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

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I found this in: Ethell's Mustang, a documentary history of the P-51 but then found it on Mike Williams' site:

TACTICAL COMPARISON WITH SPITFIRE IX
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If we look at a Spitfire VII/VIII (especially the HF) we note that the internal fuel comparison is 124IG versus 150IG for the Mustang, and these Spitfires narrow the gap slightly in terms of speed. It would have been interesting to compare the Spitfire XIV with the 90IG slipper tank to the Mustang and to a Mustang with the rear fuselage tank 1/3 full.


Ethell makes it clear that the speed improvement over the Spitfire was due to the Mustang's overall low drag design, especially the wings. He states emphatically that the radiator and cooling design of the Mustang was not a factor and that the Mustang did not benefit from the "Meredith effect".
 
The Slipper Tank Advantage​

Mustang with 2 x 62.5IG DTs:

COMBAT PERFORMANCE WITH LONG-RANGE TANKS
Speed
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Spitfire XIV and 90IG ST:
COMBAT PERFORMANCE WITH 90 GALLON LONG-RANGE TANKS
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So the 90IG ST causes a loss of ~20mph on the Spitfire whereas twin 62.5IG DTs cause a loss of ~45mph on the Mustang.
 
How Mustang Range was Calculated:




This is from Ethell and was drawn from USAAF sources. The stated cruise conditions are not very strenuous. Theoretically a stock Spitfire VIII with a 90IG slipper would have about a 325 mile radius using the above assumptions.
 
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You don't think there is a bit of patriotic chest thumping there?

Comparing parts counts between the Allison and the Merlin has to take into account the fact that Rolls-Royce used a multitude of small fasteners in places where Allison used a smaller number of large fasteners.

Packard Merlins were all 2 speed engines (apart from the experimental -11), compared to most V-1710s which were single speed. That meant extra gears, clutches, shafts, fasteners.

The statement "Just the task of converting all of the measurements from metric imperial to US Standard units was daunting enough" shows that the article is not entirely accurate. They originally stated metric, but changed it to imperial, which means they are saying it was a difficult job for Packard to convert the drawings from inches to inches.
 

In early days nobody had any real fighter combat but had good enough training that fought on near equal terms. Reading about New Guinea and Guadalcanal. We actually did an outstanding job against the Japanese. The P-39 was an effective dive bomber and low altitude fighter. Credited for saving Guadalcanal strafing Japanese positions. They did a lot more than shoot down planes.

Did an evaluation of Pearl Harbor and Philippines. Just a 15 minute warning before Japanese planes struck. Enough of our combat planes would have created a different result. They were trained enough to do substantive damage, just based off what few fighters got off the ground. Battle of Midway was another good example despite losing most of our Fighters. They still caused a good 20+% loss or out of action of Japanese aircraft.

But then again most pilots perished in all countries with a good percentage becoming aces. So the Training process in all countries typically recruited the ones that were quick learners. The Education systems at the time in the US recruited heavily from the Colleges and noted brilliant High School students. In 1940 the US Army became our largest public education system, Navy not far behind. US had the option of bringing back experienced combat pilots back to the states to help the training processes. Something that none of the other combatants had. Japan tried a bit of that with their surviving combat pilots. Biggest issue with the Axis opponents they had little fuel for training but somehow managed to train a good batch of new pilots into competent flyers.

If you read further...and other material....most everything was being moved to SAE standards. Rolls Royce did not want to go that route. Hense since there were no US suppliers to provide them all the fasteners were made in-house at Packard. As for engineers most of us have egos but fascinated how other engineers come up with solutions. US and Brits worked very hard on agreeing to the many upgrades, improvements and changes to the Merlin. Allowing a 1000hp Designed engine to exceed 2000hp. When a upgrade was approved both sides implemented the change. It was amazingly smooth.

In fact Rolls Royce engineers gave Allison some good solutions for their supercharging issues they were having and thumbed their noses up. But that was the Allison Management not the engineers.

The Allison was a much better stronger cost efficient platform than the Merlin...dominated the low mid Altitude combat scene.
 
Dan Fahey said:
If you read further...and other material....most everything was being moved to SAE standards. Rolls Royce did not want to go that route.
Click to expand...

Most everything of what was going to SAE standards? The British aero engine industry before and during WW2?

The fact is that the Merlin was designed in Britain and was in production in Britain prior to Packard making a single Merlin. To change to SAE threads to suit one factory over sevaral others does not seem like a war winning production strategy.

They had to maintain the same fasteners so there was interchangeability with UK built engines.

Packard Merlins for US consumption used SAE spline output shafts to fit with US propellers. UK engines all had SBAC spline output shafts.

Remembering that it was 1942 before Packard started making engiines in any sort of quantity.


Dan Fahey said:
Hense since there were no US suppliers to provide them all the fasteners were made in-house at Packard.
Click to expand...

Yes, they had to make their own fasteners, which I doubt was a big deal.


Dan Fahey said:
US and Brits worked very hard on agreeing to the many upgrades, improvements and changes to the Merlin. Allowing a 1000hp Designed engine to exceed 2000hp. When a upgrade was approved both sides implemented the change. It was amazingly smooth.
Click to expand...

Pretty much all the major upgrades were developed by Rolls-Royce and then implemented across the factories.


Dan Fahey said:
In fact Rolls Royce engineers gave Allison some good solutions for their supercharging issues they were having and thumbed their noses up. But that was the Allison Management not the engineers.
Click to expand...

