A Critical Analysis of the RAF Air Superiority Campaign in India, Burma and Malaya in 1941-45 (1 Viewer)

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The memo doesn't state that the P40E could outclimb the Hurricane. Here's the US Hurricane climb tests:

http://www.wwiiaircraftperformance.org/hurricane/Hurricane_II_Z-2974_Climb.pdf

0-15K ft in 5min. I think the overheating had to do with using a too steep climb AoA.

P40E:

http://www.wwiiaircraftperformance.org/P-40/P-40E_40-405_PHQ-M-19-1320-A.jpg

0-15K in 6.49 minutes.

Even with a 3min wait at 15K ft it could still outclimb the P40E to 20K ft

Terminal dive speed (Vne) says nothing about acceleration into a dive.
 

It was at latest August 1942. This was a memo issued to Fighter Command:
* Relative to an FW-190
 
The Merlin 46 was a peculiar engine, It paid for it's high altitude performance with poor low-mid altitude performance.

See: http://www.wwiiaircraftperformance.org/Merlin_46_47_Power_Chart.jpg

At the "nominal" 9lbs boost which the Australians seem to use power was little over 900 hp at sea level (not much more than a Merlin III) and rose to around 1025hp (?) at 16,000ft. again not much different than a Merlin III only instead of peaking there it kept gaining power slowly until 22,000ft where it made 1100hp compared to the Melrin IIIs approximately 750hp. It is little wonder that the RAAF's Spitfire Vs struggled to keep up either the P-40 or Zeros at altitudes much below 20,000ft. A test combat at 22,-25,000ft might have been interesting

Please note that the Merlin 46 using full 16lbs of boost is making 1440hp at 14,500ft and there would be no way the P-40 or Zero could match this. It was making 1380hp at 10,000ft and the P-40Es engine was all done at that altitude as far as using over boost goes.
Please note the difference between 16lbs of boost and 9lbs is 7lbs which is 14in or over 350mm. It is about 62in of absolute pressure (rounded off somebody can correct to exact figure) or over 1570mm which the Zero engine never came close to.


I have no idea why the Australians go this engine or why they didn't operate it at the full boost rating, or even at 12lbs.

Please note that at 15,000ft there is an almost 400hp difference between the 9lbs and the 16lb rating.
 
I would also note that test conditions varied considerably and that combat conditions also varied from many of the test conditions.

I would note in the US test of the Hurricane that one of the US requirements is spelled out. That is that the US wanted the planes to cool properly on a day where the temperature was 23 degrees C above "standard". Standard being 15 degrees C. For the celsius challenged among us (myself included) that is 59 Degrees for "standard" and 100 degrees F for the 23 Degrees above standard. This made sense for the US as it didn't know if it's planes were going to operate in Michigan or in Texas or Florida. Let alone Panama orother hot areas. The US didn't have tropical versions of aircraft. Some (not all) British aircraft got different radiators/oil coolers for tropical use.

US official use of WEP (over boost) didn't happen until late 1942. The US did use full military power for the first 5 minutes of climb.

The US overboost on the early Allison engine would be rather short lived in a climb. The engines with the 8.80 supercharger gears could only hold 56in to 4300ft on a standard day with no ram, even if they could get 66-70in at sea level. This is for the E. Boost falls to the standard 44.6 in by 11,700ft (no ram) so even 1 1/2 minutes into the climb from sea level the P-40 lost several hundred HP and lost another 300hp by the time it reached 12,000ft. The extra power was quite useful for maneuvering/repositioning the aircraft in a low altitude dog fight. It simply wasn't available at altitudes over 12,000ft. and was rapidly fading from around 5000ft to 12,000ft in a climb.
The Engine in the K was a bit better but not much. It could hold 60in to 2,500ft and fell off pretty much line the engine in the E model. It is not until you get to the M and N with the 9.60 gears that WEP lasts into the low teens. But they don't show up during this period? first showing up in the Spring of 1943.

A Merlin 45 could hold extra boost (16lbs/62in) to 11,000ft. The 46 was described above. The Merlin XX in the Hurricane could hold 16lbs/62in to 12,500ft in high gear.
Please note that this altitudes/power ratings are for the 15D C/59D F "standard" day and tests in Northern Australia and other hot areas could be off by well over 100hp.
 
