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

[Schweik]

No doubt, in Boscombe Down they seemed to be just as reluctant to use high power settings on P-40s as they were with Spit V's in Australia In the Desert and the Jungle they also seemed to be quicker to strip parts and guns, in addition to adding things like bomb racks.

But from what I gather, humidity and temperature certainly do affect performance and IIRC at least one of those Australian tests was intentionally done on a hot day.

IIRC there is a theory that both the F2A and the P-39 performed better in cold weather. Maybe that's true for the Hurri and the Spit too.

 

[Hop]

British tests usually corrected figures to standard atmospheric conditions. The Australian tests I have seen, including the test of the tropicalised Spitfire V with and without drop tanks, did so as well.

The Australian test of the clean Vc produced a speed of 334 mph at 15,000 at 3000 rpm, 9 lbs boost, and a maximum speed of 365 mph at 22,000 ft at the same rating. The test of Spitfire V AA878 in the UK found a speed increase of 35 mph below full throttle height when going from 9 lbs to 16 lbs boost, with the full throttle height falling by nearly 7,000 ft.

 

[Greyman]

We really need to try to compare like to like as a lot of things are not adding up.

From another thread. In the interest of like-with-like ...

All things being equal here is a quick sketch based on figures from (for the most part) the Ministry of Aircraft Production. Perhaps not 100% useful for what actual aircraft would do, but a good indicator of how the changes in engine/equipment will effect performance.

Spitfire V - Merlin 45 - temperate
Spitfire V - Merlin 46 - temperate
Spitfire V - Merlin 45 - tropical

Thicker lines are full throttle/+16 boost, thin lines are +9 boost

 

[Schweik]

British tests usually corrected figures to standard atmospheric conditions. The Australian tests I have seen, including the test of the tropicalised Spitfire V with and without drop tanks, did so as well.

The Australian test of the clean Vc produced a speed of 334 mph at 15,000 at 3000 rpm, 9 lbs boost, and a maximum speed of 365 mph at 22,000 ft at the same rating. The test of Spitfire V AA878 in the UK found a speed increase of 35 mph below full throttle height when going from 9 lbs to 16 lbs boost, with the full throttle height falling by nearly 7,000 ft.

Some problems you can't always correct for with a little math, for example in this Oct 1941 test

http://www.wwiiaircraftperformance.org/P-40/PHQ-M-19-1307-A.pdf

...where they mentioned that with the Hurricane "sustained high power climb cannot be made in warm weather due to excessive coolant temperatures."

They also noted that the Hurricane could not catch a B-25, B-26 or A-20A in level flight. Also perhaps due to the weather? I would expect a Hurricane should be able to catch a B-25 at least.

 

[pinsog]

Some problems you can't always correct for with a little math, for example in this Oct 1941 test

http://www.wwiiaircraftperformance.org/P-40/PHQ-M-19-1307-A.pdf

...where they mentioned that with the Hurricane "sustained high power climb cannot be made in warm weather due to excessive coolant temperatures."

They also noted that the Hurricane could not catch a B-25, B-26 or A-20A in level flight. Also perhaps due to the weather? I would expect a Hurricane should be able to catch a B-25 at least.

Anyone notice that the Hurricane only slightly outturns the SBD? Might explain SBD's being able to at least defend themselves (when bombless) against Zero's.

Could the reason the B25 is faster in this test is because it was an early version that was lighter without all the heavy defensive armament and armor of the later models? Same with B17C? (Although later models could still do 300+ at 25,000 if lightly loaded)

 

[PAT303]

Sorry, the idea that the RAAF was handicaped by the Merlin 46 vs the Merlin 45 does not hold up. Too many of the comparisons use the wrong altitudes for comparing power or the wrong boost limits. Why the Australians were limiting the boost to 9lbs is a question that doesn't seem to be answered. The Merlin 45,46 and 47 had all been cleared to use 60 1/2 inches ( 15lbs ? boost ) in Jan 1942

All fighter command Merlin 45/46/47's were cleared for 3,000rpm and 16lbs boost in August 1942, the RAAF cleared it's Merlin 46's for 12lbs boost in February 1943.

