Wind tunnels have been present in WRC history since the moment that manufacturers realized that aerodynamics could also play an important role in rallying. The role of wind tunnels in the history of the WR Championship (until 2016) is what we will try to review in the following lines. The role they have played in the current (2017) WRC car generation will be covered in the second article, to be published in a few weeks.
A wind tunnel is a facility where the wind, usually produced by fans, is used to study and measure the action of the airflow around a solid (a rally car in our case), as Bruno Chanetz defined them*. They are the best tool we have to streamline vehicles’ aerodynamic performance. Aero upgrades have always the same goals: downforce, front/rear balance and cooling at the minimal drag cost.
Citroën C4 WRC scale model wind tunnel evaluation at the Laboratoire Aérodynamique Eiffel (Paris, 2006)- picture by auto123.com
Although the first wind tunnel known is dated in 1871, the history of wind tunnels and rallying started as early as 1911. That year, the municipality of Paris forced Mr. Gustave Eiffel to move the wind tunnel he had build at the foot of his famous Tower. He then started the construction of the Laboratoire Aérodynamique Eiffel, located in the district of Auteuil, with a new wind tunnel (soufflerie in French) which is still in operation nowadays. Only two years later, Peugeot sent there their first scale model of a car for a wind tunnel evaluation. Many years later, Peugeot repeated the same operation, for the aero development of one of their most successful rally car models, the 206 WRC. The result was so good that they did it again in 2003, this time for the design of the Peugeot 307 WRC.
Peugeot 307 WRC scale model wind tunnel evaluation at the Laboratoire Aérodynamique Eiffel (LAE, Paris, 2003) – picture by LAE
Both cars were evaluated in the wind tunnels using scale models. Scale models are used in the first stages of car development. They are easy to modify, usually with clay in the past, or with plastic and thin metal parts in the present. And they can be tested at smaller (and cheaper) facilities, normally more available than full-size wind tunnels. But small scale also has problems, with the scale factor as the most important. Also, airspeed is limited in this type of wind tunnels, as hardly speeds higher than 30 m/s (108 km/h) can be achieved.
Peugeot also used the Max Sardou wind tunnel (Saint-Soupplets, near Paris) for the development of the 206 WRC, another facility for scale model evaluation. For the evaluation of full-size models, the French manufacturer took advantage of some of the excellent facilities available in France, such as the S4 wind tunnel of the Institut Aérotechnique (IAT) located at Saint-Cyr-l’École, near Versailles. They developed there the aerodynamics of the 205 Turbo 16 in 1984. Other rally cars, such as the Seat Córdoba WRC, have been developed in this wind tunnel (túnel de viento in Spanish).
Peugeot’s sister company inside the PSA group, Citroën, was also a regular customer of the Laboratoire Aérodynamique Eiffel. Scale models of some of the most successful Citroën rally cars were evaluated there, from the Xsara WRC (2001) to the C4 WRC (2006) or the DS3 WRC (2010).
Citroën Xsara WRC scale model wind tunnel evaluation at the Laboratoire Aérodynamique Eiffel (Paris, 2002) – picture by auto123.com
Even with a scale model, the use of the smoke visualization technique allows engineers to check the flow around the car at specific areas, to validate the aero design of the rally car.
Citroën DS3 WRC scale model wind tunnel evaluation at the Laboratoire Aérodynamique Eiffel (Paris, 2010) – picture by Zeppelin
The full-scale wind tunnel of S2A (Souffleries Aéroacustiques Automobiles, a consortium between PSA and Renault) located also very close to Versailles, at Montigny-le-Bretonneux, was one of the facilities used by Citroen for full-scale models aero evaluation, as they did with the C4 WRC in 2006.
Citroën C4 WRC real size model wind tunnel evaluation at the S2A facilities (Montigny-le-Bretonneux, 2006) – picture by S2A
The use of real size cars has some advantages over scale models: real conditions can be reproduced, especially in terms of wind speed, and there is no scale factor. But they are more expensive, and fewer facilities are available.
The development of full-size rally cars was also behind the success of the iconic Fiat and Lancia rally cars in the 70s and 80s. And most of this development took place in three facilities, all located around Torino.
Lancia Stratos prototype at the Pininfarina wind tunnel – picture by Lancia
The Pininfarina wind-tunnel, located at Grugliasco, started to operate in 1972, as the first wind tunnel (galleria del vento in Italian) with the ability to test full-sized cars in Italy, but also one of the first in the world at that moment. The aero development of the Lancia Stratos and the Lancia Rally 037, amongst others, took place in this facility.
Lancia Rally 037 prototype at the Pininfarina wind tunnel, 1980 – picture by Lancia
The pieces of wool that can be seen attached to both cars are one of the simplest visualization methods used in wind tunnels, known as Tuft technique. It allows engineers to evaluate the path the air follows over the car, so they can validate if it matches what they had imagined during the design phase.
