P-39 vs P-40

[tomo pauk]

The Tempest and Typhoon were also low altitude fighters.

And almost all of the Soviet fighters were low altitude fighters -and no this was not done after they had already secured a sufficient number of high-altitude fighters. The one high altitude fighter they had, the MiG 3, they basically thought was useless because it performed badly down low, and they thought the P-47 was "not a fighter" to quote the evaluation verbatim.

The early Zeros by the way, did not have very high altitude performance ceilings either, nor did Hurricanes at least not in the Med (they were often unable to intercept high flying aircraft over Malta for example) nor quite a few other early and mid war fighters.

Both Tempest and Typhoon were far better than P-40 at any altitude.Tempest was better than Fw 190A of any type at any altitude, and about as good as Fw 190D-9. Sabre was making almost twice the power of 1-stage V-1710 above 15000 ft, and 500-700 HP more under 10000 ft.
Soviet fighters being good just at low altitude was a bug, not a feature. Ditto for their performance and range. MiG-3 was too ligthly armed by Soviet standards, used the engine produced at factories that were also supplying the Il-2 needs, the cockpit was so bad that pilots preferred to fly with open cockpit (hence killing lots of speed).
In 1942, Zeroes were far better hi-alt fighters than P-40s, and Japan produced other fighters that were not Zeroes. Hurricane was a draggy affair, engine was able to help just that much.

So I don't know how many times I have to say this - there was a purpose and a need for low altitude fighters. And the Spit V LF was one example.

There was a purpose.
Please note that 1st and foremost people were trying to introduce 'all-altitude' fighters, and, once that was sattisfied, they introduced specific fighters for high altitudes and low altitudes. Unfortunately, there was no 'HF' P-40s or P-39s, due to V-1710 being about as good as Merlin 45M, altitude-wise.

 

[tomo pauk]

So I don't know how many times I have to say this - there was a purpose and a need for low altitude fighters. And the Spit V LF was one example. It matters very little to me if that used a Merlin 45 or a 45M or a 50M or whatever. Point is it wasn't just for Seafires.

By the way Wiki also mentions that the "low altitude" merlin 32 was also used on the Spitfire PR Mk. XIII (with citation from The Spitfire Story. London: Jane's Publishing Company Ltd., 1982. ISBN 0-86720-624-1. pages 182 and 185)

Spit VLF will use Merlin 45M or 50M, but not 45. Just for Seafires??
The PR XIII was a spin-off from FR versions, low-level recon, lightly armed (4 .303s), not a long-rage hi-alt recon like vast majority of PR Spits were. FR meaning 'fighter-recon'.

 

[Shortround6]

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.

In reverse.

"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."

ALL of the Ds had 4 guns, but according to some sources there were only about 30 Ds (or 30 built for the US) built before the contracts were amended to E models so the point is rather moot.
Some (all?) of the US Ds saw use in Hawaii.
With full internal tanks the D/E was good for 148 gallons, with drop tank the total capacity was 200 gallons. Point is that even with drop tank gone you can't fill the internal tanks and keep the plane under 8100lbs unless you take out guns/ammo. Filling the internal tank/s means an additional 168lbs.

"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."

I love the bit about tinkering the engines. Nobody ever says what was done. You can't do much with the timing. Allison ignition timing was fixed, there was no variable advance. You can either set it up for a little more advance or retard it a little but then either your starting and idle/slow speed cruise are affected. or the top end is affected. There were a variety of approved spark plugs and perhaps one or two degrees timing change worked better with plug han another?
You can't change the valve timing. You can change the valve clearance but why?
You can change the jets in the carburetor (assuming you have different jets or spares to drill out) but there again you have very narrow window of possibilities and what works at one temperature/air pressure situation is worse than standard at a different temperature/air pressure situation.
The big thing that could be done and was done once WEP power settings were approved was to hacksaw off the ends of the exhaust stacks to open them up and reduce back pressure at the higher power settings. please note that this may have lowered the exhaust gas velocity at standard power settings (climb and cruise) for loss of power/thrust under those conditions.
Working on supercharged aircraft engines is a lot different than working on a 1940s Chevy six or Ford Flat head V-8.

