Spitfire V Versus P-40E

[Schweik]

View attachment 589386View attachment 589387

I forgot how hard that is to read. Thanks!

Where does it say what boost settings were being used ?

 

[Mike Williams]

I forgot how hard that is to read. Thanks!

Where does it say what boost settings were being used ?

I don't think that report notes the boost settings. Maybe these apply:

 

[Schweik]

If that is reflective of the conditions of the test then the p-40 was flying at restricted power ratings as well, 43 to 46 in of Mercury. So that would mean that both aircraft were flying below their highest power ratings.

 

[Vincenzo]

The memo refers to the Typhoon II which was renamed the Tempest in Feb 1942. So your claiming that a year later the writer was unaware of the name change. The memo also notes that the Sabre IV will go into production in September 1942. The Sabre IV was the power plant for the Tempest. Neither the engine nor the airframe went into production. Again a half a year later the author didn't know that. And your case is based on?

You're right on this, but the info on the Merlin are strange, at 3rd january '42 there was a alone Spitfire with a Merlin 60 flying, the next prototype ever with a 60, not a 61, go to fly only the 6th January, so the testing for the 66 1/2 inch boost are on land, on bench (? i'm not sure of the word)?

 

[Reluctant Poster]

You're right on this, but the info on the Merlin are strange, at 3rd january '42 there was a alone Spitfire with a Merlin 60 flying, the next prototype ever with a 60, not a 61, go to fly only the 6th January, so the testing for the 66 1/2 inch boost are on land, on bench (? i'm not sure of the word)?

You're right it is called a bench test. As you note there weren't a lot of two stage Merlins around at that time it would be interesting to find out what they were testing. The Merlin 60 had the Kestel style block which wouldn't be amenable to high pressure

 

[PAT303]

In contrast the V-1710 used a downdraft carb, with air entering from the top, and so the air going to the carb had a ways to go to get there - and filters could be installed in that intake duct. Both the P-40M/N and P-51A had provisions for air filters and the Merlin Mustangs continued that feature when they had to move the intake duct to the bottom of the cowl.

The MkIX got a decent air filter arrangement, http://www.spitfireperformance.com/packard266-engine-installation.jpg unfortunately the MkV was the ugly princess that could almost be called a flying test bed for all the new equipment coming online as well as the different theaters and environments it would be used in.

 

[Shortround6]

If that is reflective of the conditions of the test then the p-40 was flying at restricted power ratings as well, 43 to 46 in of Mercury. So that would mean that both aircraft were flying below their highest power ratings.

This is quite true.

However the four combats listed in the document take place at

1. 20.000ft, about 1000ft under the book FTH of the Merlin 46(I don't know what the filter and tropical heat do to the FTH) and thousands of feet above the FTH of the P-40E.
Little or no change to the power available even if both engines are allowed higher boost, the superchargers won't deliver it at that altitude (well, maybe the Melrn 46 might get a few percent).

2. 16,000ft, two combats of the four. At this altitude the Merlin is in a quandary. at the 9lb limit power is down to about 1060hp (no ram, no filter effect, no tropical temperature. ) while at a 16lb limit it would have 1350hp (?) under the ideal conditions. (and less, the 16 lbs boost, FTH for 16lbs being 14,5000ft).
For the P-40E there is little or no change even if the boost limit was changed. It is at or above it's FTH and there is no more boost to be had. Manuals and books listing the altitude for the -39 engine in the P-40E are all over the place in regards to the altitude at which the engine could make 1150hp. From under 12,000ft to 15,000 feet depending on manifold, backfire screens and if RAM is counted or not.
Both combats descended into four digit altitudes, at the 9lb rating the Merlin 46 just gets weaker. At 8,000ft the Merlin 46 is under 1000hp at this boost limit. The -39 engine will get a bit stronger as the altitude drops from 16,000ft to that 12-15,000ft range and then start to fall off (but not as quickly as the Merlin) as the altitude goes even lower, however it should have a power advantage over the 9lb Merlin 46.
The Allison, if allowed higher boost, will start getting stronger as the altitude decreases below it's FTH and by 8,000ft will have a couple of hundred HP advantage of the Merlin at 9lbs. But the Merlin 46 will have more power at 8,000ft if allowed to use the 16lb limit.

3, the 13,000ft combat. means the P-40E is starting pretty much at FTH, the Merlin 46 is at just over 1000hp so the P-40E has about a 120-130 advantage which it keeps all the way down if both keep to the lower boost levels. If allowed higher boost the P-40E just keeps getting better down to 4-5000ft. If the Merlin is allowed 16lbs of boost the P-40 will make more power somewhere around 7,000ft (?) and is much better at the lower altitudes.

