Orifice

Orifice (pronounced awr-uh-fis or or-uh-fis)

A mouth, opening or aperture, as of a tube or pipe; a mouth-like opening or hole; mouth; vent (mostly technical or medical use).

1535–1545: From the Middle English orifice (an opening, a mouth or aperture), from the Old French & Middle French orifice (the opening of a wound), from the Late Latin ōrificium (an opening (literally "the making of a mouth")), the construct being Latin ōr- (stem of ōs (genitive oris)) (mouth (and related to "oral")) + fic- (combining form of facere; facio) (to make, to do) + -ium (the noun suffix).  The root of facere was the primitive Indo-European dhe- (to set, put).  The rare adjectival form is orificial; neither orificish or orificesque apparently exist.

Miss Schilling’s Orifice

Rolls-Royce Merlin V12.

Fuel to early versions of the twenty-seven litre (1648 cubic inch) Rolls-Royce Merlin V12 engine was supplied with a carburetor, putting the pilots in the Merlin-powered Spitfires and Hurricanes at a disadvantage against the German Messerschmitt BF109 fighters which used a fuel-injected Daimler-Benz DB601 inverted V12.  In the British planes, during a negative G-force maneuver (pitching the nose hard down), fuel was forced upwards to the top of the carburetor's float chamber rather than into the combustion chamber, leading to a loss of power. If the negative G continued, the fuel would collect in the top of the float chamber, forcing the float to the bottom. This in turn would open the needle valve to maximum, flooding the carburetor with fuel, drowning the supercharger with an over-rich mixture which would shut down the engine, a serious matter in aerial combat.

Battle of Britain era Hawker Hurricane Mk IIA and Supermarine Spitfire Mk II.

Ms Beatrice “Tilly” Shilling (1909-1990) was a pre-modern rarity, a female engineer and amateur racing driver.  While employed as an engineer at the Royal Aircraft Establishment (RAE) at Farnborough she worked on the fuel delivery problem, concluding quickly the only complete solution for fuel starvation was a pressurized fuel system such as the direct injection on the Daimler-Benz V12s but that such a development would take months to design, test, manufacture and install.  However, as a stop-gap measure, she designed a flow restrictor: a small metal disc with a central orifice, looking much like a plain metal washer.  The restrictor orifice was sized to accommodate just the fuel flow needed for maximum engine power, the setting usually used during dogfights and it solved the immediate, critical, problem of the engine shutdowns following flooding.  Officially named the RAE Restrictor or RAE Anti “G” Carburetor, the device proved popular with pilots, who much preferred to call it Miss Shilling's orifice or the Tilly orifice.  The simple and elegant solution proved effective until pressurized carburetors (essentially throttle-body injection, a simplified version of the Daimler-Benz direct fuel injection) were developed which permitted even inverted flight.  With a backpack of RAE Restrictors, she toured RAF airfields on her motor-bike instructing and assisting the maintenance crews with the installation of the devices.

RAE Anti "G" carburetor restrictor plate instruction sheet.

Ms Shilling was a serious engineer making an important contribution to the war effort and was not amused by the nick-names for her invention but reportedly regarded it as something typical of minds of men and carried on with her work.  The orifice was but a footnote in the history of the Merlin and the Allied war effort but did typify the improvisation and speed with which British industry developed "quick & dirty" solutions, especially in the early days of the war.