P-40 with Griffon engine

GregP said:

It seems there were a number of twin V-12 aircraft around. Among them were the Arsenal VB-10:

View attachment 584796

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The Kawasaki Ki-64 was similar to the VB-10 with one engine in front and one behind the pilot.

Does the Dornier Do 335 count?

Most of these examples were designed from the outset to have two engines on the aircraft centreline. It's not quite the same as sticking a heavier and longer engine into an airframe.

I never knew about the arsenal VB-10 or the Latecore 299A, great photos.

My $0.02

A souped up P-40 could have been useful if it appeared early enough, as in the entire span of 1943 through the first quarter of 44. This is when they were still using the Merlin powered P-40's pretty heavily. But that is probably too early to get it done. Obviously if you had a faster and higher-flying version that would be quite useful.

I don't necessarily think adding a few inches to the front of the fighter would have been a problem, since extending the tail was already something that was done, they added 30" to the later P-40F and K series, all the P-40L, and all of the P-40N aircraft. Weight might be more of a problem, since the Griffon 1,980 lb vs. Merlin 60 series 1,640 lbs, Allison V-170 1,445 lbs. Not sure about the Merlin XX as found in the P-40F/L but I think it was around ,1500 lbs. So you are talking about adding 500 lbs to the aircraft. The airframe could take it, but weight balance would be an issue. I guess they could put in a heavier armor plate maybe.

If you did somehow solve the balance problem, the P-40 is a bit more agile than the P-51 so it might still have a niche. The P-51 would probably still be faster and also have much better range. I would see a Griffon powered P-40 as having a somewhat similar niche as the P-47.

Keeping the radiator & oil cooler intake up front had one advantage of less plumbing further back in the wings and fuselage, this made it a bit harder to knock out the engine - somewhat like on a radial engined aircraft. It was comparatively difficult to hit the nose of a fighter, apparently. This was brought up in service in the CBI and Pacific, some pilots preferred P-40s to P-51s for that reason.

Schweik said:

Weight might be more of a problem, since the Griffon 1,980 lb vs. Merlin 60 series 1,640 lbs, Allison V-170 1,445 lbs. Not sure about the Merlin XX as found in the P-40F/L but I think it was around ,1500 lbs. So you are talking about adding 500 lbs to the aircraft.

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The Merlin XX was around 1,450lb. The V-1650-1 was 1,512lb.
The Merlin 60-series engines varied depending on the accessories fitted. 1,640lb was the lower end, the upper being over 1,700lb. The V-1650-3 and V-1650-7 weighed 1,690lb.

The single stage Griffon II/IV/V was about 1,790lb and the 2 stage Griffon 65 around 1,980lb, the 69 was 2,075lb.


Not sure which V-1710 you are talking about there.

The single stage engines were lighter than that, around 1,325-1,350lb. 1,445lb seems a bit light for the two stage engine.

Schweik said:

So you are talking about adding 500 lbs to the aircraft. The airframe could take it, but weight balance would be an issue. I guess they could put in a heavier armor plate maybe.

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The Spitfire used ballast weights in the tail to get the distribution correct.

But if you add 500lb of engine and then add armour or ballast you additional wight will be more. Especially if you choose armour, as it will be closer to the CoG and will require more to achieve the balance. Ballast can be located more remotely and can be lighter due to the leverage.

So instead of 500lb, you've add 750 or 800lb.

Then you have to account for increased cooling requirements. Going from a 1,300hp V-1710 to a 1,500hp V-1650-1 required extra cooling. Going to a single stage Griffon of around 1,800hp will require even more, and then you go to the 2,000hp+ 2 stage Griffon you need even more cooling and an intercooler radiator. Look at the size difference between the radiator ducts on the Merlin powered Spitfire VIII/IX and the Griffon powered XIV. That's going to be a sizeable chin radiator!

Schweik said:

If you did somehow solve the balance problem, the P-40 is a bit more agile than the P-51 so it might still have a niche. The P-51 would probably still be faster and also have much better range.

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Perhaps the extra weight at each end would negate some of that agility?

Schweik said:

I would see a Griffon powered P-40 as having a somewhat similar niche as the P-47.

