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

Schweik said:

First - I wouldn't normally expect the P-40 to outclimb the Hurricane to be honest, since they didn't climb that well, but the boost / WEP numbers look like maybe they could sometimes probably depending on the load. And there is also the overheating problems apparently faced by Hurricanes to consider. I wouldn't put money on it though.

If you noticed, rather similar to your comments about +9 vs +16 boost, it was discovered in the first few months of 1942 that P-40Es could be safely run at 57" vs. 45" Hg, which translates to 1470 hp vs. 1150. Which is a big difference at least at low altitude.

Second, the Hurricane, again relying mainly on anecdotal evidence from a lot of commentary, was much draggier, it had a 40' wingspan vs 37' on the P-40 or 36' on the Sptfire, and it had notoriously thick wings. I think that may have been one of the main issues with it. The fuselage, though streamlined, was also I think high, giving it that humpback appearance. This too induces drag, I know for example the bubble canopy P-51D was slower than the 'tighter' P-51B. The P-40 was draggy too with the big chin radiator scoop, but apparently not the same extent.

I assume this is why the top speed of the P-40 is always listed as higher than the Hurricane, except in that one test you posted.



I'm not sure what the power ratings were on the tests posted so far actually, but if you find any of them being tested at WEP please post them. For some reason as noted upthread though most official tests (for any of these aircraft) seem to be done at normal rated or military power, only later in the war does WEP seem to garner much Official attention.



P-40s were not used in the ETO except for early Tomahawks in the "Army coopration" role similar to the Allison engined Mustangs.

In the MTO P-40s most definitely did replace Hurricanes in the main Air Superiority Fighter squadrons. These were also by far the highest-scoring fighter squadrons in the Med until the Spitfires arrived in later 1942. 112 Sqn RAF, No 3 Sqn RAAF, No 250 Sqn RAF, No 260 Sqn RAF, and No 450 Sqn RAAF had all of their Hurricanes replaced by P-40s in 1941 or early 1942. Later more fighter wings converted throughout 1942, but the units which were still flying Hurricanes were flying almost exclusively bombing / strafing missions. And usually being escorted by P-40s.

112 RAF

• 1939–1941 – Gloster Gladiator I & II
• 1940-1940 – Gloster Gauntlet
• 1941 – Hawker Hurricane I
• 1941 – Curtiss Tomahawk I
• 1941 – Curtiss Tomahawk IIA & IIB
• 1941–1942 Curtiss Kittyhawk 1A
• 1942–1944 Curtiss Kittyhawk III
• 1944 Curtiss Kittyhawk IV
• 1944–1945 North American Mustang III

260 RAF is also fairly typical:

Nov 1940 Feb 1942 Hawker Hurricane I
Feb 1942 Mar 1942 Curtiss P-40 Tomahawk II
Feb 1942 Sep 1942 Curtiss P-40 Kittyhawk I
Jun 1942 May 1943 Curtiss P-40 Kittyhawk IIA
Dec 1942 Mar 1944 Curtiss P-40 Kittyhawk III
Apr 1944 Aug 1945 North American P-51 Mustang III
Jun 1945 Aug 1945 North American P-51 Mustang IV

And etc.



Interesting theory, I wonder if we can find any Australian or RAF documents related to why they made the choices they did.

S

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In the Pacific, the USAAF was already operating P-40E's, so there are no supply problems. The Spitfire Vc/VIII are superior to the Hurricane II in top speed, dive, climb, roll rate and range (VIII). The Hurricane II being built in 1942 stood no chance of intercepting the Ki-46-II, the Spitfire Vc could and did, even though it was slightly slower. All you need is good radar coverage and the operators to go with, things that weren't available in India.
P-40 Performance Tests
If you scroll down to the bottom of the page and look at the official performance summaries, you will find that the "in the field" top speed of all P-40's is about 350 mph as opposed to the Curtiss figures of 362/364 mph. You should treat the AAEE figures as being the most reliable as their tests included tropical / dust filters. From what I've read of both Soviet and Desert Air Force reports, the Kittyhawk was considered superior to the Hurricane, especially with regards to dive speed, roll rate and turning circle at high speeds. It was also much faster at low to medium altitudes with boost, where most of the combat on these fronts took place. The problem with the Hurricane is that its development as a fighter was discontinued in early 1941. It could have been a much better interceptor / escort fighter in 1942/43 if the FAA mods, the Soviet mods and the Merlin 24 had been incorporated into the production model, but they weren't. Personally, I'd still prefer the Kittyhawk / Warhawk for the escort / air superiority role.

