RR Merlin's (early-war): let's get it straight

Discussion in 'Engines' started by bada, Nov 23, 2008.

  1. bada

    bada Member

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    So, i'm little "in the ware" when talking about the Merlins,
    so i made a list and hope someone could correct the power/altitude and even maybe add some info, maybe some Power-vs-Alt charts, that are afwul difficult to find.

    Let's start with the M45 family:

    Merlin 45
    -3038 airframes equipped
    -used in Spitfire Mk.V
    -carburator with shilling orifice
    - 1,515 hp (1,130 kW) at 3,000 rpm at 11,000 ft (3,353 m)
    ---------------------------------------------------------
    Merlin 45M
    - Cropped version?Alt? Power?boost?
    - 266 airframes equipped, mostly LF-LR-Vb
    .-carburator with shilling orifice
    -no info
    ---------------------------------------------------------
    Merlin 46
    -3244 airframes equipped
    -high-altitude version used in Spitfire PR.Mk.IV(T),seafire IIc,Seafire LIIc,SpitVb,SpitVbT,SpitVc,SpitVcT-
    -1,415 hp (1,055 kW) at 3,000 rpm at 14,000 ft (4,270 m)
    -Carb with shiling device?
    -------------------------------------------------------------
    Merlin 50
    -503 airframes equipped-Seafire IIc,Spit Vc and mostly SpitVcT
    -no info what difference with M45-M46?
    --------------------------------------------------------------
    Merlin 50M (not in the spit production list!different name?)
    - 1,585 hp (1,182 kW) at 3,000 rpm at 2,750 ft (838 m);
    - Low altitude version with supercharger impeller "cropped" to 9.5 inches (240 mm) in diameter.
    - Permitted boost was +18 lb/sq.in. instead of +16 lb/sq.in. as on a normal Merlin 50 engine.
    - A "negative g" carburettor was fitted.(shiling orifice?New carb?)
    ------------------------------------------------------------------
    Merlin 55
    - 1256 airframes equipped-Seafire III,Spit Vc,SpitVcT
    -no info
    ------------------------------------------------------------------
    Merlin 61
    -575 airframes equipped-mostly First batch of MkIX plus few PRXI,SpitMkVII+MkVIII
    -fitted with a new two-speed two-stage supercharger providing 1,565 hp (1,170 kW) at 3,000 rpm at 12,250 ft (3,740 m), and 1,390 hp (1,035 kW) at 3,000 rpm 23,500 ft (7,170 m)
    -high-altitude version
    -Carb with shilling orifice? (G-neg sensitive)
    --------------------------------------------------------------------

    Thanks for your help:oops:
     
  2. antoni

    antoni Banned

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  3. Glider

    Glider Well-Known Member

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    Its interesting stuff can I ask what book this is in?

    Thanks
     
  4. bada

    bada Member

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    Thanks for the little "resumé", it gives a better view on the merlins family.

    Do you ,maybe,know where i could find engine charts? I find it strange that german data on Db's and Bmw's is more easy to find than data on english and americans engines:shock:
     
  5. antoni

    antoni Banned

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    Modellers Data File Merlin Engined Spitfires.
     
  6. antoni

    antoni Banned

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    Maybe the Rolls Royce Heritage Trust. I think they might have published some books as well.
     
  7. Glider

    Glider Well-Known Member

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    Thanks for the information

    Appreciated
     
  8. jerryw

    jerryw Member

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    You need a copy of "The Merlin In Perspective - the combat years" by Alec Harvey-Bailey. Rolls-Royce Heritage Trust Historical Series No. 2.
    This has 20 or so pages of data on practically every Mark of the Merlin.
     

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  9. kool kitty89

    kool kitty89 Well-Known Member

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    I dont know of a Merlin 45M, it was my impression that the Spitfire LF Mk.V had the low altitude Merlin 32.

    I believe the "negative G" (pressure injection -like the Bendix carb of US engines) carburetor was used on the Merlin 50 onward. There was still a limitation of -G time though due to the limits of the oil pump in -G conditions. (though at a few minuts this was far more than usually necessary for the duration of -G maneuvers, not to mention the pilot's amiility to cope in such conditions)

    I don't really know much of the Merlin 55 either, the 50 was basicly the same as the Merlin 45 (except for the carb) and the 50.M had the low-altitude cropped supercharger.
     
