Allison P-40 vs Merlin P-40 (or 1 speed vs 2 speed)

Discussion in 'Aviation' started by wuzak, May 31, 2015.

  1. wuzak

    wuzak Well-Known Member

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    In terms of outright speed, perhaps not.

    But where the performance was achieved was different.

    Here are tests of the P-40E and the P-40F
    http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13601_PHQ-M-19-1440-A.pdf
    http://www.wwiiaircraftperformance.org/P-40/P-40E_40-384_PHQ-M-19-1300-A.pdf

    Note that this test shows a maximum speed of 342mph @ 11,400ft and 340mph @ 15,300ft.

    A source like Joe Baugher (Curtiss P-40E (Kittyhawk IA)) quotes 362mph @ 15,000ft (Curtiss P-40E (Kittyhawk IA)). This must have been for ones with later engines - the E in the test had the V-1710-39 with 8.8:1 supercharger drive ratio, rather than the later 9.60:1 gears.

    Baugher quotes speeds of:
    335mph @ 5000ft
    345mph @ 10,000ft
    362mph @ 15,000ft

    Time to climb to 20,000ft of 11.5 minutes.
    Service ceiling was 29,000ft.

    For the F, Baugher (Curtiss P-40F Warhawk) quotes speeds of:
    320mph @ 5000ft
    340mph @ 10,000ft
    352mph @ 15,000ft
    364mph @ 20,000ft

    Time to climb to 20,000ft of 11.6 minutes.
    Service ceiling was 34,400ft.

    The test report from http://www.wwiiaircraftperformance.org only has two all out level speeds listed where the engine was flat out (3,000rpm), and two more with reduced rpm:
    320mph @ 9,800ft (2,650rpm)
    350.5mph @ 12,800ft (3000rpm)
    336.5mph @ 16,700ft (2,650rpm)
    364.5mph @ 19,270ft (3000rpm)

    Time to climb to 20,000ft of 10.2 minutes.
    Service ceiling as listed by Joe Baugher.

    The test report for the E shows a time to climb to 20,000ft of 11.82 minutes. The earlier (and lighter) D has a time to 20,000ft of 10.0 minutes in a separate test.

    The E has a higher peak climb rate (2,400fpm @ 10,000ft vs 2,210fpm @ 9,600ft). By 15,000ft the E's RoC has dropped to 1,370fpm (F: 1,860fpm), 20,000ft it is 880fpm (F: 1,480fpm) and 25,000ft it is 480fpm (F: 1,000fpm).

    The P-40E and P-40F were in different condition in the tests so far listed.

    The F had the gun ports taped over, while the E did not. The F had wing racks with shackles and stays, the E was set up for use with a belly tank (though the tank was removed for all-out level speed tests).

    A later test of the F (http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13635_FS-M-19-1578-A.pdf) showed performance at differing rpm and 18,100ft. Why 18,100ft, I do not know.

    The speed was 374 without belly tank and sway bars removed (369.5mph with sway bars in place).

    RoC was 2,185fpm @ 18,100ft and 1,380fpm @ 25,000. Quite an improvement over the earlier F.

    The later N used the V-1710-81 with the 9.6:1 gears.
    http://www.wwiiaircraftperformance.org/P-40/P-40N-5_42-105241_Eng-47-1685-A.pdf

    Max speed is shown as 350mph @ 16,400ft. The increased altitude rating of the engine comes at the cost of low altitude climb rates. The RoC at 10,000ft is 1,935fpm compared to the E's 2,400fpm, the RoC at higher altitudes is improved: 1,365fpm vs 880fpm @ 20,000ft and 760fpm vs 480fpm @ 25,000ft. The service ceiling is also improved to 31,000ft.

    So, you can see that the F definitely moves the performance up about 4-5,000ft. Without losing too much down low.

    The N loses performance down low, compared to the E, in order to improve altitude performance. That is the trade-off in using a single speed engine.

    Low down performance could be recovered by using higher MAPs/boost with the appropriate fuels.

    A multi-speed supercharger drive should enable the P-40 to retain the low down performance E while accessing the better high altitude performance of the N. There is a small weight penalty - the 2 speed Merlin gained ~75lb over its single speed brother.
     
  2. wuzak

    wuzak Well-Known Member

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  3. Shortround6

    Shortround6 Well-Known Member

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    A difference in climb is that the Allison powered planes were tested at full power (3000rpm) for the first 5 minutes and the rest of the test done at 2600rpm. Obviously in combat the P-40E could climb faster using military power of 3000rpm.

    However, the climb for the Melrin powered version was done at 2850rpm at all altitudes so it too, in combat situations, could climb a bit faster using 3000rpm.

    There is little doubt that the Merlin engine allowed for a 3-4000ft higher effective ceiling.

    As a Guess 18,100ft was rated altitude of the engine in high gear. Or that particular plane's wide open throttle altitude as it seems to be off 50rpm and 400ft.(not uncommon for many engines).

    A June 1943 dated Pilots manual for the P-40F L also gives a war emergency rating of 61 in MAP and 1300hp at both 4,800ft and 12,000ft. The Military power was 48.2in and 1240hp at 11,500ft and 1120hp at 18,500ft. Take off was 54.3in at 1300hp at sea level. At the moment I don't know when the WER rating was approved for the P-40 Merlin.
     
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