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

[Shortround6]

Even just a two speed Allison would have been a nice asset to have - just look at how much better P-40F performance was over P-40E.

The supercharger itself may have been too small.

The -33 engine in the long nosed P-40s was good for around 1040 hp at several thousand feet below where the Merlin III made 1030hp and the supercharger only had minor changes aside from the supercharger gears. The Merlin XII in the Spitfire II moved that up by about 2,000ft and the Merlin 45 with the Hooker designed/modified inlet Mover that up another few thousand ft.
What the Merlin XX did for the P-40F was to use an even higher gear than the Merlin 45 used (but not by much) and couple it with low gear that allowed a good amount of power for take-off or low altitude flying.
Just putting two gears on a standard Allison supercharger doesn't get you much better performance than the 9.60 gear engines at altitude but it does allow for higher take-off or military powers at low altitude. Merlin XX had around 100hp for take-off over a Merlin 45 at the same boost and RPM because it's low gear didn't take as much power to drive and it heated the intake air less.
100/130 fuel and WEP settings reduced the need for low gears in the superchargers.

 

[Dan Fahey]

The supercharger itself may have been too small.

The -33 engine in the long nosed P-40s was good for around 1040 hp at several thousand feet below where the Merlin III made 1030hp and the supercharger only had minor changes aside from the supercharger gears. The Merlin XII in the Spitfire II moved that up by about 2,000ft and the Merlin 45 with the Hooker designed/modified inlet Mover that up another few thousand ft.
What the Merlin XX did for the P-40F was to use an even higher gear than the Merlin 45 used (but not by much) and couple it with low gear that allowed a good amount of power for take-off or low altitude flying.
Just putting two gears on a standard Allison supercharger doesn't get you much better performance than the 9.60 gear engines at altitude but it does allow for higher take-off or military powers at low altitude. Merlin XX had around 100hp for take-off over a Merlin 45 at the same boost and RPM because it's low gear didn't take as much power to drive and it heated the intake air less.
100/130 fuel and WEP settings reduced the need for low gears in the superchargers.

That is not what the memorandum said...it said it the 2 speed engine would allow the Allison Mustang to exceed 400 mph at 21000ft

 

[Schweik]

The supercharger itself may have been too small.

The -33 engine in the long nosed P-40s was good for around 1040 hp at several thousand feet below where the Merlin III made 1030hp and the supercharger only had minor changes aside from the supercharger gears. The Merlin XII in the Spitfire II moved that up by about 2,000ft and the Merlin 45 with the Hooker designed/modified inlet Mover that up another few thousand ft.
What the Merlin XX did for the P-40F was to use an even higher gear than the Merlin 45 used (but not by much) and couple it with low gear that allowed a good amount of power for take-off or low altitude flying.
Just putting two gears on a standard Allison supercharger doesn't get you much better performance than the 9.60 gear engines at altitude but it does allow for higher take-off or military powers at low altitude. Merlin XX had around 100hp for take-off over a Merlin 45 at the same boost and RPM because it's low gear didn't take as much power to drive and it heated the intake air less.
100/130 fuel and WEP settings reduced the need for low gears in the superchargers.

I don't know if it's so hard to replace a supercharger with a larger one, seems like that was done. But your last comment there while quite interesting seems to contradict the warning in the Allison memo - namely that the 9.60 ratio engines that were coming out (with the higher altitude rating up around 16 or 17,000 ft vs. 12,000 ft for the earlier ones) would not be able to handle the overboosting, at least not to the nice levels they were getting with the V-1710-73.

If you had two gears conceivably you could have your cake and eat it too that way. Two stages ala the Pratt and Whitney engine even more so.

 

[Shortround6]

I don't know if it's so hard to replace a supercharger with a larger one, seems like that was done. But your last comment there while quite interesting seems to contradict the warning in the Allison memo - namely that the 9.60 ratio engines that were coming out (with the higher altitude rating up around 16 or 17,000 ft vs. 12,000 ft for the earlier ones) would not be able to handle the overboosting, at least not to the nice levels they were getting with the V-1710-73.

