and when and what the engines were eventually modified to stand up to.
For the US due to the distances from the factories to front lines it could often take 3-6 months for a production fighter to leave the factory and get into squadron service in a combat theater. That fighter would have had to have been ordered months if not a year before it rolled out the factory door inorder for all the subcontractor parts to be available. landing gear/tires. oil coolers, engine and propeller, instruments and a host of other parts (forgings/casting) that the factory did not make itself.
 

Well to be clear, I was talking about MAW IV which is May 43 to Sept 44, and certainly the air to air casualties went down as the flak casualites went way up in 1944 which you can see in the Air Force journal records.

If there is a difference, and I'm not sure there is, it may boil down to how things like air to air collisions, engine failure etc. are counted.

But I agree the month analysis would be good to do, it may take a while though it's very busy lots of fighting with numerous claims and losses on both sides. A lot of transcribing.
 
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Stukas were still in heavy use all through the Med in 1942 and well into 1943 - quite devastating against some of the convoys too. But also used against Allied tanks including at El Alamein and Tobruk and so on right up to the end of the war in Tunisia. Also Ju 88 being used as torpedo bombers and (shallow angle) dive bombers, and various others including Dornier 217 (I think?) being used as carriers for Fritz guided missiles, He 111, SM 79 etc. etc. and Bf 109E and 110 Jabos. All needed to be shot down down low.

In Sicily and Italy the FW 190s were the main Jabos but they too were operating at low altitude. And the Ju 88's were still being sent out frequently (and getting wacked right and left).

My understanding of Merlin 45 and 50 (uncropped) is that they were still lower power rated engines just not as low as the cropped 45M and 50M.

S
 
There were no P-39s at Darwin.

My bad - I was thinking of Port Morseby, and apparently some other towns in Australia.

Aussie P-39 Airacobra – Emergency Defender

P-39 Airacobras in defence of Australia | The Australian War Memorial


All true. Part of what a fighter has to be is versatile. P-47s and Corsairs were never (originally) intended for ground attack and were in some respects unsuited, but the radial engines and heavy carrying capacity proved valuable in that role. Spits and 109s weren't really meant for bomber escort but they had to do it.
 

It was actually not at all unusual for aircraft to start out just on the edge of enough engine power, but due to the dance between manufacturer and military, not yet equipped with all the 'stuff' needed for actual combat...and by the time that stuff was put in the plane became too heavy for the engine or the airframe. In the case of the P-40, my point was simply that the issue was the engine not the airframe.

The official engine settings (not just boost) for the earlier Tomahawk P-40 B/C and for the P-40D /E were too low. And there was a little too much weight in it. However this was changed in the field almost as soon as the aircraft went into combat. The British and Australians had figured out how to use the Tomahawk pretty quickly and had the luxury of sort of a slow ramp up in the Middle East as they were initially mostly facing not quite front line Italian fighters, Bf 110s and Vichy French fighters. When the P-40E arrived pilots really had to hit the ground running and did not have really any time to figure the plane out before they went up against elite enemy pilots flying world class fighters. This was true in North Africa where they were facing 109Fs of JG 27 etc., and in the Pacific where they were up against the best of the IJN and IJA flying A6M2s and Ki-43s.

However changes to the engine and experiments with stripping weight were going on from almost the first day of combat. They did take out guns, they took off with half fuel for intercept missions and so on during the debacle at Java and at Port Morseby / Milne Bay. The AVG also mentioned tinkering with their engines and doing all kinds of things (waxing, filling holes, sanding etc.) to speed up their Tomahawks and later Kittyhawks. Not sure about Darwin but I would be surprised if they didn't do it there as well as one of the commanders of the 49th FG had been at Java. The infamous Allison memo mentions their use "for considerable periods of time" .... "From Australia" at 70" / 20# per sq in boost and from the Middle East at 66" Hg (18# / sq. in.)." This was in Dec 42 but it's not clear how long it had already been going on. From other documents and interview excerpts I've read it had clearly become widespread practice to boost Kittyhawks to at least 60" by in the DAF mid 1942. That still leaves a few months where who knows what practices were going on at what squadrons but I have a feeling word got out pretty quickly.


They were using external fuel tanks on P-40E from early on. Not sure about the D but a lot of the D models only had four guns.

S
 

The 'ordinary' Spitfire V will have a field day against the listed Axis bombers, no need for low-alt engine. Please note that just a handful of Spitfires was deployed in Med before 1943.

My understanding of Merlin 45 and 50 (uncropped) is that they were still lower power rated engines just not as low as the cropped 45M and 50M.

S

1500++ HP is hardly a sign of low power rated engine.
 
The 'ordinary' Spitfire V will have a field day against the listed Axis bombers, no need for low-alt engine. Please note that just a handful of Spitfires was deployed in Med before 1943.

You seem to be misunderstanding me here or missing my point. Yes the Spit V can have a field day against a Stuka or Ju 88, but they were defended by Bf 109, Mc 202, Mc 205, Re 2002 etc. They also had to catch Fw 190s. Apparently they felt they needed the low altitude versions.

Large numbers of Spitfire Mk V were deployed to North Africa by mid 1942. Five squadrons: 92, 145, 601, 94, and 417 sqns were all flying Spitfires by El Alemein in Oct 42.

1500++ HP is hardly a sign of low power rated engine.

Low altitude not low power. 1500 hp at 800 meters. Get it?
 
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The Spitfire V with low-level engine (Merlin 45M, 50M or similar) cannot fight with the said fighters escorting the bombers as good as the Spit V with 'normal' engine (Merlin 45, 50) can.

Large numbers of Spitfire Mk V were deployed to North Africa by mid 1942. Five squadrons: 92, 145, 601, 94, and 417 sqns were all flying Spitfires by El Alemein in Oct 42.

Before August of 1942 there was barely a Spitfire in N.A.

Low altitude not low power. 1500 hp at 800 meters. Get it?

Merlin 45 made more than 1500 HP at 11000 ft (3350m), and more than 1000 at 20000 ft. Get it?
 
Please note that just a handful of Spitfires was deployed in Med before 1943.
Before August of 1942 there was barely a Spitfire in N.A.

Ok Tomo, you seem to be moving the bar a bit here, and I'm not sure precisely what you are getting at? You tell me why they (obviously quite on purpose) created low altitude fighters with low-altitude rated engines?

Or are you claiming that they didn't?
 

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