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1 de abril de 2022

The Ground-Effect and the return of the Venturi Tunnels to Formula 1


Antonio Eiras

There has been some confusion in the press about this year’s new F1 technical regulations. The main novelty is not the return of the ground-effect, but its optimization with the real Venturi Tunnels, imposed under very precise and restrictive limits, on the F1 sidepods’ underside, as they were used in the late 70s and until 1982.


Theground-effect is a physical concept that relates the influence of the ground proximity on the behavior of an airflow that surrounds a moving solid. With the reduction in ground clearance, the induced changes on the air that flows between the moving solid and the ground, and the consequent air pressure changes, will induce changes on the lift and drag forces over the solid body. This concept applies to and has a relevant influence not only on cars’ aerodynamics but also on airplanes, helicopters and all other aerospace vehicles or devices.


As I explain in the technical article “Wings-How they work” published in my website, a wing efficiency increases with the ground proximity, this effect becoming so notorious when the ground clearance is inferior to half the cord wing (Figure 1). The reason for this increase in the wing efficiency is the simulation of a Venturi Tunnel between the wing and the track, with the airflow acceleration on the simulated throat on the wing’s underside lowest area.


The negative side of a wing working in ground-effect is its high sensibility to the small ground clearance. When a front wing of a Formula car is placed very low, near the track, as with the last forty years’ Formula 1 cars, the small ground clearance not only can be obstructed by a turbulent airflow from the wake of another car, but also can be blocked by an excessive reduction of the ground clearance induced by the very high downforce loads. Therefore, the wing will stall, with the airflow separation in its underside, and with a sudden loss of downforce and increase in drag. With less downforce the wing recovers the upper position, and the airflow will reattach to the underside of the wing, increasing the downforce generated.


This cyclic and well-known phenomenon, once called “pitch sensitivity”, affected the Formula 1 front wings, making difficult to follow closely another car and, consequently, overtaking. And this is the phenomena the new generation of F1 cars are suffering and called “porpoising”, on and because of their very extreme sidepod’s Venturi under tunnels.

TheVenturi effect is well known, since its discovery by Giovanni Battista Venturi, in the 18th century, and refers to the fall in a fluid pressure as it flows on a constricted section of a closed system, a Venturi Tube or Tunnel (Figure 2). Between its so many mechanical applications, the carburetor is one of the most notables.


In 1981 I was in the middle of my first graduation, in Medicine, and decided to start working on race cars' technical illustration. By doing this I intended to make some money, of course, but mainly to satisfy my so great passion for this sport, in a very special way for Formula 1.


Those were times of great changes in F1, with the spread and so fast evolution of the turbocharged engines, first introduced by Renault in 1977, and the development of the so called “wing cars”, that made use of inverted wing profiles on the sidepods to generate great amounts of downforce, a technical solution first introduced in Colin Chapman’s Lotus 78, also in 1977 (Figure 3).


In the “wing cars” of 1977 to 1982, the enormous amounts of downforce were generated on the real Venturi Tunnels that were created using inverted wings profiles on those cars sidepods, working near the track. Those Venturi Tunnels were laterally closed by the sidepods lateral walls, that extended until the ground with the help of the infamous mobile “skirts”. With this technical solution the ground-effectwas maximized, and the high levels of downforce generated on the sidepods' Venturi Tunnels lead to the reduction on the front and rear wings dependence and dimensions, as they were used to trim the front/rear downforce to each circuit.


In my Medical studies and practice, Cardiology has always been my favorite area, and from Physiology I was very familiar with the Bernoulli equation, that expresses on Physics and Math’s the Venturi effect.


And, so, for my first work I’ve made a full article, with text and illustrations, on ground-effect, with an extensive historical review, from the infamous Auto-Union Type D Streamliner record car of 1938, the Chaparral 2J “vacuum cleaner” and the March 701 of 1970, analyzing the Lotus 78 and 79, the outlawed Lotus 88, leaving the open future to its widespread motorsport and road sports cars use. The article was published in three issues in December 1981 on the Portuguese weekly newspaper “Motor”.


The following year would be marked by several Formula 1 accidents, that revealed the lack of security of both cars and circuits, given the overall high performance and speeds, mainly in curves, of the new “wing cars”. To avoid the “porpoising” effect and optimize the ground-effect on the Venturi Tunnels, the suspensions were made very stiff, which made the cars increasingly dangerous.


