Winning the Battle of Britain with Miss Shilling’s Orifice

In the pantheon of iconic aircraft, perhaps none is more revered than the Supermarine Spitfire. Considered one of the most beautiful fighters ever designed, along with its stablemate the Hawker Hurricane the Spitfire has become emblematic of  Britain’s determined resistance against Nazi Germany in the early days of the Second World War. Yet despite its legendary reputation, the Spitfire was far from a perfect machine. Its narrow landing gear made landings precarious, its widely-spaced wing-mounted guns reduced its concentration of firepower, and at higher speeds its elegant elliptical wings had a tendency of flexing, often leading to fatal crashes. But the Spitfire’s greatest achilles heel lay in a component almost as celebrated as the aircraft itself: its Rolls-Royce Merlin engine.

Whenever the Spitfire executed a negative-G maneuver, such as entering a dive or flying inverted, the engine would suddenly lose power, cut out, or stall altogether – a potentially lethal occurrence in a dogfight. Indeed, German fighter pilots quickly learned to exploit this weakness, and when attacked by British fighters would suddenly pitch down, causing the pursuing Spitfire or Hurricane to lose power and giving the German pilot enough time to escape or come up from behind.

The issue lay with the Merlin’s SU carburetor, which was a standard float-type originally developed for automobile engines. Carburetors regulate the mixture of fuel and air reaching the engine; in the SU type, a piston exposed on one side to the air inlet manifold is linked to a jet and needle valve connected to the fuel supply system. When the throttle is opened, more air is drawn into the engine and the air velocity in the manifold increases. This in turn lowers the pressure in the manifold, drawing the piston down and opening the needle valve, allowing more fuel to enter the airstream. The fuel supply is thus matched to the engine’s demand for air. Before reaching the jet and needle valve, the fuel first passes through a float chamber, in which a float linked to an inlet valve keeps the fuel at a constant level – and thus a constant pressure. While this works perfectly well in an automobile or civil aircraft which stays more or less level, exposure to negative Gs causes the float tank to flood and deliver an overly-rich fuel-air mixture to the engine, decreasing its power. The Spitfire’s opponent, the Messerschmitt Bf-109, did not suffer from this fault as its Daimler-Benz DB-605 engine was fuel-injected.

With Britain fighting for its life, the race was on to find a solution. Rolls-Royce attempted to develop an improved carburetor, but Fighter Command could not afford to send any of its aircraft or their engines back to the factory to be modified. In the end, a solution was found by one Beatrice Shilling, an engineer working at the Royal Aircraft Establishment. Miss Shilling’s fix was simplicity itself: a small thimble-shaped flow restrictor fitted to the float tank inlet valve, which allowed just enough fuel to flow through it to supply the engine at full power while also preventing the float tank from flooding under negative Gs. And as a bonus, it could quickly be fitted to aircraft in the field. Simplified to a plain steel washer, the restrictor was quickly fitted to all of Fighter Command’s aircraft by RAE teams – often lead by Miss Schilling herself. While officially known as the “RAE Restrictor”, appreciative RAF pilots soon dubbed the device “Miss Shilling’s Orifice.”

While countless factors contributed to Britain’s victory against the Luftwaffe in the summer of 1940, Miss Schilling’s elegant solution to the Merlin’s cut-off problem doubtless played a significant role by allowing the Spitfire to tangle toe-to-toe with the Bf-109. Of course, Miss Shilling’s Orifice was only ever intended as stopgap solution, and eventually all Merlin-equipped fighters were fitted with new Bendix pressure carburetors which did not rely on gravity to operate.

As for Beatrice Shilling, she would go on to a long, productive career at the RAE, working on such projects as the Blue Streak ballistic missile and measuring aircraft braking distances on wet runways until retiring in 1969 at the age of 60. Her personal life was no less eventful; an avid motorcycle racer,  in the 1930s she set numerous records with her modified Norton M30, becoming one of only three women to win the British Motorcycle Racing Club’s Gold Star for completing a lap of Brooklands racing circuit at 160 km/hr. Indeed, it is sometimes reported that she refused to marry her husband, bomber pilot George Naylor, until he himself accomplished the same feat. After the war, she raced cars at Goodwood circuit until shortly before her retirement from the RAE. She died in 1990 at the age of 81.

