The Fabulous 'Tilly' Shilling!
Shilling's 'Penny' (or Shilling's Orifice), was central to the elegant, and simple solution to the negative and positive 'g' carburation problem in early Supermarine Spitfires during the second world war, and was originated by a remarkable woman - Beatrice (or Bee) Shilling - known affectionately by those close to her as 'Tilly'…
Beatrice Shilling was born at Waterlooville, Hants, on March 8th 1909; the daughter of a local butcher. As a 14 year old her sisters outstripped her on their pedal bikes, so, to compete, she acquired a Royal Enfield motorcycle. It gave her not only far greater range but afforded enormous fun and interest. After teaching herself how to dismantle and rebuild every part of her machine she became captivated by engineering and physics.
Moving with her parents to North Devon she took the unprecedented step of finding work as an apprentice electrician and electrical linesmen for a local firm. Not having sufficient money to pay for University tuition fees, she borrowed the £100 necessary from the National Society for Women's Service. She later recalled that most of the Society members had been suffragettes, but were the most polite of women. She could not see them knocking off policeman's hats "though many had!"
Beatrice read electrical engineering (BSc) at Manchester University, and then (through lack of job prospects) carried on with research on internal combustion engines for an MSc. But even after completion of her research her gender, but mainly the economic depression of the thirties, made it difficult for her to find a job. Fortuitously, she was made aware that the Royal Aircraft Establishment (RAE) at Farnborough were recruiting, and in 1936 obtained a position as an Assistant III in the Technical Publications Department. Here, her first encounter with officialdom occurred as her pragmatism came up hard against bureaucratic niceties. Writing an instruction leaflet for the maintenance of the Bristol Pegasus engine, the matter of cooling
valve seats for insertion in the cylinder head was considered. Knowing that RAF depots had no cooling equipment she advised that maintenance officers should stop an ice-cream van, get some sacks of dry-ice (solid carbon dioxide), mix with meths and make a cooling solution. "I had a bit of fun with that" she later said, dismissing the furore it had created. However, her abilities were apparent and, propriety aside, she was transferred to the Engine Department. There she built a reputation as a 'no nonsense type' with a very good hands-on approach.
She married an RAE colleague, George Naylor, in 1938 but retained her maiden name. "It was much less complicated that way" she was reported to have said, though it is known that later war-time security caused some problems. Just prior to her wedding the workshop personnel gave her a presentation set of stocks and dies for her wedding present, on the basis that since she borrowed theirs so often, she might as well have her own set!
'Tilly', as she was known from childhood, became a renowned motorcyclist and in the early thirties was often to be seen hurtling around Brooklands on her 'tweaked' Norton 500. She was subsequently awarded a coveted Gold Star for lapping in excess of 100 mph. In 1935 she raced her 'tuned' Lagonda Rapier around Silverstone, again at speeds in excess of 100 mph. By the time the second world war broke out she was a byword in motor racing, not only for motorcycles but also for racing cars. By this time too, she was pivotal to the RAE engine department operation.
As the Battle of Britain raged, British Hurricanes and Spitfires - engaging with German Me109f fighters - found they were severely disadvantaged. Combat manoeuvres often entailed fierce aerobatics and early Mark 1 Spitfires and Hurricanes were forced to turn on their backs to avoid a momentary loss of power which ensued when 'putting the nose down' into a power dive. If this 'nose down - tail up' power dive was carried out, negative g momentarily caused fuel starvation. Turning out of the dive then created a positive g, swamping the engine with fuel. The German aircraft had no such handicap - the Daimler-Benz engines were fuel injected. The same solution could have been taken for the Merlin, but fuel injection units were severely limited and untested. A solution was imperative, and one which didn't include the obvious one of replacing the carburettors.
Tilly Shilling was the more perceptive in her group and realised that the problem was to do with the fuel line gear pumps, which would pressure surge if the SU carburettor float needle 'locked shut' and, subsequently, fuel was forced from the top to bottom of the SU carburettor as the g forces changed. Thus two immediate problems occurred - a weak cut (from negative g causing fuel to rise in the carburettor thus starving the jets) and a fuel surge (as negative g changed to positive g) swamping the engine as the g forces varied and the float opened the jets to maximum.
The immediate answer, Tilly reasoned, was a 'restrictor'. This was a small disc, actually the size of a threepenny or shilling bit (about 12.5mm), which had a small hole (orifice) drilled into it. Curiously, the orifice cost less than a shilling to make (it should have been called Shilling's shilling!). This was fitted to the carburettor fuel line and created enough of a pressure gradient to limit the surge effect of the pumps in a dive.
Later examples of the Merlin engine were fitted with negative g and anti g carburettors, in the first instance by fitting a restrictor to the end of the float needle. Later Bendix carburettors and single point SU injection systems (which were insensitive to g) eventually replaced modified units and were extensively used until the end of the war.
Contrary to popular belief Shilling's 'Penny' was only a stop-gap solution, and was actually fitted to very few aircraft during the Battle of Britain - possibly no more than a trial of six. But it rapidly led to a more effective method, than that of an anti g version of the SU carburettor. It was not in fact the restrictor which led to Tilly Shilling's fame, rather her clear understanding of the problem and its immediate solution. Even as the fame of 'Shilling's Penny' (or Orifice) swept into RAE and RAF folklore, Tilly and her teams got down to the job of engineering a substantive solution. The ultimate outcome was the RAE-Hobson injection carburettor fitted to the Bristol Hercules engine.
