1. #1
    If the P-51 had the same R.R. Merlin engine as the Spitfire, what did they do to the P-51 to avoid the negative g induced carburetor cut out experienced by the Spitfire?
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  2. #2
    If the P-51 had the same R.R. Merlin engine as the Spitfire, what did they do to the P-51 to avoid the negative g induced carburetor cut out experienced by the Spitfire?
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  3. #3
    berg417448's Avatar Senior Member
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    "One of the great problems as discerned by pilots was the tendency for the carburetted engine to cut out under negative 'g'. Luftwaffe pilots learned to escape by simply pushing the nose of their aircraft down into a dive, as their fuel- injected engines did not cut out under these circumstances. Many authors have criticised this aspect of the Merlin design. In reality, like most engineering, it resulted from a design compromise- the drop in temperature developed in a carburetor results in an increase in the density of the fuel-air mixture when compared to that of a fuel injection system. As a consequence the Merlin produced a higher specific power output (horse power per pound) that the equivalent German engine. It was felt that this gave a higher power to weight ratio for the fighter and (rightly or wrongly) that this outweighed the disadvantages. By 1941 Miss Tilly Shilling in Farnborough had developed a partial cure for the problem. A diaphragm across the float chambers with a calibrated hole (the infamous "Miss Shilling's orifice"!) allowed negative 'g' manouvres, and was fitted as standard from March 1941. Sustained zero 'g' manouvres were not sorted out until somewhat later. In 1942 an anti-g version of the SU carburetor was fitted to single and two-stage Merlins. 1943 saw the introduction of the Bendix-Stromburg carburetor which injected fuel at 5psi through a nozzle direct into the supercharger and was fitted to the Merlins 66, 70, 76, 77, and 85. The final development was the SU injection carburetor which injected fuel into the supercharger using a fuel pump driven as a fuction of crankshaft speed and engine pressures, which was fitted to the 100 series Merlins. "

    http://www.spitfiresociety.demon.co.uk/engines.htm
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  4. #4
    Thanks berg417448
    I had wanted to find that out for a long time and finaly got around to ask . This is the best forum on the planet!
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  5. #5
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sooocool:
    This is the best forum on the planet! </div></BLOCKQUOTE>

    This perception of things will change in a while, be sure.
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  6. #6
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">This is the best forum on the planet! </div></BLOCKQUOTE>

    Got chart?
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  7. #7
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  8. #8
    Xiolablu3's Avatar Senior Member
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    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Ignored post by Sooocool posted Sat August 11 2007 20:51 Show Post

    Previous Topic | Next Topic powered by eve community </div></BLOCKQUOTE>

    By the end of the Battle of Britain (1940) the RAF was fitting 'Mrs Shillings Orifice' to SPitfires to stop the engine cutting out under negative G.

    By 1941 almost all SPitfires had this in place.
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  9. #9
    Then presumably, the same 'Mrs. Shillings Orifice' was used on the Mustang engine too?
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  10. #10
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sooocool:
    Then presumably, the same 'Mrs. Shillings Orifice' was used on the Mustang engine too? </div></BLOCKQUOTE>

    Actually, no.

    Mrs. Schillings Orifice was superceded by the "Negative G" version of the Rolls Royce SU carburettor in the early parts of 1942, which allowed longer periods under negative G before the engine cut out (and up to 15 seconds inverted). There were actually several variations of the Negative G SU carb, but the differnces are relatively minor.

    This was then itself superceded by the Bendix-Stromberg carburettor, and similar Rolls Royce carburettors, used on the Merlin 60 family of engines. This engine family includes the V-1650-3 (similar to the Merlin 61) and V1650-7 (similar to the Merlin 66) which powered the P-51B/C and P-51D/K, respectively. These injected fuel at around 5 PSI into the engine, allowing pilots to sustain negative G and inverted manouvers.

    The final solution was the automatic direct injection carburettor, which was fitted to the Merlin 100 series engines (112/113, 145 SM and others) and used a crank driven fuel pump to automatically regulate fuel pressure.
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