On a final note, many sources refer to Shilling by the nickname ‘Tilly’, but this moniker is unlikely to have ever been used in her presence. ‘Tilly’ being military slang for a utility truck, the name was likely intended as a dig at Shilling’s supposedly plain appearance – a cruel jab at a woman who did so much to save Britain in her darkest hour.

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Bonus Fact:

A commonly touted fact on the interwebs is that one of the most beautiful women in Hollywood in the 1940s, none other than Hedy Lamarr herself, helped invent the wireless technology we all known and love today.  But is this actually true? Well, not exactly, but the non-sensationalized facts of the matter are no less fascinating, involving Hollywood, the World War II Axis Powers, remote control technology, and, yes, actress Hedy Lamarr.

To begin with, Hedwig Eva Maria Kiesler, better known as “Hedy Lamarr”, once really did patent a “Secret Communication System”, meant to foil the Axis during WWII. It was specifically designed to be used as a remote control system to securely guide torpedoes while getting around the problem of jamming.  Her idea at its core was really part of the larger concept of “frequency-hopping”, with her device developed with composer George Antheil.

Long forgotten until relatively recently, when it was re-discovered by researchers in 1997, the methods used in her invention were far ahead of their time, with the principles behind it paving the way for wide spectrum communication technology we enjoy today in Bluetooth and other wireless technologies.

More specifically, during WWII, the National Inventors’ Council was formed to recruit Americans to pitch in with ideas to foil the Axis Powers. Technological inventions aimed at breaking encoded communications and encryption were especially sought.

Lamarr submitted an idea for a radio-controlled torpedo. As mentioned, Hedy’s idea, in collaboration with the Avant garde musician George Antheil who had previously experimented with automated control of musical instruments, used “frequency hopping”, wherein transmitter and receiver communicated via a channel that constantly changed frequencies, making it difficult to detect and jam.

The idea of the torpedo communication system was to utilize a piano roll like punch tape to create signals within 88 different frequencies (emulating the keys of a piano) of the radio spectrum, in a sequence shared only by the torpedo’s receiver and the transmitter on the ship.

As laid out in her and Antheil George’s patent (US2292387):

“Briefly, our system as adapted for radio control of a. remote craft, employs a pair of synchronous records, one at the transmitting station and one at the receiving station, which change the tuning of the transmitting and receiving apparatus from time to time, so that without knowledge of the records an enemy would be unable to determine at what frequency a controlling impulse would be sent…. in our system such a record would permit the use of 88 different carrier frequencies, from one to another of which both the transmitting and receiving station would be changed at intervals. Furthermore, records of the type described can be made of substantial length and may be driven slow or fast. This makes it possible for a. pair of records, one at the transmitting station and one at the receiving station, to run for a length of time ample for the remote control of a device such as a torpedo.

The two records may be synchronized by driving them with accurately calibrated constant speed spring motors, such as are employed for driving clocks and chronometers. However, it is also within the scope of our invention to periodically correct the position of the record at the receiving station by transmitting synchronous impulses from the transmitting station…”

By thus rapidly hopping from one frequency to the next, the enemy monitoring the radio waves had no hope to intercept and jam the signal, allowing the torpedo to continue to be controlled throughout its journey towards an enemy ship.  Previous to this, a problem existed in that the guidance signal could be detected and jammed, allowing the enemy ship to simply move out of the way of the previously remotely controlled torpedo.

Lamarr and George presented this technology to the National Inventors Council in 1940.  But wouldn’t you know it, the military brass chose to ignore the brilliant idea from the beautiful actress and the avant-garde experimental composer, even though it would have proved extremely useful and quite practical, using existing technologies of the day, rather than needing expensive new technologies to be developed to make it work.