The third technical revolution of that period, introduced in 1981 by John Barnard, with the carbon fiber composite monocoque chassis of the McLaren MP4/1, had just begun, and immediately proved to be a much safer technology than the old aluminum sandwich monocoque chassis, with John Watson’s notorious and terrific accident at Monza, during that year’s Italian GP.


With the limited car’s security and the outdated security of many of that time circuits, the alarmed FIA reacted to the dangerous way F1 was driven and forbid the use of the Venturi under tunnels, imposing, from 1983, a flat underfloor from the front axle to the rear wheels.


The different teams reacted to this sudden change in the technical regulations, with its own solution. Gordon Murray created a successful Brabham BT52 with short arrow shaped sidepods, Bernard Dudot conceived the also very competitive Renault RE40, that presented long sidepods with blow-diffuser, Rory Byrne remained faithful to its very peculiar concepts and the Toleman TG183B presented a massive bodywork with short sidepods and a double rear wing.


The new McLaren MP4/1C revealed the way to go, with a second revolution from John Barnard. With its own and methodic work, the Briton conceived, with the help of Alan Jenkins, in the already fabulously designed MP4/1 original sidepods, the “Coke bottle” concept, that would be copied and adopted by all the other technicians in their Formula’s cars (Figure 4). Until now, forty years later!


The original idea of Professor Barnard was to narrow smoothly the sidepods, at the engine level, as the Coca-Cola bottleneck, to create a splitter in front of each rear wheel, also forcing, using the Coanda Effect, the airflow away from those wheels and over the ramp of the rear lateral diffusers. With this concept, Barnard not only reduced the drag of the rotating rear wheels, but, mainly, achieved a considerable gain in the downforce generated by the splitter and on the improved rear lateral diffusers (Figure 5).


By the time, the different technicians also understood that they could achieve a considerable downforce amount from the flat underfloor. As I explain in another technical article, also published in my website, “Flat Underfloor-A big hidden wing”, the use of a rear diffuser can simulate a Venturi Tunnel under the flat underside of a race car, with the rear limit of the flat Reference Plan working like the Venturi throat (Figure 6).


And so, during the eighties, all the other teams copied the innovative McLaren MP4/1C and the “Coke-bottle” rear configuration of the longest possible sidepods became the way to follow for the most efficient aerodynamics of a Formula 1 car, and still is, near forty years later, as Ferrari proved recently with its F1-75 so effective new car!


The new F1 technical regulations are excessively complex and restrictive. The different teams followed their own way for the first year, but, as soon as one solution reveals to be the one to follow, there is a risk of all the cars will look very much similar.


And with all the time and effort to develop and apply the new regulations, the anachronic DRS still is so crucial in overtaking and, consequently, so conditioning of race results.


In my opinion, here was no need to impose so big changes to improve competitivity and increase overtaking. This could have been made with the old regulations, but also can with the new ones, and some changes:


• The raise of the front wings, increasing the minimal ground clearance to over half the wing's cord, to avoid the ground-effect and reduce these wings sensitivity.


• The reduction on the brake’s efficiency and consequent increase in the braking distances.


• The reduction on weight, wheelbase, and overall length of the cars, that would be more agile and with better handling.


Among the current F1 technicians, the best prepared to make good use of these so deep changes of the technical regulations, was, without no doubt, Adrian Newey, not only a great innovator and passionate for aerodynamics, but also, as far as I remember, the only one who was working on Formula 1 at the “wing cars” era. He started working with Harvey Postlethwaite, at Skol Fittipaldi Team in 1980, just after it’s graduation in Aeronautics and Aerospace Engineering at the Southampton University, with a last year’s work on “Ground-effect aerodynamics as applied to a sports car”. 


All the other great technicians that marked those so fast changing times in Formula 1, like John Barnard, Patrick Head, Mauro Forghieri, Frank Dernie or Rory Byrne, already retired or even prematurely died, as Colin Chapman, Gérard Ducarouge and Harvey Postlethwaite.

As usual and expected, the high competitiveness of the new Red Bull RB18 is the natural result of both Newey's genius and its forty years race cars' experience.


The last dominant “wing car” of the 80s was a Ferrari, the 126C2 (Figure 7), developed by Postlethwaite, that won, for the Scuderia, the 1982’ Constructors World Championship title, just like this year’s so competitive F1-75, that revealed a resurgent Scuderia and won the first race of a new Formula 1 era.

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2 de janeiro de 2023

How do I do it


Antonio Eiras


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