P-39 vs P-40

Discussion in 'Aviation' started by gjs238, Jun 18, 2009.

  1. gjs238

    gjs238 Well-Known Member

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    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?
     
  2. Colin1

    Colin1 Active Member

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    I don't think it did
    the P-39 didn't get much of a look-in with western air forces but the Soviet Union employed it in numbers and with it Soviet pilots regularly mixed it up with the Luftwaffe. It fell short with later versions of the Bf109 and the arrival of the Fw190 but that was later, rather than earlier in the war. Soviet pilots were impressed with its low-level performance, manoeuvrability, heavy armament and structural strength.

    It's also worth noting that of the top 5 Soviet aces, P-39 drivers occupied slots 2, 3 and 4.

    It had handling problems, I think spinning was one of them. In its initial configuration, it had the altitude of the P-38 but curiously, Bell thought they could improve the type by shortening the wings, lengthening the fuselage and lowering the canopy profile; this impinged on the available space and supercharging fell back on a single-stage arrangement. This was quite unlike the P-40 which never had the altitude performance from the outset.
     
  3. davebender

    davebender Well-Known Member

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    Spinning is about the worst possible problem to have when you are flying at low altitude. I suspect some pilots were afraid to fly the P-39 at max ability for fear of a low altitude spin.

    Low endurance is a huge problem, as the Luftwaffe discovered during the Battle of Britain.
     
  4. Colin1

    Colin1 Active Member

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    #4 Colin1, Jun 19, 2009
    Last edited: Jun 21, 2009
    Never doubted it for a minute

    The Soviets seemed to get the best out of it

    Low endurance was a huge problem for the western Alllies until late 1944 but of course, by then the P-39 had been supplanted by better designs. It was not quite such a problem for the Soviets, who principally used it to:

    Protect ground units from enemy aircraft
    Escort bombers
    Suppress AAA in the area of bombers
    Reconnaissance
    Free hunt
    Attack soft targets (i.e. troops, convoys, supply dumps, railroads, airfields, barges or other small naval craft)
    Protect high-value friendly targets (i.e. bridges, amphibious landing forces, reserves, command and control, major cities, etc)


    rather than long-range escort duties or even just hopping across the Channel. That's not to say that range wasn't an issue, more is clearly better but if the Soviets were doing all of this then they were obviously locating all of their P-39 units just behind the action on the ground and largely negating any endurance issues.
     
  5. gjs238

    gjs238 Well-Known Member

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    Endurance:
    If I understand correctly, the plane was submitted as a response to Circular Proposal X-609 - didn't that contain any criteria for endurance?

    Turbocharger:
    Mounting the turbocharger close to the engine, as was done on the P-38 and bombers, makes for a clean, simple and compact package. The P-39 seemed to provide a great opportunity for this.
    I always read about how the mid-engine placement was ideal for the nose mounted cannon and a streamlined profile, but I can't help but feel that turbocharger placement was a great beneficiary of this layout.

    P-39 vs. P-40 statistics:
    Do we know how the P-39 compared to the P-40 statistically?
    - Early war years in Pacific theatre.
    - In Soviet Union.
     
  6. timshatz

    timshatz Active Member

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    Think the Soviets also took some of the armor out as well as dumped a few machine guns. Made it a lighter bird, closer to the original spec.
     
  7. Colin1

    Colin1 Active Member

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    The problem
    with turbocharger arrangements is the hefty volume of ducting to and from the engine and the double problem is where would you put it all in the P-39? It sat behind the pilot in the P-47 (a substantially bigger bird than the P-39) but with the engine behind the pilot in the P-39, it clearly can't go there; Bell needed to weigh up the pros and cons of their lower-profile canopy vs the choice of single or two-stage supercharging, it might have had a different history altogether with the western Allied airforces.
     
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  8. gjs238

    gjs238 Well-Known Member

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    The prototype XP-39 flew with the turbocharger and performed well.
    The P-38 mounted the turbo behind the engine in the nacelle nicely.
    Extensive ducting is not required.
     
  9. Colin1

    Colin1 Active Member

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    My apologies
    I was under the impression the XP-39 flew with two-stage supercharging
     
  10. Juha

    Juha Well-Known Member

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    IIRC there was capacity promlem in turbocharger production, bombers needed it also. At least part of USAAF hierarcy saw the main function of US fighters as protection of USA beaches against invasition, so low altitude work, so no need to put turbo into all fighters.

    Juha
     
  11. gjs238

    gjs238 Well-Known Member

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    There were plenty of turbochargers for the P-38 P-47, both of which reached operational status after the P-39.
    Decision seemed to be made by NACA for aerodynamic reasons.
     
  12. Juha

    Juha Well-Known Member

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    You might well be right, but the fact that there was plenty of turbos available later doesn't prove in itself that the supply was adequate earlier when the decision was made. But as I wrote, you might well be right.

    Juha
     
  13. davebender

    davebender Well-Known Member

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    The P-38 and P-47 cost twice as much as many other fighter aircraft. Which suggests to me that turbochargers and their associated ducting were very expensive. Not even the U.S. can afford to turbocharge the entire fighter force.
     
  14. ssnider

    ssnider New Member

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    I got to talk to a pilot severial years ago who flew both the P39 and P40 in combat. For him the biggest differance was in reliability. He said that the some part of the P39 electical system failed on evey mission, and everything was electic. he said the P40 was ok and dependable. He had also flew P36s before the war and finished the war in a P51, which he considered vastly better then anything else.
     
  15. gjs238

    gjs238 Well-Known Member

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    Sure didn't stop them from turbocharging the bombers.
    I doubt this is why NACA removed the turbo from the XP-39.
    And the P-38 needed TWO turbos per plane.
     
  16. Marshall_Stack

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    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.
     
  17. Colin1

    Colin1 Active Member

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    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.
     
  18. Colin1

    Colin1 Active Member

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    #18 Colin1, Jun 19, 2009
    Last edited: Jun 19, 2009
    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
     

    Attached Files:

  19. Marshall_Stack

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    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?
     
  20. VG-33

    VG-33 Banned

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

    Regards
     
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