 

[pinsog]

Some problems you can't always correct for with a little math, for example in this Oct 1941 test

http://www.wwiiaircraftperformance.org/P-40/PHQ-M-19-1307-A.pdf

...where they mentioned that with the Hurricane "sustained high power climb cannot be made in warm weather due to excessive coolant temperatures."

They also noted that the Hurricane could not catch a B-25, B-26 or A-20A in level flight. Also perhaps due to the weather? I would expect a Hurricane should be able to catch a B-25 at least.

Also notice the Spitfire had worse visibility than any of the other fighters including the P38. We all get hung up on an extra 10 mph top speed or 200 fpm rate of climb but you can't avoid them if you can't see them. The Spitfire was difficult to see out of, the view out of the Zero was like sitting in a chair in your driveway.

 

[RCAFson]

Anyone notice that the Hurricane only slightly outturns the SBD? Might explain SBD's being able to at least defend themselves (when bombless) against Zero's.

Could the reason the B25 is faster in this test is because it was an early version that was lighter without all the heavy defensive armament and armor of the later models? Same with B17C? (Although later models could still do 300+ at 25,000 if lightly loaded)

I don't see any reference to the Hurricane having trouble catching the A-24.

Regarding the other bombers, it might have been necessary for the Hurricane to use overboost but it also seems likely that the bombers themselves were somewhat lighter and faster than the variants used in actual combat since the speed recorded for the Hurricane II in USAAC testing should be sufficient to overtake any of the bombers:
http://www.wwiiaircraftperformance.org/hurricane/Hurricane_II_Z-2974_Level.pdf

 

[pinsog]

I don't see any reference to the Hurricane having trouble catching the A-24.

Regarding the other bombers, it might have been necessary for the Hurricane to use overboost but it also seems likely that the bombers themselves were somewhat lighter and faster than the variants used in actual combat since the speed recorded for the Hurricane II in USAAC testing should be sufficient to overtake any of the bombers:
http://www.wwiiaircraftperformance.org/hurricane/Hurricane_II_Z-2974_Level.pdf

No trouble catching A24 (SBD), but it only slightly outturns it.

Says in the test the Hurricane couldn't catch them. For the B17C thats no surprise since I think it did about 315 mph at 25,000 feet. The A20 would do 349 mph at 12,000 feet and I think 333 at 5,000 feet so that isn't a surprise either. B26 was fast down low as was the early unarmored and lightly armed B25.

 

[pinsog]

A20 test late 1941

 

[Greyman]

Anyone know of a good resource where I can see all of the US engine designations and their export designations? I'm constantly foiled by this.

Looking at Boston/Havoc tests at the A&AEE the bomber has about 18 mph on the Hurricane II at 10,000 ft. And maybe 30 mph under 5,000 ft. due to the lower gear.
These are on Bostons/Havocs without flame dampers on. With them on they're about equal to the Hurricane II at 10,000.

(This is a +9 boost Hurricane II, not +12 or +16).

The US test above is about 15-20 mph faster than the fastest examples the A&AEE tested. This seems to happen all the time, not sure if it's a lack of equipment fitted, different methods of reduction, or what.

 

[RCAFson]

No trouble catching A24 (SBD), but it only slightly outturns it.

.

If we look at the wing loading of an SBD-1, clean 1/2 fuel, we get a weight of ~7600lb and a wing loading of 24.4lb, for the SBD-3 we get ~8600lb and 27.1lb. The corresponding figure for the Hurricane IIa was ~25.2lb so it's not surprising that the turn radius is similar.

 

[Shortround6]

Part of the problem is that sometimes the test/s were done at standardized altitudes (or some in between altitudes are left out?)
a chart that shows speeds at 5,000ft intervals not show the A-20 or B-25 to best advantage? if FTH of the engine was at 12-13,000ft?? and chart shows speed at 10,000ft and 15,000ft?