Taking weight out helped but please look at the factory strippers. The Early P-40L and the Early P-40N. the chances of any squadron mechanics getting a P-40 pf any type down to the weight of an an early P-40N are about zero unless they had access to aluminium radiators and oil coolers, maganismum wheels, lighter tires, used four guns and restricted the four guns to 200 rounds per gun, pulled out the electric starter for the engine (leaving hand crank only) and took out the battery or substituted much smaller one ( a mark of desperation for a plane that used an electric propeller. If the generator fails how long before the prop becomes a fixed pitch prop at best or runs away at worst.

1/2 fuel mans what? 100 US gallons if you count the drop tank? 74 US gallons if you don't ? 60 US gallons (50 imp gallons) if it is 1/2 the "book" combat fuel load?
A P-40E was going to use over 40 US gallons just starting, taking off and climbing to 20,000ft. Figure another 8-13 gallons to make it to 25,000ft.
In combat the engine might use 1 to 1/2 gallons a minute at high altitude. (much more at lower altitudes).

Sorry, gliding back to the airfield after an intercept doesn't sound like that great of an idea. Reduced fuel yes but 1/2???

"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. "

Now this needs a bit of looking at too as there were several changes to the engines used in the Tomahawk P-40 B/C that do NOT show up as changes in the engine type.
Allison had to call back 277 (?) of the original -33 engines and rework them at company expense because they were failing well before the expected overhaul life. Changes included but were not limited to a new crankshaft and new crankcase. Until the rework was done the planes continued to fly with the engine restricted to 2770 rpm and with restricted boost pressure. I don't know if the British got any of these engines or if all went into early US production. In any case it may well have made both Allison and the US army at bit hesitant to approve high boost levels on that "2nd" generation -33 engine until the service life was proved out (and it did have considerably more life than the originals, not just meeting the original goal).
You also run smack into the the fuel situation. British (and commonwealth) fuel in 1940 and 1941 was the equivalent to 100/115-120 so a fair amount of over boosting could be done as shown by the Merlins in the BoB going from 6lbs (42in) 12lbs (54in) however US fuel at this time was 100/100. Over boost this stuff at your own risk. The US did specify/but and issue (for testing?) some 100/125 and many US engines of this time period (1940-41) were rated to use this grade but information on use in service is limited (nearly no existent one way or the other). The British and the US coming up with the first of many specifications for 100/130 fuel (1st specification limited the lead use to 3cc per imp gallon). The 100/130 fuel showing up about the time many of the planes were (although the amount of 100/130 fuel in the Philippines might be subject to question).
Back to the engines, the first Allisons used a "plain" steel crankshaft. I don't know when it was changed, Plain steel means a high grade steel alloy suitable heat treated. At some point they went to shot peening the crankshaft. I don't know if this was part of the fix for the early engines or if it came latter. These crankshafts had much improved fatigue life. By the end of 1941 ( and after over 1000 P-40Es had been built) the crankshaft was changed to one that was both nitrided and shot peened for another very significant increase in both strength and fatigue life. It was this crankshaft that allowed the 1325hp take of rating in the P-40K (after hundreds if not thousands of hours of testing, both factory and operational).
Saying that early P-40Es could have been over boosted like the P-40Ks were given the different crankshaft and possibly different fuels is pushing things.
They were were overboosted but squadron records don't seem to show the failure rate. And the failure rate has to take into account the availability rate (number of planes grounded with metal bits in the oil waiting for an engine change) and not just the number of crashes due to engine failure. How many minutes/hours at how much over boost before engine failure?
compounded by the crappy operating conditions. does the crankshaft fail from fatigue before or after the engine bearings are wrecked by sand/grit in the oil?

" 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."

There was no "dance" between the manufactures and the military. In 1939-40 there was a change in what was required in military aircraft in many countries. Curtiss lost over $14,000 when the 2nd XP-46 with full military equipment failed to come close to the projected performance figures. Please note that the P-40D/E was a back up to the XP-46 using the same engine as a low risk----low loss of production alternative.
Armor, self sealing tanks, good radios and more than a handful of rifle caliber machine guns were all just starting to be fitted to most fighter aircraft in 1939/early 1940.
Early Bf 109Es having just four 7.9mm machine guns, little or no armor and no self sealing tanks during the attack on Poland. Trying to say that aircraft companies/designers were using smaller than needed engines and getting by by skimping on military equipment is not an accurate picture. There simply weren't any more powerful engines in a suitable stage of development using the fuel available to each country at the time. In 1939/40 the US didn't have any liquid cooled engine anywhere near production status except the Allison and there was no good air cooled radial alternative. For instance the 1700hp version of the Wright R-2600 didn't start design work until the same month the P-40D/E was ordered. The first prototype engine ran a few months later (about the start of the BoB) but the 5th production engine was not built until over a year later. Oct of 1941

