With safety again in front
HYLO: High Yaw Lift Off
Problem and solution
HYLO stands for “High Yaw Lift Off.” The story behind this phenomenon regarding a DTM car: If such a touring car prototype, built according to the Class 1 regulations, moves out of its forward head-on direction of travel and begins to rotate more than 135 degrees at a speed of over 180 km/h, then there is a risk of the wheels losing contact with the ground. The cause: If the air flows over the car at an angle whilst the car continues moving forward, the aerodynamic downforce generated by the vehicle through its body, front spoiler, underbody, rear diffuser and rear wing is lost. At the same time, forces of aerodynamic lift are generated. If these forces of lift exceed the weight of the racing car, it can take off.
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Without HYLO: Flow mostly uninterrupted, areas of low pressure are clearly present (marked in blue).
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With HYLO: Flow interrupted, areas of low pressure are reduced (marked in blue) and a point of stagnation pressure is introduced.
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With HYLO: The movement of the air over the HYLO when moving forward through the air side on.
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With HYLO: The movement of the air over the HYLO in the normal forward driving direction.
This lifting is prevented by the HYLO system developed by Audi: The surface area of the rear wing supports is enlarged by additional profiles attached to both supports. The extended rear wing surfaces offer more resistance when the car breaks away or rotates when the air flows over the left or right sides of the vehicle. This interrupts the airflow. The built-up air creates pressure on the rear of the car and acts against the forces of lift being generated there. When this stagnation pressure is greater than the aerodynamic forces of lift, the risk of the car, which has lost control, beginning to lose contact with the ground through its wheels, is significantly reduced.
Garry Paffett’s accident at Norisring in 2017.
The triggers
Two accidents induced the development of the HYLO at Audi Sport: Firstly, Augusto Farfus (BMW) at the Lausitzring in 2016, and secondly Gary Paffett (Mercedes) at the Norisring in 2017. Their DTM cars began lifting off of the ground after they started rotating at very high speeds. A third incident like this also occurred at Brands Hatch in 2019, which emphasises the purpose of a new security system like the HYLO.
Pietro Fittipaldi’s accident at Brands Hatch in 2019.
At Brands Hatch, Pietro Fittipaldi’s Audi RS 5 DTM lost contact with the ground whilst the car was spinning during qualifying. The car flew backwards over the gravel into a tyre barrier. Fittipaldi’s fortune: The road was wet. Therefore, the pace at which the Brazilian spun was slower than usual. On dry tarmac and therefore at higher speed, his racing car would have experienced even more lift and would have lifted even higher.
Yannick Mangel
Development and developers
The first inquiries for further safety measures on DTM cars began at Audi Sport in 2018. From the spring of 2019, discussions followed with the ITR, the DTM umbrella organisation, and the competition. Key point: The new system must not affect the competitiveness of the cars. The HYLO should not create any advantages or disadvantages for anyone.
With the help of CFD technology (Computational Fluid Dynamics) in particular, Audi Sport further developed its HYLO system in the summer of 2019, using flow simulation. In this way, a wide variety of geometric shapes for the new additional profile for the rear wing supports were virtually configured to save time and money. Their effects in all possible driving conditions were also modelled and checked in this way. Three engineers were in charge: Axel Löffler, Head of Development Vehicle/Aerodynamics at Audi Sport, and his colleagues Yannick Mangel and Axel Burnier.
Design and testing
The HYLO system consists of two panel components that are attached to the left and right rear wing supports. The cover plates, which are fitted by a frame, are made of carbon composite material.
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The HYLO highlighted on the Audi RS 5 DTM.
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The HYLO construction highlighted.
The HYLO from Audi was tested on the racetrack for the first time at Jerez in December 2019. A model of the Audi RS 5 DTM specially designed for testing was exclusively equipped with the new system. The most important finding: the new add-on components actually have no influence on the conventional downforce, the balance and the air resistance values. “The system also proved to be performance-neutral in practice,” says HYLO project manager Axel Löffler. In June 2020, a vehicle from competitor BMW was also equipped with the HYLO for the first time during the DTM test at the Nürburgring.
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Audi RS 5 DTM without the HYLO at the Nürburgring ITR test.
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Audi RS 5 DTM with the HYLO at the Nürburgring ITR test.
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Testing the HYLO on the Audi RS 5 DTM at Vallelunga.
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BMW testing the HYLO from Audi at the Nürburgring ITR test.
Audi R8 tire pressure sensor (2001).
Progress through safety
All-wheel drive, turbo, diesel, hybrid, pure-electric drive: In line with its slogan “Vorsprung durch Technik,” Audi has made significant technical advances in motorsport for almost 40 years. Equally important to the brand with the four rings are effective innovations in the active and passive safety of its racing cars.
A milestone in Audi’s safety initiatives in racing came in 2001: After the fatal accident during testing involving factory driver Michele Alboreto, Audi went through much effort to develop tyre pressure sensors that indicate losses in pressure in good time before a failure or accident, even in its racing cars. In addition, the vehicle developers from Ingolstadt also devoted themselves more intensively than ever to the risks of taking off with a Le Mans prototype (LMP).
Audi A4 DTM carbon fibre monocoque (2004).
Audi transferred important design advancements from the Audi R8, which won the Le Mans 24 Hours five times and a total of 63 of its 80 entered races, to its first factory-built car of the new DTM generation. A seat fully integrated in the carbon fiber monocoque was created for the Audi A4 DTM in 2004. In addition to maximum head protection, this also offers the driver optimised comfort. Thanks to its ventilation from behind, the act of driving in the often very warm touring car cockpit is made considerably easier.
Audi continued transferring further construction advancements from its Le Mans project to the DTM car. Like the innovative roof structure integrated into the overall concept of the Audi A4 DTM, with newly introduced support structures for more stability and protection. These measures proved to be particularly effective in the violent DTM accidents of Tom Kristensen (2007) and Alexandre Prémat (2010): The roof of the car remained intact and provided both drivers critical room and protection for their survival.
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Audi A4 DTM #7 (Audi Sport Team Abt), Tom Kristensen (2007).
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Tom Kristensen’s accident at Hockenheim in 2007.
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Audi A4 DTM #9 (Audi Sport Team Phoenix), Alexandre Prémat (2010).
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Alexandre Prémat’s accident at Adria in 2010.
With the introduction of the new DTM technical regulations in 2012, Audi proceeded to transfer its safety technology yet again. The Audi RS 5 DTM, which has been used in the version with the turbocharged engine since 2019, consists of a driver’s cell that is standardised for all DTM cars. It was also developed by Audi Sport based on the experience gained over many years of designing LMP racing cars. This also applies to the crash absorbers installed in all current DTM cars. These crash absorbers, in the event of an impact at the front, rear or sides, deform and absorb the forces acting on them, with the deformation occurring as designed through precise calculations.
This process comes full circle with the introduction of the HYLO system for the 2020 DTM racing cars. Audi is once again delivering safety advancements gained from practical experience and from ever-increasing research. Whether for the Le Mans sports prototypes or the DTM cars, Audi has been looking for and finding innovative ways and means to counter the risk of lifting racing cars that are rotating or spinning at speed for almost 20 years. And whether with a step built into the front diffuser, with an angled underbody, with a “shark fin” over the rear, with openings in the fenders or now with HYLO on the rear wing supports, Audi always makes motorsport a bit safer.
HYLO
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