P-39 vs P-40

[Colin1]

I'm curious, how did the weight go up after removing the supercharger and putting in a smaller engine? Did the "improved" model include armor and self-sealing fuel tanks?

Even more curiously
it was rolled out with no armament and still didn't have one by Jan40, no mention of where the extra weight was coming from.

As a final note to the wind-tunnel testing carried out by NACA, one NACA official said on satisfactory completion of the tests "We have eliminated a million and one aerodynamic problems by removal of the turbocharger"

... and left it with one big one

 

[Marshall_Stack]

Even more curiously

As a final note to the wind-tunnel testing carried out by NACA, one NACA official said on satisfactory completion of the tests "We have elmininated a million and one aerodynamic problems by removal of the turbocharger"

... and left it with one big one

They should have put that official in a castrated P-39 up in the air with Zeroes over the Solomon Islands.

I have also read that Mr. Bell (Larry?) tried to persuade the USAAF to keep the turbocharger but didn't press the point since his company needed the money. It would have been nice if he continued testing / developing a model with the turbo on his own dime. Easy for me to say of course.

 

[Colin1]

I have also read that Mr. Bell (Larry?) tried to persuade the USAAF to keep the turbocharger but didn't press the point since his company needed the money. It would have been nice if he continued testing/developing a model with the turbo on his own dime

Larry Bell ran his company a damn sight more conscientiously than Vaughn did Curtiss-Wright but he was nonetheless more bean-counter than engineer.

The P-39 really was a victim of 30s USAAC doctrine, bombers were regarded as the primary force in aviation, modest demands were placed on fighter design; the idea that fighters would routinely partake in high-altitude combat was not envisaged.

It wasn't just Bell, both Curtiss-Wright and Allison were ploughing ahead with their myopic, blinkered vision of what made a great fighter, completely lacking in adequate supercharging and no-one, not in the industry or the military found it remarkable. Allison, though a small company at the time (a division of General Motors) would not have come up with an engine so rigidly constrained by the standardised intregral mechanical power section if they hadn't believed they were on the proper course.

The Army eventually dropped its requirement for the turbocharger and even Bell saw this as a good move, solely for financial reasons; there was no hesitation in deleting the requirement from the planning or development process. The Army's outmoded views on fighter requirements had more or less infected the industry across the board and this would come back to hurt the USAAC in the early years of the war.

It's a great shame because the turbocharged P-39 would have been a match for the A6M and Bf109 at any altitude, in any climate or on any day of the week. Bell, Allison and the USAAC made the P-39 the mediocre fighter that it was but it was no different to events being played out a few hundred miles away where Curtiss-Wright were busy emasculating the P-40.

 

[Njaco]

Could also be that Soviets flew ops at a lower altitude than Western Front pilots and the P-39 handled better at those heights.

 

[gjs238]

where Curtiss-Wright were busy emasculating the P-40.

How so?

 

[gjs238]

It's a great shame because the turbocharged P-39 would have been a match for the A6M and Bf109 at any altitude, in any climate or on any day of the week.

Would it really have been?
Is it possible the NACA changes to the XP-39 improved low/medium level performance?
(not making an argument, just a question)

 

[gjs238]

Bell, Allison and the USAAC made the P-39 the mediocre fighter that it was

Allison?
Was the Allison supercharger design so out of touch with other contemporary designs?

Later on, yes - but in 1939?
How did DB600 and RR Merlin superchargers compare in 1939?

 

[Juha]

Hello Njaco
Normally aircombats over Eastern Front were fought under 5000 meters, most clearly lower.

Juha

 

[Juha]

Marshall_Stack
self-sealing fuel tanks were introduced later, first to have them was P-39D.

Juha

 

[Juha]

Hello
what Colin1 wrote
Quote:"firstly, when the P-39 was being designed, US turbochargers weren't that reliable..."

might well explane why P-38 had turbo but P-39 and P-40 didn't. It would not be surprising if USAAF. while thinking that most of fighter job would be at low and medium level and so no need for turbo to all fighters there might be some need to high altitude capacity, so they decided to keep turbo in one type and because of reliability problems still around put them in twin engined fighter.

Juha

 

[gjs238]

It would not be surprising if USAAF. while thinking that most of fighter job would be at low and medium level and so no need for turbo to all fighters there might be some need to high altitude capacity, so they decided to keep turbo in one type and because of reliability problems still around put them in twin engined fighter.

The P-40 was not designed for a turbocharger and never had one to remove.
The XP-39 changes by NACA seem to be limited to aerodynamic streamlining, not other issues.

Turbo equipped planes could be optionally produced sans turbo, such as the P-38's that were sold to Great Britain pre-Pearl Harbor.

 

[Juha]

Hello gjs
Quote:"The P-40 was not designed for a turbocharger and never had one to remove."

I knew that

Juha

 

[davebender]

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF. Look at the cost to develop the B-29. A fraction of that money would have provided every Allison engine with a decent supercharger or turbocharger.

 

[gjs238]

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF. Look at the cost to develop the B-29. A fraction of that money would have provided every Allison engine with a decent supercharger or turbocharger.

Academically, that statement is true.
But is that the reason the P-40 didn't have a turbo and the turbo was stripped from the P-39?

I suspect it wasn't an issue of funding or availability, but HOW to make it work.
How would one turbocharge the P-40?
The little I've read indicates that NACA stripped the turbo from the P-39 as one of many aerodynamic streamlining recommendations.

 

[claidemore]

Heavy bombers had priority for the U.S. Army Air Corps just as they did for the RAF.

But they did not yet see the necessity for escort fighters. Early in the war they (the US) thought the bombers would be able to protect themselves.

 

[davebender]

There you have it. The U.S. Army Air Corps thought their fighter aircraft would be operating at mostly low altitude. So why spend the money putting a decent supercharger / turbocharger on the Allison engine?

 

[gjs238]

There you have it. The U.S. Army Air Corps thought their fighter aircraft would be operating at mostly low altitude. So why spend the money putting a decent supercharger / turbocharger on the Allison engine?

Something is wrong with this...

So the Army issued Circular Proposal X-608 for a high-altitude interceptor aircraft having "the tactical mission of interception and attack of hostile aircraft at high altitude."
The result was the P-38 (which required TWO turbochargers.)

The Army also issues Circular Proposal X-609, a similar single-engine proposal.
The result was the P-39.
Both proposals required liquid-cooled Allison V-1710 engines with turbo superchargers.

Then the P-43 was developed, and fielded, with a turbo supercharger.

The P-43 morphed into the P-47, famous for its turbo supercharger.

Yet, the Army decides for reasons speculated in earlier posts to remove the turbo supercharger from the P-39?
I still strongly suspect is was NACA and the reasons were aerodynamic.

 

[gjs238]

That's right, but they were very keen on interceptors.

 

[gjs238]

Why did the P-39 perform, or seem to perform, so much more poorly than the P-40 - particularly in the early war years?

Both were V-1710 powered, sans turbocharger with single stage/single speed supercharger.

I know the P-39 had short endurance.
But what else?

Getting back to where this thread started...

 

[fastmongrel]

Did they ever try to fit a Merlin engine into the P39. The low level rated Merlin 24 engine with 1600 hp could have made it into a pretty rapid fighter.