Please note that a Merlin 45 (regular) is around 85-100hp more powerful than the Merlin 46 at the lower altitudes.

Basicly the P-40E gets very little boost in power until about 10,000ft (1200hp) and by 8,000ft it is about 1300hp.

For low level combat (under 8,000ft) the Boosted P-40 gets a considerable advantage but MK V Spit is going to show a very large advantage is allowed to use higher boost in the 5 digit altitudes.

 

[varsity07840]

23rd Fighter group had mostly P-40E and P-40Ks. Most of their Aces flew P-40K, according to the Osprey book.

Some of the P-40E and Ks sent to China went to Chinese units (Chinese American composite group squadrons, 3rd and 5th FG), some went to India to the US 51st FG, and a few apparently to the 81st FG though maybe after already being used by the 23rd.

The 23rd and 51st FGs were flying P-40Ms and P-40Ns through much of 1944.

 

[Schweik]

This is quite true.

However the four combats listed in the document take place at

1. 20.000ft, about 1000ft under the book FTH of the Merlin 46(I don't know what the filter and tropical heat do to the FTH) and thousands of feet above the FTH of the P-40E.
Little or no change to the power available even if both engines are allowed higher boost, the superchargers won't deliver it at that altitude (well, maybe the Melrn 46 might get a few percent).

2. 16,000ft, two combats of the four. At this altitude the Merlin is in a quandary. at the 9lb limit power is down to about 1060hp (no ram, no filter effect, no tropical temperature. ) while at a 16lb limit it would have 1350hp (?) under the ideal conditions. (and less, the 16 lbs boost, FTH for 16lbs being 14,5000ft).
For the P-40E there is little or no change even if the boost limit was changed. It is at or above it's FTH and there is no more boost to be had. Manuals and books listing the altitude for the -39 engine in the P-40E are all over the place in regards to the altitude at which the engine could make 1150hp. From under 12,000ft to 15,000 feet depending on manifold, backfire screens and if RAM is counted or not.
Both combats descended into four digit altitudes, at the 9lb rating the Merlin 46 just gets weaker. At 8,000ft the Merlin 46 is under 1000hp at this boost limit. The -39 engine will get a bit stronger as the altitude drops from 16,000ft to that 12-15,000ft range and then start to fall off (but not as quickly as the Merlin) as the altitude goes even lower, however it should have a power advantage over the 9lb Merlin 46.
The Allison, if allowed higher boost, will start getting stronger as the altitude decreases below it's FTH and by 8,000ft will have a couple of hundred HP advantage of the Merlin at 9lbs. But the Merlin 46 will have more power at 8,000ft if allowed to use the 16lb limit.

3, the 13,000ft combat. means the P-40E is starting pretty much at FTH, the Merlin 46 is at just over 1000hp so the P-40E has about a 120-130 advantage which it keeps all the way down if both keep to the lower boost levels. If allowed higher boost the P-40E just keeps getting better down to 4-5000ft. If the Merlin is allowed 16lbs of boost the P-40 will make more power somewhere around 7,000ft (?) and is much better at the lower altitudes.

Please note that a Merlin 45 (regular) is around 85-100hp more powerful than the Merlin 46 at the lower altitudes.

Basicly the P-40E gets very little boost in power until about 10,000ft (1200hp) and by 8,000ft it is about 1300hp.

For low level combat (under 8,000ft) the Boosted P-40 gets a considerable advantage but MK V Spit is going to show a very large advantage is allowed to use higher boost in the 5 digit altitudes.

Yeah I think you're right, the advantage that would be gained by using higher boost would break down differently by altitude between the two planes, and the p-40 would have much more of an advantage below 8000 feet whereas the Spit would have a higher critical altitude with boost and would still own the fight at 20k ft. And that would match the real world situation of course and I think they both did have significant advantages with boost.

But I don't think that it therefore follows that if the spitfire did the test that + 12 boost or + 14 and the P-40E was doing the test at 57 in of mercury that would mean that the spitfire would have a much bigger advantage in general or that the test would have come out different. Similarly if the boost went all the way to + 16 / 60 or 65 in.

I also suspect that a P-40L would have done pretty well in this test regardless of what boost levels were stipulated. But of course so would a Spit VIII or Spit IX (probably quite a bit more so).

 

[Mike Williams]

If that is reflective of the conditions of the test then the p-40 was flying at restricted power ratings as well, 43 to 46 in of Mercury. So that would mean that both aircraft were flying below their highest power ratings.

+9 lbs boost for the Spitfire and +44" Hg. for the P-40E may be what the authorities at the Australian testing establishments thought those aircraft should be operating at during 1942-43 period. I've no idea what powers the operational units used in the field.