  10. kool kitty89

    kool kitty89 Well-Known Member

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    Rolls Royce Merlin 61

    The Merlin 45M was the cropped version. Late model 45's also had the negative-g carb.
    The Merlin 32 was a low altitude engine (for the RN) with a single speed supercharger, but I'm not sure it used the "cropped" impeller. It may have use the standard Merlin XX/45/50 series supercharger but with the low speed gearing of the XX rather than the high speed gearing of the XX adopted for the 45/50 series. (I believe the Merlin 46/47 had even higher speed gearing for altitude performance)

    The Merlin 32 was used on the Seafire IIC, the Merlin 45 was used on the Seafire IB.

    Spitfire Variants
    Spitfire Variants
     
  11. bada

    bada Member

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    Thanks JerryW for the info about the book, will check that on the web.

    Just a question: are there power charts available in this book?

    Ps: The merlin45M was still used and mounted on spitfire as replacement engine even in 44. It look like it was really a great really-low-level engine.
    (2400ft max power at max emergency boost)
     
  12. antoni

    antoni Banned

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    The Merlin 32 was a low-level version, with cropped supercharger, of the Merlin 30. It was also fitted with a Coffman starter. The Merlin 30 was for the Barracuda MK I. The original engine for the Seafire, Mk I and early MK II was the Merlin 45. The maximum efficiency of this engine was at an altitude of 13,000 ft. For naval operations most interceptions occurred below this height. For lower altitude a new engine was required and the navy were quick to ask for examples for the Seafire. It was difficult to obtain Merlin Mk32s at that time because they were earmarked for the Barracuda Mk II. Eventually a number were diverted and when fitted with a four bladed propeller the low altitude performance of the Seafire IIC improved dramatically. The cropped blades of the supercharger enabled more power to be provided to the propeller instead of being used to provide more air flow for operation at high attitude. The designation of this Seafire variant was changed to L IIC. The only Spitfire variant that used the Merlin 32 was the PR XIII, only 24-26 were built, all conversions.

    For the Seafire Mk III, the Merlin 55 series was specified. This had the same hp as the Merlin 45 but had automatic boost control with barometric governing. The Seafire Mk II was also fitted with the Merlin 55M for low altitude performance and they were designated LF Mk III.

    The RAF would have liked to have more Mustangs but it was agreed that the bulk of production should go to the 8th Air Force. Britain could not produce enough Spitfire MK IXs for its needs so in late 1943 and 1944 numbers of well worn Spitfire Mk Vs were converted to the LF configuration. They were limited to a low level role, much used against hit-and-run attacks by low flying FW 190s. The introduction of the Mustang Mk III in early 1944 saw the withdrawal of most Mk Vs from operations over the continent. Some Mk Vs in squadrons assigned to Air Defence Great Britain would continue to be used over France and the Low Countries well into 1944.
     
  13. jerryw

    jerryw Member

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    This claim by Antoni that, "The Merlin 32 was a low-level version with cropped supercharger, of the Merlin 30." is quite incorrect.
    The Merlin 30 with the rating R.M.2.M had a supercharger with a diameter of 9.75" and so did the Merlin 32, which had a rating of R.M.5.M.
    This is the size of supercharger the engine was designed with from the start. "Cropped superchargers" came about due to production engines being subsequently modified and therefore did not have R.M. ratings, eg the Merlin 45M.
    The Merlin 30 was used in the Fairey Fulmar, not the Barracuda which used the Merlin 32.
     

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  14. peril

    peril New Member

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    Jerry, does your Merlin book show information on the Merlin 46/47?
     
  15. dairwin

    dairwin Member

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    Peril - the first attachment below, is the summary page from "The Merlin in Perspective" regarding Merlin 46/47. Another useful reference is "British Piston Aero-Engines and their aircraft", by Alex Lumsden. Attached is the page from that publication covering the Merlin 46/47.
     

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  16. peril

    peril New Member

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    Again we see the Merlin 45 producing more hp above 14,000ft than the high alt rated Merlin 46.

    Of note above is the rated power difference between the 46 47, most likely accounting for the loss of power to the cabin pressure drive, although this is the first reference to show that difference.

    Makes little sense on face value to have a high alt engine with no gain, perhaps a perpetuated error from the same original source?


    [​IMG]

    [​IMG]

    More detailed research needed into original data I'd say.



    This is an 'example' of the trends expected from increasing the impeller sizes, this is not accurate in power, just a hypothetical curve shape based on expected improvements from impeller changes. Note the curve looses a little max hp but is shifted in height and this is where the gain over the lower engine would be obtained.

    Just and example, not meant to be accutite.

    [​IMG]
     
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