One difference from the Spit V experience over Darwin vs. the Wildcats experience in the Solomons, at Midway etc. is altitude. Most of the early USN and USMC combat with IJN and IJAAF forces involved dive bombers attempting to destroy ships and airfields. These were somewhat urgent attacks since the Japanese were planning to invade, rather than at Darwin where as we now know (though they didn't then) it was more of a harassment type of bombing.

If you want to sink a carrier, or really knock out an airfield like at Wake Island or Henderson Field, you need to bomb and strafe from a relatively low altitude, and really press the issue. D3A and B5N bombers didn't usually fly at 30,000 in combat. They certainly couldn't hit anything from that height. More often they would come in at 10-14,000 ft. Typically they would be dropping bombs from much lower altitude than that - dive bombers would go down to Sea Level, obviously well within the effective altitude of the Wildcat (and within the altitude of P-40s and P-39s).

Escorting Japanese fighters did sometimes fly in at much higher altitude, or had covering elements up there (which is one of the reasons why the P-400s had so much trouble) and sometimes they did come in high with G4M and Ki-21 level bombers, but a lot of the 'action' so to speak took place down low. When they used dive bombers certainly they had to commit the fighters down low to protect them. This gave Allied fighters a better chance.

I also do think though that Wildcats were better fighters than we tend to assume. I saw an FM2 put through its paces at an airshow not long ago and it was quite dynamic, performing loops immelmans, chandelles with apparent ease. I had been so conditioned to think of it as a rather sedate, clumsy fighter that I was surprised to see it so agile. No doubt on reduced fuel and no ammunition etc. I went up afterward and looked into the cockpit though and it did still have armor.

S

Kevin J said:

In the Pacific, the USAAF was already operating P-40E's, so there are no supply problems. The Spitfire Vc/VIII are superior to the Hurricane II in top speed, dive, climb, roll rate and range (VIII). The Hurricane II being built in 1942 stood no chance of intercepting the Ki-46-II, the Spitfire Vc could and did, even though it was slightly slower. All you need is good radar coverage and the operators to go with, things that weren't available in India.
P-40 Performance Tests
If you scroll down to the bottom of the page and look at the official performance summaries, you will find that the "in the field" top speed of all P-40's is about 350 mph as opposed to the Curtiss figures of 362/364 mph. You should treat the AAEE figures as being the most reliable as their tests included tropical / dust filters. From what I've read of both Soviet and Desert Air Force reports, the Kittyhawk was considered superior to the Hurricane, especially with regards to dive speed, roll rate and turning circle at high speeds. It was also much faster at low to medium altitudes with boost, where most of the combat on these fronts took place. The problem with the Hurricane is that its development as a fighter was discontinued in early 1941. It could have been a much better interceptor / escort fighter in 1942/43 if the FAA mods, the Soviet mods and the Merlin 24 had been incorporated into the production model, but they weren't. Personally, I'd still prefer the Kittyhawk / Warhawk for the escort / air superiority role.

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I agree with most of that though I suspect they were actually faster in the field (at least down low) because they were overboosting to much higher Hp. Also you missed this test which clocked the Kittyhawk II at 370 mph. (they also did some tests with a 'dust cleaner' which slowed it down a great deal)

Schweik said:

I agree with most of that though I suspect they were actually faster in the field (at least down low) because they were overboosting to much higher Hp. Also you missed this test which clocked the Kittyhawk II at 370 mph. (they also did some tests with a 'dust cleaner' which slowed it down a great deal)

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The 370+ mph was achieved without the drop tank shackle and sway braces. I think that in the real World of combat that you need these two features for the P-40F/L to be an effective air superiority fighter, which it was. The 354 mph for the AAEE tests to me seem more realistic, even the Bf 109G-2 TROP of the same era only did 373 mph at 6000 metres, below that height the P-40F/L was competitive and the victories scored by them in the Med show that.

