The 2007 Technical Review (part II)

In 2007, a few truly new solutions were developed. But the convergence of other design ideas made most cars fundamentally the same, with the widespread adoption of zero keels, seamless-shift gearboxes and pod wings.

Some of the new rules changes challenged the teams, particularly the single tyre supply and engine freeze, leading the teams to rework their cars' layouts to suit the new tyres, and correspondingly, forcing the aerodynamics teams to match the cars' new weight distributions.

Tyres

As the most far-reaching change, the new single tyre supply affected the season more than any other regulation change.

From the data provided by Bridgestone ahead of the pre-season tyre tests, and at the tests themselves, the new generation tyres had a tendency to wear the rears and under-work the fronts if run with a weight bias suited to the 2006-spec cars.

So, the teams knew ahead of time that the cars would need more weight over the front axle. This could be accommodated partly through shifting ballast around, but a more permanent solution would require altering the layout of the car.

The car's weight is made up of three major components - the engine, the gearbox and the monocoque. Altering the placement of these along the car's length will have a fundamental impact on the weight split front to rear.

At the same time, the teams want the fuel cell to be placed centrally, so as not to affect weight distribution as the fuel load lightens. The size of the tank is determined by the longest stints that the teams expect to run in races.

Shortening the monocoque or lengthening the gearbox pushes weight forwards. Clearly, some teams underestimated how much this needed to be altered. Changing the layout of monocoque and gearbox length is nearly impossible during the season, thus some teams were held back by their layouts from an early stage in the season.

As well as demanding different weight distribution, the new tyres also differed greatly from the Michelins in the way they deformed from cornering forces.

Although tyres appear to remain firm and upright all the way around the lap, the tyre's frontal area is actually constantly shifting. The tread being pulled sideways from cornering, or the sidewalls squashed upwards by downforce or braking loads. Thus, the car's aerodynamics are constantly being affected by the changing shape of the tyres, and even the ride height is being altered.

For Renault and Honda, these issues overshadowed all other problems - the cars never provided the aero figures the wind tunnel suggested.

Bridgestone had supplied rubber pneumatic tyres to all teams for wind tunnel testing - these replicate, to some extent, the deformation the tyres experience in racing conditions. But making these truly realistic is not possible, and highlights the limitations in wind tunnel testing.

Most teams are now focusing on increased CFD simulations, as it is possible to recreate tyre deformation more accurately with the CFD software.

On the track, the tyres proved to have some specific handling traits which largely related to the way front tyres worked. Due to the stiffer sidewalls the tyres gave grip, but would yield grip if the driver turned into a corner too aggressively.

Thus, drivers with a sharp turn-in driving style found that they lost speed on corner entry from understeer. This forced the driver to either alter his style, or set the car up for more oversteer to make the car turn quickly enough without inducing the understeer.

Of course some drivers' style didn't suit oversteer either. By mid-season, most teams and drivers had found a style and set-up to deal with this issue.

Engines

With the teams having been forced to develop smaller capacity V8 engines featuring dimensional and material restrictions, this year marked the first year of what will now be a ten-year engine development freeze.

Engine development has been relentless in F1, and engine speeds and outputs have grown in an effort to improve lap times. Last year's engines would have revved to 20,000rpm and produced around 750bhp. The new freeze restricts development, and sets peak engine speed to 19,000rpm.

An F1 engine is made up of more than a thousand parts. Most of these are internal, and critical in allowing more power through better breathing, reduced weight or friction.

These areas are now frozen, leaving only a handful of components free to develop. Thus, only the airbox, inlets, exhausts, ancillaries and electronics can be freely developed. These items add only a very small amount to the engine's performance, and this year the gains made were a fraction of those found in previous years.

Additionally, as engine revs are limited, more power cannot be gained. The teams can only look for more power at lower revs via tuning of the airbox and exhausts.

Gearbox and hydraulics

Formula One cars had adopted the electro-hydraulic sequential shift system by the mid-1990s. This change affected the mechanisms that select the gears. But even though this semi-automatic box was a revolution, the core of the gearbox was still very much the same.

The constantly-meshed gear pairs are engaged to drive the differential from the engine by dog rings engaging on teeth set into the face of the gears. These dog rings are moved into engagement by the selector forks, driven by the selector drum.

Despite shift speed being reduced to a few milliseconds, there is still the need to disengage one gear and engage the next. This process can be sped up only so far.

