Thursday, 7 January 2010

Tilly Shilling's Orifice

My wife is a member of the Women's Engineering Society. One of the society's earliest members was Beatrice Shilling, pictured here (in the mid 1930's) with her Manx 500 on which she became the first woman to lap Brooklands at over 100mph. She later added her own homemade supercharger in that inevetable search for more power. The supercharger didn't work that well but it helped in bringing her to the attention of the Royal Aircraft Establishment who employed her as a scientific officer and charged her with the task of resolving a fueling problem with the Rolls Royce Merlin aero engine. This engine was used in more than 40 different planes but most famously in the Supermarine Spitfire and Hawker Hurricane. However, with a normal carburettor it suffered fuel starvation in negative g and this meant it was unable to turn the nose down into a dive in straight flight. To avoid this pilots put the plane into a half roll and let it drop sideways before pulling up and turning back onto the original course. Despite being faster than the German planes this manoever lost a lot of time and German pilots soon learned that the easiest way to shake off a British fighter was to take a dive. Ms Shilling's solution was to fit a steel diaphram into the float bowl which prevented the fuel surging upwards in negative g. And hence the nickname "Tilly Shillings Orifice". It wasn't perfect but once tested it was installed on every operating Spitfire and Hurricane within a few months and allowed the planes to pull negative g without misfiring.

1 comment:

  1. Regarding the Spitfire;
    How unfortunately typical of British mfr's not to address this issue IMMEDIATELY when it became apparent to pilots, who were being shot at! So frustrating that a gorgeous, superior-performing machine should be let down by a very simple glitch, which took a 'backyard tinkerer' to fix!

    If you see echoes of this in the British Motorcycle Industry, you are quite correct! This is part of the reason they ultimately died out..lack of impeccability. Their engineers needed a bit more of that Teutonic technical obsessiveness to complement their design flair. Performance yes, handling yes, style yes, technical superiority no.