Spitfire V Versus P-40E

[PAT303]

All front line Spitfires got a field modification involving fitting De Havilland CS props starting in June 1940, the Rotol CS prop had bee fitted since 1939 but required changes to the Merlin to fit it so limited it's use.

 

[Reluctant Poster]

Circling back to the Spitfire for a moment, I would put it like this.

The original very broad Spitfire legend is that it dominated the Bf 109 and won the Battle of Britain. When we drill down a little deeper into the data we find that the early Spit (I and II) was pretty evenly matched with the 109E, but that the 109 suffered a bit more from the Tactical situation of having to fly escort (and sometimes ill conceived close escort) and often near the limits of their operational range, as well as going against an integrated air defense with radar. We also know that Hurricanes shot down most of the German bombers.

Then the Spit V and Bf 109F arrived, with the Fw 190 not long after, and once again the conventional wisdom was that the Spit V was inferior.

The Franz was a major improvement over the Emil. It was far better streamlined, had a significantly more powerful engine, had more ammunition and (arguably) more accurate guns. From what I understand they got the leading edge slats working properly in the F model.

The Spit V was also a big leap forward but it was initially plagued with a number of minor flaws and issues. The guns were prone to jamming and the cannons only had 60 rounds each, and they could sometimes freeze at high altitude. The carb would still flood with a negative G push-over. The Merlin 45 engine though more powerful than the Merlin II or III on the Spit Mk I, was not up to it's full potential. And in the Med they had a lot of problems with the Tropical filters.

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When the British started trying to fly provocation raids over the Channel, they were reversing roles and were now the ones facing an integrated air defense. This was a big part of the problem. But initially it's clear the early Spit V was inferior to the 190 and a bit so compared to the 109F-2

But the Bf 109F and the Spit were both around for a long time. The Franz came out in 1941 but it was still being used at least in the Med all through 1942 and even in 1943. The Spit V lasted even longer, still equipping some units in 1944.

The F went basically from the F-2 to the F-4, improving from a 15mm cannon to a much more deadly 20mm. They improved the engine power by about 100-150 hp.

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But the Spit V improved even more. They got the 130 octane fuel and increased the allowed boost, and put in engines with more horsepower - it went from ~ 1,200 hp to routinely up to 1,585 at high boost. Rate of climb and acceleration improved. Dive was faster because there was no carb cutout with the Bendix carb. They fixed most of the problems with the air filter. They replaced the drum based cannon with belt fed cannon that gave twice as much ammunition and reduced the tendency to jam. They improved heating systems to keep the guns from freezing. They made specialized LF and HF versions. And they improved their tactics - it took a while to start using the finger four / pairs system in the MTO for whatever reason, even though it was already done in the BoB, but once they were doing that and a lot of other things in the Med, it made a difference. They got better and more reliable radios.

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A Spitfire LF Mk Vc with a Merlin 50 or 50M, (let alone a 55M though those came later) was a pretty dangerous aircraft and definitely could hold it's own anything the Axis had in the MTO Theater. The IX was still better, but the late model Vc was clearly on par with an MC 202 or the 109F-4 and didn't seem too bothered going up against a 109G-2 or G-4 either.

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I would argue that the P-40 history in the Med was kind of similar. The Tomahawk arrived and brought success to the DAF. It was dominant over the G.50, MC 200 and Bf 110, and could hold it's own with the 109E. It's arrival hurried the replacement of the 109E with the F. The F was superior to the early P-40s (both Tomahawk and Kittyhawk) and took a heavy toll from winter of 41/42 through the first few months of 42. The early Kittyhawk had a 1,050 hp engine and many of the same problems as the Spit - wing guns jamming, engine running below full potential, bad tactics and so on.

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But the British, Australians, South Africans and Americans flying the P-40 got the new high octane gas and started increasing the boost. They adopted pairs and formation tactics. Curtiss made improvements to the guns which reduced jamming, and lengthened the fuselage to improve high speed stability. The newer V-1710-73 Allison Engines could go up to 1550+ HP down low, and the V-1650 Packard-Merlin engined variants were good for 1,350-1,400 hp and raised the performance ceiling by 8,000 ft. That is when the tide started to change with those units as well.

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The Spitfire V never had a Bendix carb

 

[Schweik]

Merlin 50 & 55 did I believe

 

[Reluctant Poster]

Merlin 50 & 55 did I believe

They did not.
Merlin 50 Diaphram type carburetor. Rolls Royce developed.
Merlin 55 R.A.E. Anti g type carburetor
Both of these were modified SU carburetors. The diaphragm feed was abandoned in favour of the R.A.E. modification. To quote Lumsden: "These trials resulted in a retrospective modification on all Merlins fitted with S.U. carburettors."
Rolls Royce Piston Aero Engines - a designer remembers figures 90 and 91 illustrate the SU carburetor and the SU carburetor with anti g modification developed in conjunction with RAE Farnborough respectively.