RCAFson said:

The IJN/IJA revised their tactics after 1942 and in 1943 and in the main, only used high altitude bombing against Darwin, thus forcing the Spitfires high enough to cause the trilogy of fuel, prop and cannon failure. Many of the high altitude raids over Port Moresby and Guadalcanal were not intercepted due to theP-40/P39/F4F's poor climb rate. Over Darwin in 1942 the P-40s still had problems but typically had enough radar warning to climb above the Medium altitude bombing raids, but they typically couldn't intercept recon flights.

But of the 28 that were stated as shot down, there's no way to know how many had suffered from in-flight failures enumerated above, which in turn, contributed to their loss.

Again, we have to look at all kills not just fighter versus fighter, and then the kill ratio was about 1-1.

The IJN/IJA fighters were based much closer to Darwin than to Guadalcanal. IJN fighters over Guadalcanal were at the extreme end of their range and most had to retain their their DTs, for example [See First Team V2 for details], whereas over Darwin they released them. Additionally the IJN employed A6M3s and Ki-43IIs on some of their raids. The A6M3, as we've discussed has considerably superior performance compared to the A6M2, especially it's roll rate due to the clipped wings and superior HV 20mm cannons. The A6M3 didn't have the range to make it to Guadalcanal and didn't participate there.

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I found the other thread. In the other thread you actually counted 5 Zeros and 14 bombers shot down in exchange for 28 Spitfires, 26 to Zeros 2 to KI43's. 28-19 is a 1.48 ratio against the Spit.

I have never seen anyone try to defend their fighter choice (Spitfire) by claiming they weren't actually shot down, but they fell out of the sky on their own. Or, they weren't shot down, (Spitfire) they ran out of gas because they had to fly so high over their own airfield to intercept the Zeros, which incidentally were also at that extreme height after flying 500 miles and after running the Spitfires out of gas they will turn around and fly 500 miles back to their base. Total Spitfire losses appear to be over 70 for this time period.

If your theory is correct, the Japanese could have wiped out the entire RAAF Spitfire squadron by sending unarmed Zeros on the raids and just letting the Spitfires chase them around until eventually all the Spitfires ran out of gas and crashed or just broke and fell out of the sky.

pinsog said:

I found the other thread. In the other thread you actually counted 5 Zeros and 14 bombers shot down in exchange for 28 Spitfires, 26 to Zeros 2 to KI43's. 28-19 is a 1.48 ratio against the Spit.

I have never seen anyone try to defend their fighter choice (Spitfire) by claiming they weren't actually shot down, but they fell out of the sky on their own. Or, they weren't shot down, (Spitfire) they ran out of gas because they had to fly so high over their own airfield to intercept the Zeros, which incidentally were also at that extreme height after flying 500 miles and after running the Spitfires out of gas they will turn around and fly 500 miles back to their base. Total Spitfire losses appear to be over 70 for this time period.

If your theory is correct, the Japanese could have wiped out the entire RAAF Spitfire squadron by sending unarmed Zeros on the raids and just letting the Spitfires chase them around until eventually all the Spitfires ran out of gas and crashed or just broke and fell out of the sky.

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There's been a number of other threads, and information accumulates over time, so maybe you could post a link.

Here's a kill/loss summary:

http://www.darwinspitfires.com/index.php?page=2-raaf-air-combats-in-nwa

28 Spitfires lost to enemy action versus 28 IJ aircraft lost to enemy [Spitfire] action

Aircraft were lost constantly on all sides due to mechanical failure and/or pilot error. For example some F4F-4s were lost over Guadalcanal due to oxygen failure, others upon landing. TO, and taxiing, Many F4F-4s were lost at Midway from fuel starvation.

As I've pointed out IJ bases on Timor were much closer to Darwin than Rabaul to Guadalcanal. IJN fighters used bases on eastern Timor, that were ~320nm from Darwin, The IJAF units flow a low-high-low mission profile, but used a cruise climb to minimize fuel consumption during time spent beyond RAAF radar coverage. A high power climb by a Spitfire to ~30K+ ft uses a lot of fuel, but losses from fuel starvation were minimal after the 30IG DT was used.