The issue was not the engine, it was the airframe/service load.
Please compare the Allison to the Merlin 45. You could drop a Merlin 45 into a P-40 with not a lot of change in performance until you get to around 18,000ft. You could drop an Allison into a Spitfire MK V and if you allow over boosting probably get similar performance up until about 18,000ft.
The Allison is about 3.6% bigger in displacement and uses about 10% more compression so at the same rpm and boost pressure it should make a bit more power.

from this test : Spitfire F. Mk.VB Climb and level speed performance

we can see that a Spitfire V with a cropped impeller Merlin 50 engine could hold 6lbs boost (42in ) to 16,000ft with the RAM supplied by climb speed. At max level speed it could hold 6.2 pounds to 18,000ft. it can only hold 18lbs/66in (18.2 in the test airplane) to 3800ft when climbing so it isn't that different from an Allison with 8.80 supercharger gears.

 

[tomo pauk]

...

The issue was not the engine, it was the airframe/service load.
Please compare the Allison to the Merlin 45. You could drop a Merlin 45 into a P-40 with not a lot of change in performance until you get to around 18,000ft. You could drop an Allison into a Spitfire MK V and if you allow over boosting probably get similar performance up until about 18,000ft.
The Allison is about 3.6% bigger in displacement and uses about 10% more compression so at the same rpm and boost pressure it should make a bit more power.

from this test : Spitfire F. Mk.VB Climb and level speed performance

we can see that a Spitfire V with a cropped impeller Merlin 50 engine could hold 6lbs boost (42in ) to 16,000ft with the RAM supplied by climb speed. At max level speed it could hold 6.2 pounds to 18,000ft. it can only hold 18lbs/66in (18.2 in the test airplane) to 3800ft when climbing so it isn't that different from an Allison with 8.80 supercharger gears.

Welcome back
Now to the point - with P-40, it was very much about engine, too. In 1941-late 1942, Merlin 45 vs. V-1710-33 or -39 means at least 25% extra power for no gain in weight. For example, at 15000 ft, it is 1030 HP vs. 1300+. No ram.
Come late 1942, Spitfire gets Merlin 61, P-40 gets an improved V-1710 - no contest at all, Spitfire's engine has more power at 25000 ft than P-40s at 15000 ft.

 

[wuzak]

Well I guess it depends on your definition of low altitude. The P-40F (also made in 1941) and L had a Merlin 28, essentially Merlin XX, and a critical altitude of about 20,000 ft. Which is considered low - certainly not high enough for escorting B-17s. According to this page Merlin 45 had 1,515 hp at 11,000 ft and 1,210 hp with +3 boost at 18,000 ft which sounds kind of similar. Is it wrong?

20,000ft is what would have been considered mid-altitudes.

The advantage a higher critical altitude engine is maintained at altitudes above that critical altitude, if not widening the gap.

+3psi boost would be a cruising setting.

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

This shows the 45 as having:
1,185hp @ 3,000rpm for take-off, +12psi boost
1,515hp @ 3,000rpm @ 11,000ft, presumably at +12psi boost
1,200hp @ 2,850rpm @ 16,000ft - probably a +9psi boost (rated power)
1,060hp @ 2,650rpm @ 14,500ft - cruising.

The Spitfire inability to escort the B-17s was not because of altitude performance, but because of range.

At 30,000ft the Spitfire V with Merlin 45 could still do ~340mph TAS.
http://www.wwiiaircraftperformance.org/Spitfire_V_Level_Speed_RAE.jpg

Also, the Spitfire Mk.III with Merlin XX would have been a genuine 400mph aircraft, but production requirements saw the V go into production instead, it basically being a Mk II with a Merlin 45 and not requiring extensive changes.

A while back I think I posted a bunch of data from Shores MAW Volume III in one of the air battles a Spit IV PR blundered into a dogfight between P-40s and Bf 109s and got shot down by the latter, I think it's in the p-40 vs. 109 thread which I believe you also posted to.

So, one PR.IV gets shot down at a lower altitude = PR.IV was a low altitude aircraft?

Question: Where did this occur? Near home base for the Allies?