 

[Shortround6]

We also know that Hurricanes shot down most of the German bombers.

Well, there were a lot more Hurricanes in service so that did tend to affect the scoreboard.

The Merlin 45 engine though more powerful than the Merlin II or III on the Spit Mk I, was not up to it's full potential.

In part due to the Fuel and in part due to the fact that the MK V and it's engines were in production for along time, Mk Vs first show up in the Spring of 1941 and the last are built in the summer of 1943(?). The P-40 didn't stand still either. The first P-40D being delivered May 7th 1941 and by the summer of 1943 Curtiss was building P-40N-5s.

The early Kittyhawk had a 1,050 hp engine

Typo? 1150hp?

But the Spit V improved even more. They got the 130 octane fuel and increased the allowed boost, and put in engines with more horsepower - it went from ~ 1,200 hp to routinely up to 1,585 at high boost.

The 1585hp engines were the ones with the cropped impellers. the 1585hp was at 2750ft (no ram) at 18lbs boost. The standard Merlin 45s were eventually approved for 16lbs boost and either 1515hp at 11,000ft or 1470hp at 9250 depending on exact model and carburetor. The 1200hp figure was at a bit above 18,000ft.
Question on the Spit MK V is when the units in the field went from 9lbs boost to 12lbs and then when they changed from 12 to 15/16lbs boost.
I don't know if the cropped impeller was an interim solution. As in if it was allowed higher boost first and then the full size impeller engines were allowed to use the high boost later?

The cropped impeller engines made 45hp more for take-off at 3000rpm and 12lbs boost than the full size impeller engines.

 

[Schweik]

They did not.
Merlin 50 Diaphram type carburetor. Rolls Royce developed.
Merlin 55 R.A.E. Anti g type carburetor
Both of these were modified SU carburetors. The diaphragm feed was abandoned in favour of the R.A.E. modification. To quote Lumsden: "These trials resulted in a retrospective modification on all Merlins fitted with S.U. carburettors."
Rolls Royce Piston Aero Engines - a designer remembers figures 90 and 91 illustrate the SU carburetor and the SU carburetor with anti g modification developed in conjunction with RAE Farnborough respectively.

Ok I'm going by Wikipedia which is always a little risky. It says:

Merlin 50 - Merlin 50 series was first to use the Bendix Stromberg "negative-g" carburettor.[10][18][19]

Their first source is this which says: "Merlin 50 series / Similar to Merlin 45. Majority of production engines fitted with anti-G carburettor."
Their second source is this book - but I can't read what it says because it's behind a paywall.
Their third source is this which says "The only difference between a Merlin 45 and 50 is the fitting of a "negative g" carburettor and a fuel de-aerator on the latter engine, and these are unlikely to have a marked effect on performance. "

 

[Schweik]

Well, there were a lot more Hurricanes in service so that did tend to affect the scoreboard.


In part due to the Fuel and in part due to the fact that the MK V and it's engines were in production for along time, Mk Vs first show up in the Spring of 1941 and the last are built in the summer of 1943(?). The P-40 didn't stand still either. The first P-40D being delivered May 7th 1941 and by the summer of 1943 Curtiss was building P-40N-5s.


Typo? 1150hp?

You are right, I transposed the number from the Tomahawk which was 1040 for takeoff. The V-1710-39 on the P-40D / E was initially rated for 1,150 hp at 42" Hg, then this was changed (I think in April 1942) to 1,240 hp for takeoff at 45.5" Hg (5 minute rating) and then later around June or July 1942 (probably with the newer engines with the strengthened cam shaft etc.) bumped up to 1,470 hp at 56" Hg (5 minute rating).

The V-1710-73 on the P-40K was 1,325 hp at 51" Hg for takeoff and 1,550 hp at 60" Hg WEP (5 minutes at Sea Level) with military power back down to the 1,150 hp rating at 42"

The 1585hp engines were the ones with the cropped impellers. the 1585hp was at 2750ft (no ram) at 18lbs boost. The standard Merlin 45s were eventually approved for 16lbs boost and either 1515hp at 11,000ft or 1470hp at 9250 depending on exact model and carburetor. The 1200hp figure was at a bit above 18,000ft.
Question on the Spit MK V is when the units in the field went from 9lbs boost to 12lbs and then when they changed from 12 to 15/16lbs boost.
I don't know if the cropped impeller was an interim solution. As in if it was allowed higher boost first and then the full size impeller engines were allowed to use the high boost later?

