Flexing Wings and Deflecting Controversy

Cries of foul and flexing wings were resounding around the pitlane and press room over the opening two Grands Prix of the season. Some television from Malaysia footage showed a highly visible example of flex in Ferrari's front wing, and issues surrounding the team's rear wing in Bahrain the week before further fuelled this controversy.

But flexi-wings are not a new phenomenon. Arguments over moving bodywork hark back to the first days when wings were tried in F1 and have reappeared regularly ever since. In the nineties, improved knowledge of aerodynamics and carbon fibre conspired to create new semi-rigid and hence flexible wings available to the teams.

Ever since then, the abiding rules - which demand all bodywork parts (and hence wings) are rigid - have been probed and tested by the teams. Therein lies the perennial problem of what is said by the rules and what is implied by the rules. A Standard FIA approach to rules is to have blanket definition (the spirit of the rule) and back it up with clarifications (the letter of the rules). As soon as one interpretation is felt to be outside the spirit, then a clarification is issued and the teams have to head off to find other areas to gain competitive advantage.

In understanding bodywork and rules demanding it be rigid, we have to consider what is possible in the real world. Of course any structure cannot be 100% rigid, especially when it has to be fitted to a light racing car, passing through the air at 200mph.

So the spirit of the rules is to infer that any benefit obtained by parts being overtly flexible is banned. To back this up, the FIA has specified the amount of deflection a part can have under a specific load. Simple tests with brackets, weights and measuring devices are carried to enforce these rules. These so-called deflection tests are the letter of the rules, so to an extent if the team's parts meet these tests, then they must be legal.

There is a real benefit to wings flexing. This allows good top speed and downforce around the corners, giving the driver the performance he needs when he needs it. With such advantages on offer, it is tempting and even unavoidable that teams have to embrace this flex - or "aero elasticity", as the aerodynamicists call it.

With this in mind, we must understand that the accusations pointed at Ferrari can also be pointed to many other teams. So when we come to cover the different applications of flexible wings, we are not including or excluding any specific team.

Wing and slot gap theory

A wing shaped aerofoil will create downforce if its angle of attack is increased - a Formula One car's immense grip is based on this simple theory.

As the car's speed increases, the downforce the wing produces increases; a doubling in road speed equals to a squaring of the downforce produced. This rapid increasing rate of grip is offset by drag; drag stops the car reaching high straight-line speeds. Just as downforce squares with speed, drag cubes with speed. This means that at even higher speeds, the engine has to work harder to push the car faster.

Thus, the ratio of speed, downforce and drag is fixed for any given wing. As most circuits demand a mix of straight-line performance and cornering speed, the compromise is how much downforce and drag need to be traded for the best laptimes.

This process of adding or removing "wing" during practice is all about finding the right set-up compromises for the wing. If the teams could have a wing that was steep for the corners and set at a shallower angle for straights, then the cars could lap faster. But the rules demand that aerodynamic bodywork is neither moveable nor flexing.

Another factor in wing performance is the so-called slot gap. As a single element wing gets set at steeper angles of attack, the flow underneath the wing can't keep up. This flow stalls and separates from the underside of the wing, breaking down the downforce and hence drag the wing creates.

To overcome the need to run ever-steeper wings, race cars split the wing into two. The slot created in between the two elements feeds fast-moving, high-pressure air from above the wing to speed up the flow underneath the wing.

This prevents separation, so the steeper wing angles can create the extra downforce the car needs. Conversely, if the slot gap is too large, the high pressure above the wing escapes and compromises downforce and drag.

Types of wing flexing

There are several types of wing flex. Some are specific to the front wing and others the rear wing.

The rear wing now has two upper elements (the main plane and a flap) and a lower beam wing. Each of these elements is mounted to the endplate and can beneficially flex in two ways, either to reduce the angle of attack or to alter the slot gap.

Flexing the lower beam wing

Back in the early nineties, teams flexed the lower beam wing; this tilted the whole wing backwards, reducing its angle of attack. This effect was clearly visible by the skewed angle of the endplate at speed.

This practice was soon outlawed by a deflection test puling the wing backwards from its front upper edge. With this method prevented by testing, teams ran relatively rigid wings for several years.

Flexing the upper flap

With the endplate now effectively fixed, teams realised the flap was not subject to the deflection test's loads, hence the part could flex and still meet the test. By making the flap flexible, it would bend backwards at speed, reducing its angle of attack.

However, rear facing TV cameras were perfectly suited to view this behaviour, and the FIA stepped in with a new deflection test to pull the flap backwards with three brackets fixed to its trailing edge. With this second rearwards pulling test, all the avenues to make wings flatten at speed were closed.

Opening the slot gap

With tests making the flap and endplate rigid, and reducing angle of attack not possible, the teams' aerodynamicists soon used another basic wing tuning method to achieve similar results.

They found that if they flexed the wing's main plane (the upper forward element), it would open up the slot gap. The high pressure created above the wing bled through the gap and reduced downforce, reducing drag at the same time.

