How F1 moved away from subjective scrutineering on issues of flexing

From time to time we hear teams complaining that the bodywork on a rival’s car is too flexible. Often this leads to yet another test imposed by the FIA to ensure the principles of the regulations are being adhered to. But what are those principles and why is there a continual battle to find the limit of acceptability? 

Article 3 of the Formula 1 technical regulations covers aerodynamic components, and this regulation requires that all aerodynamic components or bodywork influencing the car’s aerodynamic performance must be rigidly secured and immobile with respect to their frame of reference. That, in the case of the majority of the bodywork and wings, is the chassis.

Now of course no engineering component is infinitely rigid. In 1987, 300,000 people walked over the Golden Gate Bridge to celebrate its 50th anniversary. The deflection was measured at 7 feet which sounds alarming but was, in fact, only 75% of the safe deflection limit for the 895,000-ton bridge.

So, if a structure this over-engineered can deflect this amount, it’s not surprising that the bodywork of a Formula 1 car deflects a few millimetres at speed. The important thing, though, is to establish what is an acceptable limit and what contravenes either the specifics or the intent of the regulations.

This is nothing new. Even before we were able to couple computational fluid dynamic (CFD) simulations with finite element (FE) calculations, in other words link aerodynamic calculations to structural ones, we adjusted the stiffness of components using empirical methods.

We would have several constructions of front-wing flap, for instance, which would back off in different ways. So if the driver was complaining of the car being nervous in high-speed corners, rather than just backing the flap off and therefore losing front end in medium-speed corners, we would fit a more flexible flap which would lose load at high speed while maintaining its angle of attack at medium speed.

Tests in those days were rudimentary and often the adherence to legality was a matter of opinion. But equally in those days the final judgement lay with the late Charlie Whiting and his opinion would determine what was right and what was wrong.

Before coupling CFD simulations with FE calculations, teams adjusted the stiffness of components using different wing tweak methods

Photo by: Steven Tee / Motorsport Images

I remember one instance when I was at Renault where our rear wing flap was designed to back off at speed to reduce drag, something all flaps would do to some extent. After a wet race Charlie came to see me and asked me to come with him to the scrutineering area to explain something on our rear wing.

As I approached the car I could see straight away that we were bang to rights. The deflecting flap was acting like a windscreen wiper on the rear wing endplate, leaving a perfectly clean arc on the otherwise rain and mud-streaked endplate. As always with Charlie the instruction was to get it fixed by the next race and, again as always, we did.

As analysis techniques improved, we were able to link our simulations such that the CFD-derived loads could be automatically applied to the FE programme to determine the deflection under load, and this deflected shape then fed back to the CFD to determine the new loads. After some iterative cycles of this, eventually, an equilibrium would be achieved.

As always, the skill of the engineers is to take things to the limit of the regulations to maximise competitive advantage but no further

The other aspect that helped our understanding a lot was when we started to apply these deflected shapes to the wind tunnel model and measure something more akin to reality than was obtained from the extremely stiff model.

While it might appear simple and logical that a CFD simulation and an FE model can be linked it is, unfortunately, not a simple process. Both techniques appear, at a first glance, to be similar.  They both sub-divide an area into many very small elements by applying a geometric mesh to them. In the case of FE, the mesh is applied to the solid structure, while for CFD it’s applied to the surface of the structure and the surrounding air. 

These small elements can conform to the shape of the object and hence the conditions at each of these small areas can be calculated more simply than would be the case for the entire object. In this case the FE equations will be solved for the mechanical properties of the structure, while for the CFD the fluid dynamic equations will be solved.

Both require slightly different types of mesh but with care a compromise can be found that will allow the mesh to be suitable for both without increasing the number of elements, and hence computing time, too much. 

Over 2,000 words in F1's technical regulations specifically cover the tests that teams must conduct to ensure bodywork flexing doesn't exceed the limits

Photo by: Zak Mauger / Motorsport Images

Care must also be taken that an FE analysis determines values at the nodes or intersections of the small elements while CFD solves for the centre of the elements. Luckily with the elements being very small, this slight inaccuracy can be accepted.

In a practical sense, things have moved on a long way from the subjective scrutineering favoured by Charlie Whiting. Today over 2,000 words in the Technical Regulations cover the various tests that teams have to carry out to ensure the flexibility of the bodywork is within acceptable limits.

These generally consist of a given load being applied to the component and the deflection being measured at the point the load is applied. A more general technique was introduced in mid-2021 which required teams to put small circles with crosshairs on the rear wings such that the rearward-looking onboard camera could be used to look for any excessive deflection.

As always, the skill of the engineers is to take things to the limit of the regulations to maximise competitive advantage but no further. Using complex layups of the carbon fibre plies that make up the bodywork components, carefully tuning fibre type and orientation, allows them to get just the degree of flexibility that achieves this without incurring the wrath of the scrutineers and stewards.

Since mid-2021 small circles with crosshairs are used on rear wings to help onboard cameras look for excessive deflection

Photo by: Mark Sutton