If you had two gears conceivably you could have your cake and eat it too that way. Two stages ala the Pratt and Whitney engine even more so.

You need a new supercharger. For some reason many companies didn't want design or build a number of different superchargers (inlets, impellers, diffusers.) when they thought they could get away with tinkering (changing gear ratios). It may have been penny wise and pound foolish?

As to the Allison and the 9.60 gears, the altitude was improved from about 12,000ft to 15,500ft static (no ram), with ram it went from about 14,000ft (or a bit over) to the 16-17,000ft range. The 9.60 gears did NOT improve things by 4-5000ft. We have to compare like to like and unfortunately some of the manuals either don't specify ram or put the numbers in the wrong column.
Now please note the -73 engine was rated at 1325hp for take-off and that was not WEP, it was also never going to happen with 100/100 octane fuel. Better fuel and stronger engine parts allowed for an increase of 175hp at take-off over the -39 engine using the same supercharger gears (and almost 300hp over the -33 engine in the long nosed P-40s)

The British went to two speed superchargers when they had 87 octane fuel because the fuel would't stand much more than 6lbs of boost. Wright was the first American company to use two speed superchargers, P&W jumped to two stage (with two/three speeds on the extra stage, three if you count neutral) and this was done when most of their engines (commercial) were running on 87 or 91 octane fuel. Allison's were never used in a production bomber or transport and the need for high HP for take-off and climbing out wasn't there.

It would have been nice if Allison had a two speed supercharger but without a whole new supercharger it wouldn't have really changed things much.

 

[Schweik]

The V-1710-73 on the P-40K / Kittyhawk III (which as you note, is essentially a strengthened V-1710-39, both are classified V-1710-F series by Allison) made 1,550 hp at the official WEP rating (standard by third quarter of 1942) of 60" Hg, compared to the V-1710-39 on the P-40E / Kittyhawk Ia WEP of 1,470 hp at it's official rating of 56" Hg. Without even getting into unsanctioned overboost ratings*, this is a very helpful increase of power for low altitude, saving the lives of many pilots by allowing them to easily disengage from A6M or Ki-43s and keep up with Bf 109s at low altitude. The problem is both engines are on the 8.8-1 supercharger gear which resulted in a critical altitude of about 12,000 ft, and an effective performance ceiling of about 14 - 15,000 ft. Above that, the airplane is anemic. And this is a problem since so many medium bomber raids were coming in at about 18,000 - 22,000 ft especially in the early to mid war years.

The 9.6-1 geared V-1710-81 of the P-40M had a critical altitude almost 4,000 ft higher and the V-1710-115 of the P-40N-5 at 16,400 ft (meaning reasonable performance up to about 19,000 anecdotally). This is a big advantage in certain Theaters, and for example makes it much easier to catch those medium bombers, but it comes at the price of having that very useful low altitude performance. So I think if you had one gear at 8.10-1 or 8.8-1 and the second gear at 9.6-1 you would have a much wider band of effective performance. Still not a high altitude plane but more of a legitimately medium altitude plane that didn't have to dive so far to recover genuine fighter-like performance.

In other words, I don't see why a two speed V-1710 would have been that different from the Merlin XX, maybe a little more power down low and not quite as high of a critical altitude, but pretty close. And the sortie to loss and victory to loss ratios tell us that the Merlin powered P-40s fared much better, particularly in the MTO.

* which the Allison memo documents were producing 1,770 hp at 2,000 feet with ram at 66" Hg

 

[Schweik]

Per wikipedia V-1710-101, -119, and -121 had an "auxiliary supercharger with an aftercooler". Those are in fact two stage engines which gave great performance but they were just developed a year or two too late.