The cropped impeller engines made 45hp more for take-off at 3000rpm and 12lbs boost than the full size impeller engines.

There are a couple of references to the LF types in MAW, with kind of a hint that they were 'hot', but they usually don't specify that much detail, typically they just say Spit Vb or Vc or sometimes they only say Spit V

Do you know the answer about the pressurized carb?

 

[Shortround6]

The Book "The Merlin in Perspective" by Alec Harvey-Bailey lists the different carbs used on Merlin engines but gives model number. No way of knowing if one of the later ones is a Bendix type under a different name or licence

However.
Merlin 45................A.V.T. 40/193 or 214 carburetter.
Merlin 45M............same with stronger boost control spring. Mod 615
Merlin 46................same with larger chokes.
Merlin 47...............same as Merlin 46
Merlin 50...............A.V.T. 40/ 214 carburetter
Merlin 50M..........same with stronger boost control spring. Mod 615
Merlin 55..............A.V.T. 40/ 216 carburetter
Merlin 55M..........as Merlin 55.

 

[Schweik]

I couldn't find anything under "A.V.T. 40/ 214 carburetter" or carburetor

 

[Shortround6]

Using the spelling in the book

 

[Schweik]

I figured... never seen that one though

 

[Schweik]

Anyway do you agree or disagree with my contention that the 1943 Spit V was far more formidable than a 1941 Spit V?

Whether or not it was an LF variant is a secondary factor, it could be good if fighting low as was often the case in N/A, and the LF had that dynamite roll rate, but it may be giving up the altitude advantage to the Luftwaffe. Presumably you could use both types though.

 

[buffnut453]

Thanks I'll adjust my notes on that. I think he got several with the Buffalo too.

All his other kills (6 in total) were in the Buffalo.

 

[PAT303]

Question on the Spit MK V is when the units in the field went from 9lbs boost to 12lbs and then when they changed from 12 to 15/16lbs boost.

Merlin 45's were cleared for 16psi boost @3,000rpm in July '42, 18psi in Feb '43, MkV LF's with Merlin 50's 18psi boost @ 3,000rpm May '43.

 

[PAT303]

Anyway do you agree or disagree with my contention that the 1943 Spit V was far more formidable than a 1941 Spit V?

Against the FW190 the '41 version was outclassed, by '43 the Anton pilot needed to have is brain in gear, what made his job even worse was the Mk IX looked the same except for being 9'' longer, and both had reliable belt fed Hispano's loaded with SAPI rounds.

 

[wuzak]

Against the FW190 the '41 version was outclassed, by '43 the Anton pilot needed to have is brain in gear, what made his job even worse was the Mk IX looked the same except for being 9'' longer, and both had reliable belt fed Hispano's loaded with SAPI rounds.

And there was also the Mk XII in 1943. Also looking similar to the V, at least from a distance.

 

[Reluctant Poster]

I couldn't find anything under "A.V.T. 40/ 214 carburetter" or carburetor

Once again I point to Figure 91 of Rolls Royce Piston Aero Engine by A A Rubbra. it is a "TYPE AVT 40 ANTI-g". It is an "SU carburettor with anti-G modification developed in conjunction with R.A.E. Farnborough."
From the same book: "To deal with this problem a negative "G" carburettor was designed which provided a diaphragm controlled fuel supply to the carburettor as a replacement for the normal float and needle. This proved unsuccessful in service trials and an anti "G" version of the S.U. carburettor (91) was developed, with modified valving in the float chamber. This worked satisfactorily and was in use to the end of the war on both single and two stage engines."
In references you provided the only mention of Bendix is the Wiki article. Ant -g does NOT automatically mean Bendix.

 

[Schweik]

As long as it works in negative G it's basically the same outcome right?

 

[Reluctant Poster]

As long as it works in negative G it's basically the same outcome right?

I really don't care if it had warp drive all I care about is that it wasn't a Bendix

 

[MIflyer]

The negative G problem with the Merlin featured a "Lean Cutout" and a "Rich Cutout."

When the nose was shoved over the fuel in the carb float chamber rose to the top, and therefore could not be sucked into the engine. This was fixed by putting a standpipe in the float chamber giving a path for the engine to inhale the fuel from the top of the float chamber.

After positive G was regained the float chamber had become full of fuel during the negative G period, resulting in an excessively rich mixture and another loss of power, typically evidenced by a burst of black smoke coming out of the exhaust. This was fixed by putting an orifice in the fuel line that limited the amount of fuel that could get into the float chamber.

In contrast, the Bendix Pressure Carb commonly used on US high power engines was completely different and injected fuel into the center of the mechanical supercharger inlet so it was a form of "Throttle Body Injection" and was immune to the G load situation. The British eventually adopted the Bendix carb, seen below on a V-3420.