Spitfire (F) Mk.VB W.3322 Report
If the FAA's Sea Hurricane's use of boost is anything to go by, then in 1941, 12 lbs of boost for 5 minutes, and in 1942, 16 lbs of boost for 3 minutes. So it's not going to last you very long. The document I attached gives no clues to performance with 12/16 lbs of boost, but then the Merlin 46 is optimised for use between 18 and 22.5 thou feet and the boost is only available below this, clearly for emergencies only. At a guess, I'd say a Spitfire Vc Trop would do about 352-355 mph over 20 thou feet which is not a large margin over an A6M3.
 
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P-40E and K were officially rated for 1150 hp with 42" Hg @ 12,000', P-40M was still making 1125 hp at 17,300'. And it went into combat in Nov of 42.

A Merlin 45 could hold extra boost (16lbs/62in) to 11,000ft. The 46 was described above. The Merlin XX in the Hurricane could hold 16lbs/62in to 12,500ft in high gear.
Click to expand...

You are perhaps forgetting about P-40F and L with Merlin 28 (Packard version of Merlin XX). Those were in combat by June of 42.

S
 

The WEP was "officially" for 5 minutes only on the Allison engines too. What was done in combat at squadron level may be quite different.
The Early Sea Hurricane rating was for some of the planes used on CAM ships which were going to ditch at the end of the flight so how long the engine lasted till overhaul was sort of a moot point. The Merlin III in the Sea Hurricane was rated at 1440hp at 5500ft at 16lbs boost. It could use the 12lbs of boost (54in?) up to 9000ft. Later Merlins than the III got stronger parts and were slowly allowed greater boost pressures.

The difference in time I was referring to was in the climb, where the extra boost disappears with altitude. If you increase your climb rate by hundreds of feet per minute you wind up getting to an altitude where the supercharger simply cannot deliver the air flow needed to sustain WEP/over boost that much quicker.
If you stay at low altitude it is not so much a problem.
 
There was about 1 fighter group (if that) that used P-40Fs and Ls in the Pacific.

The M did not go into combat in Nov 1942. Production started in Nov/Dec of 1942 and even if a few made it out the factory door in Nov 42 there was darn little combat around Buffalo New York. It took weeks to get a plane from the factory to a combat zone.
 

Looking through my files I found this telegram dated 6 Sept 1943 (originally downloaded from the Australian Archives website). It reports the results of RAAF Spitfire V/Merlin 46 speed tests with different types of cowlings and it clearly shows the use of 16lb boost at lower altitudes:

As speeds of:
(1) AT SEA LEVEL (A) 312 (B) 318 (C) 316.

(2) AT 10,000 FEET (A) 355.5 (B) 355.6 (C) 360 MPH.

were only achievable at 16lb boost. These speeds were well above RAAF test results for the P40E and A6M3 "HAP" and it shows how vital 16lb boost was for the high altitude rated Merlin 46, when used at low altitude.
 
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RCAFson said:
I also found this data in my files from the Australian Archives:

View attachment 497889

Which is a very interesting comparison. The range and endurance figures for the Hurricane and P40 seem to have used different methods of calculation.
Click to expand...
Are these figures for when tropical / dust filters have been fitted? In the case of the Hurricane, that 335 mph should be maintainable up to 22000 feet, but what about the P-40E?
 

Well I see two problems here.

Problem 1 is that you are talking about two different tests. Which seems a little odd and kind of a pattern. I was referring to this Oct 1941 test which you posted in Post 203. In that test, on the second page (section 3.b) they compared the Hurricane to the P-40E and after pointing out the Hurricane could out turn the P-40 (and all the other fighters including the Spitfire) noted:

"The P-40E can outdive the Hurricane and is faster in level flight up to approximately 20,000 ft. The Hurricane can outclimb the P-40E at any altitude for short periods of time, but sustained high power climb cannot be made in warm weather due to excessive coolant temperatures."

This to me sounds like they are saying the Hurricane did not in fact manage to outclimb the P-40E and was also of course slower and less capable in a dive, even though in Oct 1941 they would have been using lower power settings on the P-40. I also don't agree that this was a 'broken' Hurricane because similar problems with overheating were described in the Med.

They also noted that of all the fighters tested at that time, "only the P-38 was a really effective pursuit airplane against the the B-17C bomber" at 25,000 feet, which is a bit odd considering that that altitude should be within the performance envelope of the Spit and theHurricane (though they don't specify which models).