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A high-altitude fighter thrust into the role of a low level ground pounder?

If low-level work is the likely outcome, there is little point wasting a 2 stage Griffon. Better off with a single stage Griffon - less power, but less weight and less cooling required.

Schweik said:

Keeping the radiator & oil cooler intake up front had one advantage of less plumbing further back in the wings and fuselage, this made it a bit harder to knock out the engine - somewhat like on a radial engined aircraft. It was comparatively difficult to hit the nose of a fighter, apparently. This was brought up in service in the CBI and Pacific, some pilots preferred P-40s to P-51s for that reason.

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The problem with concentrating all that up front is that you have to balance that out as well. Larger coolant and oil coolers up front mean even more ballast. So you may be heading for 700lb or 800lb extra in the nose, which would then require 1,100-1,200lb total weight gain.

The Spitfire's radiators and coolers were close to the CoG, as were the P-51's.

Good points. I agree a single stage Griffon might make more sense, both because it would weigh less and because it would still improve performance (probably) in the area that they would actually use the P-40, i.e. lower altitude combat, escorting medium bombers, fighter sweeps over airfields, and CAS. The Russians would have loved it, assuming they could keep a Griffin running. On the other hand a P-40 with high altitude capability was really what everybody else wanted, it would have helped a lot in every Theater of war. Even a boost up to comfortable performance at say 25,000 ft would have been a big improvement.

I still think keeping the radiator in the front might be the best route, especially if you were flying CAS, but I could be talked out of it.

Even with the extra added weight of the engine, I think the P-40 would still be more maneuverable than a P-51. The P-40F was 1,000 lb heavier than a P-40B/C but it was undoubtedly a more effective fighter. They could also do some of the tricks they used in the war to lighten the plane like using aluminum radiators & switching to four guns instead of six.

Curtiss would have had to move fast though and do everything right, and by the middle of WW2 that didn't seem to be within their capability any more.

Maybe for weight saving you could put an armored oil reservoir in the back behind the pilot. Though putting weight (fuel) there seemed to cause problems with the P-51 and other planes. The fuselage tank wasn't used much on the P-40.

I don't count the Do.335 because the engine in the back was not even close to the same as an front / mid engine mount for two V-12's. Also, if you were stupid enough to ever get the Do.335 into a spin, I seriously doubt it would ever come out of the spin (kind of like a twirling baton). Not the same for a front-engine double V-12 or even a front-mid double V-12 where the rear engine is more or less on the CG. For the purposes of a stretched P-40, I'd think the only logical candidate was a plane with two V-12's in front of the pilot since it lends some credence to stretching an engine compartment.

I'm assuming the Late 299A and the M.C.72 were designed with engine mounts buried in the fuselage, but an engine mount for a longer 2-stage Allison or Merlin is not much of a stretch, especially if you add a tail extension. Both would be a matter of inches ... perhaps 25 - 50 cm. You'd have to do a load calculation to be sure. I know what a 2-stage Allison or Merlin weighs, but I do NOT know the CG of same. I am also not in possession of a P-40 weight an balance sheet, and would not suggest building it in the first place. So, I have little incentive to complete a weight and balance for a 2-stage P-40 airframe.

But I think a cleaned-up P-40 with a Merlin 60 series is not too far from being rather easily possible, even if not exactly indicated as the right way to go. I have looked rather closely at some Reno racers.

1. Thom Richard was running a Griffon P-51 (Precious Metal) and may again after it is repaired.
2. Race 232 is a Sea Fury with an R-3350 in it. That is MUCH MORE of a stretch than a 2-stage Merlin in a P-40.
3. The so-called Super Corsair is also an R-4360 in what had been an R-2800 airplane. Same statement as 2. above. It is more of a stretch than a 2-stage Merlin P-40.

I think the 2-stage Merlin P-40 would be rather easy to build and might require only a slightly larger vertical fin with the same rudder on a stretched tail.

My question would be whether or not anyone thought it would be worth it to build it. I'd say yes only if we had a combination of the backwater theaters where the P-40 was the main fighter really needing a better fighter combined with also having a surplus of 2-stage Merlins. Without some further study, I'd say the beast would never likely be built. Real life WWII never saw one, so I'm guessing the right incentive to make a production run of 2-stage Merlin or Allison P-40s just never reached the top of the priority heap.

