Spitfire V Versus P-40E

Schweik · Jul 24, 2020

Mike Williams said:
Googled this P-40K specific engine flight chart that shows 60" emergency boost.

View attachment 589607

Well done! I tried googling that & found zip.

Schweik · Jul 25, 2020

So how fast is a P-40 with 1550 hp?

Kevin J · Jul 25, 2020

Schweik said:
So how fast is a P-40 with 1550 hp?

If an A-36 did AFAIK 344 at sea level, 364 at both 5000 and 15000 feet then surely if a P-40K does 362 at 15000 feet then it should do 362 at 5000 and 342 at sea level. Clean condition, take off 12 for in the field. Spitfire LF VC Merlin 55M did 331 at sea level, 358 at 5900 so closely matched at similar powers.

Schweik · Jul 25, 2020

I don't know about that. A-36 was far better streamlined I think. Pseudo-laminar flow wings etc.

Kevin J · Jul 25, 2020

Schweik said:
I don't know about that. A-36 was far better streamlined I think. Pseudo-laminar flow wings etc.

Agreed, except the A-36 had bomb racks and dive brakes. So let's say that costs 20 mph. P-51 does 382 mph P-40E 362 mph. Ipso facto the speed gap is now closed. P-51A does 378/409 mph, fasted P-40N, 378 mph, same armament, speed gap opened again.

Schweik · Jul 25, 2020

It's a reasonable speculation but it's still conjecture. I'd love to see a speed test they must have done one.

How many other early- to mid-war fighters could do over 300 miles an hour down at sea level?

Kevin J · Jul 25, 2020

Schweik said:
It's a reasonable speculation but it's still conjecture. I'd love to see a speed test they must have done one.

How many other early- to mid-war fighters could do over 300 miles an hour down at sea level?

The Whirlwind, Spitfire, Typhoon in the RAF.

Schweik · Jul 25, 2020

LF model or spit 8/ 9 or later though right?

Kevin J · Jul 25, 2020

Schweik said:
LF model or spit 8/ 9 or later though right?

Spitfire I: 12 lbs boost, 305 mph; 16 lbs boost, 319 mph? Rolls Royce mod'd a Whirlwind, under engine radiators, 362 mph; Whirlwind on 100 octane, 329 mph IIRC.

Schweik · Jul 25, 2020

I had somehow missed this before, but this is the highest performance (speed) I've seen on an official test for the P-40F. This is a 6 gun P-40F full fuel, but no ammunition. Test was April 1943.

Top speed at 18,000 ft was 374 mph without the belly tank sway braces, 369.5 with the sway braces.

http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13635_FS-M-19-1578-A.pdf

Schweik · Jul 25, 2020

Kevin J said:
Spitfire I: 12 lbs boost, 305 mph; 16 lbs boost, 319 mph? Rolls Royce mod'd a Whirlwind, under engine radiators, 362 mph; Whirlwind on 100 octane, 329 mph IIRC.

Whirlwind was a damn beast down low. I was just reading the Tempest V had 376 mph at Sea level that's incredible. But Whirlwind was right at the beginning. I know I got shouted down for saying this before but they should have kept that project going.

One chart for the Beaufighter VI shows 312 mph at 4,000 ft so it's probably up around 300 mph in speed at Sea level, which helps explain how it survived combat with single engined fighters down low.

Looks like 109E-3 was around 270-290 mph at Sea Level
I couldn't find any specific chart on the 109F
109G could do 310-320 mph at Sea Level depending on a variety of factors.

A6M2 was ~ 270 mph at Sea Level and broke 300 mph at 6,000 ft
A6M5 was about 295 mph at Sea Level at WEP
Ki-43 was about 290 mph at Sea Level with WEP

PAT303 · Jul 26, 2020

Schweik said:
I don't know about that. A-36 was far better streamlined I think. Pseudo-laminar flow wings etc.

Remember too that you sacrifice speed to gain in other area's, the Hispano cannon barrels cost the Spit about 7 mph but each hit with the power equivalent to three .50 brownings, the Mustang lost speed changing from the birds cage to the Malcolm hood, then the bubble canopy but pilots aren't going to complain about the better visibility.

Mike Williams · Jul 26, 2020

I'm uncertain how useful this comparison is. Different P-40 variants with different engines, conditions and engine powers. It shows quite a range of performance obtained during testing if nothing else.

Schweik · Jul 26, 2020

There is another data point on the P-40F or L from the RAF in Sept 1942 here, giving speeds at two altitudes

http://www.wwiiaircraftperformance.org/P-40/Kittyhawk_II_performance_9sept42.jpg

Schweik · Jul 27, 2020

Could you add those last two data points to the chart? I think it would make a short line...

Conslaw · Jul 30, 2020

Kevin J said:
Spitfire I: 12 lbs boost, 305 mph; 16 lbs boost, 319 mph? Rolls Royce mod'd a Whirlwind, under engine radiators, 362 mph; Whirlwind on 100 octane, 329 mph IIRC.

Perhaps someone can clarify something. The converter that I found online equates 16 lbs/sq.inch to only 33 inches of mercury. 33 inches of mercury isn't much at all. Am I missing something?

Schweik · Jul 30, 2020

Conslaw said:
Perhaps someone can clarify something. The converter that I found online equates 16 lbs/sq.inch to only 33 inches of mercury. 33 inches of mercury isn't much at all. Am I missing something?

Yes that's wrong. It's not a direct conversion as IIRC boost and manifold pressure are measured at different stages of the supercharging process

wuzak · Jul 30, 2020

Conslaw said:
Perhaps someone can clarify something. The converter that I found online equates 16 lbs/sq.inch to only 33 inches of mercury. 33 inches of mercury isn't much at all. Am I missing something?

The British system used boost pressure above standard sea level pressure.

It is usually indicated by the plus (+) or minus (-) sign in front of the boost number. +16psi boost is 30.7psi absolute pressure.

So the MAp of +16psi is ~62.5inHg.

Todd Secrest · Jul 30, 2020

What was the cost to manufacture the Allison V-12 vs the Merlin V-12?
I heard the Merlin used almost twice as many parts, compared to the Allison?

pbehn · Jul 30, 2020

Todd Secrest said:
What was the cost to manufacture the Allison V-12 vs the Merlin V-12?
I heard the Merlin used almost twice as many parts, compared to the Allison?

The answer comes out as "how long is a piece of string". Merlins from Glasgow were probably extraordinarily cheap as far as payment to RR goes, once the government had built the factory, put all the tools in, built the workers houses and recruited the workforce that they also guaranteed payment and work for one way or another.

Spitfire V Versus P-40E

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