 

[Shortround6]

Anyone know of a good resource where I can see all of the US engine designations and their export designations? I'm constantly foiled by this.

I don't think there is a single source for this.
However US engines are not quite as bad (confusing) as it might appear. Many of the model numbers for the radials just denote different magnetos or carburetors (without performance change) or another characteristic that affects maintenance and not performance.

however http://www.enginehistory.org/reference.shtml

is a good place to start, specifically Model Designations of U.S.A.F Engines

which does not cover navy engines or commercial.

there are number links further down on the page that cover P & W and Wright radials.

For Wright the most confusing engine is the R-1820

The R-2600 is fairly simple, there are 3 of them that count in WW II (around 100 made pre war?)

The 1600hp A Series
The 1700hp B Series (summer of 1941)
The 1900hp BB Series ( summer of 1943)

each series used pretty much the same supercharger gears (often from series to series) even if the crankcases changed. So military, commercial (?) and export models all were functionally identical. None got water injection, none got a service turbo, none got a service two stage mechanical supercharger. If you have a power curve/chart for a 1600hp R-2600 you pretty much have the power curve/chart for all 1600hp take-off Wright R-2600s. Same for the 1700HP B (or BA) series. All had two speed superchargers using the same gear ratios (at least in any versions produced in more than a handful)

For P&W the R-1830 is the confusing engine. Like the Wright R-1820 the period from around 1938-41 has different model engines (different construction) rated for different fuels (US threw in 90-91 octane in addition to 87 and 100) they used both two speed and single speed superchargers (and sometimes different gear ratios although that was ending at the beginning of WW II) and P&W had the two stage engines and both wound up with turbos. As the war went on things got a bit simpler as the older engines were phased out and fuel was more standardized.

Few, if any, Wright R-3350s were exported during the war.

The P&W R-2800 is a bit tricky but basically you have the A series at 1850hp for take-off (two speed supercharger) which was used in the early B-26 and some shipped off to England to be used in the Warwick. No production single speed,, no production turbo, no production two stage engines.
The B series gets all the variations but the basic engine was good for 2000hp (dry) for take-off. Single speed engines all got turbos which makes things simple.
The C series doesn't show up until 1944 (late) which also keeps most of the war simple.

Hope this helps.

 

[Simon Thomas]

What fuel were the RAAF using during 42-45? Was it from an Australian refinery or was it imported from the US? I doubt any Australian refinery was making 100 octane in 42. Would this have limited the available boost for the Mk V Spitfires?

 

[Kevin J]

What fuel were the RAAF using during 42-45? Was it from an Australian refinery or was it imported from the US? I doubt any Australian refinery was making 100 octane in 42. Would this have limited the available boost for the Mk V Spitfires?

My guess is that the tropical filter has been removed as top speed is stated as 365 mph and Rolls Royce has recommended or prevented the use of override boost. The Seafire IIc with the Merlin 46 was a bit slow too, 280 at sea level, 345 mph at 22,000 feet; no tropical filter either.

 

[Shortround6]

By 1942 the Australians would have been using 100 or 100/130 fuel. The P-40s/P39s needed it. The Merlin would have been limited to 6lbs boost or less with 87 octane, not 9lbs.
Heck, even the Brewster Buffaloes needed 100 octane.

 

[fubar57]

Boulton Pual P.94: Defiant without the turret...Boulton Paul P.94

 

[Schweik]

Boulton Pual P.94: Defiant without the turret...Boulton Paul P.94

"The aircraft would have been powered by the 1,260hp Rolls-Royce Merlin XX engine, which was expected to give it a top speed of 380mph at 23,500ft. "

Wow if that was even close to true it sounds like it might have been a useful addition to the fleet so to speak, instead of making all those Hurricanes. I guess they saw it as competitor to the Spit so they nixed it.

 

[fubar57]

from this site​