As long as three years ago, McLaren and Honda (nee BAR) raced seamless-shift gearboxes. It took time for the other teams to catch up with this revolution - only this year did we have a near-full grid of seamless gearboxes; Spyker and Toro Rosso being the only teams not having access to a seamless set-up.

Despite the systems having been in use for several years, there is still little information coming from the teams on how they work. What is known is that the systems retain the conventional two-shaft gearbox and single clutch. A double clutch would provide a seamless shift, but this is banned under the current rules.

Where the seamless gearbox differs is in the dog rings, and how the control systems move the selector forks. The concept of the seamless-shift box is that one gear can be engaged and the next gear gear can be pre-engaged ready for the shift.

In the pre-engaged state, the next gear is effectively like a ratchet. When the shift occurs, the ratchet switches to engage the gear and disengage the other. As the system changes only the relatively small dog rings, the weight penalty is as low as 1.5kg.

If the weight penalty is small the lap time gain is significant - depending on the circuit, the car can gain as much a 0.2s from not losing so much drive between shifts.

While almost all teams have seamless boxes, the choice of gear case material varies greatly, with the choice being between aluminium, titanium or carbon fibre, along with the additional choice of hybrids of the metals bonded with carbon fibre.

In 2007, only Honda and McLaren ran full carbon fibre cases, and Ferrari evolved their titanium skeleton with bonded carbon skins. All of the other teams ran a metallic gearbox, albeit with some level of carbon fibre bonded to specific areas for stiffness.

Underpinning the gearbox, clutch and differential is the car's hydraulic system. This largely unseen system actually controls most of the mechanical functions on the car, with the power steering, fuel flap and throttle being powered from the same system as the gearbox.

At its heart is the hydraulic pump, which feeds the accumulator with 3000psi of pressure. The accumulator then sends the compressed fluid to the disparate systems around the car.

The fluid moves actuators to exert the force to move the mechanical parts of the car. Controlling of the rate of fluid flow to the actuators are electro valves commonly termed 'moog valves', the name taken from the Dutch supplier of the valves.

With such high pressures and delicate actuators, the hydraulic system is prone to failure. Contamination in the fluid, breakages in the pumps/actuators or leaks will render some or all of the system inoperable.

This year, the catch-all term 'hydraulic failure' accounted for more retirements than any other in the season. Clearly, many teams have yet to fully get their hydraulic system under control.

Suspension

Much like seamless-shift gearboxes, zero keel suspension has become standard on the cars over the past few years. This year Ferrari and Red Bull switched the zero keel set-up, leaving only Renault with their v-keel.

A zero keel is where the lower front wishbones are mounted directly to the monocoque's lower edge. This negates the need for a heavy keel structure, such as the central single keel or out-of-fashion twin keel.

Zero keel aids aerodynamics, largely by placing the wishbones higher, which works better with the front wing. Also, the small obstruction caused by the keel itself is removed, which aids flow under the nose.

Of course the penalty for this set-up is getting the wishbones to keep the tyre at the right angle to the track. This task is much more complicated with a zero keel.

The conventional double-wishbone arrangement and how it alters camber change and roll centre is well documented in technical books. Moving the wishbones higher up makes this more difficult, and analysing how the teams make their suspension work is not an intuitive task.

Red Bull, for example, maintained a small metal keel to mount the lower wishbone. This small change helped set the geometry and lower the roll centre. Honda placed the lower wishbone mounts slightly under the nose of the car rather on the edges, which helps maintain camber control.

In a similar manner, Ferrari added an extension to the side of the monocoque to place the flexible joint of the wishbone further out, again to aid camber control.

Another method to aid the tyres gripping in corners is mounting the pushrod on the upright. Normally, a race car would have the pushrod mounted to the lower wishbone, meaning that the steering of the car would not have an effect on the suspension.

But teams are now actively encouraging this effect by mounting the pushrod on the upright and spacing it from the steering axis. As the wheels are turned, the upright lowers the inside wheel and raises the outboard wheel, shifting weight to the inside wheel.

This improves slow speed grip, especially as F1 cars do not run a large amount of Ackerman steering. (ED: The term 'Ackerman steering' describes the steering geometry where the inside front wheel turns more tightly than the outside front wheel).

Thus, the wheels tend to be nearer parallel in when turning. This aids high-speed stability, but impedes the car in slower turns. Having this pushrod set-up makes the car work more like a go-kart in slow turns by moving weight across the front axle.