This was the engine they put in the doomed P-40Q, (itself just a P-40K with clipped wings, a bubble canopy and the new engine) which probably got cancelled due to a prototype crash (and politics / since War Dept was already fed up with Curtiss by then). They should have just done it a bit earlier, instead of their bizarre designs for the P-46 and P-60.

However I'm not sure if Allison had really figured out how to make a reliable two stage engine.

 

[Kevin J]

Per wikipedia V-1710-101, -119, and -121 had an "auxiliary supercharger with an aftercooler". Those are in fact two stage engines which gave great performance but they were just developed a year or two too late.

View attachment 548903

This was the engine they put in the doomed P-40Q, (itself just a P-40K with clipped wings, a bubble canopy and the new engine) which probably got cancelled due to a prototype crash (and politics / since War Dept was already fed up with Curtiss by then). They should have just done it a bit earlier, instead of their bizarre designs for the P-46 and P-60.

However I'm not sure if Allison had really figured out how to make a reliable two stage engine.

Bottom line is that the Q doesn't have any customers for it. The USAAF, RAAF & RAF want the Merlin powered Mustang and the USSR wants the Kingcobra.

 

[buffnut453]

Per wikipedia V-1710-101, -119, and -121 had an "auxiliary supercharger with an aftercooler". Those are in fact two stage engines which gave great performance but they were just developed a year or two too late.

View attachment 548903

This was the engine they put in the doomed P-40Q, (itself just a P-40K with clipped wings, a bubble canopy and the new engine) which probably got cancelled due to a prototype crash (and politics / since War Dept was already fed up with Curtiss by then). They should have just done it a bit earlier, instead of their bizarre designs for the P-46 and P-60.

However I'm not sure if Allison had really figured out how to make a reliable two stage engine.

I think it was less to do with politics and more to do with the XP-40Q being about 2 years too late. The initial P-40Q flew in June 1943 and the P-40Q2, which had the bubble canopy, followed in December 1943. To put it in context, the prototype P-80 first flew in January 1944. In short, the P-40Q was too late and offered insufficient advantage over current in-service types, at least compared to the emerging jet fighters that were coming down the pike.

 

[Schweik]

Bottom line is that the Q doesn't have any customers for it. The USAAF, RAAF & RAF want the Merlin powered Mustang and the USSR wants the Kingcobra.

Well the RAF and RAAF were still using a significant quantity of P-40s quite late, so I think they could have used some of the Q, The Aussies and New Zealanders in particular liked P-40s I'm sure they would have welcomed a 420 mph version. North American could only produce so many Mustangs and Mustangs weren't ideal as fighter-bombers anyway (better for high altitude). As for the Kingcobra, I think the P-40Q is just a better fighter all around and the Soviets would have liked it, though by the time it was available they already had the La-7, Yak-3 and Yak-9T etc.

Aside from just arriving too late, after Curtiss wasted all that time on the P-46 and P-60 etc., it was clear by late 1944 that Curtiss was having some serious problems, including with P-40 production. The company had just become corrupt, it wasn't a good candidate for investing money in. Better to focus on newer companies that were not so top heavy.

 

[Schweik]

I think it was less to do with politics and more to do with the XP-40Q being about 2 years too late. The initial P-40Q flew in June 1943 and the P-40Q2, which had the bubble canopy, followed in December 1943. To put it in context, the prototype P-80 first flew in January 1944. In short, the P-40Q was too late and offered insufficient advantage over current in-service types, at least compared to the emerging jet fighters that were coming down the pike.

I don't disagree with any of that, but I do also think politics (the problems with Curtiss) were real. I also think the P-40Q was on the edge of being accepted for (limited) production in spite of everything, if it weren't the prototype crash(es)

 

[Schweik]

Would those engines work properly with just an aftercooler or did they need an intercooler too?

 

[wuzak]

I don't disagree with any of that, but I do also think politics (the problems with Curtiss) were real. I also think the P-40Q was on the edge of being accepted for (limited) production in spite of everything, if it weren't the prototype crash(es)

Where do you get that idea from?