Problem 2 is with this second test you posted from Dec 1941. The thing is that test was done in 1941, before the P-40E had been used much in combat. Just as you mentioned the 16 lb boost for the Spit V, there was essentially the same issue for the P-40. We now know from sources like this one that P-40Es were not limited to 1150 hp for takeoff as used in that test (which the original recommended max throttle setting of 45" of Hg would deliver) because by mid 1942 they were officially approved for 57" / 1470 hp, so that would probably translate to increased speed and rate of climb.

In fact Allison had acknowledged 60", and noted that some squadrons were resetting the throttle to 66" and 3200 RPM.

To put it in perspective, here is a quote from this interesting report on the British use of P-51A / Mustang I which were powered by the same V-1710-39 engine as the P-40E (items 33 and 36) :


33. This aircraft is powered with the Allison 1710-39 engine having a rated power of 1150 H.P. at 3000 R.P.M. and 44" Hg. at 12,000 ft. The engine was originally equipped with an automatic boost control limiting the manifold pressure at the lower altitudes to 44". The British remove this so as to get the vastly increased performance at lower altitudes thru the judicious use of over-boost.

36. In view of the British operation and the fact that we have an approved war emergency rating on the 1710-39 engine of 56", it is suggested that immediate steps be taken to remove the automatic boost controls from our P-51 airplanes in this theatre and that the instrument dials be marked with the proper lights. The British have operated at full throttle at sea level (72" Hg) for as much as 20 min. at a time without hurting the engines. According to them, the Allison is averaging 1500 hours between bearing failures as compared to 500 to 600 hours for the Merlin. The Allison, they have found, will drag them home even with the bearing ruined.



At 56" Hg 1470 hp. I think the fighter would climb a bit better, at least for the first 5,000 feet, it would probably cut the climb time to 15,000 ft considerably, especially lets say in a scramble situation. I'm not even going to speculate about 70 or 72". The P-40E was also rated 1,150 hp at @12,000 ft at military power (45" Hg).

I suspect this, along with varying weight loads (like carrying an external fuel tank or not) is the actual reason why reported P-40 climb rates varied so widely.

S
 
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RCAFson said:
I also found this data in my files from the Australian Archives:

Which is a very interesting comparison. The range and endurance figures for the Hurricane and P40 seem to have used different methods of calculation.
Click to expand...

This must have been a hell of a clapped out P-40 and the worlds fastest Hurricane.

This July 1941 test showed a top speed of 354 mph for a P-40D at 15,175 (1085 hp)

This Sept 1941 test shows a speed of 340 mph for a P-40E with a 52 gallon belly tank

This July 1942 test shows a speed of 374 mph at 19,270 ft for a P-40F (clean)

This June 1942 test (I believe British) shows a P-40F or L (Kittyhawk II) at 370 mph at 20,400 ft and still 347 mph at 30,000 feet.

This test gives an example of what i was alluding to earlier, i.e. climbing at higher boost. They took a P-40N-1CU and climbed at 57" mercury (nominal WEP rating)

Climb rates were

Sea Level
1000 ft / 57" / 3100
2000 ft / 57" / 3140
3000 ft / 57" / 3180
5000 ft / 57" / 3220
6800 ft* / 57" / 3370
7500 ft / 55.5" / 3270
10000 ft / 50.5" / 2930
12500 ft / 46.25 / 2610
15000 ft / 42.25 / 2300

*6800 ft was the 'critical full throttle height' ,meaning after that the boost started gradually declining.

Note that in the test - the plane got to 15,000 feet in 5 minutes flat. Which is as good as the time quoted on that Hurricane II test. Rate of climb actually increased until the plane got to 6800 ft.

By comparison the climb rate for the same plane at military power was 2,300 Ft / minute at military power (43.8" Hg) .

The really big question to me though, is if the Hurricane was anywhere near as good as you are saying it was, since they definitely had plenty of them, why didn't they use them for the defense of Australia at Darwin or in Milne Bay etc.? Why were they clamouring for Spirfires if the Hurricane was practically as good, and why did they rely on P-40s until they could get the Spits?

Why were they using P-40s at Darwin especially considering the altitude limitations of the Allison engined P-40s they had.

Why did they replace the Hurricane in the Med with the P-40 and then the Spit?

Why didn't the Americans get some via 'reverse lend - lease' like they did with the Spit V?

Why did the Russians replace all their Hurricanes with P-40s and then Yaks etc. as soon as they could?