It wasn't quite as simple as fighting over their own field either, they had a lot of ground to cover with numerous targets all around the Darwin area, and they had to intercept the actual Japanese formation which took quite a while to find. And they really were plagued with mechanical problems, that wasn't just an excuse. The ammunition was so bad they had to presort every round beforehand. The issues with the props and guns freezing took a while to even figure out, as did the issues with the coolant systems.

I am not convinced that a ('healthy') Spit V was seriously overwhelmed by the A6M. To the contrary, I think they did have an edge. I think the guys who did that test were just dismayed by the superior low speed maneuverability of the A6M, and probably not using boost. The problems they had with the Spit V were similar to the problems with all the ultimately successful types - teething, essentially. Maintenance, training, tactics. Of course the Spit V had some weaknesses, but the speed / performance advantage they had was substantial enough that they had means for victory with those aircraft - if you fought in a disciplined way to your aircrafts strengths.

Keep in mind, no fighter, not the P-38, nor the Hellcat nor the Corsair nor the P-51 or P-47, was truly ever safe from an A6M flown by a good pilot. Zeros continued to shoot down Allied fighters right to the end of the war.

I think the A6M and especially Ki43 (per the original post in this thread) are underrated - they were dangerous opponents for the Allies. May not have had armor of self sealing tanks (until too late) and the Ki43 had relatively light armament, but you don't need that many .50 caliber bullets to take down a fighter, even a fairly well protected Allied fighter. As the Japanese noted, with the liquid cooled engines especially, one bullet in the radiator could do the trick. It's a tradeoff with armament vs. agility - if armament was all that mattered, the Me 110 would have been a world beater, but after the Battle of France it was barely surviving.

I do also think the Wildcat was and is underrated. It may not have had the best speed, best roll, best dive, best acceleration etc., but it was pretty good in all these areas. Turn rate was very good, handling - that difficult to quantify quality so important in not just dogfighting but also landing and taking off from an Aircraft Carrier or a short, primitive runway, was also very good. Guns were hard - hitting. Protection was good, not to mention a radial engine less vulnerable to that one magic bullet. The supercharging system gave it pretty good high altitude performance. I suspect it may be the combination of a lot of moderately virtuous traits, rather than one single outstanding trait, that made this fighter a success.

As previously noted, the F4F / FM2 did not exactly suffer grievous harm in encounters with Bf 109s either.

Kevin J said:

The 370+ mph was achieved without the drop tank shackle and sway braces. I think that in the real World of combat that you need these two features for the P-40F/L to be an effective air superiority fighter, which it was. The 354 mph for the AAEE tests to me seem more realistic, even the Bf 109G-2 TROP of the same era only did 373 mph at 6000 metres, below that height the P-40F/L was competitive and the victories scored by them in the Med show that.

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You might be right - I'm sure the Sway Bars did slow it down somewhat, but I doubt it made a 20 mph difference. I'd expect maybe a 5 or 10 mph difference. There were a lot of other speed tests with the P-40F and L (I'm learning about more and more of them as the P-40F seems to have been a benchmark used to evaluate many other aircraft0 and they usually ended up between 362 and 370 mph.

Assuming no heavy dust filter and good maintenance, and good fuel, they may have gotten better speed in the field actually. Aside from hot rodding the engine (rewiring throttles, over reving and so on), they did also do things like wax planes, fill in holes, repaint and sand down rough spots and protrusions, strengthen certain parts so they wouldn't flex at high speeds, even remove radio masts (from P-40L). I know the AVG did this kind of thing for sure as they mention it in some of their histories. I suspect but can't prove that USAAF squadrons in the Med did it (when they could). Almost without a doubt RAAF units did and probably RAF too.