In a country that has P-38s, P-47s and P-51s, where does the P-40Q fit?

 

[wuzak]

Well the RAF and RAAF were still using a significant quantity of P-40s quite late, so I think they could have used some of the Q, The Aussies and New Zealanders in particular liked P-40s I'm sure they would have welcomed a 420 mph version.

I'm sure that a faster version would have been useful, but I'm not sure they would have preferred that over an even faster P-51.

North American could only produce so many Mustangs and Mustangs weren't ideal as fighter-bombers anyway (better for high altitude).

You do know that P-51s were being licence built in Australia from 1943 or 1944?

And that a P-40Q with 2 stage supercharger would be a "high altitude" aircraft?

As for the Kingcobra, I think the P-40Q is just a better fighter all around and the Soviets would have liked it, though by the time it was available they already had the La-7, Yak-3 and Yak-9T etc.

Which is exactly the point. By the time the P-40Q got into service it would be late 1944, at the earliest. Probably early to mid 1945.

And there were far better options by then.

Aside from just arriving too late, after Curtiss wasted all that time on the P-46 and P-60 etc.,

Not sure that the time spent on the P-46 and P-60 would have made much difference to the P-40 program.

 

[wuzak]

They should have just done it a bit earlier, instead of their bizarre designs for the P-46 and P-60.

What exactly was so bizarre about the P-46 and P-60.

As originally flown, the P-60 was a P-40 with a new wing and engine (the Merlin 28).

 

[wuzak]

Would those engines work properly with just an aftercooler or did they need an intercooler too?

I believe they had an intercooler, but not an aftercooler.

I cannot confirm at the moment, as I am away from my books.

 

[Shortround6]

despite the numerical designations the P-46 and P-60 were much earlier in timing than the P-40Q,

So early that their impact on the P-40Q project was just about nonexistent. (my opinion)
The Army ordered two XP-46s in Sept of 1939. They were to use the newly announced (but not anywhere production) V-1710-39. the Stripped prototype (no guns, armor, self sealing tanks, etc) flew in Feb 1941, the fully equipped version flew in Sept 1941 but it was an academic exercise. It had been decided in 1940 to build the P-40D using the same engine and without a miracle (fully equipped P-46 does well over 400mph?) the XP-46 was a dead duck in late 1940 to mid 1941. The P-40D entered production in May of 1941. The Prototype P-40F flew June 30th 1941.

The XP-60 started as the XP-53 (from Joe Baugher's web site)
"This was the Curtiss Model 88, which was basically an improved XP-46 powered by the yet-to-be-built 1600-hp Continental XIV-1430-3 twelve-cylinder liquid-cooled inverted Vee engine. The Model 88 was to use the fuselage and tail assembly of the P-40D combined with a NACA laminar flow wing."

"On October 1, 1940, the USAAC ordered two examples of the Model 88 under the designation XP-53"

"However, in a conference held six weeks later, the USAAC informed Curtiss-Wright of its need for a fighter combining laminar flow wing technology with the British Rolls-Royce Merlin engine. Since the XP-53 was already being designed for laminar-flow wings, Curtiss proposed to convert the second XP-53 airframe (41-19508) to the Merlin engine while it was undergoing construction"

"The Model 90 (XP-60) flew for the first time on September 18, 1941, only eleven days before the first flight of the disappointing XP-46. The performance of the XP-60 was disappointing as well, with a top speed of only 387 mph at 22,000 feet."

Yes the XP-60 project staggered on for while but it was just desperate attempts to find a powerful enough engine for an oversized and overweight airframe.

" However, on November 17, 1941, it was concluded that the P-60A would be underpowered if the Allison engine were used, and that either a more powerful engine should be found or else another fighter be built instead of the P-60A"

So three weeks before Pearl Harbor the 3rd version of the P-53/60 is considered to be underpowered with a turbocharged Allison of a proposed 1425hp model.