But it certainly wasn't without possibility. Perhaps it SHOULD have been tried. If so, the 2-stage Merlins flew in 1942 (Merlin XX). I'm guessing we COULD have had 2-stage Merlin P-40s in late 1942 - early 1943, had the need been pressing enough. But ... it never happened in real life, at least in any well-documented way. I have actually heard they made one 2-stage P-40, but I have never seen proof of same, so I am guessing it was a paper design or we'd have seen a pic or a report by now. Either way, there is no real proof they ever actually made one as far as I know.

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Seems like there was a post there and now it's gone ....?

If the question was "if it was so easy to put in a two stage Merlin, why didn't they do it?" - I would say the main issue was just a matter of the availability of the engines, and their preference for the P-51. For some reason the first production run of Packard Merlins was the single stage, two speed Merlin XX. That is what they used in the P-40 F and L (and also squandered in some other aircraft that weren't used or were re-engined before use, in part because the British seemed to have an aversion to the Packard built Merlins, at least initially).

By the time Packard was making the 60 series Merlins, or V-1650-3, the military brass far preferred the P-51 due to it's superior range and very high speed. No doubt a P-40 with a two-stage Merlin would have broken 400 mph, if only because peak engine power would be achieved at higher altitude and in the thinner air, but it would not have been as fast as a P-51B. The P-51A series was ~40 mph faster than a P-40 with the same Allison engine. That was the advantage of all that streamlining.

The P-40 was probably a bit better in terms of manueverability and resistance to damage, but USAAF was really interested in speed above all other qualities. Even range, which ultimately seemed to matter more, took a back seat.

I assume the reason they didn't use the two-stage Allison V-117 type that was used in the Kingcobra was because it was much more bulky..?

Schweik said:

Seems like there was a post there and now it's gone ....?

If the question was "if it was so easy to put in a two stage Merlin, why didn't they do it?" - I would say the main issue was just a matter of the availability of the engines, and their preference for the P-51. For some reason the first production run of Packard Merlins was the single stage, two speed Merlin XX. That is what they used in the P-40 F and L (and also squandered in some other aircraft that weren't used or were re-engined before use, in part because the British seemed to have an aversion to the Packard built Merlins, at least initially).

By the time Packard was making the 60 series Merlins, or V-1650-3, the military brass far preferred the P-51 due to it's superior range and very high speed. No doubt a P-40 with a two-stage Merlin would have broken 400 mph, if only because peak engine power would be achieved at higher altitude and in the thinner air, but it would not have been as fast as a P-51B. The P-51A series was ~40 mph faster than a P-40 with the same Allison engine. That was the advantage of all that streamlining.

The P-40 was probably a bit better in terms of manueverability and resistance to damage, but USAAF was really interested in speed above all other qualities. Even range, which ultimately seemed to matter more, took a back seat.

I assume the reason they didn't use the two-stage Allison V-117 type that was used in the Kingcobra was because it was much more bulky..?

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Why didn't they do it? Why didn't they use an engine change to make a very mediocre fighter into possibly a great fighter? Especially a fighter that was already in series production?

It was unlikely the P-40 would ever get a two stage Merlin. The first Packard two stage Merlin didn't come off the line until April '43. It would be in Mustangs in combat by December of that year. The two stage P-40 likely wouldn't have been able to make it into combat any sooner than the Mustang, and for every P-40 using the two stage Merlin that meant one less Mustang. And the Mustang was better than the P-40 because of its much greater endurance. P-40 wasn't getting a two stage Merlin.

Another question is why wasn't the Allison mechanical two stage engine developed sooner? Not a new engine, just an add-on to existing engines. In development since 1940 but first series production in April '43. Why so long to develop a standard impeller in a standard diffuser driven by a simple jackshaft? Sure it had a hydraulic clutch and that was a nice feature, but the device would have worked well with a standard friction clutch. Sooner high altitude performance for the P-40 and P-39.