List of Rolls-Royce Merlin variants - Wikipedia

Merlin 45M 1,230 hp (917 kW) at 3,000 rpm 1,585 hp (1,182 kW) at 3,000 rpm, +18 psi (124 kPa) boost, 2,750 ft (838 m) Spitfire LF Mk.V Version of Merlin 45 with "cropped" (smaller diameter) supercharger impeller allowing greater boost at low altitudes.

Yes, the 45M and 50M were the low altitude versions of the 45 and 50, respectively.

 

[Shortround6]

Well I guess it depends on your definition of low altitude. The P-40F (also made in 1941) and L had a Merlin 28, essentially Merlin XX, and a critical altitude of about 20,000 ft. Which is considered low - certainly not high enough for escorting B-17s. According to this page Merlin 45 had 1,515 hp at 11,000 ft and 1,210 hp with +3 boost at 18,000 ft which sounds kind of similar. Is it wrong?

a lot depends on timing and actual missions to be performed. A "critical altitude" of 20,000ft was actually not bad in the early part of 1942 when the P-40F went into production (basic engine was well over a year old having gone into Hurricane IIs in the fall of 1940. It had a critical altitude about 7,000ft higher than an Allison in a P-40E and not that different than the two stage supercharged P & W R-1830 Used in the F4F. Please note that the two stage R-2800 used in the Corsair and Hellcat is months away from quantity production ( more than 20 or so a month) .

The power quotes you give are using the retrospectroscope. When introduced in the spring of 1941 the Melrin 45 was limited to 9lbs of boost. As time went on it was cleared to use 12lbs and then 15lbs and then 16lbs of boost. see:
http://www.wwiiaircraftperformance.org/Spitfire_V_Level_Speed_RAE.jpg

The cropped impeller engines gained power in three ways. It took less power to turn the impeller to get the same boost at low altitudes. The intake air was heated less (meaning it was denser at the same pressure.) and because of the cooler intake temperature more boost could be used before hitting the detonation limit.

This is from the wiki:

List of Rolls-Royce Merlin variants - Wikipedia

Merlin 45M 1,230 hp (917 kW) at 3,000 rpm 1,585 hp (1,182 kW) at 3,000 rpm, +18 psi (124 kPa) boost, 2,750 ft (838 m) Spitfire LF Mk.V Version of Merlin 45 with "cropped" (smaller diameter) supercharger impeller allowing greater boost at low altitudes.

It is not "wrong" but it is misleading. At times the SPitfire V with the standard 45/50 engine was book limited to 3 minutes at the higher boost levels. the cropped impeller engines may have had a more lenient time limit?

The power needed to turn an impeller (and the boost made by the impeller) are proportional to the square of the impeller tip speed. soooooo...
the cropped impeller will take about 86% of the power to turn as the larger impeller and heat the intake charge proportionally less. Right up until you hit the flow limit.

 

[Shortround6]

Welcome back
Now to the point - with P-40, it was very much about engine, too. In 1941-late 1942, Merlin 45 vs. V-1710-33 or -39 means at least 25% extra power for no gain in weight. For example, at 15000 ft, it is 1030 HP vs. 1300+. No ram.
Come late 1942, Spitfire gets Merlin 61, P-40 gets an improved V-1710 - no contest at all, Spitfire's engine has more power at 25000 ft than P-40s at 15000 ft.

Yeah but you have to find somewhere to stick the intercooler for the Merlin 61 (or two stage V-1710) that doesn't use up a fair amount of the power in extra drag

Plus you have several hundred pounds of extra engine weight.

Hooker certainly pushed the Merlin engine into a new catagory with both the new single stage and two stage superchargers.

 

[wuzak]

The cropped impeller engines gained power in three ways. It took less power to turn the impeller to get the same boost at low altitudes. The intake air was heated less (meaning it was denser at the same pressure.) and because of the cooler intake temperature more boost could be used before hitting the detonation limit.

And because of the lower pressure ratio (boost) the throttle could be opened fully at a lower altitude (and could be opened wider than before at even lower altitudes) reducing pumping losses.

 

[Shortround6]

The P-40 was absolutely critical to the US and allies simply because it was there when needed, not because it was an under appreciated wonder plane with a bad press agent.