S
 
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Commonwealth trials of the P40 variants don't show such optimistic speeds for the P-40E. Most of the really impressive results seem to have come from Curtiss directly.

The Hurricane is lighter than the P-40 and has lower wing loading. Why would you expect the P-40 to be able to climb as well, especially with the early model Allison engines? The P-40 pulling maximum boost via WEP is just about even with a Hurricane II using normal climb power, but what do you think would happen when the Hurricane II pilot pulls the plug and uses WEP as well?

The later model P-40s with superior engines have better low/medium altitude speed than the Hurricane II but the P-40E's advantage is marginal

The P-40 supplemented the Hurricane in the ETO/MTO, it didn't replace it.

AFAIK, the RAAF used P-40s because they could get them, and the USAAF used them because they had them. P-40 production was roughly the same as Hurricane production but P-40 production was greater from 1942 to 1944. The RAF and Commonwealth AFs had expended thousands of Hurricanes prior to the P-40 arriving in any numbers. One reason that the P-40 was available for the PTO was that the USAAF was receiving hundreds of reverse LL Spitfires, and they even got the MK VIII before the RAAF, IIRC.

The Spitfire VC Trop was still ~30mph faster than a Hurricane II. But it is good question as to why Australia didn't get Hurricanes; Hurricane development as an air superiority fighter ended in early 1941, which probably was a factor and the RAAF wanted the best available high altitude fighter. However, there's no doubt that the Hurricane II could have done a credible job in lieu of the Spitfire Vc trop/Merlin46 and perhaps done better if it didn't suffer the same issues with the CS prop unit and cannon jams. It would have had a lot more trouble catching high altitude IJ recon aircraft though.
 
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The RAAF report on the P-40 and Hurricane hardly constitutes two separate tests.

The USAAC seem to have tested the B-17C at maximum speed which was somewhat unrealistic for a bomber expected to fight it's way to the target at cruise speed. However, the B17C could do ~300mph at ~25K ft which was a tough proposition for any late 1941 fighter.

The US climb trials with the Hurricane II clearly show that it could climb to 15K ft without pause for cooling and could do it faster than a P-40.
 
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I think you hit the nail on the head when you said that production of the Hurricane II as an air superiority fighter ended in early 1941. It could have been improved and would have done better in combat. The Russians certainly improved it. If a Sea Hurricane IIc could do 342 mph while a Hurricane IIc only 336 mph then if you put the same mods on the Hurricane IIc you'll be looking at about 349 mph which is not far short of the Spitfire Vc with the Merlin 46 at 363 mph. If you put the same mods on a Hurricane IIa then you get 355 mph.
 
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We are back to the difference in test procedures/ climb ratings and the use of WEP/ high boost.
we are also getting into the same old discussions of when/where the Allison was allowed to over boost and at what cost.

British climb figures, unless the test specifically states otherwise were done at a 1 hour rating. Obviously climbing at a 5 minute (or 3 minute) rating would improve things in combat.
American climb figures were done, unless the test specifically states otherwise, using full military power (5 minute or 15 minute depending on date of test and engine, the 15 minute was later) for the first 5 minutes and then dropping back to max continuous which was a 1 hour or longer rating (again depending on date of test and engine).

It doesn't matter if the air force was the RAF or the AAF or the US Navy. EACH AND EVERY use of overboost was supposed to be recorded in the the aircraft log book and appropriate maintenance procedures decided upon by the squadron technical officer. This could be a simple as taking a look at an oil sample for metal particles and changing (or cleaning) the spark plugs more often (but not after every time WEP was used), it could lead to reducing the time between overhauls.
This depended on the officer involved and his experience with the engines, as they gained more experience the restrictions became a bit less.

The Allison is a real can of worms because it changed considerably (and always for the better) as time went on and due to the fact that better parts were sometimes substituted for the originals during overhauls. Allison switched from a shot peened crankshaft to a shot peened and nitrided crankshaft in Dec/jan of 1941/42 which had a much higher fatigue life. The Engine in the P-40Es also had a number of improvements over the engine used in the P-40C/Tomahawks.
The Allison actually would often get the pilot home after seeing considerable abuse (like the 20 minutes of overboosting) but then would fail at normal cruise power settings one or two flights later. Tracing the failure back to the use of over boosting on the earlier flight took a lot of experience and looking at the wrecked engine. You also don't hear from the pilot who didn't make it home after beating the crap out of his engine for 20 minutes.

