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Formula One exhausts: Henri Coandã must be laughing in his grave


By Berthold Bouman

Formula One exhausts: Henri Coandã must be laughing in his graveSome great inventors were already a legend during their lifetime, others, like aerodynamicist Romanian Henri Coandã, became famous after they died and therefore never saw much of the fruits of their labour. The ‘Coandã effect’ is the magic word in Formula One today, as teams are searching for means to control the airflow under the car.

The FIA has banned the practice of using exhaust gases to boost the effect of the rear diffuser, two years ago Lotus even moved the exhaust outlets to the front of the side pods, where the gases were mixed with the airflow under the car.

Controlling that airflow is important as it generates most of the downforce for the rear of a Formula One car. By using the exhaust gases and the Coandã effect, the Formula One boffins now created a curtain of air (the exhaust gases) between the inner wall of the rear tyre and the rear-wing end plate, in such a way that the air under the car is trapped and can only escape through the rear diffuser.

According to Wikipedia, “The Coandã effect is the tendency of a fluid jet to be attracted to a nearby surface. Coandã used it for his Coandã -1910 aircraft which mounted an unusual engine designed by Coandã. The motor-driven turbine pushed hot air rearward, and Coandã noticed that the airflow was attracted to nearby surfaces. He discussed this matter with leading aerodynamicist Theodore von Kármán who named it the Coandã effect.”

The VZ-9 AV Avrocar - Photo: Wikimedia

The VZ-9 AV Avrocar – Photo: Wikimedia

It is used in a variety of applications, the most famous being the Avro ‘flying saucer’ built in 1958. The VZ-9 AV Avrocar was a Canadian vertical take-off and landing (VTOL) aircraft developed by Avro Aircraft Ltd. as part of a secret U.S. military project carried out in the early years of the Cold War. Two prototypes were built as test vehicles, the project remained classified until 2012.

In a traditional hovercraft design, the air is blown into a central area and directed down with the use of a fabric or rubber ‘skirt’. The Avrocar was in fact an ‘inside out’ hovercraft-like aircraft from which the air exited in a ring around the outside of the aircraft and was directed by being ‘attached’ to a flap-like ring.

That same ‘curtain’ of air is now used in Formula One cars as well, while it is also used in aircrafts and helicopters, in modern helicopters the mechanical tail rotor is replaced by a controllable air jet to provide the anti-torque necessary to prevent the helicopter from spinning around the axis of its main rotor.

Coandã was an aerodynamics pioneer and inventor, he died in 1972 at the age of 86, not knowing that the effect named after him, would, more than 40 years later, cause so much turbulence in the world of Formula One.

The latest controversy surrounding the Coandã effect, was sparked by the design of the Williams exhaust outlets, regulations say the outlet has to have one aperture, however, in an effort to further control the airflow, Williams Technical Director Mike Coughlan has come up with a solution that, at first glance, divides the outlet in two apertures. But examined closely, the piece that divides the airflow has a small gap in it, which would make it legal.

The Williams 'solution', exhaust outlet is still one aperture - Photo: Williams

The Williams solution, exhaust outlet is still one aperture – Photo: Williams

Coughlan said, “Ours is OK, because if you look at ours it’s actually not a single piece it’s two pieces. The rule is an aperture size, and ours is an aperture size; ours is one aperture because it’s joined by a small piece in the middle.” And he added, “You’re governed by total aperture size, but singular aperture, and ours is a single aperture joined by a very small slot. So it’s actually two pieces, if you look closely you’ll see.”

ESPN today reported Williams ‘are now seeking further clarification on this and a decision as to whether this design will be carried forward will be made before the first race.’

To be continued …

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