The New Curtiss book started By Dean has an interesting production table of US fighters in 1940.

out of 1685 fighters built in US factories in 1940 (of 12 different types) Curtiss built 481 P-36/H75 Hawks and 778 P-40/H81As and 27 CW-21/CW-21Bs so Curtiss built over 75% of the US fighters in 1940.
Republic built a total of 104 EP-1/P-35 and YP-43s (2) while Bell built 13 YP-39s and 11 of those twin engine Buck Rogers monstrosities.
Brewster built 160 F2A/ 239/339 aircraft and Grumman built 103 F4F/G-36 export aircraft.

Curtiss would go on to build 2248 P-40s in 1941 and 3854 P-40s in 1942 and while these numbers would be dwarfed by later US production they were the lion's share of production in 1941 and 1942. Waiting around for a "better" engine than the Allison or improved Allisons before building these fighters would have left the US and it's allies thousands of planes short in 1942.

Please remember that many things changed with time. The Allison engine of 1940 was every bit as good as the DB 601 of 1940 and better than the French Hispanos and Russian M-100/M-105 series of engines and as good or better than the Italian and Japanese copies/developments of the DB 601.

But saddling the P-40 with 900lbs of guns and ammo and accessories in the wing with the engines available in 1940/41 could only end one way ( and the planes were actually designed to hold an additional 140lbs of ammo).

Why this was done is subject to speculation but let's remember that the service .50 cal Browning of early 1940 was a 600rpm gun (if you were lucky) and not the 800-850rpm gun in would become in late 1940/early 1941 although reliability at the higher rates of fire left something to be desired in the early days. The guns didn't break but they seemed to more than a bit fussy about the feed arrangements. The types of projectiles in service in 1940 was also rather limited. What was being planned or how far along they were in development (and initial manufacture) is unknown but the target effect of a six gun battery of early 1940 .50 cal machine guns may be quite a bit lower than the target effect of six 1943 .50 cal guns.
But like I said before, you can't go back in the field and make the wing smaller, fit lighter landing gear and tires, make the spars thinner and so on. You are stuck with the airframe built to take a 1/2 ton of guns and ammo. which is way more than even a Bf 109G-6 gun boat or even a FW 190 that had MG/FFM cannon in the outer wing. It was nearly as much as the guns and ammo in a Hawker Typhoon with four 20mm cannon.

 

[Greyman]

Quick Spitfire graph to illustrate the Merlins;
Merlin 45 (+16) - Merlin 46 (+16) - Merlin 45M (+18)

 

[Schweik]

Both Tempest and Typhoon were far better than P-40 at any altitude.

Once again you are missing my point. Tempest wasn't introduced to combat until 1944 so I would hope it would be better than a P-40 introduced in 1941. Typhoon I'm not so sure but I don't care enough to argue that point!

Soviet fighters being good just at low altitude was a bug, not a feature. Ditto for their performance and range. MiG-3 was too ligthly armed by Soviet standards, used the engine produced at factories that were also supplying the Il-2 needs, the cockpit was so bad that pilots preferred to fly with open cockpit (hence killing lots of speed).

I don't think you understand the Soviet battlefield then. I'm sure in theory the Soviets would have welcomed the technology of the two stage supercharger, and they were eventually given Spitfire Mk IX's so they did undoubtedly have it. But why spend the extra steel, the rare materials, and added weight for an aircraft to fly 3 miles above the cloud ceiling over the actual battlefield?

Much later, after the end of the war was a foregone conclusion, they experimented with high altitude fighters probably mainly in case the Americans decided to start sending heavy bombers into Russia in a continuation of the war, and to catch the occasional Ju 86..

In my opinion, later war Soviet fighters were perfectly adapted to the conditions they were needed for. Soviet planes were required to be small, cheap (especially in metals), simple to fly and agile enough to cover the front. They needed to protect the Sturmoviks that destroyed the panzers, and destroy the stukas, the jabos and the Hs 129s. The Germans weren't sending four engine heavy bombers to bomb the Russians and the Russians weren't sending any into Germany. The battle was at the front line.

That's why even the Spit IXs they got were relegated to PVO duties behind the lines. Important work no doubt, but not war-winning work for that Theater.

And that is why the Yak 3 and La 5 FN are widely considered two of the best fighters of the war certainly both better than P-40s, but more importantly, better than Bf 109s and Fw 1980s for where they fought, which was all that mattered... even though they were pretty much useless at 28,000'.