GregP said:

I don't count the Do.335 because the engine in the back was not even close to the same as an front / mid engine mount for two V-12's. Also, if you were stupid enough to ever get the Do.335 into a spin, I seriously doubt it would ever come out of the spin (kind of like a twirling baton). Not the same for a front-engine double V-12 or even a front-mid double V-12 where the rear engine is more or less on the CG.

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The engine placement on the Do 335 was similar to the Ki 64 and VB 10. Just that the rear engine drove a pusher prop instead of a coaxial prop at the front.

I'm guessing the prop and gearbox at the extreme rear is why the Do 335 would be like a "twirling baton"?

GregP said:

I'm assuming the Late 299A and the M.C.72 were designed with engine mounts buried in the fuselage, but an engine mount for a longer 2-stage Allison or Merlin is not much of a stretch, especially if you add a tail extension. Both would be a matter of inches ... perhaps 25 - 50 cm. You'd have to do a load calculation to be sure. I know what a 2-stage Allison or Merlin weighs, but I do NOT know the CG of same. I am also not in possession of a P-40 weight an balance sheet, and would not suggest building it in the first place. So, I have little incentive to complete a weight and balance for a 2-stage P-40 airframe.

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I think a 2 stage Merlin would have been an easier install, simply because it was shorter.

Surely the weight could be balanced by ballast, rather than require extra stretch in the fuselage. SO long as the extra weight of the engine and ballast doesn't negate the reason for doing the conversion.

GregP said:

But I think a cleaned-up P-40 with a Merlin 60 series is not too far from being rather easily possible, even if not exactly indicated as the right way to go. I have looked rather closely at some Reno racers.

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In a way a two stage P-40 derivative was built - the XP-60D.

The XP-60 used the fuselage from a P-40D (IIRC) with the new laminar flow wings and a Merlin 28 (V-1650-1). That was later converted to 60-series Merlin. I believe both of those engines were ex-UK, since the US production versions of those engine types weren't available at the time the XP-60 and XP-60D flew.

GregP said:

1. Thom Richard was running a Griffon P-51 (Precious Metal) and may again after it is repaired.

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Yes, Rolls-Royce were keen for a Griffon 65 powered Mustang, but NAA were not. I suppose because they had to extensively redesign the P-51 for the Merlin, and did not have time or resources for an even more extensive redesign to fit the Griffon.

Maybe the lack of plans for licence built Griffons put them off as well.

GregP said:

2. Race 232 is a Sea Fury with an R-3350 in it. That is MUCH MORE of a stretch than a 2-stage Merlin in a P-40.

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Why do you say that? The Bristol Centaurus and Wright R-3350 were pretty much the same size and weight, within a few inches and pounds.

GregP said:

I think the 2-stage Merlin P-40 would be rather easy to build and might require only a slightly larger vertical fin with the same rudder on a stretched tail.

My question would be whether or not anyone thought it would be worth it to build it. I'd say yes only if we had a combination of the backwater theaters where the P-40 was the main fighter really needing a better fighter combined with also having a surplus of 2-stage Merlins. Without some further study, I'd say the beast would never likely be built. Real life WWII never saw one, so I'm guessing the right incentive to make a production run of 2-stage Merlin or Allison P-40s just never reached the top of the priority heap.

But it certainly wasn't without possibility. Perhaps it SHOULD have been tried. If so, the 2-stage Merlins flew in 1942 (Merlin XX). I'm guessing we COULD have had 2-stage Merlin P-40s in late 1942 - early 1943, had the need been pressing enough. But ... it never happened in real life, at least in any well-documented way. I have actually heard they made one 2-stage P-40, but I have never seen proof of same, so I am guessing it was a paper design or we'd have seen a pic or a report by now. Either way, there is no real proof they ever actually made one as far as I know.

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Production of the engine was the issue.

Was never going to get a V-1650-3 powered aircraft in 1942. As it was, the P-51B was delayed by slow initial deliveries from Packard.

The problem with the 2 stage Griffon is that it is larger in most or all dimensions than a 2 stage Merlin. And larger, except length, than a 2 stage Allison. And much heavier than either of those.

P-39 Expert said:

Why didn't they do it? Why didn't they use an engine change to make a very mediocre fighter into possibly a great fighter? Especially a fighter that was already in series production?

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Based on the records, I don't think it actually was mediocre.