The picture above also includes (on top) an example of some of the results that are usually obtained during a wind tunnel test: the drag coefficient (Cx) and the front and rear axis lift coefficients (Cza and Czp). These coefficients are obtained after measuring the drag and lift forces in the wind tunnel. The lift forces are measured using load cells, which are connected to the sensors visible in the picture under the wheels.
The Pininfarina wind tunnel is still in use: one of the latest models evaluated recently this year was the Hyundai i20 Coupé WRC, where Hyundai engineers had the chance to test all the modifications introduced in the car in the last year.
Hyundai i20 Coupé WRC test at Pininfarina wind tunnel, 2020 – picture extracted from this video by Hyundai Motorsport
A second wind tunnel in Italy was behind the success of the Italian rally cars in the 80s. It was the FIAT wind-tunnel located at Orbassano, where the aerodynamics of models such as the Lancia Delta S4, the ECV (prototype of Group S) or the Lancia Delta HF was developed.
Lancia Delta S4 prototype at the Fiat Wind tunnel, 1985
In addition to the external aerodynamics, wind tunnels are also very useful in the development of cooling internal flows. For that purpose, Fiat and Lancia used the climatic wind tunnel of the Industria Piemontese Radiatori per Automobili (IPRA) located at Pianezza, also near Torino. The advantage of this facility was the fact that it allowed working at different air temperatures.
Porsche’s alma matter Ferdinand Piëch always showed great faith in aerodynamics as one of the key tools to win races. He first used the wind tunnel (Windkanal in German) for the improvement of the aero design of the Porsche cars competing at Le Mans as early as in 1966. The result was that the Porsche 906 won the Protos 2l category that year and finished in the 4th, 5th and 6th position in the final absolute classification. So, when it was clear that his most successful design ever, the Porsche 911 had a tendency to lift its front end at high speed, the solution was obvious. His team of engineers, led by Tilman Brodbeck, developed a series of experiments in the wind tunnel at Stuttgart University to confirm how the air was lifting the front end of the 911. To solve it, they designed a lip (known since then as ducktail) and they obtained a 50% reduction in lift.
Porsche 911 Carrera RS 2,7 real size model evaluated at Stuttgart University wind tunnel (Stuttgart, 1973) – picture by Porsche
The image above also shows how the load on each axis was measured in those years: employing hanging supports for each axis, connected to load cells.
Ferdinand Piech was not only a pioneer in the use of wind tunnels for sport auto. He was also one of the first to consider crucial keeping the secrecy in wind tunnel testing. A very good example of it was the design process of the Audi 100. Its aerodynamic body concept emerged from no fewer than five wind tunnels, each contracted to work on a separated section of the car, while no-one was allowed to see the car in its totality. Such secrecy is the reason why it was (and still it is) so difficult to find images of rally car testing in wind tunnels, especially from German or Japanese manufacturers.
The Audi wind tunnel at Ingolstadt saw the aero development of the different Audi Quattro models, as well as other rally car models from the VAG group, such as the Skoda Fabia WRC. But no images have been found from any of these tests.
Also, we found no images of the wind tunnel testing of the successful VW Polo WRC. The initial development was carried out in 2012 at the wind tunnel available at Volkswagen facilities in Wolfsburg. However, due to the lack of moving ground, most of the tests were developed at the wind tunnel of the Research Institute for Automotive Systems and Vehicle Engines (FKFS) of the University of Stuttgart. This was one of the only few full-scale facilities with moving ground available in that period in Europe, and it was also used occasionally by Škoda Motorsport.
Video about the wind tunnel of the Research Institute for Automotive Systems and Vehicle Engines (FKFS) – University of Stuttgart
Unfortunately for Volkswagen Motorsport, the moving ground was incorporated into the VW Wolfsburg’s wind tunnel in 2017, too late for the team, as they had already withdrawn from WRC competition then.
Ford Climatic Wind Tunnel, Merkenich – picture by Ford Europe
Similarly, there are no images available from the Ford rally cars wind tunnel tests, which have been consistently developed at the Climatic wind tunnel available at the Ford’s Merkenich design site in Köln. The design and development of Ford models such as the Ford RS 200, the Sierra Cosworth RS, the Escort Cosworth RS, the Focus WRC or the Fiesta WRC took place there. The only images we have found are from the design studio where the models to be evaluated at the wind tunnel were prepared.
Ford Escort Cosworth RS model for wind tunnel evaluation at MGA DesignStudio – picture from Stephen Harper
Japanese manufacturers Mitsubishi and Subaru developed the aero of most of their successful rally models at their own wind tunnels (風洞 in Japanese). But, because all of them relied on European structures for the management of their WRC programs, very often the refinement or further development took place in European facilities, mostly located in the UK, as we will see later.
Mitsubishi did the aero design of the different Lancer Evo Group A models at the wind tunnel inside the Mitsubishi Heavy Industries Headquarters located at Hyogo-ku, near Kobe.
