2007 Brazilian GP Technical Review

The 2007 F1 season finally came to an end with the seventeenth race of the year in Brazil.

The track commonly known as Interlagos, but correctly called the 'Autodromo Jose Carlos Pace' is a classic track that has a unique mix of demands for the cars and teams.

If the track were new to F1, people would believe it was designed by Herman Tilke. Indeed elements of its layout were taken to inspire some of his tracks, particularly the opening corners.

With Interlagos not having any specific set-up requirements, the cars were, not surprisingly, devoid of visible developments. Only the chance for the teams to run engines for just one race, rather than having to manage their use for two weekends, meant that there was a little more freedom in their tuning and operation.

Meanwhile, tyre choice was difficult both due to the choice by Bridgestone of the super-soft tyre, and because the track has been newly resurfaced for this year.

Layout

Interlagos closely reflects the Shanghai circuit layout. A long curve/straight from the last sector opens the lap before a right/left pair of turns slows the cars.

The middle sector has two faster corners, including a tricky double apex bend after the back straight. Finally, the track slows before the cars are let loose on the long curved climb to end the lap.

In general the cars are set up with medium to high downforce; the long straights are important, but the twistier sectors around the back of the circuit have a bigger impact on lap times.

In many respects this is a classic track which offers overtaking opportunities, and the region provides unpredictable weather.

Historically, the track has been blighted by bumps as the track surfaces settles into the dusty landscape. This year's resurfacing has eradicated the bumps, for now at least. Thus, the teams were able to run their cars stiffer and lower to the benefit of aerodynamics.

However, the new dark tarmac proved grippier than expected as it rubbered in, and the super-soft tyre proved marginal for lasting a long stint. Even in qualifying, the tyre needed management in order to last the full lap.

Lastly, the track sits well above sea level. At this altitude the engines and aerodynamics are less efficient, however there is little that can be done to offset this loss and the disadvantage is the same for all teams.

Engine upgrades

As the season has an odd number of races, combined with the fact that there were so few engine failures, most teams arrived at Brazil with engines only required to last one race, rather than the usual two.

This presented a small opportunity to tune the engines differently. However under the current engine regulations, changes to the engine are limited to electronics, inlets and exhausts, and the engines are limited to 19,000 rpm. So the potential compared to previous years was limited.

In the media reports of a 10 bhp advantage being found were probably wide of the mark, as this represents somewhere near a 1.3 percent gain. This would probably constitute a major proportion of the total engine gain for the year.

Without being able to the change the internals or rev ceiling, the engine builders are severely limited in how they can increase peak power. Tuning the inlets and exhausts could reap some drivability gains which could still provide a lap time gain, but it won't bring a 10 bhp peak power increase.

Aside from tuning, the engineers are also able to allow the engine to reach its rev limit for more time over the weekend. As the engines are freshly installed for Saturday morning practice, they aren't stressed too highly until qualifying begins, and this represents a limited number of laps.

This leaves the race as the main chance to exploit more revs, which in turn means the driver can have a little more power for more of the race, depending on their fuel strategy.

Hamilton's gearbox problem

The championship decider in Brazil started to slip away from Lewis Hamilton as early as lap 12 when, going through the 'Descida do logo' corner, his car lost drive and dropped him towards the back of the field.

Such was the significance of this issue, there has been a great deal of conjecture as to what actually happened, apportioning blame between either a gearbox sensor or driver error.

Looking at the on-board footage and understanding the operation of an F1 car, we can perhaps shed some light on what actually happened at Interlagos.

Having run down the 'Reta opposto' back straight, Hamilton appeared to keeping pace with Alonso in front of him. As he braked for first of the pair of corners, Hamilton ran down the gearbox to a lower gear with the left-hand gearshift paddle.

As he turned in the car appeared to become unsettled. A couple of seconds after selecting the lower gear, Hamilton pressed the green button on the top left of the steering wheel.

He then almost immediately tried to select a gear on the right-hand (upshift) gear paddle. By now the car had rounded the second corner and coasted down the hill. Hamilton kept trying for a gear with the upshift paddle, and twice pressed the neutral button.

The green button he pressed on corner entry is clearly marked 'N/Rev' in pictures taken on the same car at the same race. 'N/Rev' is the neutral/reverse button. Thus if he did hit that button while the car was running at speed, it would send the car in neutral and then the car would freewheel until a gear is selected.