I know 1) they were aware of the effects of such efforts, 2) that there was some competition between ground crews to get the fastest aircraft, and 3) pilot accounts mention that certain planes were known to be considerably faster than others. One USAAF P-40F was involved in a 'friendly fire' incident when it shot down an RAF Spitfire Mk Vc after a long chase and a probably lucky long distance shot. This aircraft was mentioned in the (understandably extensive) written documentation in this incident as being the fastest of the squadron - the pilot asked for and got permission to leave the formation and chase down the 'bogy'.

Australian Ace Bobby Gibbes also described a kind of similar incident in which he used a Kityhawk Mk III (P-40K or M) which he mentioned was faster than the Kittyhawk Mk IIs he was flying with, to catch and shoot down a Bf 109 out of a formation of three which had flown over their unit. He was embarrassed because he actually hit the one behind the one he was aiming at. This probably represents either overboosting or a 'cleaned up aircraft' or both. He also mentioned that he had 'stolen' the Kittyhawk Mk III and later had to give it back to the RAF.

I don't know what the experience was, by the way, with dust filers on the P-40s but the DAF sources don't mention as many problems as they had with the Vokes filter on the Spit and Hurricane. I gather they did eventually fix that or come up with another filter system, right? But not sure by what date.

I have also come to understand that dust filters were 'bypassed' after takeoff but I assume there is still some performance penalty?

The Vokes filter also looks to me like it would constrain airflow a bit and therefore might affect cooling / overheating. Did it?

S

Kevin J said:

The roll rate of the Hurricane I was better than the IIb/c because it had less weight in the wings. The IIb especially had a weight distribution which adversely affected roll rate. The Soviets solved these problems by replacing the armament with a pair of 20 mm cannon and another pair of 0.5 in guns.

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Quite interesting. So after 1941 they (Hawker) concentrated on Typhoon development exclusively?

When was the Hurricane MK IV produced? Was the Mk X- XII purely a product of the Canadian factories? What are the stats on the MK XII? Is that the 350 mph one?

Worth noting that the Russians do not seem to have liked the Hurricane much so I'm not sure how much their field modifications really helped. Would be interesting to learn more there is only really the one article on lendlease.ru and a couple of pilot interviews to go by.

S

Schweik said:

Quite interesting. So after 1941 they (Hawker) concentrated on Typhoon development exclusively?

When was the Hurricane MK IV produced? Was it purely a product of the Canadian factories?

S

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Canadian Hurricanes were designated Mk X, XI, or XII, IIRC, and some of the Mk XII's were factory built as Sea Hurricane IIAs in mid 1942 onward. The Mk IV was purely a UK built aircraft and entered production in mid 1943.

RCAFson said:

Canadian Hurricanes were designated Mk X, XI, or XII, IIRC, and some of the Mk XII's were factory built as Sea Hurricane IIAs in mid 1942 onward. The Mk IV was purely a UK built aircraft and entered production in mid 1943.

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Yeah I mistyped that initially and went back to correct.

So it sounds like they did continue development on the Hurricane, at least to some extent.

Since you are the resident expert on the Hurricane can you break down performance (max level speed, ceiling, climb rate, Hp, max boost, dive speed, critical altitude etc.) for the various subtypes?

Mk 1
Mk IIa
Mk IIb
Mk II (Russian Field Mod)
Mk IV
Mk XX
Mk XI
Mk XII
Mk XIIa

And max roll rate if you know or care to estimate ?

Just read this not too stellar April 1942 encounter with A6Ms by Hurricanes from the Wiki:

When a Japanese carrier task force under the command of Admiral Chūichi Nagumo made a sortie into the Indian Ocean in April 1942, RAF Hurricanes based on Ceylon saw action against Nagumo's forces during attacks on Colombo on 5 April 1942 and on Trincomalee harbour on 9 April 1942.[128]