It was unlikely the P-40 would ever get a two stage Merlin. The first Packard two stage Merlin didn't come off the line until April '43. It would be in Mustangs in combat by December of that year. The two stage P-40 likely wouldn't have been able to make it into combat any sooner than the Mustang, and for every P-40 using the two stage Merlin that meant one less Mustang. And the Mustang was better than the P-40 because of its much greater endurance. P-40 wasn't getting a two stage Merlin.

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That is pretty much what I said in the previous post. The only way they could have done it would have been to either rush production of the 1650-3 / 60 series or to push for a faster development of a 2 speed Allison.

Another question is why wasn't the Allison mechanical two stage engine developed sooner? Not a new engine, just an add-on to existing engines. In development since 1940 but first series production in April '43. Why so long to develop a standard impeller in a standard diffuser driven by a simple jackshaft? Sure it had a hydraulic clutch and that was a nice feature, but the device would have worked well with a standard friction clutch. Sooner high altitude performance for the P-40 and P-39.

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They probably needed to "borrow" the two speed supercharger system developed by RR. I may be wrong but I believe the RR system was the most compact two stage ever made, probably because it was designed for the Spitfire. Alternatively I would think they could have borrowed tech from Pratt & Whitney which may have been more viable. They had the R-2800 running pretty early. Maybe you could fit one of those on a P-40 LOL. Seems like Allison could have adapted their supercharger technology.

I know part of the issue was that Allison had decided to go with an integral, simple / single stage (but pretty reliable and cheap to make) supercharger on the original V-1710 and creating a more modular system would have been a challenge they may not have been up to. I think they were already a subsidiary of GM, they may have lost some of their 'agility' as an institution already by the beginning of the war. The Allison engines weren't bad, though the need for 2 stage or at least 2 speed superchargers was already obvious by early 1942 at the latest, arguably they should have realized it after the Battle of Britain.

wuzak said:

In a way a two stage P-40 derivative was built - the XP-60D.

The XP-60 used the fuselage from a P-40D (IIRC) with the new laminar flow wings and a Merlin 28 (V-1650-1). That was later converted to 60-series Merlin. I believe both of those engines were ex-UK, since the US production versions of those engine types weren't available at the time the XP-60 and XP-60D flew.

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P-60D with Merlin 61


P-60C with P&W R-2800


P-60E with R-2800

Judging from the rather ugly, stout airframe they came up with for most of the P-60 variants, they were having trouble fitting all the cooling / plumbing. That may have just been an issue with Curtiss or it may have been the rapidly design requirements from the USAAF, as they did eventually make the P-40Q farily nice and streamlined looking. That, (P-40Q) really would have been the souped up P-40 we were talking about, and might have been developed if only in smaller numbers, except for a series of prototype crashes.



If they could have had a reliable flying P-40Q six months earlier it could have possibly been a helpful addition to the arsenal.

Schweik said:

If the question was "if it was so easy to put in a two stage Merlin, why didn't they do it?" - I would say the main issue was just a matter of the availability of the engines, and their preference for the P-51.

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The availability of the engines was the big issue.

Schweik said:

For some reason the first production run of Packard Merlins was the single stage, two speed Merlin XX.

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Because the Merlin 60-series was only in the early days of supercharger development (that is, supercharger on a test bed and not on an engine) when the deal for licence production by Packard was signed.

Schweik said:

That is what they used in the P-40 F and L (and also squandered in some other aircraft that weren't used or were re-engined before use, in part because the British seemed to have an aversion to the Packard built Merlins, at least initially).

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So, the first contract witch Packard was for 9,000 20-series Merlins. Of which 6,000 were for British use and 3,000 were for US use. The latter was a requirement that the US put in place as it was still neutral. I don't think that the USAAF had a specific use in mind for 3,000 Merlins at the time of the contract.

Possibly the purchase of that number of Merlins by the USAAF was a kick in the ass for Allison.

As for "squandering" them the British used Packard Merlins in the Hurricane, Lancaster and Mosquito, especially in Canadian production of those aircraft.

I don't know where you get the idea that the British had an "aversion" to Packard built engines. It would seem to go against the history of the British seeking out a US manufacturer to build the Merlin.