In 1942, Zeroes were far better hi-alt fighters than P-40s, and Japan produced other fighters that were not Zeroes. Hurricane was a draggy affair, engine was able to help just that much.

There was a purpose.
Please note that 1st and foremost people were trying to introduce 'all-altitude' fighters, and, once that was sattisfied, they introduced specific fighters for high altitudes and low altitudes. Unfortunately, there was no 'HF' P-40s or P-39s, due to V-1710 being about as good as Merlin 45M, altitude-wise.

In the long run, there didn't need to be. P-40s defeated the Zeros and the Hayabusas at Port Morseby, and Milne Bay, and above the Kokoda Trail, and over the Solomons. They drove them away from the cargo planes flying over the Hump in the Himalayas and along the Burma Road. They defeated them over their own armies in China and helped turn the tide of that land war. That is what really matered.

 

[Schweik]

In reverse.

"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."

ALL of the Ds had 4 guns, but according to some sources there were only about 30 Ds (or 30 built for the US) built before the contracts were amended to E models so the point is rather moot.

Uh, no it's not - More P-40D and E were used in North Africa by the RAF and DAF Commonwealth units, where they played a very important role. It's not all about US use. Similarly most of the Tomahawks that saw combat were used by either the RAF / DAF or the Soviets.

 

[Schweik]

The P-40D had a production run of 583 aircraft, 23 went to the US, 560 went to the RAF. Only the first 20 sent to the RAF had 4 guns, I think all of the American ones did. However some were used in the field (in North Africa) with four guns and some with six.

Of the P-40E, 8209 went tot he US, 1,500 went to the RAF of which a few hundred ended up in Russia and a few hundred ended up in Australia and New Zealand.

I love the bit about tinkering the engines. Nobody ever says what was done. You can't do much with the timing. Allison ignition timing was fixed, there was no variable advance.

You are making a ton of assumptions here as to what I meant, why not just ask before you go off on a tangent? It gets weary spelling every single thing out and my posts are too long as it is but if I don't cover every possible nuance of what I mean I get this sort of thing.

To clarify: I was just referring to over-revving the engines (reported by the Russians) and overboosting the engines. I believe this is what Australian P-40 double ace Bobby GIbbes meant when he said "later when we got our Kittyhawks running properly - were getting better performance - they were a better aeroplane."

The various strengthening measures to the crank shaft and crank case on the V-1710 were already being done as early as the -33 model and the peened crank shafts about midway through the -39 production run. As engines wore out (whether through abuse, battle damage, dust, tropical conditions, bad maintenance or whatever) they were often replaced with newer engines - some Kittyhawk Mk1 and Ia (P-40D and E) in RAF service flying in late 1942 apparently had V-1710-73 engines in them which contributed to some accidents on takeoff due to pilots not being used to the extra power. When the P-40Ks came out incidentally with automatic boost control many pilots had the throttles rewired to remove it so they could 'tinker' with the boost.

Saying that early P-40Es could have been over boosted like the P-40Ks were given the different crankshaft and possibly different fuels is pushing things.

The famous Allison memo and the memo about the RAF use of the P-51A / Mustang I etc. both specifically mention the high overboosting being done with the V-1710-39 (i.e. P-40E) engines and US units were specifically mentioned in the Allison memo. The Allison memo also notes they had previously 'accepted' WEP settings of 60" Hg.

Taking weight out helped but please look at the factory strippers. The Early P-40L and the Early P-40N. the chances of any squadron mechanics getting a P-40 pf any type down st.

We have been over this before. They took out fuel, fuel tanks, a pair of guns, and some armor that you don't think existed.

1/2 fuel mans what? 100 US gallons if you count the drop tank? 74 US gallons if you don't ? 60 US gallons (50 imp gallons) if it is 1/2 the "book" combat fuel load?
A P-40E was going to use over 40 US gallons just starting, taking off and climbing to 20,000ft. Figure another 8-13 gallons to make it to 25,000ft.
In combat the engine might use 1 to 1/2 gallons a minute at high altitude. (much more at lower altitudes).

Sorry, gliding back to the airfield after an intercept doesn't sound like that great of an idea. Reduced fuel yes but 1/2???

Actually from what I understand they sometimes took off with two guns and less than half fuel. Not just with P-40s they did it with Hurricanes too. I'm just repeating what the sources say they did.

