How good a plane was the P-40, really?

PAT303 said:

The Spitfire had one handicap verse's every other aircraft and that was the RAF's refusal to fit aux tanks, the fact that it was replaced by lesser aircraft that did have the fuel to get to the fight was mindboggling in my mind, as per the Darwin test the lower the the Spit went the worse they became because the merlin 46 was a purpose designed high altitude engine, low altitude, low boost, trop filter and overall poor condition made both the A6M and P40 look good in comparison.

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Taking a stab at it, could the narrow undercarriage been a factor in not carrying drop tanks?

SaparotRob said:

Taking a stab at it, could the narrow undercarriage been a factor in not carrying drop tanks?

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That's a good guess, though the similarly narrow-track Bf 109 managed a centerline tank, and they did put external tanks of various types on Spitfires, just never seemed to do it en-masse

Wild_Bill_Kelso said:

That's a good guess, though the similarly narrow-track Bf 109 managed a centerline tank, and they did put external tanks of various types on Spitfires, just never seemed to do it en-masse

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That just looks wrong. I think it's the first pic I've seen of a Spit with drop tanks. Bombs I've seen.

SaparotRob said:

Taking a stab at it, could the narrow undercarriage been a factor in not carrying drop tanks?

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Having drop tanks is no harder than any other aircraft, all Spitfire's should have had at least the lower 33G rear tank fitted plus plumbing for DT's as standard, then fit the upper 33-42G as required depending on theater of operation.

SaparotRob said:

That just looks wrong. I think it's the first pic I've seen of a Spit with drop tanks. Bombs I've seen.

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Replace those with a centerline 90G DT with 26G in each leading edge plus 75G in the rear fuselage, done.

Wild_Bill_Kelso said:

That's a good guess, though the similarly narrow-track Bf 109 managed a centerline tank, and they did put external tanks of various types on Spitfires, just never seemed to do it en-masse

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Lets not use drop tanks on Spitfires to carry fuel, beer on the other hand, no objections.

PAT303 said:

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Having drop tanks is no harder than any other aircraft, all Spitfire's should have had at least the lower 33G rear tank fitted plus plumbing for DT's as standard, then fit the upper 33-42G as required depending on theater of operation.

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I was thinking more about the Spitfire's ground handling characteristics.

Wild_Bill_Kelso said:

Do you have a source for the official approval of 61" boost?

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From Pilot's Flight Operating Instructions for Army Model P-40F and P-40L.

Thank you.

we need to note the typographical errors. As noted earlier somebody just copied the Take-off power for the War Emergency power.

There may be some debate about the critical altitudes being in the wrong column. Or only some of them being in the wrong column.

Greyman said:

From Pilot's Flight Operating Instructions for Army Model P-40F and P-40L.

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Thanks, if this isn't on WW2aircraftperformance, it should be.

As SR6 noted, the horsepower at WEP will be up considerably over 1300 hp, does anyone know how to calculate it precisely? Would it be 1468 hp?

The fact that P-40F/L can make WEP at 12,000 feet is also notable.

Also I notice the fuel grade, would these numbers be any different with 120 or 150 octane? Is there any documentation of that?

SaparotRob said:

That just looks wrong. I think it's the first pic I've seen of a Spit with drop tanks. Bombs I've seen.

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I agree, I think those are 52 gallon drop tanks from P-40, or even bigger ones. But they just look too big for that wing.

This is a more plausible centerline tank, which I think is a different type with a flatter shape. Those are apparently Seafires... ?

I still don't understand why the use of drop tanks never seemed to become very common with Spitfires, or did I miss something?

Looks like it could have been grand... these numbers for range (and cruising speed) are very good, but it's not clear to me what kind of tanks these are, slipper or regular detachable type

The BHP for the Merlin XX (~Packard V-1650-1) at +15.25 lbs (61"Hg) boost, no RAM

~1400 BHP at 11,600 ft
~1525 BHP at 5,000 ft

* Note that these are calculated values, but they should be within +/- 20 BHP, as the calculated values for the Merlin XX-45 (using the same methods/formulas) come out to within +/- 20 BHP of the 'standard' British charts/values (ie from RR, RAE, etc). The standard atmosphere calculated critical altitudes of the Merlin XX-45 come out to within +/- 200 ft. The differences in critical altitude between the V-1650-1 and Merlin XX may be due to several factors - ie carburettor type, supercharger epicyclic gearing vs spur gearing, differences in testing methods, method of measuring/calculating the BHP, or some sort of error.

So that is close to the same (maybe 30-40 more) horsepower as a P-40E or K at 5,000 feet, but an extra 250 hp over the Allison types at 12,000 ft.

Which is a big bump.

And it's still producing what they can make at 12,000 feet all the way up to 18-19,000 ft. Keep in mind in the Aussie test, the P-40E, with a critical altitude of ~12,000 ft, was still performing pretty well 4,000 feet above that. Similarly, the P-40F/L were still chuffing around pretty well at 22-23,000 ft.