At the rear of the car, the suspension set-ups have also evolved to be of a near-standard layout. The torsion bars and dampers are mounted atop the gearbox, with the torsion bars being longitudinally mounted. Only Renault maintains the vertical torsion bars.

Equally, the use of rotary dampers at the rear was been reduced to just Ferrari, with Spyker having switched to linear dampers on their B-spec car. The use of third dampers at the rear was highlighted by Ferrari when theirs failed twice at Monza, leading to speculation that their damper might be more complex than other teams' set-ups.

Aerodynamics

In unison with the new tyre's demands for forward weight distribution, the aerodynamics also need to move their load forwards.

The balance of front to rear downforce is known as the aerodynamic centre of pressure, and it tends to sit a few percent behind the centre of gravity. Thus, teams needed to get the front ends working harder to match the great weight placed over the front axle.

So this year, we saw a lot of front wing development. Wings tended to be larger, with greater plan areas to create the downforce without having excessive angles of attack.

Having too steep a wing tends to upset flow the rear of the car. With larger wings comes the risk of the flow separating from the underside of the wing. To reduce this, many teams ran three-element front wings - the extra slot keeps the flow attached to the wing's surfaces, maintaining efficiency.

But as the shape of the wing becomes more complex and diverse across its span, the needs for the extra slot is not required in some areas.

BMW Sauber worked out a clever solution where their two-element wing was given a slot moulded into the steepest section in the middle. This gave the steep section the extra flow it needed, and didn't compromise the other shallower sections of wing. Renault adopted a similar wing later in the year, albeit with the slot moulded into the main plane rather than the flap.

As teams struggled to find enough front-end downforce early in the season, many makeshift solutions were tried to add a little extra load over the front tyres.

Different fins and flaps were added, while new wings were developed at the factories. Last year, cascades and bi-plane elements were fitted above the main front wing to create extra-efficient downforce. These were retained this year, and joined by a new derivative - the bridge wing.

McLaren debuted the bridge wing, which spanned from one endplate to the other. Their low nose made the full-width flap possible, so that the new middle section could be used to shape the flow over the rear of the car, rather than carry downforce.

Other teams adopted the bridge wing format with higher nose tips, necessitating unsightly bends in the flap to pass over the nose tip.

While front end development continued at great pace, the solutions to keep the rear wing working effectively grew ever more complicated.

Teams aim to separate the flow feeding the rear wing from disruption from other flow around the car. They also aim to keep this flow at high pressure to maximise use of the wing. Pod wings and cockpit fins have been the main innovation in this area.

Pod wings are the crescent-shaped fins mounted to the front shoulders of the sidepods. They keep the messy front wheel flow away from the rear wing, and pick up the faster flow passing in between the wheels and off the top of the bargeboards, sending it cleanly to the rear wing.

An extension of this concept was McLaren's conjoined pod wing and chimney. Together, the pair formed a continuous channel over the top of the sidepods. Later a slot was made in the pod wing to allow some flow to pass around the flanks of the sidepod.

Also, the use of fins mounted close to the cockpit were widely adopted. We have previously seen smaller fins over the top of the front suspension; these new rearward-mounted versions worked to channel the flow passing upward from the wing and divert it back down over the sidepods to the rear wing.

Wheel fairings

One of the most surprising innovations this year was Ferrari's development of static wheel fairings. Last year, the rules were eased on bodywork around the wheels and notions of what constituted brake ducts. Consequently, Ferrari raced carbon fibre fairings added to the rear wheels.

This year, the front wheels came in for similar attention. Unlike Ferrari's rear wheels, their front wheels need to be open to let the hot air out from the brakes. Thus, a fully enclosed fairing would inhibit brake cooling, while a partially open fairing would be compromised as the wheels are steered.

A novel concept was making a fairing static in relation to the spinning wheel - this allowed the hot air outlet to be placed in the ideal location. Using the natural flows around a spinning wheel, the hot air could be vented into a low pressure region, which helped pull air from within the wheel and reduced the drag created by the low pressure region behind the front wheel.

Normally the hot air ejected sideways from the front wheel, which is seen as clouds of black dust under braking. Ferrari's set-up aimed the brake dust behind the wheel, making the car effectively narrower - which in turn reduces drag.

This solution required special front hubs to accept the fairing/wheelnut combination. The hollow hub allowed an extension from the fairing to reach through and fix to a spline mounted to the back of the upright.

As this set-up required new front uprights, few teams followed its example during the season. Toyota raced with their fairings, while Williams only tested their version.

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