This is the assertion made by the Canadian media after alleged remarks made by Hamilton after the race. While it is possible that Hamilton did inadvertently press the button, it is likely that the team have a lock-out on that button that prevents the neutral being selected above certain speeds, to prevent accidental selection.

The other buttons sighted near the neutral button are for the pit limiter, drinks bottle and a scroll button. Having to move his thumb some way around the steering wheel grip to reach the button, his finger couldn't have slipped. It would also be unusual that any of these other functions would be needed as he entered a high-speed turn.

The other theory is that the gearbox was already in neutral as he approached the corner, Hamilton pressing the N button was the first step in trying to regain his gears.

This theory is backed up by McLaren's official comments. It seems that the problem may have occurred as Hamilton selected the lower gear braking for the corner - if a sensor failed at this point, the gearbox could have been dropped into neutral.

This would tend to send the car into oversteer, as the rear-end freewheels rather than having the assistance of engine braking. It could explain why the car was unsettled going into the bend. The almost simultaneous pushing of the neutral button and shift paddle were not causing the problem; Hamilton was only trying to reset the gearbox and find a gear.

F1 gearboxes are complex devices, especially since the advent of the seamless shift, which only further complicates the selection and engagement mechanism. A fault with a gearbox sensor could send the gearbox in a self-protection mode, taking the gears out of engagement to prevent further damage.

Resetting the gearbox after such a fault could either allow the system to continue to use the sensor, or if it continues to be faulty, then ignore it and run in a safe mode.

It was reported that Hamilton's gearbox was opened up by he team in parc ferme after qualifying, to assess a potential fault. According to the FIA scrutineers, no parts were changed on either McLaren in parc ferme.

Looking at the footage, it seems the fault is more likely to lay with a sensor in the gearbox than the driver in the cockpit.

Fuel temperature

Even if the season was over on the track, the scrutineers found some discrepancies in the temperatures of the fuel delivered by some teams fuel rigs in the race.

Under the current regulations, the fuel contained within the fuel rigs is allowed to be 10 degrees below ambient temperature. This rule was created after teams in the eighties super-cooled their fuel to beat the fuel restriction rules during the turbo era.

Cooled fuel is denser, and thus more can be put into the fuel tank. The situation in the eighties got the point where the unregulated fuel rigs became heavily frosted, cars ran fuel warmers to bring the petrol back up the icing point, and this all presented a safety risk.

Not to mention the fact that the trick effectively beat the rules governing the volume of fuel that can be used. Thus, a limit on the temperature was introduced, and teams routinely cool to the fuel right down to the limits allowed.

Nowadays the advantage of cooling fuel is three-fold. Either the teams want more fuel in the tank to run longer on a stint, or they want the usual amount of the fuel added in less time. Additionally, the cooled fuel provides a power boost, as the colder fuel condenses the air entering the engine, increasing its volumetric efficiency.

This power boost is a short-lived advantage, as the fuel in the tank will soon heat up from the hot surroundings and return fuel feed putting hot fuel back into the engine.

BMW Sauber

BMW ran with much the same set-up as in China. The new viking wings have been raced since Japan, while the extra flips under the main side pod flip-ups and diffuser gurney flap were new for China.

The latter changes are aimed at improving rear downforce, while the viking wings probably aid the car in yaw and cross winds.

Red Bull

As well as running the crash box fin seen in China, the team also produced a new wing flap for Brazil. Based on the new medium/high downforce wing introduced at the German GP, the wing uses a new flap with a different trailing edge.

Rather than having a pinched middle section, the wing chord is longest at its middle point and then tapers toward the tip, where a slightly longer chord returns. As with most tapered or twisted wing designs, the shallower wing profile towards the tips reduced drag created from vortices created at the endplate.

The longer outer sections probably act to improve the low energy flow between the wing and endplate, further reducing drag.

Honda

In the wet practice on Friday, Honda ran their usual shelf wing to bring more downforce. In addition to the aerofoil placed between the wheels (although mounted to the wing endplates), the team used a new gurney flap in the middle of the wing (yellow).

This would work the middle of the wing a little harder and is placed to potentially benefit the deeply dipper section of the rear trailing behind it.

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- The Autosport.com Team

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