This method was raced during 2005 and was again picked up by evidence from the onboard TV cameras. A third deflection test was devised, and the main plane was pulled downward to try to recreate the effect.

Closing the slot gap

Perhaps tried at the same time as the open slot gap, was the opposite effect. When the slot gap is closed, the wing stalls and the downforce and drag reduce. It is this effect that has been protested in the opening races - as Ferrari do not have the small support between the flap and main plane, teams believe the wing can flex and close the slot gap.

However, it is worth noting that existence of the support does not mean that the wing is not flexing. The slot gap could close across all or only part of the wing's span. Hence, teams with a support in the middle could still have the outer ends fold in to close the slot gap at speed.

As yet no test has been specified to combat this kind of flex, but some clarifications could be expected at Melbourne.

Front wing flex

Just as rear wings can be engineered to flex beneficially, the front wing can also be made to do that.

This is somewhat simpler at the front, and just as important, as the aerodynamic balance front to rear would be upset if the rear lost downforce and not the front. Even though the car would be at speed, some sweeping corners are taken at high speed to have the rear wing partially closed off.

Due to the pendant-like mounting of the front wing from beneath the nose, the front wing can flex in an additional way to the rear wing's slot gap and angle-of-attack.

By drooping from the middle, the front wing can move its endplates closer to the ground for better sealing. However, as the front wing is now much higher from the ground, the practice is not as beneficial as it used to be. This drooping has a deflection test that applies a weight on the plate and any deflection is measured.

Otherwise, front wings are regularly seen from the nose mounted on-board cameras to bend backwards, reducing the angle of attack. I do not know of a test that is applied to the trailing edge of the front wings, to combat this common form of flex.

Other flexible bodywork

As just every air-licked surface on the car has been designed for maximum aerodynamic effect, any part on the car could benefit from flexing. Those directly affecting downforce and drag production are the most likely for lateral interpretations of the bodywork rules. Some of these have already had clarifications and FIA deflection tests applied to them.

The first of the front shadow plate, this is the small portion of floor and the raised monocoque (to meet the flat bottom regulations). As this protruded further and further from the car, the FIA stepped in with a regular test to ensure it did not flex to alter the flow to the diffuser.

The diffuser has also been the subject of controversies. As the diffuser produces very little drag, it can go on to make more downforce without affecting top speed. Suggestions have been made that flexible mounts have been used to allow the diffuser to droop at speed, creating a better seal to the ground and hence more downforce.

More recently, the converse has suggested that a leading team's diffuser could be designed to stall at speed. This would reduce downforce, but critically it would not reduce drag, making the solution somewhat pointless. Hence, this may be just another baseless pitlane rumour.

Other parts of the cars that are often seen to flex, are the various bargeboards, winglets and flip-ups. However, whether that creates any real benefit is arguable. It is more likely that these highly visible parts are simply mounted to a light and hence flexible sidepod cover.

How effective are the FIA tests?

Despite the rules demanding rigid bodywork, the tests do account for a degree of deflection. With relatively light loads placed at specific points on the wing, small deflections of a few millimetres are allowed. In this respect, the tests are effective at catching overtly flexible bodywork, as has been described in the previous sections.

However, the test must be seen as flawed, as both the loads it exerts are too low and the teams' literal interpretation of the test can create loopholes.

Simply raising the loads is one option, but the wings are not designed to take the point loads of the FIA's tests, and sudden failure of a wing under load in an open pitlane is a real safety concern. Equally, the loopholes in the current deflection tests would be equally applicable to the tests with increased loads.

So how do the teams work around the tests? This is of course subject to much speculation; however, the theory is quite simple, and well-informed sources have highlighted some alleged methods.

Firstly, as the test is a specific load - and the wings are then subject to a greater load when out on the track - the most obvious way is to create wings that will progressively bend. This way they meet the FIA test but then bend at a greater rate to create the desired effect. This is a classic example of meeting the letter but not the spirit of the rules.

The progressive flex in the wings can be met in several ways - most obvious is to engineer the carbon fibre lay-up of the wing to create the correct spring-like quality.

Despite the powerful simulation and lay-up software, this is not an exact art, largely due to the manual method of layering the carbon plies into the wing mould. Any small defects between the layers of carbon fibre could lead to sudden catastrophic failure of the wing. It is this safety concern that drives a lot of the fears about flexing wings.

Another method is a more mechanical approach with sprung wing mounts. This rumoured solution uses mounts that meet the deflection test loads, but again progressively give way to move the wing into the desired position.

If the tests can be so easily overcome, then the very nature of the tests needs to be reviewed; or the wings could be made more rigid, by specific design criteria for the mounts and supports, to keep the wing in place.

However, as with traction control, maybe the best way to defuse the controversy is to simply allow the teams a greater freedom for flexing wings to begin with.

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- The Autosport.com Team

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