Her design for a “Secret Communication System” using frequency hopping was patented, filed, and forgotten for a time, though later the U.S. military would use this same idea during the Cuban missile crisis. And of course, today this same idea is used all over the place in various wireless technologies.

Eventually, Lamarr’s was given credit for her idea in 1997 when the Electronic Frontier Foundation awarded her with a “Pioneer Award”, and she also received the prestigious Bronze BULBIE Gnass Lifetime Achievement Award, given “to outstanding individuals whose lifetime achievements in the arts, sciences, business, or invention fields significantly contributed to society…” Incidentally, she was the first woman to win that latter “Academy Award of inventors”.

One year later, in 1998, Wi-LAN Inc. purchased a 49% stake in Lamarr’s patent in exchange for some undisclosed amount of company stock, which despite our sincerest efforts we were unable to find how much she got from the swap.

Now, at this point you might be wondering where the actress got the idea and munitions expertise to create such a thing? Hedy Lamarr was born 1913 in Vienna. Her movie debut, at the age of 18, was Gustav Machaty’s Extase (Ecstacy), a 1931 film which is notorious even today for its nudity and a very convincing female orgasm scene.

Shortly after making that film, she attempted to free herself of a domineering husband, Friedrich Mandl, who was a wealthy Austrian munitions dealer she had married at the age of 19. Like a fabled princess, she was all but captive in her castle home in Austria, Schloss Schwarzenau.

Hedy’s husband presided over numerous meetings with leaders of the military industry and, despite both he and his wife having Jewish ancestry, hobnobbed at dinner parties with the likes of Hitler and Mussolini.

Partially as he liked to keep an eye on her, she often accompanied her husband to many conferences and business meetings with various engineers and scientists who specialized in weaponry. It is during this period that Hedy is thought to have augmented her skill with mathematics with valuable information about weapons systems, particularly being privy to technologies her husband’s company and others were trying to develop to use to detect and jam communications systems used by enemy military powers.

To escape her oppressive and ultra-controlling husband, along with her virtual prison in his castle, according to her autobiography, Ecstacy and Me, in 1937, she drugged a maid that looked something like her, then disguised herself as the maid, and managed to leave the castle and flee the country under her stolen identity.

Her Hollywood career was launched before she even arrived in the United States, when she met MGM mogul Louis B. Mayer in Europe. At that time, he convinced her to change her name to Hedy Lamarr (with the “Lamarr” in homage to famed silent film star Barbara La Marr) in order to distance herself from the Ecstasy stigma that had followed her since the film.  She soon had a distinguished career playing alongside a who’s who of great actors such as Clark Gable and Spencer Tracy.

As noted, in the end, Hedy’s unrealized contribution to World War II and wireless technology lay dormant for many years. She didn’t invent wireless itself, as you’ll often read, but she did patent an idea with huge potential. The technology in her “Secret Communication System” patent was broad enough to have wide application and its brilliant use of frequency hopping at its core is essential to many wireless technologies we have today; so technically the industry couldn’t proceed without applying this idea of hers in certain technologies, which first occurred in the public sector in the late 1950s when Code Division Multiple Access (CDMA) was being developed and her invention was re-discovered during a patent search.

Expand for References

Spencer, Michael,  Miss Shilling’s Orifice: Simple Solutions to Technical Issues Can Make All The Difference, The Sir Richard Williams Foundation, September 15, 2017

Heald, Henrietta, Don’t Mention Miss Shilling’s Orifice, Unbound, March 8, 2017

Miss Shilling’s Orifice, Oppo, February 22, 2016,

Beatrice Shilling – Engineer and Battle of Britain Heroine, University of Manchester, September 18, 2015–engineer-and-battle-of-britain-heroine/

Reese, Peter, Beatrice ‘Tilly’ Shilling: Celebrated Aeronautical and Motorcycle Engineer, The History Press,

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