Most planes can operate pretty well 3-5,000ft above the critical altitude of the engine.
Of course we have to define operate and we have to figure out what the opposition is doing.

Working our way down from service ceiling (rate of climb is 100ft/min or 5-8 minutes to climb that last 1000ft) we have

Operational ceiling (British definition) which is a climb of 500ft/min. This was considered the power margin that a small group of planes needed in order to stay in formation while navigating. Think worst plane in the group being in the outside of a formation while making a turn and not getting left behind. You can initiate a diving attack from this altitude.

Combat ceiling (British definition) where the climb is 1000ft/min. This is the altitude the planes can actually fight at (sort of) and not loose to much altitude while turning and not doing violent maneuvers. Also note that max climb rate and max speed are often over 100mph apart. you don't get both at the same time.

Planes like the early Spitfire and Hurricane had service ceilings of over 35,000ft. They had operational ceilings of 31,500-34,000ft. Early Spits and Hurricane IIA's had climb rates of 1000fpm just over 30,000ft. A lot of this was due to the light weight, not engine power.

Be careful with test reports, most British reports are not done at full throttle, With Merlin engines they are done at 2850rpm (Mostly). The Americans often use 3000rpm for the first 5 minutes and 2600rpm and lower boost after that which really makes the US planes look like they dropped and anchor in the middle of climbing.

But most of the Allison engine P-40s from the D/E onward had service ceilings (100f/m) of around 30,000ft (clean, no drop tank) so by they time they get down to where they can climb at even 1000f/m even at full throttle, they are in the low 20,000ft range, very low 20,000ft range.
The planes with -81 engines gained 3-4000ft. Problem is that it is not 1941-42 anymore. The Germans and Japanese also have planes with several hundred hp more in the low 20,000ft area.

For the P-40vs Hurricane question, the Hurricane IIC was over 1000lbs lighter than a P-40F and they used engines that were within 20-30hp of each other at just about any altitude.
The P-40 had less drag, the Hurricane was going to climb better, enough better than the Japanese????

Wild_Bill_Kelso said:

I agree, I think those are 52 gallon drop tanks from P-40, or even bigger ones. But they just look too big for that wing.

This is a more plausible centerline tank, which I think is a different type with a flatter shape. Those are apparently Seafires... ?

I still don't understand why the use of drop tanks never seemed to become very common with Spitfires, or did I miss something?

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I should have written wing tanks. I was thinking about remarks made about the safety hazards of drop tracks out weighing their usefulness during peacetime. The Spitfire was wobbly enough.*

*Source: miscellaneous musings from the voices in my head.

Shortround6 said:

Most planes can operate pretty well 3-5,000ft above the critical altitude of the engine.

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Exactly

Shortround6 said:

Of course we have to define operate and we have to figure out what the opposition is doing.

Working our way down from service ceiling (rate of climb is 100ft/min or 5-8 minutes to climb that last 1000ft) we have

Operational ceiling (British definition) which is a climb of 500ft/min. This was considered the power margin that a small group of planes needed in order to stay in formation while navigating. Think worst plane in the group being in the outside of a formation while making a turn and not getting left behind. You can initiate a diving attack from this altitude.

Combat ceiling (British definition) where the climb is 1000ft/min. This is the altitude the planes can actually fight at (sort of) and not loose to much altitude while turning and not doing violent maneuvers. Also note that max climb rate and max speed are often over 100mph apart. you don't get both at the same time.

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Right, and with regard to the P-40F/L, I was being conservative. P-40F can still climb at 1,000 fpm at 25,000 ft. as you can see here, and it's shown climbing 1040 fpm at 28,000 feet here, and that is with six guns at 8,450 lbs. A lightened F or L with four guns and etc., can probably still consider 30-32,000 within combat ceiling.

Which doesn't make it a high altitude fighter. It just makes it a pretty tough medium altitude fighter that can deal a little higher up (much higher up than a P-40E).

Shortround6 said:

Planes like the early Spitfire and Hurricane had service ceilings of over 35,000ft. They had operational ceilings of 31,500-34,000ft. Early Spits and Hurricane IIA's had climb rates of 1000fpm just over 30,000ft. A lot of this was due to the light weight, not engine power.

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I think generally, both a Spit up to version V and a Hurricane II has better altitude performance than any P-40. However, altitude performance also depends on weather conditions, and Hurricanes at any rate seem to have had some problems in the tropics.

More pertinent though, is as you noted, "we have to figure out what the opposition is doing."

In the Battle of Britain, or while escorting B-17s, you need very high altitude performance. In North Africa, or the Solomons, or New Guinea, or Burma, or China, or India, you can go through sources like Shores or Claringbould and you'll find that 90% of the combat is taking place well below 20,000 feet, often it's more like 7 or 8,000 feet or even lower. The reason is the simple rule that fighters follow the bombers, (or else they are acting like bombers themselves).

