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Miss Shilling's orifice
Miss Shilling's orifice was a very simple technical device made to counter engine cut-out in early Spitfire and Hurricane fighter aeroplanes during the Battle of Britain. While it was officially called the R.A.E restrictor, it was normally referred to under various names, such as Miss Tilly's diaphragm or the Tilly orifice in reference to its inventor, Beatrice "Tilly" Shilling.
==Engine cut out problems==
The early versions of the Rolls-Royce Merlin engine came equipped with a SU carburettor. When these aeroplanes performed a negative G force manoeuvre (pitching the nose hard down), fuel was forced upwards to the top of the float chamber of the carburettor rather than into the engine, leading to loss of power. If the negative G continued, the fuel would collect in the top of the float chamber, forcing the float to the floor of the chamber. This would in turn open the needle valve to maximum, flooding the carburettor with fuel and drowning the supercharger with an over-rich mixture. This would lead to a rich mixture cut-out, which would shut down the engine completely, a serious drawback in combat.〔Price 1986, p.78.〕
Negative G commonly occurs when manoeuvring to fire on an enemy aircraft in a dogfight. Moving the stick forward would starve the engine of fuel, producing a sudden loss of power. This would let the enemy get away, and if continued the manoeuvre would cause the carburettor valve to open, provide far too rich a mixture and stop the engine. During the Battles of France and Britain, the German fighter aeroplanes had fuel injected engines and therefore did not suffer from this problem as the fuel injection pumps kept the fuel at a constant pressure whatever manoeuvres were made. The German pilots could exploit this by pitching steeply forward while pushing the throttle wide open, the pursuing British aircraft being left flat footed since trying to emulate the manoeuvre would result in loss of power, or fuel flooding and engine shutdown. The British countermeasure, a half roll so the aircraft would only be subjected to positive G as they followed German aircraft into a dive, could take enough time to let the enemy escape.
Negative G engine cut-out was not a problem unique to Merlin-powered fighters since many other pre-war aeroplanes also used carburettors containing a float chamber. For example, in 1942, the United States acquired a flyable, Japanese Mitsubishi A6M Zero, known as the ''Akutan Zero''. When test-flown, this aircraft was also found to experience engine cut-outs, due to the float-type carburettor of its ''Nakajima Sakae'' engine. The Americans devised tactics to counter the Zero in combat that took advantage of this and other results of testing the aircraft.〔Rearden (1995), p.73〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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