When did Rolls-Royce engineers have anything to do with Allison? And why would they?


Dan Fahey said:
The Allison was a much better stronger cost efficient platform than the Merlin...dominated the low mid Altitude combat scene.
Click to expand...

Yes, the Allison V-1710 was a good, solid design.

Don't know about it being more "cost efficient" and I doubt it could be claimed that the V-1710 "dominated the low mid Altitude combat scene".
 
Nope.

Miles M20

The Merlin XX was pretty much the same engine as the V-1650-1 used in the P-40F.
Granted shifting 306lbs worth of radiator and coolant to the rear of the plane vs the chin helps balance the longer heavier Merlin 61 engine.

The plane as it stood was slower than a Hurricane II using the same engine, it was a lot slower than the P-40F using the same basic engine.
Wiki says 154 imp gallons of fuel which is not double what the Hurricane carried but a bit over 60% , Wiki could be wrong.
A P-40f carried about 123 IMP gallons of fuel in the internal tanks.

The Miles M 20 was designed so fast because they used a Lancaster (and Beaufighter) "power egg". change the engine and change the radiator location (and add retracting landing gear) and you are changing things considerably.
 
Dan Fahey said:
US and Brits worked very hard on agreeing to the many upgrades, improvements and changes to the Merlin. Allowing a 1000hp Designed engine to exceed 2000hp. When a upgrade was approved both sides implemented the change. It was amazingly smooth.
Click to expand...

Actually RR had a very good idea that the basic engine would survive power in the high teens (1500-1800hp) due to work on the engine for the Speed Spitfire record attempt plane.
That power level was achieved using a special racing fuel but they did it at time when the Allison was lucky to break 1000hp (late 1938 and early 1939)
Yes a few minor tweaks were needed to really get the reliability RR wanted but over 10 hours on the test stand at those power levels and peak output of over 2000hp showed there were no fundamental flaws in the Merlin engine.

It would have been stupid for Packard to try to make the Merlin to SAE standards when the main customer (the British) wanted as much intercanagbility as possible with the British built engines. And indeed in North Africa the British gave the US up to 600 engines (many used) to help the US overhaul the engines in the P-40F & L, something that would not have worked had the engines been built to different standards.
It also would have been stupid for the US to try to redesign the Merlin in 1943 to SAE standards with the hit to production that would have entailed or the problems of setting up 2nd production line with the British still getting British standard engines and the US getting the SAE engines.

Please note that the lead in fuel swapped back and forth just a bit. British using 87 octane (rich number unknown but quite possibly higher than US 87 octane or even 91 octane?)
US went to 100 octane first but the Under 2% aromatic fuel had no rich rating or no improvement in rich response while the British 100 octane not less than 20% aromatic fuel offered the performance of 100/115-120 in the later rating numbers. The US specified a 125 PN number fuel but quickly changed to a joint specification of 100/130 with the British.

It was this fuel that allowed much higher pressures (and temperatures) inside the cylinder that allowed the engines to make so much more power than when they started.
 

What makes you think the radiator doesn't gain from some of the Meredith Effect?

So, you take a Merlin 61 and put it into the Miles M20 and get the speed of a Spitfire V? IX? XIV? I'm going to go with the speed of a Spitfire V.

Meanwhile, you are taking a Merlin 61 away from an actual Spitfire IX.

Where's the advantage in that?
 

Just to add that when Packard were struggling to get the V-1650-3 into volume production in 1943 Rolls-Royce were developing the 65/66 (which would become the V-1650-7 in US production) and by mid 1943 were attempting to run the Merlin 66 at +18psi boost for 100 hours continuously, succeeding in late 1943. This was part of the development of the 100 series, a version of which would become the Packard V-1650-9.

By early 1944 Rolls-Royce were working on the RM.17SM, which was rated at 2,200hp in MS gear and 2,100hp @ 15,000ft in FS gear. Notably this was without ADI, which the V-1650-9 used to get similar ratings. The RM.17SM was flight cleared for 2,380hp.
 
Correction. The M20 had twice the fuel of the Hurricane after take off, climb to height and forming up for combat. The objective is to have in service by 1943 a single seat, single engine fighter escort for the USAAF for the Schweinfurt raids. So first individual exhaust ejectors should bring the speed up to 350-360 mph for the 1941/42 timeframe and 2x 62.5 IG drop tanks should bring range up to 1840 miles. For 1942/43, install Merlin 61/63/66, shift the radiator a la Mustang under the fuselage, 33 IG rear fuel tank, 2x 75 IG underwing drop tanks, range 2210 miles, speed a la Spitfire. So fuel load and performance should be sufficient for Schweinfurt raids. For 1944/45, put second 33 IG fuel tank in rear fuselage, use 90 IG tanks and range goes up to 2650 miles, so Iwo Jima to Tokyo and back so that we can help the Yankees out again as they would never have built the Mustang.
 
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The Canadians build the M20, the Americans end up building the P-38K and the P-40Q.
 
wuzak said:
Still don't know why you'd build the P-40Q. You already have the P-51B/D/H and P-47D/M/N (and the P-38K in your scenario) by that time.
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The Brits by building the M20 have built the perfect army cooperation fighter with its fixed undercarriage so the Mustang never gets built.
 

96G main, 66 or 75G rear, 26G wings, 50 or 90G dropper, fixed.
 
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