2015 Subaru WRX STI NBR wind tunnel evaluation at Subaru Facilities in Gunma – picture by Subaru Motorsport
Similarly, the aero design and development of most of the different Subaru Impreza WRC models was undertaken by the Fuji Heavy Industries (FHI) Design Team at its own wind tunnel, available inside FHI headquarter’s in Gunma.
Toyota motorsport activities in rallying have been managed from Europe since the creation, in the 70s, of the Toyota Team Europe. Then, it is not surprising that Toyota has carried out most of the aero development work in European wind tunnels. In fact, Toyota posses two 50% scale wind tunnels in its European Headquarters in Köln. But, for the evaluation of full-scale models, they used other facilities. That was the case of the aero development of the Corolla WRC, which took place at the facilities of the German-Dutch Wind Tunnels Foundation (DNW) located in Marknesse (Netherlands). The video below shows nice images from the tests developed for the design of the Corolla’s rear wing.
Toyota Corolla WRC real size model wind tunnel evaluation at DNW facilities, from the video Toyota Corolla WRC. The making of, by ModelMotorsport
As, explained, and due to the common practice of private rally teams (Ralliart, Prodrive, M-Sport or Tommi Mäkinen) managing the rally activities of big manufacturers (Mitsubishi, Subaru, Ford or lately Toyota), it is also usual that teams use closer (European) wind tunnels during the development of new car’s evolutions. In the case of Ralliart, in addition to the Mitsubishi wind tunnel in Japan, they used other facilities for the development of the different Lancer Evo group A: the S10 wind tunnel at the IAT at Saint-Cyr-l’École or the wind tunnel of the British Motor Industry Research Association (best known as MIRA) located at Nuneaton, Warwickshire). However, for the Lancer WRC04, the team asked for help from Lola, not only because of their scale model wind tunnel, located in Cambridgeshire but also for the aero design capabilities of the Lola team, who developed the unique aero package of this model, as we already reviewed in a previous post.
Mitsubishi Lancer WRC04 scale model at the Lola wind tunnel, Cambridgeshire 2003.
The image above shows another method to measure loads in a wind tunnel: using a supporting arm, connected to load cells on top of the wind tunnel.
Subaru (Prodrive) Ford and Austin also used the MIRA facilities during the aero development work of some of their WRC models: the Impreza WRC in the case of Prodrive (which was carried out under the guidance of Peter Stevens), the Ford RS 200 or the Sierra Cosworth RS in the case of Ford, and the MG Metro 6R4 developed by Austin-Rover Group Aerodynamics with the support of Williams F1 Team, in the case of Austin.
Subaru Impreza WRC S3 clay-modified for wind tunnel evaluation – Images extracted from video Developing the 1997 Subaru Impreza World Rally Car, by Rallysights (full video).
Since Hyundai officially joined the WRC Championship in 2014, the aero development of the different i20 WRC models has been always done by Hyundai’s Aerodynamic Development Team in the full-scale Hyundai Aero-acoustic Wind Tunnel (HAWT) available at the District B of the Namyang R&D Center (southwest of Seoul).
Diagram of the Hyundai Aero-acoustic Wind Tunnel (HAWT) in the Namyang R&D Center – picture by Hyundai
Hyundai’s wind tunnel (풍동 in Korean), like most of the full-scale wind tunnels, is a closed-circuit (Göttingen) wind tunnel. It is an ideal facility for WRC cars, as winds up to 200 km/h can be generated. With a cost of 45 million dollars, it was built by Aiolos, one of the biggest wind-tunnel suppliers in the world.
The increase in the capacity and power of numerical (CFD) simulation tools have allowed some manufacturers, in the last years, to design their rally car models without any wind tunnel support. One of the first rally cars exclusively designed by CFD was the latest evolution of the Subaru Impreza, the S14 WRC’08 that took part in the WRC Championship in 2008.
P.Solberg/P.Mills, Subaru Impreza S14 WRC’08, Rally Catalunya 2008, 5th – picture by Subaru World Rally Team
The use of only CFD-based tools has proven to be efficient, but numerical results always require to be experimentally validated. So did Subaru (Prodrive) months after the car appeared in the WRC Championship, by sending the car to the wind tunnel to validate the design. It is proof that wind tunnels still play (and will continue to play) a key role in the aero development of (rally) cars. Long-life to wind tunnels!
This is the first of a two-articles series devoted to the role of wind tunnels in WRC history. The second one, about the role of the wind tunnels in the current (2017) WRC car generation will be posted in a few weeks.
If you find or have missing information or pictures about this post, do not hesitate to contact us, by sending an email to firstname.lastname@example.org. We love to learn!
*A century of wind tunnels since Eiffel, Bruno Chanetz, Comptes Rendues Mecanique 345 (2017) 581–594