Schweik said:

By the time Packard was making the 60 series Merlins, or V-1650-3, the military brass far preferred the P-51 due to it's superior range and very high speed. No doubt a P-40 with a two-stage Merlin would have broken 400 mph, if only because peak engine power would be achieved at higher altitude and in the thinner air, but it would not have been as fast as a P-51B. The P-51A series was ~40 mph faster than a P-40 with the same Allison engine. That was the advantage of all that streamlining.

The P-40 was probably a bit better in terms of manueverability and resistance to damage, but USAAF was really interested in speed above all other qualities. Even range, which ultimately seemed to matter more, took a back seat.

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Range was quite important for fighters come the latter half of 1943. By that time, without effective long range escorts, the 8th AF were getting their arses handed to them.

Schweik said:

They probably needed to "borrow" the two speed supercharger system developed by RR. I may be wrong but I believe the RR system was the most compact two stage ever made, probably because it was designed for the Spitfire.

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It was designed for the Wellington high-altitude bomber, as an alternative to turbocharged Hercules.

The head of Hives suggested one be put in a Spitfire, but it had been under development prior to that.

Schweik said:

I assume the reason they didn't use the two-stage Allison V-117 type that was used in the Kingcobra was because it was much more bulky..?

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"Even less available" is the answer you are looking for.

wuzak said:

The availability of the engines was the big issue.

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Agreed, though the 'need for speed' was also a factor, as was growing exasperation with Curtiss.

As for "squandering" them the British used Packard Merlins in the Hurricane, Lancaster and Mosquito, especially in Canadian production of those aircraft.

I don't know where you get the idea that the British had an "aversion" to Packard built engines. It would seem to go against the history of the British seeking out a US manufacturer to build the Merlin.

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Because from what I've read, many of the Packard-engined aircraft (largely made in Canada) that were sent to Britain were subsequently re-engined with British made Merlins. Many were also kept in Canada as a kind of tertiary level of defense where they never did much. If you had doubled the number of P-40 F / L in the Med in say 1943 and 1944 that would have helped. I think the Soviets could have used them too.

Or for that matter if you had doubled the number of Mosquitoes would have helped basically anywhere except the CBI / Pacific.

Range was quite important for fighters come the latter half of 1943. By that time, without effective long range escorts, the 8th AF were getting their arses handed to them.

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It was a major issue in the Pacific as well. For example, in the 49th FG where the famous US Aces Richard Bong and Thomas McGuire originally flew, only 1 of the 3 squadrons was flying P-38s, the others were still flying P-40s into 1944 and still did quite well in combat, but they missed out on half of the engagements due to their limited range. Same problem affected the ANZAC Air Forces. This was the main problem with Hurricanes and Spitfires in that Theater as well, even the Spit VIII wasn't long legged enough for those vast distances.

In fact I would say in the Pacific and CBI what you really needed was a longer-ranged P-40, as the combat record of P-40 units got steadily better and better after early 1942. It was really only against the Germans where the higher altitude performance and faster speed / climb rate was really a major issue, and that was almost rectified with the P-40 F / L, they just never came up with another incremental improvement after those models.

I am aware of the engine placement on the Do. 335 Wayne, but it has much more mass at the end of the rear fuselage than a plane with both props up fron2t. Not only is there the remote gearbox and the propeller assembly but also the beefing up of the tail structure to handle the torque and power of the rear propeller. You don't seriously think the tail structure wasn't much stronger than a standard tail with no propulsive power being transmitted through it, do you?

2-stage Merlin an easier install? I said that.

Wasn't talking about the XP_60, particularly the radial versions. Was talking about a revised P-40. The XP-60A or XP-60B kght be close, but still not what I ws talking about.

I said what i said about Race 2332 because the amount of fuselage in front of the wing leading edge seems to be longer than for a stock Sea Fury. That's my eye talking, not a tape measure.

Stock:

Look at the length in front of the leading edge above. Now look at Race 232 below.



Just seems a bit longer to me. Perhaps not. It's not a LOT, but also not quite the same. Perhaps in the eye of the beholder. Either way, not really a major point. They COULD have stretched a P-40 to accommodate a 2-stage Merlin without a lot of fanfare.