They were were overboosted but squadron records don't seem to show the failure rate. And the failure rate has to take into account the availability rate (number of planes grounded with metal bits in the oil waiting for an engine change) and not just the number of crashes due to engine failure. How many minutes/hours at how much over boost before engine failure?
compounded by the crappy operating conditions. does the crankshaft fail from fatigue before or after the engine bearings are wrecked by sand/grit in the oil?

I'm sure they wrecked a lot of them, the new Shores book Volume IV shows a lot of engine problems and engine failures with the P-40Ls in particular. I don't think the pilots cared though.

There was no "dance" between the manufactures and the military. In 1939-40 there was a change in what was required in military aircraft in many countries. Curtiss lost over $14,000 when the 2nd XP-46

I know we have had this debate before too and you side with the manufacturers, I'm not pitting one against the other in this comment, I'm just pointing out that the

The issue was usually that the engines (in every country) took longer than expected by the aircraft designers to achieve the promised power output and the airframe inevitably had to carry more weight in fuel, ordinance, radios, batteries, fire suppression gear, armor and self sealing fuel tanks and other "unexpected" things which quickly put the plane over the tipping point. Manufacturers also had to do a fair amount of fine tuning which took a while to get the best speed out of a new airframe, and they were often struggling to reach performance benchmarks while trying to meet demands for extra gear.

And then they were often stripped of extra things in the field by resourceful crews and the pilots themselves responding to battlefield conditions. Sometime that happens faster with a foreign aircraft. That is what the Finns did with the Buffalo and it's what the Russians and RAF and Australians did with the P-40. By the time Americans were engaged in the Med they followed suit.

For fighter vs. fighter combat incidentally I do think four .50 cal guns were enough, which is why it was standard for a while for P-40F pilots to remove two guns during the heaviest fighting in Tunisia - though part of the strategy developed by P-40 units in the Med, and to a lesser extent in the Pacific and CBI, to face attacking fighters coming from above was to turn into the attack all guns blazing - the Axis fighters whether German, Italian or Japanese usually gave ground first in the resulting game of chicken because it was just too many large caliber bullets heading their way at too high a velocity. If they didn't they usually went down.

S

 

[Schweik]

20,000ft is what would have been considered mid-altitudes.

The advantage a higher critical altitude engine is maintained at altitudes above that critical altitude, if not widening the gap.

+3psi boost would be a cruising setting.

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

This shows the 45 as having:
1,185hp @ 3,000rpm for take-off, +12psi boost
1,515hp @ 3,000rpm @ 11,000ft, presumably at +12psi boost
1,200hp @ 2,850rpm @ 16,000ft - probably a +9psi boost (rated power)
1,060hp @ 2,650rpm @ 14,500ft - cruising.

The Spitfire inability to escort the B-17s was not because of altitude performance, but because of range.

At 30,000ft the Spitfire V with Merlin 45 could still do ~340mph TAS.
http://www.wwiiaircraftperformance.org/Spitfire_V_Level_Speed_RAE.jpg

Well performance to a P-40F or L seems to be fairly close then because according to this September 1942 Ministry of Aircraft Production memo, P-40F was able to make 370 mph at 20,400 ft and 347 mph at 30,000 ft. So it wasn't a total wash.

 

[Stig1207]

Thanks for the PDF

 

[Stig1207]

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.

I've only had MAW IV a few days and I haven't got through June '43 yet, so I can't comment on anything about '44 yet

However, it seems to me, that we both get the impression from MAW II and III that there are more USAAF fighters losses to flak than the Statistical Digest gives, so I think it's safe to say that there is conflicting information for 1943.

 

[tomo pauk]

Yeah but you have to find somewhere to stick the intercooler for the Merlin 61 (or two stage V-1710) that doesn't use up a fair amount of the power in extra drag

Plus you have several hundred pounds of extra engine weight.

Hooker certainly pushed the Merlin engine into a new catagory with both the new single stage and two stage superchargers.

Intercooler can go in the wing, the XP-40 housed it's radiators there. Several hunderds pounds of extra weight was easily accomodated by Spitfire, Fw 190, P-51 and Bf 109 when new engines were added, the trade off was worth it.

Once again you are missing my point. Tempest wasn't introduced to combat until 1944 so I would hope it would be better than a P-40 introduced in 1941. Typhoon I'm not so sure but I don't care enough to argue that point!

