Sentinenal28a. Your source is incomplete.Let me start with a post from  a Alison web site:

The few turbo-supercharged Allisons that were made, were allocated to P-38s..., making the high-altitude performance of that plane its best feature. All 14,000 P-40s got gear-driven superchargers, and as a result, were never first-class fighter planes. Donaldson R. Berlin, the P-40's ...designer, has said that P-40s ...experimentally equipped with turbo-superchargers outperformed Spitfires ...and Messerschmitts ...and that if it had been given the engine it was designed for, the P-40 ...would have been the greatest fighter of its era. This may be to some extent the bias of a proud parent, but there is no doubt that the deletion of the turbo-supercharger ruined the P-39 ....

 

Next: I will refer you to copies of the Allison P40B/C power charts complete with supercharger blower and gear compression ratios:

 

Note the supercharger type and actual performance data.

 

 

 

 

 

 

 

Since the P39 and the P40 have the exact same engine are about the same size weight and wing loading, why is there such a difference in the type's combat records?

 

Answer:  ?

 

 

Rocky:

 

Russians seem to love P-39 a lot, to the degree that they made contract with Bell to produce P-63. 

 

Herald:

 

I don't know. Inline engines were killed due to jet engines. Otherwise, fighter with inline engines do have higher speed in general. Bearcat is slower than Mustang. The problem with V-1710 is that USAAF never fund a project to develop high performance two-stage, two-speed superchargers, while the turbosupercharger used is optimized to R-2800 and other radial engines. When, later in the war, V-1710 did got two-stage superchargers, it performs only slightly inferior to Merlin despite pretty un-optimized work.

 

What USAAF should have done is to have Plan B funded for two-stage superchargers just in case turbosupercharger fail.

Short comment. Each nation develops a "fighting style"  I submit that the P-39 was well suited to the Russians'  tactical air support style because they wanted an aircraft that could not only fight enemy aircraft at low to medium altitude but also provide some "Sturmovik" like support.

Engine cooling with a fluid evaporator or a refrigerant cycler as opposed to a direct heat radiator means that you can operate at theoretically higher engine temperatures. The only problem I see with your thesis is that the radials were headed into the same materials and physics revolution we have today where we use forced black-body cooling.for direct radiant cooling. Failing the jet revolution, we would have used our high temperature alloys knowledge to prooduce the radials we needed. Most aviation piston engines today are air cooled boxers. Why?      

www.wwiiaircraftperformance.org/p-38/p-38-wayne.html

 

 [quote]

 As it turned out, exhaust thrust was very important. Approximately one-third of the heat energy produced by a piston engine is available for useful work, the rest is wasted! A well-designed jet (ejector) exhaust system can capture a considerable amount of this energy, and can easily increase rated horsepower by 10 per-cent or more. At 25,000 feet a 400-mph airplane could expect a gain of around 20-25 mph? and it cost almost nothing.

[unquote]

Some interesting stuff:








This is the only source about jet ejector. If jet ejector can provide such amount of thrust, then why bother with turbocharger at all?

It didn't work in the Camproni. Plus Frank Whittle came along......

 

 

There was nothing wrong with the P-39's engine--it was that the airframe was too small for everything else done to it, like heavy armament, armor plate, wing guns, etc.  After the Materiel Division was done with it, the P-39 went from being a sporty, unstable little fighter to a dog.

 

I don't have an answer for you on the P-40--I'm just passing on what Perret wrote.

Speed comparisons of the P51 and F8F aren't quite so simple.  The F8F was actually equal in speed to the P-51D from sea level to 20k ft.  Only above that height did the Mustang have an advantage.  On the other hand, the Bearcat's rate of climb made the P-51 look sick.  As the two a/c had nearly indentical empty weights, with slightly greater wing area on the Grumman, and both used two-stage, two-speed blowers, it came down to the fact that the Bearcat's intended critical altitude was 19,700 ft and the Mustang's was 25,000.
Similarly, the F4U-1A was half a ton heavier, empty, than a P-51D and had much greater wing area (314 sq. ft. vs 233).  But the Corsair was actually FASTER than the Mustang from sl to 16K ft, and roughly equal in speed to 24K., with superior climb up to 24K and equal climb rate above that and better turn rate and agility (pitch and roll rates) at all atlitudes.  The Marines deliberately tested the two against each other and concluded that the Corsair was a better fighter "UNLESS MOST COMBATS ARE EXPECTED TO OCCUR ABOVE 24 THOUSAND FEET."
Trying to compare different designs for performance involves much more than what type of engine drove them.  The Bearcat and Mustang are about as close as you're likely to get, but even there, too many design decisions were made differently.