On 5 April 1942, Captain Mitsuo Fuchida of the Imperial Japanese Navy, who led the attack on Pearl Harbor, led a strike against Colombo with 53 Nakajima B5N torpedo bombers and 38 Aichi D3A dive bombers, escorted by 36 Mitsubishi A6M Zero fighters.[129] They were opposed by 35 Hurricane I and IIBs of 30 and 258 Squadrons, together with six Fairey Fulmars of 803 and 806 Squadrons of the Fleet Air Arm.[130] The Hurricanes mainly tried to shoot down the attacking bombers, but were engaged heavily by the escorting Zeros.[131] A total of 21 Hurricanes were shot down (although two of these were repairable),[132] together with four Fulmars[133] and six Swordfish of 788 Naval Air Squadron that had been surprised in flight by the raid.[134] The RAF claimed 18 Japanese aircraft destroyed, seven probably destroyed and nine damaged, with one aircraft claimed by a Fulmar and five by anti-aircraft fire. This compared with actual Japanese losses of one Zero and six D3As, with a further seven D3As, five B5Ns and three Zeros damaged.[131][135]

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35 Hurricanes +6 Fulmars vs. 36 Zeros and 91 bombers results in 1 Zero and 6 D3A shot down for 21 Hurricanes and 4 Fulmars. Not so great.

S

Schweik said:

Just read this not too stellar April 1942 encounter with A6Ms by Hurricanes from the Wiki:



35 Hurricanes +6 Fulmars vs. 36 Zeros and 91 bombers results in 1 Zero and 6 D3A shot down for 21 Hurricanes and 4 Fulmars. Not so great.

S

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There was a radar and comm failure on 5 April 1942. The Hurricanes and Fulmars were caught on the ground and during TO, and losses were severe as a result; many aircraft were shot down with LG still extended. OTOH, pilot reports from Hurricane IIBs that TO in time to meet the raid at altitude commented favourably about comparative performance vs the A6M2.

Schweik said:

Yeah I mistyped that initially and went back to correct.

So it sounds like they did continue development on the Hurricane, at least to some extent.

Since you are the resident expert on the Hurricane can you break down performance (max level speed, ceiling, climb rate, Hp, max boost, dive speed, critical altitude etc.) for the various subtypes?

Mk 1
Mk IIa
Mk IIb
Mk II (Russian Field Mod)
Mk IV
Mk XX
Mk XI
Mk XII
Mk XIIa

And max roll rate if you know or care to estimate ?

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I'll reply in detail later today.

Schweik said:

You might be right - I'm sure the Sway Bars did slow it down somewhat, but I doubt it made a 20 mph difference. I'd expect maybe a 5 or 10 mph difference. There were a lot of other speed tests with the P-40F and L (I'm learning about more and more of them as the P-40F seems to have been a benchmark used to evaluate many other aircraft0 and they usually ended up between 362 and 370 mph.

Assuming no heavy dust filter and good maintenance, and good fuel, they may have gotten better speed in the field actually. Aside from hot rodding the engine (rewiring throttles, over reving and so on), they did also do things like wax planes, fill in holes, repaint and sand down rough spots and protrusions, strengthen certain parts so they wouldn't flex at high speeds, even remove radio masts (from P-40L). I know the AVG did this kind of thing for sure as they mention it in some of their histories. I suspect but can't prove that USAAF squadrons in the Med did it (when they could). Almost without a doubt RAAF units did and probably RAF too.

I know 1) they were aware of the effects of such efforts, 2) that there was some competition between ground crews to get the fastest aircraft, and 3) pilot accounts mention that certain planes were known to be considerably faster than others. One USAAF P-40F was involved in a 'friendly fire' incident when it shot down an RAF Spitfire Mk Vc after a long chase and a probably lucky long distance shot. This aircraft was mentioned in the (understandably extensive) written documentation in this incident as being the fastest of the squadron - the pilot asked for and got permission to leave the formation and chase down the 'bogy'.

Australian Ace Bobby Gibbes also described a kind of similar incident in which he used a Kityhawk Mk III (P-40K or M) which he mentioned was faster than the Kittyhawk Mk IIs he was flying with, to catch and shoot down a Bf 109 out of a formation of three which had flown over their unit. He was embarrassed because he actually hit the one behind the one he was aiming at. This probably represents either overboosting or a 'cleaned up aircraft' or both. He also mentioned that he had 'stolen' the Kittyhawk Mk III and later had to give it back to the RAF.

I don't know what the experience was, by the way, with dust filers on the P-40s but the DAF sources don't mention as many problems as they had with the Vokes filter on the Spit and Hurricane. I gather they did eventually fix that or come up with another filter system, right? But not sure by what date.