I care.
Typhoon was well able to compete with Fw 190 at 15000-20000 ft as it was the case for 5000-7000 ft, while P-40 was not capable on taking on Fw 190s at 15000-20000 ft.

I don't think you understand the Soviet battlefield then. I'm sure in theory the Soviets would have welcomed the technology of the two stage supercharger, and they were eventually given Spitfire Mk IX's so they did undoubtedly have it. But why spend the extra steel, the rare materials, and added weight for an aircraft to fly 3 miles above the cloud ceiling over the actual battlefield?

Much later, after the end of the war was a foregone conclusion, they experimented with high altitude fighters probably mainly in case the Americans decided to start sending heavy bombers into Russia in a continuation of the war, and to catch the occasional Ju 86..

I'll stop ignoring the 'I don't think you understand' remarks any minute now.
2-stage engines don't require any rare materials above what it was usualy used on engines' superchargers. Soviets experimented with hi-alt fightes already in 1930s, adding turboes at I-16 for example, while in ww2 they were designing 2-stage supercharged versions of VK-105 (overheated alot, so they later added ADI; still produced in penney packets only), as well as with intercooled AM-37. Plus turbocharged MiG fighter prototypes, all of whose were to fight high flying German recons and bombers.

In my opinion, later war Soviet fighters were perfectly adapted to the conditions they were needed for. Soviet planes were required to be small, cheap (especially in metals), simple to fly and agile enough to cover the front. They needed to protect the Sturmoviks that destroyed the panzers, and destroy the stukas, the jabos and the Hs 129s. The Germans weren't sending four engine heavy bombers to bomb the Russians and the Russians weren't sending any into Germany. The battle was at the front line.

That's why even the Spit IXs they got were relegated to PVO duties behind the lines. Important work no doubt, but not war-winning work for that Theater.

No problems with that.

And that is why the Yak 3 and La 5 FN are widely considered two of the best fighters of the war certainly both better than P-40s, but more importantly, better than Bf 109s and Fw 1980s for where they fought, which was all that mattered... even though they were pretty much useless at 28,000'.

The La5FN managed to barely emulate Fw 190A1 and Bf 109F-4 performance 2 years later, dito for Yak 3. Fighters that were useless at 28000 ft probably can't be considered when talking about best fighters, ditto for fighters that are inable to fly 400-500-600 miles away, fight well, and return the said amount of miles. All while having half of firepower of many Western or Japanese fighters

In the long run, there didn't need to be. P-40s defeated the Zeros and the Hayabusas at Port Morseby, and Milne Bay, and above the Kokoda Trail, and over the Solomons. They drove them away from the cargo planes flying over the Hump in the Himalayas and along the Burma Road. They defeated them over their own armies in China and helped turn the tide of that land war. That is what really matered.

Those examples prove many other things (while I don't necessarily agree that P-40 actually won all of you've listed):
-side with better logistics & intel wins long, attrition wars
-wars are combined arms affair
-rarely, if ever, a silver bullet decides the outcome
-outnumbering the enemy has it's appeal

 

[wuzak]

Intercooler can go in the wing, the XP-40 housed it's radiators there. Several hunderds pounds of extra weight was easily accomodated by Spitfire, Fw 190, P-51 and Bf 109 when new engines were added, the trade off was worth it.

The XP-40 had the radiator under the rear fuselage, but it was moved forward under the nose when it was found to not work very well.

Curtiss, XP-40, Model 75P by SDASM Archives, on Flickr

An XP-40K had the radiators under the wing centre section

Ray Wagner Collection Image by SDASM Archives, on Flickr


The size of the intercooler need not be huge

de Havilland DH98 Mosquito B.35 'TA634 / 8K-K' (G-AWJV) by Alan Wilson, on Flickr

The intake under the spinner is for the intercooler, while the gills on either side of the nacelles just ahead of the carburetor intake are the outlets.

 

[tomo pauk]

The XP-40 had the radiator under the rear fuselage, but it was moved forward under the nose when it was found to not work very well.

Whoops, my bad in nomenclature - the XP-40Q was the one with radiators in the wing.

 

[Timppa]

I love the bit about tinkering the engines. Nobody ever says what was done. You can't do much with the timing..You can change the jets in the carburetor...etc.
Working on supercharged aircraft engines is a lot different than working on a 1940s Chevy six or Ford Flat head V-8.

Increasing the boost pressure, of course. The most effective way to increase power of supercharged engine.