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Kitchen Table Kibitzing Friday: Blitz Soup and the 'Tilly Orifice' [1]
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Date: 2025-09-19
Battle of Britain Day happened this week. I grew up with cars without fuel injection. Similarly carburetors were the early standard equipment for aircraft internal combustion engines until the advent of superchargers. Issues prior to fuel injection were important just after the Phoney War, during the Battle of Britain whose engagements were mainly aerial combat during the German bombing campaign over Great Britain in 1940. For want of a flat washer.
Aircraft designer/patriot R. J. Mitchell, alarmed at growing German militarism, works to perfect a defense against the German Messerschmidt at the cost of his health.
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and other Allied countries before, during, and after World War II. It was the only British fighter produced continuously throughout the war. The Spitfire remains popular among enthusiasts. Around 70 remain airworthy, and many more are static exhibits in aviation museums throughout the world.
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Complaints from pilots over engine cut-out during dives and brief inverted flight led to a concentrated search for a solution. Engine manufacturers Rolls-Royce produced an improved carburettor, but this failed in testing. It was Beatrice 'Tilly' Shilling, an engineer working at the Royal Aircraft Establishment at Farnborough, who came up with a simple device which could be fitted without taking the aircraft out of service. She designed a thimble-shaped brass flow restrictor (later refined to a flat washer) with precisely calculated dimensions to allow just enough fuel flow for maximum engine power. It came in two versions, one for 12 psi manifold pressure and another for the 15 psi achieved by supercharged units.[2]
en.wikipedia.org/…
The wartime Tillies were low-powered pick-ups produced by British car manufacturers for use by the armed forces.[16][17] In 2015, a collection of her racing badges and trophies was bought by the Brooklands Museum.[18] en.wikipedia.org/...
While not completely solving the problem, the restrictor, along with modifications to the needle valve, permitted pilots to perform quick negative G manoeuvres without loss of engine power. This improvement removed the RAF's Rolls-Royce Merlin-powered fighters' drawback versus the German Messerschmitt Bf 109E machine, whose Daimler-Benz DB 601 inverted V12 powerplant had had fuel injection since 1937. During early 1941, Shilling travelled with a small team to fit the restrictors in one RAF base after another, giving priority to front-line units. By March 1941 the device had been installed throughout RAF Fighter Command. Officially named the 'R.A.E. restrictor', the device was immensely popular with pilots, adopting the affectionate nickname 'Miss Shilling's orifice' or simply the 'Tilly orifice', given to the restrictor by Sir Stanley Hooker, the engineer who led supercharger development at Rolls-Royce at the time.[3]
This simple measure was only (and was literally) a stopgap: it did not allow inverted flight for any length of time. The problems were not finally overcome until the introduction of Bendix and later Rolls-Royce pressure carburettors in 1943.
en.wikipedia.org/...
The Hawker Hurricane is a British single-seat fighter aircraft of the 1930s–40s which was designed and predominantly built by Hawker Aircraft Ltd. for service with the Royal Air Force. It was overshadowed in the public consciousness by the Supermarine Spitfire during the Battle of Britain in 1940, but the Hurricane inflicted 60% of the losses sustained by the Luftwaffe in the campaign, and fought in all the major theatres of the Second World War.
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