I have also come to understand that dust filters were 'bypassed' after takeoff but I assume there is still some performance penalty?

The Vokes filter also looks to me like it would constrain airflow a bit and therefore might affect cooling / overheating. Did it?

S

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The AAEE figures are always for a P-40 fully equipped to fight in the Western Desert (dust filter, belly tank shackles and sway braces) so they are always going to be lower than any figures that Curtiss may have come up with. As for the Vokes filter. it wasn't just a dust filter, it held extra oil in it for the fighter on a flight carrying 90/170 gals of ferry tanks, that's why its so big and causes so much of a loss in performance at altitude; its certainly over engineered for normal combat operations, that's why the Aboukir oil filter was developed and was so much more streamlined and had less impact on performance, because in practice the Spitfire Vc could only realistically operate with a 30 gal (slipper) combat tank.

Kevin J said:

The AAEE figures are always for a P-40 fully equipped to fight in the Western Desert (dust filter, belly tank shackles and sway braces) so they are always going to be lower than any figures that Curtiss may have come up with.

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Yes, I get that and understand your point - and the implication is that Curtiss will "clean the plane up" as much as they can get away with before running one of their tests so that they can get the highest possible number, since this certainly influenced contracts and so on. Top speed being one of the main benchmarks that War Dept. Officials cared about in an aircraft.

My point though is that in those tests, Curtiss would also be limited in certain respects (they would be required to load the plane to a certain weight, and would be limited in how far to push the engine), and conversely, in the field, in the units on the ground, we know they could do many of the same things Curtiss would do: repaint, sand down uneven or rough surfaces, fill gaps and holes with putty, wax the plane and so on.

They could and did also do things Curtiss could not necessarily (legally or contractorally) do: run at higher than recommended throttle settings, run at increased RPM, remove a pair (or even two pair) of wing guns, run with reduced fuel, run on better fuel that wasn't available when Curtiss ran their tests and so on.

As for the Vokes filter. it wasn't just a dust filter, it held extra oil in it for the fighter on a flight carrying 90/170 gals of ferry tanks, that's why its so big and causes so much of a loss in performance at altitude; its certainly over engineered for normal combat operations, that's why the Aboukir oil filter was developed and was so much more streamlined and had less impact on performance, because in practice the Spitfire Vc could only realistically operate with a 30 gal (slipper) combat tank.

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Aha, interesting. I see these were "field mods" done in Egypt so in 1942? and these spread to the Pacific too?

So many of the improvements in the DAF seem to come from the pilots and maintenance personnel rather than the high leadership.

S

Schweik said:

Yes, I get that and understand your point - and the implication is that Curtiss will "clean the plane up" as much as they can get away with before running one of their tests so that they can get the highest possible number, since this certainly influenced contracts and so on. Top speed being one of the main benchmarks that War Dept. Officials cared about in an aircraft.

My point though is that in those tests, Curtiss would also be limited in certain respects (they would be required to load the plane to a certain weight, and would be limited in how far to push the engine), and conversely, in the field, in the units on the ground, we know they could do many of the same things Curtiss would do: repaint, sand down uneven or rough surfaces, fill gaps and holes with putty, wax the plane and so on.

They could and did also do things Curtiss could not necessarily (legally or contractorally) do: run at higher than recommended throttle settings, run at increased RPM, remove a pair (or even two pair) of wing guns, run with reduced fuel, run on better fuel that wasn't available when Curtiss ran their tests and so on.



Aha, interesting. I see these were "field mods" done in Egypt so in 1942? and these spread to the Pacific too?

So many of the improvements in the DAF seem to come from the pilots and maintenance personnel rather than the high leadership.

S

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The Aussies experimented by removing the Vokes filter on the Merlin, but screwed it up so that they didn't get a speed advantage. The Aboukir filter is a 1942 field mod. In the Western Desert they realised that you could also get 1750/1780 hp out of the Allison engine. Remember the Allison had a 1500 hour life as opposed to the 500 hours of the Merlin, so yes you could stress the Allison engine out a lot more. In the UK we used the Allison engined Mustangs until 1945 with high boost pressures, so that they could do 375/380 mph at sea level. It was a bloody good low altitude engine. Just think how fast the Kittyhawk went, they certainly scored a lot of victories and it was rated superior to the Hurricane. The Russians were using Kittyhawks in the East until the end of the war either as escorts or fighter bombers, it was definitely not obsolete.