Looking at a couple of reports from Australia gives some context to the Comparitive Tests:
Kittyhawk Trials, Report No. F.8
Performance of Spitfire Vc - Tropicalized Version, C.S.I.R. Report F.12/1
Report on Comparitive Tests Capstan v. Kittyhawk (P40E)

Charts out about like so:

 

[BobB]

RAAF pilot Nat Gould said that he never loved the Kittyhawk the way that he loved the Spitfire but that it brought him home with damage that would have destroyed a Spitfire and that the Spitfire simply couldn't have done the job in New Guinea due to its short range.

 

[Schweik]

The 23rd and 51st FGs were flying P-40Ms and P-40Ns through much of 1944.

They only had a few P-40M, those were intended for export primarily, though they did get some through I don't know what path. P-40N did arrive in 1944 but by then they (23rd) were transitioning to Mustangs, and they were also still flying some K model fighters.

These pics are from the Osprey book on the 23rd Fighter Group. Notice the preponderance of P-40K'sm The majority of Aces flying for the group flew the P-40K.

 

[Schweik]

The 23rd and 51st FGs were flying P-40Ms and P-40Ns through much of 1944.

+9 lbs boost for the Spitfire and +44" Hg. for the P-40E may be what the authorities at the Australian testing establishments thought those aircraft should be operating at during 1942-43 period. I've no idea what powers the operational units used in the field.

Looking at a couple of reports from Australia gives some context to the Comparitive Tests:
Kittyhawk Trials, Report No. F.8
Performance of Spitfire Vc - Tropicalized Version, C.S.I.R. Report F.12/1
Report on Comparitive Tests Capstan v. Kittyhawk (P40E)

Charts out about like so:

View attachment 589479View attachment 589480

That is pretty eye opening.

 

[overbeck]

The RAAF didn't raise the boost pressure until February 1943, and only to 12psi, all RAF Merlin 45 and 46's had been cleared for 16 psi in July 1942.

Temperature is the likely reason for lower limits in Australia. The attached test (from https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093190.pdf) is for an Allison with 6:1 compression and 9.6:1 blower gears, but the Merlin would be affected similarly. Knock occurs at 16 lbs boost at 60°F vs 11 lbs at 120°F. The mean in Darwin is 90°F, so maybe around 11.5 13.5 lbs for the Allison, less for the Merlin.

 

[Mike Williams]

I got curious as to how typical the Australian test results were so had a look at other P-40E and Kittyhawk tests. The operational limitations of the V-1710 F3R engines which obtained at the time of the tests were generally 42" Hg., 3000 R.P.M. maximum for all out level or Military with the exception of the Australian test which was 44" Hg. The Australian P-40E performance doesn't look too bad in this context.

 

[PAT303]

Temperature is the likely reason for lower limits in Australia. The attached test (from https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093190.pdf) is for an Allison with 6:1 compression and 9.6:1 blower gears, but the Merlin would be affected similarly. Knock occurs at 16 lbs boost at 60°F vs 11 lbs at 120°F. The mean in Darwin is 90°F, so maybe around 11.5 13.5 lbs for the Allison, less for the Merlin.

How were African/Mediterranean Spits able to run higher boost?, all RAF MkV's were cleared for 16 psi by August '42, all Australian Merlin 46's were cleared for 12 psi in Feb '43.

 

[P-39 Expert]

Interestingly this chart for the Merlin 46 & 47 dated 27 March 1942 shows the +12 take off rating as well as the +16 Emergency rating.

View attachment 589238

These un-dated Operational Notes for Pilots on Merlin 46 Engines show the +12 take-off and climb rating.

Those figures are with ram, right?

 

[overbeck]

How were African/Mediterranean Spits able to run higher boost?, all RAF MkV's were cleared for 16 psi by August '42, all Australian Merlin 46's were cleared for 12 psi in Feb '43.

North Africa is not tropical, for example Tobruk is 32°N, while Darwin is 12.5° S and usually hotter than Tobruk. Also cloud formation lowers the rate at which temperature falls with altitude, and that's much more common in Darwin. However, Merlins would have been running a bit harder in Africa/Med too than northern Europe. I guess not enough for the RAF to care about.

The RAAF only raised limits to 12 psi after the RAF raised theirs to 16, so were always 4 psi below. It's possible they didn't factor in temperature and were just being conservative because very long supply line.

 

[Mike Williams]

The RAAF only raised limits to 12 psi after the RAF raised theirs to 16, so were always 4 psi below.

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.

The RAAF didn't raise the boost pressure until February 1943, and only to 12psi, all RAF Merlin 45 and 46's had been cleared for 16 psi in July 1942.

What sources did you guys use that support your statements related to dates and amount of boost? Thanks.

 

[Mike Williams]

Those figures are with ram, right?

The Merlin 46 & 47 chart shows max all-out level conditions, etc.