The P-40Q was nearly 2 years later. Two P-40Ks were modified and one P-40N. Several different 2 stage Allisons were used (one airframe got two, if not three, different engines) and while fast there seems to be a disconnect between the weight/armament of the prototypes and the intended service armament. The first pilot's report on http://www.wwiiaircraftperformance.org

says that they were flying the plane at 8200lb with 160 gallons but armament is not listed, This was in Nov 1943.
By April of 1944 (how many Mustangs being built per month by then?) using a different engine the weight is given as 9000lbs with full fuel (unspecified but 150-160 gallons?) full oil, 11 gallons of water for the injection system but only four .50 cal guns with 235rpg. Production armament was suggested to be either six .50 cal guns or four 20mm cannon.

Six guns with 275 rpg would add around 360lb or more to the weight.

I don't know when Allison was promising what with the 2 stage supercharger but in 1942 and very early 1943 they were fooling around with a prototype engine that used the same size impeller in the auxiliary supercharger as the main supercharger, direct mechanical (single speed-drive) and a few other features that would not see the light of day on a production engine. Until Allison could come up with at least a viable prototype 2 stage engine the P-40Q project was going nowhere and having the Curtiss engineers and prototype shop workmen sit on their hands for several years by canceling the XP-46 and P-60 projects was not going to speed up the P-40Q/
The first V-1710-101 as used in the early P-40Q was not tested on a ground stand until July of 1943.

 

[Schweik]

It's late so just three quick points.

• P-60 development may have started in 1941 but it continued until 1944. The P-60A flew on Nov 1942, the P60C flew on January 1943, and the P-60E flew in January 1944, and the complete version not until July 1944. Even Curtiss thought that was a waste of time and asked the War Dept to be let out of their contract.
• You mentioned the P-40Q weight was 9,000 lbs and you try to nudge it up from there, but the P-60Chad a gross weight of 11,835 lbs! With four .50 cal guns.
• It also had a 41' wingspan, vs. the 35' span of the P-40Q. (the latter was heading in the right direction)

P-60E, they all looked radically different

It may have been impossible to have gotten it working early enough to matter due to the trouble with the two stage Allison, but I think you can look at that, and compare it to the P-40Q I posted, and tell which one was a more viable design.

So what I mean by saying they shouldn't have wasted their time with it is they should have gone in that design direction (longer, slimmer, more streamlined, shorter wings, and yes a two stage or at least two speed supercharger but not a turbo) earlier instead of wasting their time for three years with the P-60.

 

[wuzak]

The XP-60 first flew in September 1941 with a Merlin 28.

The XP-60A with Allison V-1710 and turbo first flew a year later.

Curtiss apparently did not ask to get out of P-60 development until May 1944. The whole program amounted to 5 or 6 prototypes.

XP-60 (Merlin 28, first flight September 1941)
XP-60A (V-1710 + turbo, first flight November 1942)
XP-60B (V-1710 + different turbo - completed as XP-60E)
XP-60C (originally to be Chrysler IV-2220 but ended up with R-2800 and contra-props, first flight January 1943)
XP-60D (XP-60 was changed to fit the V-1650-3) - this crashed in May 1943, still before the XP-40Q was a thing.
XP-60E (XP-60B airframe completed with R-2800 and single rotation propeller, first flight May 1943).

The XP-60 had disappointing performance, but it was still 20mh faster than a P-40F, despite having a huge wing (45ft span), weighing more and using from an engine that wasn't producing full rated power.

 

[wuzak]

Wiki's caption for this one is the XP-60B, but it is either the XP-60 or XP-60D

This one is labelled as the XP-60D

Curtiss P-60 - Wikipedia

With a 3 blade propeller I suspect that is the XP-60.

The fuselage for these was that of the P-40D.

 

[Milosh]

Curtiss wanted their own version of the P-47.