We seem to operating under the assumption that all the P-40 pilots had to do was simply over boost their engines when ever they wanted to in order to equalize the climb with other aircraft.
We need to look at the climb to altitude without WEP as routinely beating the crap out of the engines to get to intercept altitude is a really bad idea, especially if you are at the end of a long and iffy supply chain and operating in an area with lots of dirt/dust that will shorten engine life considerably regardless of the power settings used.
Sometimes you do what you have to do but trashing engines this week to make intercepts may mean not enough aircraft left running next week to intercept next weeks raids.
By the summer/fall of 1942 most of the P-40s in service would have the stronger crankshafts and the block had also been made stronger about the same time.
The official approval of WEP ratings for the Allison has to be looked at in that light. there may have been some foot dragging but perhaps not as much as some people believe.
 

Do you have a source for that?

There are a few issues with that American test of the Hurricane. The report simply calls it a Hurricane II, ( it's serial number identifies it as a a II a), its weight at 6,848 also indicate it is a NON tropicalized IIa, meaning it doesn't have the cooling modifications for hot tropical weather.

Also they may have been climbing at too steep of an angle and at too low of a speed. The initial climb rate, in the test, is 3,200 ft/min and it is still climbing at 3,000 ft /min at 10,000 ft. Those are very high numbers for a Hurricane IIa at 9 lbs boost. Its making great time,4.98 mins to15,000 ft, and then it has to cool down for three minutes as it was overheating.

Typical climb rates for a Hurricane IIa are, initial 3,050ft/min, 2,360 ft/min at 10,000 and a time too 15,000 ft of 6.2 mins , and as it hasn't overheated at these rates its time to 20,000 ft is 8.2 minutes.
 

Interesting analysis - and yes the V-1710-73 (used in the P-40K - in combat in mid 1942) had a greatly improved (tempered steel) crankshaft, thicker crank case and other adjustments, not to mention increased availability of higher octane "Amendment V" fuel. I think you are overstating the case when you assume that 20 minutes of WEP is 'trashing the engine'. The USAAF report on the Mustang I is pretty definitive when they say:

The British have operated at full throttle at sea level (72" Hg) for as much as 20 min. at a time without hurting the engines. According to them, the Allison is averaging 1500 hours between bearing failures as compared to 500 to 600 hours for the Merlin. And this is presumably the earlier and not as robust V-1710-39.

I am going to go out on a limb with a couple of assumptions here:

  • When the officer says they could run 20 minutes at 72" Hg without hurting the engines, recommends throttle settings be modified upwards, and then in the same paragraph, notes that the Allison was lasting 1500 hours between bearing failures, he may know whereof he speaks.
  • Seeing as even the much lower 60" or 57' Hg throttle setting would amount to a vast improvement in climb rate and no doubt, level speed, I would assume that these could also be safely used for 20 minutes under equivalent maintenance regimes, and therefore probably safe. Sure mark it in the log book, check the oil and change the spark plugs, but it may not actually mean greatly reduced engine life.
  • It seems likely that the agenda of Allison and that of the pilots is a bit in conflict, but the squadron and Wing commanders in the RAF certainly wouldn't want to run out of engines or lose planes to sudden engine failures.

Of course, equivalent maintenance regimes may be one of the key issues here. RAF Mustangs were being operated from nice well maintained airfields in England, with proper hangar facilities, ample spare parts and nice big clean dry indoor hangars. A-36 and P-40s were more typically operated in difficult field conditions, out in the baking sun all day, subject to monsoon rains in the CBI, typhoons in the Pacific, dust storms in the Med, and freezing temperatures lower than most of us can imagine in Russia. Certainly the Russians noted that they had a lot of maintenance issues with P-40s in particular and have quoted engine life as low as 100 hours. They in fact ran out of engines for their first Tomahawk unit in about two months.

However that said, in the field it's clear that they did run the engines pretty hard, including overboosting quite a bit, and outside of Russia, P-40s did not have a reputation for being hangar queens, quite to the contrary. Maybe it's just a matter of Allied supply chains being better and allied maintenance crew being more familiar with everything to do with it. But the Allison engine itself had a good reputation for reliability.

S
 

What specifically are you asking for a source for? I think it was RCAF who posted the document claiming a 5 minute to 15,000 ft climb rate for Hurricanes.

S
 
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