Why did the problem only show up under combat conditions? Why was it that countless previous test flights by Supermarine, Hawker and Rolls-Royce failed to show up the problem before pilots died finding out? Simply, it seems, because at first it was not considered to be a problem! According to authorities, simulating combat conditions was the job of the RAF and although RAF pilots (and civilian test pilots) were quite aware of engine 'fluffing' during dives, it never appeared to be crucial; not until desperately violent manoeuvres in real combat conditions (most prohibited in flight tests), against closely matched aircraft, made the negative g problem and its momentary loss of performance, a very real matter of life or death. (Alex Henshaw, chief test pilot for Vickers-Armstrongs at Castle Bromwich, which during the war turned out thousands of Spitfires, notes in his book Sigh for a Merlin that at one time in early 1940 it was suggested that engines were being damaged by inverted flying during test. He replied that it was never done - aircraft were never inverted, only rolled, but this entailed an inverted glide "but as the engine cuts immediately on negative g there is no power in use". He had discussed this at length with Rolls-Royce "and they were happy that no damage occurs")
But for a fighter pilot the engine cutout, momentary though it was, was a 'severe psychological blow and a dangerous loss of performance' ( more than 50 mph) - 'especially with an enemy fighter closing on you'.
Post War, Tilly Shilling developed her interests more widely but was always faithful to her first love - engines. She learnt to fly under the Tech-Flight scheme at Farnborough and although she logged some 200 hours never considered herself a good pilot, having to build up the control pedals to reach them. She spent all her working life at the RAE, and much of this time as senior scientific officer involved in the aero engine department covering aero engine carburation and engineering physics.
After the war, (1945) Tilly moved to RAE supersonics division and thence to the guided weapons department. In 1952 she was transferred to the mechanical engineering department (later Engineering Physics) and stayed until 1969 when she retired. Amongst other things, she was senior engineer in teams working on cabin air conditioning, internal cooling of high speed aircraft, aircraft aquaplaning (following the Munich air crash which killed most of Manchester United FC), solid fuel rockets, the RAE high altitude plant, and evaluating the liquid oxygen tanks for Britain's Blue Streak 'stand off' nuclear missile. Along the way her fame and respect grew apace - she was listed OBE in 1948, promoted Senior Principal Scientific Officer at RAE in 1955 (on an 'individual merit' basis), was awarded the Lightfoot medal for 'best paper' from the Institute of Refrigeration and received an honorary doctorate from the University of Surrey in 1970. Her OBE was cited by Sir Stafford Cripps as an honour 'so well deserved.'
As noted above, Tilly Shilling remained at RAE until 1969 when she retired. Even after this she remained very active, carrying out consultancy work for a number of concerns in the aero industry.
As an individual she was often thought to be essentially shy by those who knew her well, but under this modest persona was a very strong and determined personality which, some say, capitalised on the fact that she was a woman in a man's occupation. Yet she was undoubtedly professional, pragmatic and thoroughly capable and had no problems about 'rolling her sleeves up'. Having a fully equipped workshop at home she made herself skilled in all workshop procedures. She related that on one occasion a fitter challenged her to braze a butt-joint between two pieces of copper pipe using basic equipment without jigs. This she did, won the half-crown bet, and proved that her joint was actually stronger than the pipe itself!
During her retirement ceremony and in later RAE newsletters she was described as '- outspoken with authority as she was helpful to junior staff' and in her closing address typically lambasted the 'top-heavy administration' which had often been the cause of 'late deliveries and cancelled orders'.
Her retirement years, as with her working life, had few dull moments. She was a keen pistol shot (Camberly Pistol Club) and while she remained active she was to be seen screaming around town in what was probably the fastest Triumph Dolomite Sprint in the country. She died on November the 4th 1990 having packed more into her life than most, forever immortalised by the pilots she had saved.
Sincere thanks to:
Mike Evans and Richard Hague at the Rolls-Royce Heritage Museum, Derby.
Alex Henshaw - Supermarine Spitfire Test Pilot
Squadron Leader Jones. Mitchell Museum, Southampton.
Tom Bowling - ex RAE, Farnborough.
Helen Gristwood - DERA Pyestock Archives, Farnborough.
Bernard Jacobson - Lagonda Rapier KG 5363 Owner
Tilly on her Norton
Rolls Royce Merlin Engine
RAE-Hobson injection carburettor
And you thought the Women's Institute was all about cakes and knitting. The Farnborough WI are made of sterner stuff and, of course, Tilly is their poster-girl.
In March 2014 The Mirror newspaper celebrated International Women's Day. Tilly was one of their '10 Inspirational Women to Make You Think'.
In July 2011 J D Wetherspoons opened a new pub in Farnborough. Named in Tilly's honour.
Triumph Dolomite Sprint
Tilly's Racing Rapier...
KG 5363 has had three distinct and different lives. It was first registered on 8th June 1935 as a Fixed Head Coupe. Then again in the 1950s when Beatrice Shilling rebuilt it as her personal idea of what a competition two-seater should look like. Finally, I rebuilt it again using one of the Rapier Register’s (replica) Eagle two-seater bodies. During my ownership the engine capacity has changed from 1100cc to 1232cc and finally 1500cc.
We are indebted to Bernard Jacobson, the current owner of Tilly's car, for the following...
I bought the car in very run-down condition in 1978. All Lagonda Rapiers were extremely individual – the Lagonda Company did not supply the bodies on any Rapier chassis. EVERY Lagonda Rapier was 'different', even if only in small details.
Photos courtesy Bernard Jacobson
Tilly Shilling racing
A line of subtly different Rapiers
The beautifully restored KG 5363 today