WW2 fighter combat isn't competitive performance. It needs to have an impact on the ground war. Most tactical bombers can't even fly at 30,000 ft, and typically operate down much lower.

It's still good to be able to climb and to fight at considerably higher up, which is probably the main reason P-40F and L were lightened - (i.e., altitude, not speed or handling). Because you still need top cover.

Shortround6 said:

Be careful with test reports, most British reports are not done at full throttle, With Merlin engines they are done at 2850rpm (Mostly). The Americans often use 3000rpm for the first 5 minutes and 2600rpm and lower boost after that which really makes the US planes look like they dropped and anchor in the middle of climbing.

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I'm well aware!

Shortround6 said:

But most of the Allison engine P-40s from the D/E onward had service ceilings (100f/m) of around 30,000ft (clean, no drop tank) so by they time they get down to where they can climb at even 1000f/m even at full throttle, they are in the low 20,000ft range, very low 20,000ft range.

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Agreed for D/E/K

Shortround6 said:

The planes with -81 engines gained 3-4000ft. Problem is that it is not 1941-42 anymore. The Germans and Japanese also have planes with several hundred hp more in the low 20,000ft area.

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Again, that very much depends on the Theater and the nature of the ground war going on there. Allison engined P-40s did very well in Burma and China, and held their own in the Solomons right to the end of 1944. They were still holding their own in the MTO in British use through early 1943, but the Americans wanted the F/L to cope with the ever faster German and Italian fighter types.

Keep in mind that other good fighters, including the early A6M and the Fw 190, and almost all the much-maligned Soviet fighters, were not necessarily high altitude planes.

Shortround6 said:

For the P-40vs Hurricane question, the Hurricane IIC was over 1000lbs lighter than a P-40F and they used engines that were within 20-30hp of each other at just about any altitude.
The P-40 had less drag, the Hurricane was going to climb better, enough better than the Japanese????

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Hurricane climbed better, depending on loadout, and definitely had a higher ceiling, had a shorter takeoff run, was easier to fly, and had heavier armament, at least with the IIc variant.

The Hurricane also turned tighter, though that was closer than some people think (some versions of P-40 have shorter turn time in the Soviet tests)

But the Hurricane had a lot more drag

Hurricane wings are 40 ft (12.19 m) span and 257.5 sq ft (23.92 m2) wing area, and a very thick cross section.
P-40 wings are 37 ft 3.5 in (11.367 m) span and 236 sq ft (21.9 m2) wing area, with a much thinner cross section.

P-40 had about twice the roll rate and a much faster dive acceleration than a Hurricane.
P-40, depending on the versions, was 20-50 mph faster than a Hurricane
P-40 did not require a Vokes filter at any time, which apparently had a significant impact on the speed and overall performance for the Hurricanes operating in Tropical Theaters.

P-40 also had better range. Carried more bombs. Was more strongly made.

And, bottom line, P-40 units had a much better survival rate and true victory to loss ratio than the Hurricane in both North Africa and in the CBI. Anecdotally, the Soviets liked them a lot better too though we don't have any hard numbers from them.

I learned fairly recently from Ehlers Mediterranean Air War that the British strategy in North Africa largely based on the Kittyhawk specifically.

Wild_Bill_Kelso said:

However, altitude performance also depends on weather conditions, and Hurricanes at any rate seem to have had some problems in the tropics.

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So did most other aircraft. Some had more problems than others. The Hurricane was marginal in speed compared to other allied fighters and that was before they hung the Vokes filter on it.
The Hurricane climbed better than P-40s, but thay may not show up as often. Some Japanese aircraft had trouble with cooling due to small openings in the cowl.
Hotter, thinner air is hotter, thinner air. It doesn't care who make the plane, It matters what the wing loading is and perhaps the boost being used by the engine. But the changes are are going to be percentages.

Wild_Bill_Kelso said:

P-40 did not require a Vokes filter at any time, which apparently had a significant impact on the speed and overall performance for the Hurricanes operating in Tropical Theaters.

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And we get to individual aircraft. P-40F & Ls never got Vokes filters. They also went through engines at a much higher rate than the P-40E/K/M/N did.
Part of the difference between the over cowl intake and carb intake being in radiator/oil cooler opening in the Merlin P-40s.
This is why the British gave the Americans 600 used Merlins as a source for rebuilds.
Maybe the P-40Fs should have gotten a better filter even at the cost of performance?
A slower plane that is flying is of more use than an plane waiting for a replacement engine (or crashed).

The largest performance differences are between the Merlin powered versions and all the others. The -81 engine difference made up some of the difference in altitude but only about 1/2

SaparotRob said:

I should have written wing tanks. I was thinking about remarks made about the safety hazards of drop tracks out weighing their usefulness during peacetime. The Spitfire was wobbly enough.*

*Source: miscellaneous musings from the voices in my head.

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Any plane loaded up with fuel or ordinance is a handful on the ground as well as in the air at least until the fuel is burnt off and bombs dropped. There's plenty of room in the leading edge for 50G of fuel which is a much better option.