R-2800 2-stage supercharging hi-altitude performance

Discussion in 'Aviation' started by gjs238, Jun 7, 2013.

  1. gjs238

    gjs238 Well-Known Member

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    Looking at Wikipedia, at appears that the R-2800 was 2-stage supercharged early in it's life.
    How well did R-2800 high altitude performance compare to the other 2-stage supercharged or turbo-supercharged engines?
     
  2. Shortround6

    Shortround6 Well-Known Member

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    What are you looking for?

    Power to weight at a certain altitude?

    Power to drag at a certain altitude?

    Cruise power at a certain altitude?

    There aren't that many 2-stage supercharged or turbo-supercharged engines to compare that actually made it into production in any numbers ( several hundred).

    The British had TWO 2-stage supercharged engines in several versions. The Merlin and Griffon.
    The Americans had:
    Turbo R-1820s of 1200-1380hp in B-17s
    Turbo R-1830s of 1200-1350hp in B-24s (P-43s)
    Turbo V-1710s of 1100-1600hp in P-38s
    Turbo R-2800s of 2000-2800hp in P-47s
    2 stage R-1830s of 1200hp TO in F4Fs, C-47s (and a few others?)
    2 stage V-1710s in P-63s
    2 Stage Merlins in P-51s
    2 Stage R-2800s in F6F, F4U, and P-61s.

    French, Italians, Japanese and Russians had 0 that got out of the experimental stage.
    The Germans had 0 that got out of the experimental stage or service trail stage I believe.

    The 2 stage R-2800 was big, it was heavy, it was draggy, it had 1650hp at 21-23,000ft (depending on RAM) Military (not WER) power in 1942.
    The Turbo R-2800 was even bigger, heavier, draggier but had 2000hp at 25,000ft.
    The Merlin 61 (V-1650-3) the only other real game in town in 1942, had 1340hp at 23,500ft using 15lbs boost.

    Things change with time.
     
  3. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The turbo V-1710 was managing, in 1943 and later, 1425 HP from 25000-29000 ft, military power, no ram. WEP rating was 1600 HP, up to 7000 ft (P-38H), up to 26500 ft (P-38J) and up to 28500 ft (P-38L). In early 1942 and earlier the usual military power was only 1150 HP, later upped to 1325 HP.
    2-stage V-1710 was good for 1150 HP, military power, no ram, at 22500 ft (earlier models, installed in the P-63A), later it was 1100 at 25000 ft and even later at 28000 ft. If the engine was equipped with water injection and/or was able to make 3200 rpm, the engine power was considerably higher.

    You might want to check out the sticky thread at the 'Engines' subforum for extra reading :)
     
  4. VBF-13

    VBF-13 Well-Known Member

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    What is this, a contest? :lol:

    It did well enough to get us upstairs, quickly, and that's all we needed.
     
  5. gjs238

    gjs238 Well-Known Member

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    Just wondering why a 2-stage supercharged R-2800 couldn't provide the altitude performance for ETO.
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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    #6 tomo pauk, Jun 7, 2013
    Last edited: Jun 7, 2013
    It could.
    At 22500 ft it was providing at least 400 Hp more (1/3rd more) than BMW-801; price being greater weight and bulk. Point was to mate the 2-stage R-2800 into an airframe that would be tailored for speed (= thinner wing, not that big wing area), rather than for good CV handling (= big, thick wing basically, along with CV 'compatibility' extras, eg. folding wings, necessary strengthening and hook), like it was done historically with proper CV birds, Hellcat Corsair.
    Basically, we're looking at Tempest II airframe + 2-stage R-2800.
     
  7. VBF-13

    VBF-13 Well-Known Member

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    Now this is something even a simple mind like mine can understand. :)
     
  8. Shortround6

    Shortround6 Well-Known Member

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    And it was up against the P-47 turbo. 21% more HP several thousand feet higher. The P-47s engine/powerplant grew faster.
     
  9. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The raw horsepower tells only half of a story, turbo vs. 2-stager.

    The 2-stager needed to smartly devised exhaust stacks, in order to generate as much exhaust thrust as possible. The R-2800 in USN service did not have had anything like what we can see on Fw-190, Hayate, La-7, Tempest II/Sea fury - individual exhaust stacks, as well faired in as possible. We know that, for example, Mosquito was to gain ~20 mph with exhaust stacks of better design.

    Then we have another thing, the usage of ram effect to 'elevate' the full throttle height (FTH), the gain being proportional to plane's speed and how good/bad the air intake was devised. The Merlin Mustang was able to gain as much as 5000 ft in FTH, static engine vs. in-flight engine at max speed (430-440 mph). Spit VIII/IX was gaining some 4000 ft when flying 400-410 mph. On the other side, the F4U was able to gain only 2000-2500 ft when flying 400-415 mph, a major minus for a plane that wants to be good at high altitude.
    Another plane that was been able to gain, through ram, only about 2000 ft for FTH was the Fw-190A; the same plane equipped with external intakes was better at higher altitudes, but that modification never went into large use (only several planes used it operatively?).
     
  10. Shortround6

    Shortround6 Well-Known Member

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    All good points Tomo.

    The only thing with exhaust thrust is that it doesn't do for climb any where near what is does for level speed.

    From Wiki;

    T=(dm/dt)v
    where:
    T is the thrust generated (force)
    dm/dt is the rate of change of mass with respect to time (mass flow rate of exhaust);
    v is the speed of the exhaust gases measured relative to the rocket.

    The thrust changes with the speed of the plane even with the same exhaust mass and same exhaust speed.

    Of course a 30-100lb set of exhaust pipes/nozzles is a lot lighter than the turbo-supercharger installation :)
     
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