Look at a Vultee V-11:


Now look at the same aircraft with an Allison in it.





Now, looking at the above, I think they could stretch a P-40 by a little to accommodate any 2-stage V-12 IF the desire was there.

Based on the records, I don't think it actually was mediocre. Speaking of the P-40.

Well, the P-40 was about the most mediocre fighter plane in the US inventory. Allison versions were slow but climb was the main problem. A clean P-40 climbed a little slower than a contemporary P-39 carrying a drop tank. Couldn't get above 20000' in clean condition. Barely faster than a Zero. Even the F/L with the single stage Merlin had about exactly the same performance as an early 8.8 powered P-39D/F/K/L.

The P-40 really needed a two stage engine (Merlin or Allison) to be a truly competitive plane at all altitudes.

The P-40 didn't climb well, but exactly how badly it climbed depended on the variant. and the power setting. You are referring to a D or E used at lower rated takeoff or military power. The Tomahawk (B, C) had a 2,800 fpm + initial climb rate. The K had almost a 3,000 fpm rate as well if climbing at higher power settings they used in the field up to about 12,000 ft. The P-40L-10 climbed at 3,300 fpm according to "The Curtiss Hawks", Wolverine Press, 1972 - P.234 and Carl Molesworth's, "Snub nosed Kittyhawks and Warhawks" (2013), P. 32

P-40F was the same as the L when they were stripped down for fighter combat, as they usually were in the MTO. But climbing performance wasn't the only measure of a fighter.

Without any doubt we could debate stats all day long which would be quite pointless. I'm not talking about performance stats, I'm talking about the operational history. The P-39 and P-40 were used roughly in the same quantities in the Pacific, in fact there were more P-39s deployed during several key battles such as at Guadalcanal (probably because on paper they looked like they would be better) and yet P-39 units claimed less than half as many victories as P-40 equipped units did (288 for P-39s vs 660 for P-40s) suffered more losses, and had a lower morale. If you include the ANZAC P-40 units that's another 248 victories. So I would say P-40s did a lot better there.

In the CBI the ratio was 5 claims for P-39 equipped units vs. 973 for P-40 units (only counting US and not Chinese units here). I don't think that many P-39s were used in the CBI though.

In the MTO, where P-39s were available in some numbers and for a comparatively long time, US units equipped with that fighter only claimed 25 victories, vs. 592 for P-40 equipped units. If you add Commonwealth units equipped with P-40s that goes up to 1042.

The total number of victory claims for US P-40 units in WW2 was 2225, making it 5th for all US fighter types, abvoe the F43U and the F4F. The total for the P-39 was 320.5, making it 10th, just above the SBD Dauntless. Source

There was also only one pilot who made Ace in the US military who flew P-39s, vs. at least 86 for the P-40. Not counting another 46 British Commonwealth pilots who became Ace while flying the P-40.

Now of course we know overclaiming was a thing, and I'm sure actual victories were far lower than 2225, but there is no reason I can think of to assume that that units equipped with P-40s, recruited from the same pool of pilots as the units equipped with the P-39s, would have been overclaiming at a higher rate.

In the Med, the P-39 was considered so ineffective in combat that they were relegated for a long time to 'Coastal Patrol' operations. At the same time the P-40 equipped units were bearing the brunt of combat with the Luftwaffe and Regia Aeronautica. Only later when improved models became available were P-39s used for CAS and bombing strikes, though they were limited in this role by their short range.

The P-39 proved it's merit in Russian hands, but with the Western Allies it was a major disappointment and when it came time to face the enemy, they failed in the litmus test, underperforming, whereas the P-40 tended to overperform vs. expectations, paticularly in the mid-war period. P-39s were tricky to fly and accidents also cost the lives of some very talented pilots flying for the Italian Co-Belligerent Air Force and the Free French. The Soviets may have been uniquely qualified to use it, or maybe the Americans just didn't give it the propepr work up it needed. The bott

I would also add that while the P-40 was of limited popularity with the Russians, and they certainly preferred the P-39 to all other Allied fighters, it did fairly well in Soviet use, in addition to doing well with the British, Australians, and New Zealanders.