Get your mind out of the gutter. It’s not what you think.


Author’s Note: Please enjoy this article from the Wingspan archives as I work to catch up in the New Year. 


The Supermarine Spitfire and Hawker Hurricane were the two principal RAF fighters of WWII, and both are revered for the important role they played in turning the tide of war in Europe. Both were powered but the mighty Rolls-Royce Merlin engine, but early versions of the 12-cylinder powerplant had a nasty habit of losing power, or cutting out altogether, during high-G maneuvers or too much inverted flight. Unlike the fuel injected Daimler-Benz DB 605 engine of the Messerschmitt Bf-109, the Merlin was fitted with an SU carburetor (or carburettor, if you prefer the British spelling for a British engine). During certain maneuvers, such as a hard pitch down of the nose, the fuel was forced upwards to the top of the float chamber of the carburetor, flooding the engine. This led to a loss of power, or a complete cutoff of the engine, which is really not something that you want to have happen in the middle of a pitched dogfight.

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A permanent solution was found by using a Bendix or Rolls-Royce pressure carburetor, but until that unit could be developed, a stopgap solution was discovered by Beatrice “Tilly” Shilling, an engineer working at the Royal Aircraft Establishment at Farnborough. She devised a flow restrictor (officially called the R.A.E. Restrictor, but nicknamed “Miss Shilling’s Orifice,” the “Tilly Orifice, and “Tilly’s Diaphragm”) which limited fuel flow to the maximum the engine could use during a dogfight and, along with a revised carburetor needle, it solved the fuel flooding problem until the permanent fix could be found. Miss Shilling toured England with a group of mechanics, retrofitting the engines of the RAF fighters, with priority given to front line units. By the end of 1941, all the Merlins had been modified and were back in the fight, much to the relief of the beleaguered pilots.

Tilly Shilling was born in 1909, earned degrees in both electrical and mechanical engineering, and worked for the Royal Aircraft Establishment from 1936 to 1969. She raced motorcycles in the 1930s, and earned the Gold Star for lapping the circuit at Brooklands at an average speed of 106 mph. And she refused to marry her RAF bomber pilot husband George until he completed the same feat. After the war, the pair kept their own shop for tuning racing cars, and both raced with modest success. Tilly also landed her expertise to Dan Gurney in 1967 when he needed help overcoming problems with overheating in his Eagle Mk1 F1 car. Shilling died in 1990 at age 81.

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Beatrice Shilling with her Norton motorcycle

Connecting Flights


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