Kevin J said:

The Aussies experimented by removing the Vokes filter on the Merlin, but screwed it up so that they didn't get a speed advantage. The Aboukir filter is a 1942 field mod. In the Western Desert they realised that you could also get 1750/1780 hp out of the Allison engine. Remember the Allison had a 1500 hour life as opposed to the 500 hours of the Merlin, so yes you could stress the Allison engine out a lot more. In the UK we used the Allison engined Mustangs until 1945 with high boost pressures, so that they could do 375/380 mph at sea level. It was a bloody good low altitude engine. Just think how fast the Kittyhawk went, they certainly scored a lot of victories and it was rated superior to the Hurricane. The Russians were using Kittyhawks in the East until the end of the war either as escorts or fighter bombers, it was definitely not obsolete.

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Agreed, though I think by mid 1944 the Russians were using their remaining Kittyhawks as PVO (air defense) fighters and I think maybe some maritime units in the Baltic. Those were still in combat but not in the high-intensity meat grinder any more. They (and Tomahawks) were in the front line (VVS) squadrons from 1941 through 43 and into early 44 in some places. The Russians seem to have worn out the P-40 engines pretty quickly and a lot of them that had been used for more than 2 or 3 months of combat were no longer able to make 300 mph. In 1944 they got some new P-40M and N but these mostly sent to PVO or maritime units operating around the Baltic Sea. By then they had plenty of Yak 9s and La 5FN for the front line.

They seemed to do best with the P-40K. But in general they seemed to have more maintenance issues with P-40s than they did with the P-39s, even though the latter had nearly identical engines.

S

Kevin J said:

In the Western Desert they realised that you could also get 1750/1780 hp out of the Allison engine. Remember the Allison had a 1500 hour life as opposed to the 500 hours of the Merlin, so yes you could stress the Allison engine out a lot more.

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Do you have real source for that or are we back to the bearing failure thing again.

RR themselves only claimed a "life" for the Merlin in 1945 of 360 hours for a fighter engine, 420 hours for a bomber engine and 500 hours for a transport engine.
"The Merlin in Perspective- the combat years" Rolls-Royce Heritage trust Historical series No2 page 90.

You have to very careful reading and interpreting some of these figures.

For instance if you had 30 fighters with Allisons and ran them for 100 hours each (3000 hours total) and got 2 bearing failures you would be averaging one bearing failure every 1500 hours of operation. Do the same thing with 30 Merlin engines and if you had 6 bearing failures in 3000 hours of operation you would be averaging 500 hours between bearing failures.

It may not mean that the engines lasted either 1500 hours or 500 hours in service. Only a really desperate squadron commander or technical officer would fly a plane in combat that was hundreds of hours past the manufacturers recommended overhaul life.

The hours I listed earlier were the not a guaranteed life. They were a MAX life. IF the engine made to that number of hours without being pulled for some sort of problem (excessive oil consumption, low compression, metal bits in the oil, etc) the Manufacturer strongly recommended pulling the engine for overhaul regardless of how well it was running. In the early part of the war it was quite common to order 50% more engines than the number of single engine airframes in order to allow for a good supply of spare engines/parts. If engines lasted for 1500 hours why bother to do that?

I would note that even in transport service it took until after WW II for engines to get approved for over 1000 hours.
Pre war there were some DC-3s that had gone through 12 sets of engines in just 4-5 years.

Please not I am not claiming the Merlin was the equal of the Allison in regards to strength or durability.
I am questioning the use of a particular type of engine failure as a measuring stick for overall engine durability/life. There are plenty of other ways for an engine to fail (in sometimes spectacular fashion) aside from bearing failure.

Schweik, you mentioned something about japan not intending to invade northern Australia. That's not entirely correct.

This is a link to some source material that you may find interesting

Battle for Australia: Japanese debate Invasion of Australia