P-39 vs P-40

[Marshall_Stack]

I have read in Warren Bodie's book on the P-38 that NACA said that the turbo installation had too much of a drag penalty on the P-39 and that is why it was deleted. I have read other accounts that there was a problem with the turbo on the P-39 and they deleted it because of this trouble.

[Colin1]

Originally Posted by ssnider

...the biggest differance was in reliability. He said that the some part of the P-39 electrical system failed on every mission, and everything was electric...

Throughout its service life, many considered the P-39 to be a maintenance nightmare, largely owing to

not-too-reliable electrical systems
engine-cooling problems
excessive vibration fatigue with the long, geared propeller drive

there were efforts to correct these over the period 1942-44 with mixed results. Alot of the problems could have been nipped in the bud during the design phase but never were.

Lt Winton W 'Bones' Marshall
Las Vegas Army Airfield, Nevada, 1944:

The P-39 had an electric, motor-driven worm gear to raise and lower the landing gear. In the event of an electrical power failure, you had to make endless rotations by hand, of a landing gear crank, to get the gear down. On one occasion with electrical power failure, I had cranked my gear down but the landing gear would not lock in place. So I held the crank handle with all my might on landing to keep it from collapsing.
As the aircraft slowed, the crank and the landing gear started to unwind. I tried to grab it again with my hand but it was going too fast and hard to catch. As I immediately stopped the P-39 on the runway, the gear crank continued to unwind to within an inch of the propeller hitting the runway. My hand was black and blue for a week.

[Colin1]

Originally Posted by gjs238

I doubt this is why NACA removed the turbo from the XP-39

The XP-39B was flown on 25Nov39 and was the XP-39 prototype rebuilt with considerable modification.
Gone was the 1,150hp V-1710-17(E2) B-5 turbocharged powerplant and in came the 'improved' 1,090hp V-1710-37(E5) unit with single-stage integral mechanical supercharger.
The removal of the turbocharger was recorded as necessary for two reasons, firstly, when the P-39 was being designed, US turbochargers weren't that reliable and secondly, NACA noted that the original Airacobra design had numerous lift and drag problems.
The changes made by NACA were done in stages, most were put in place at Langley Field, Virginia and the wind-tunnel tests determined a need for the improvements that were incorporated into the XP-39B. These included:

streamlining and reducing the size of the wheel doors
lowering and streamlining the canopy
moving the carburettor air scoop from the left side of the cockpit to directly behind the cockpit and
moving radiators from the fuselage sides to the central wing-root leading edges

along with a slightly altered fin and an all-up weight increased by about 15%

Top photo: The prototype P-39 (38-326), progenitor of all Airacobras to follow, poses at Wright Field around the time of its 06Apr39 maiden flight. The P-39 had a radiator and oil cooler on its starboard side behind the exhaust outlets and a three-bladed Curtiss-Wright propeller. The details of the cockpit underwent numerous changes from the drawing board to the flight line. via Dave Ostrowski

Lower photo: The XP-39B in its initial configuration at the Buffalo plant on 05Dec39. Bell via Truman Partridge

[Marshall_Stack]

Originally Posted by Colin1

The XP-39B was flown on 25Nov39 and was the XP-39 prototype rebuilt with considerable modification.
Gone was the 1,150hp V-1710-17(E2) B-5 turbocharged powerplant and in came the 'improved' 1,090hp V-1710-37(E5) unit with single-stage intregral mechanical supercharger.
The removal of the turbocharger was recorded as necessary for two reasons, firstly, when the P-39 was being designed, US turbochargers weren't that reliable and secondly, NACA noted that the original Airacobra design had numerous lift and drag problems.
The changes made by NACA were done in stages, most were put in place at Langley Field, Virginia and the wind-tunnel tests determined a need for the improvements that were incorporated into the XP-39B. These included:

streamlining and reducing the size of the wheel doors
lowering and streamlining the canopy
moving the carburettor air scoop from the left side of the cockpit to directly behind the cockpit and
moving radiators from the fuselage sides to the central wing-root leading edges

along with a slightly altered fin and an all-up weight increased by about 15%

Top photo: The prototype P-39 (38-326), progenitor of all Airacobras to follow, poses at Wright Field around the time of its 06Apr39 maiden flight. The P-39 had a radiator and oil cooler on its starboard side behind the exhaust outlets and a three-bladed Curtiss-Wright propeller. The details of the cockpit underwent numerous changes from the drawing board to the flight line. via Dave Ostrowski

Lower photo: The XP-39B in its initial configuration at the Buffalo plant on 05Dec39. Bell via Truman Partridge

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 sefl-sealing fuel tanks?

[VG-33]

Originally Posted by 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?

My advice, read Golodnikov in english at lend lease airforce ru.

Regards

[Colin1]

Originally Posted by Marshall_Stack

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]

Originally Posted by Colin1

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]

Originally Posted by Marshall_Stack

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]

Originally Posted by Colin1

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

How so?

[gjs238]

Originally Posted by Colin1

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]

Originally Posted by Colin1

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