23/08/2004
NEWS STORY
Renault technical director's Pat Symonds and Denis Chevrier (engine) look ahead to this weekend's Belgian GP at Spa-Francorchamps.
Pat Symonds
2004 will see Formula 1 make a welcome return to Spa-Francorchamps after a brief sabbatical. Spa is the classic road circuit, and presents challenges enjoyed by drivers, engineers and spectators alike. Getting close to perfection through the difficult, high-speed corners makes significant differences to the lap time, and gives a great feeling of satisfaction when we get it right.
Of these corners, the most famous is of course Eau Rouge and over the years, this complex has perhaps created the biggest challenge in Grand Prix racing. When we consider the nature of this challenge, and how it has evolved over the years, it is interesting to see that just as it seems to be getting easier, a change to the cars can put the ball right back in the teams' court. Indeed, this is what we expect to happen for 2005.
Speeds through the corner increased up until 1998 (peaking at 286 kph in 1997), when the introduction of grooved tyres and narrow track cars brought a significant decrease in grip, and hence cornering speeds. From 1998 onwards, we see a steady increase in speeds once more, with a significant jump in 2001 as the tyre competition begun the previous year got into full swing. An equally significant step was made in 2002, when not only did the tyres develop further, but the corners where slightly realigned and also resurfaced, in the interests of safety. This led to the corner being easily flat in qualifying that year, although in the race it still required a small lift of the throttle through the corner. Having said that, even when taken flat, the high lateral accelerations and hence tyre scrub, coupled with the steep rise in elevation, result in the car losing around 20 kph from entry to exit of the corners.
From an engineering point of view, the corner is an important one as good speed through here provides an overtaking opportunity at the end of the straight. In order to negotiate the complex quickly, it is important to have the right level of grip, and hence an aerodynamic set-up that does not compromise the high straightline speeds required (around 320 kph). In addition, the drivers need complete confidence in the car through this series of corners, and in order to achieve this it is necessary to have good high speed stability, and maybe even a touch of understeer.
Finding this handling "sweet-spot" is not just a case of achieving the correct aero balance, as the dramatic elevation changes in the corner have severe effects on the suspension. The left hand part of the corner generates a lot of suspension compression, and the car goes light in the final part. It is necessary to ensure the car does not hit the ground hard in the compression, but also that during this phase, any non-linear behaviour in the suspension, such as the bump rubbers, do not produce a sudden change in handling as the car tries to bottom out. Equally, ride heights can vary by as much as 25 mm through the sequence. When choosing set-ups, just a couple of millimetres can make a significant difference to handling, and it is therefore obvious that the car needs aerodynamic characteristics that do not cause large movements in the centre of pressure even when ride heights and pitch angles vary. If these factors are managed correctly, if the driver has the grip he expects, and if the grip and the balance of that grip remain constant through the corner, then the challenge becomes a much easier one.
This year, we expect to negotiate Eau Rouge at approximately 310 kph, compared to 286 kph in 1997. Furthermore, with the progress in both car and tyre design over the past two seasons, the corner should be taken flat out for much of, and perhaps all, the race. Next year, though, the situation will change once more, as it has done through recent F1 history. Just considering the losses from the aerodynamic changes that we will be accepting for 2005, we can expect the minimum speed through Eau Rouge to drop by over 20 kph (to 1997 levels), and indeed the top speed at the end of the straight will be 9 kph lower. The drivers will also be lifting off the throttle for around 0.4 seconds, a level similar to that which we saw in 2000. The challenge of taking Eau Rouge flat, superseded by advances in car and tyre design since 2002, will return, and Spa will be all the more a true classic circuit for it.
Denis Chevrier
From a reliability point of view, Spa can be considered as the most demanding circuit of the season. From the hairpin at La Source to the chicane of Les Combes at the top of the hill, the cars spend 22 seconds at full throttle, which is significantly higher than the season average of 13.5 seconds.
As we have noted earlier in the season, a continuous full throttle period is significantly more demanding for the engine than a number of repeated shorter bursts, and this additional load is exercised on certain components in particular: the pistons, the valves and also the crankshaft and con-rods.
Of course, we are familiar with the demands of the circuit, but these additional constraints make the balance between performance and reliability even harder to judge when defining the engine specification.
Furthermore, this 22 second period at full throttle includes the passage through Eau Rouge. This section of the track generates very high vertical "g", which has an influence on the engine's oil feed.
When designing and testing the lubrication system, this is a factor we have to take into account and while we cannot wholly eliminate the potential risks associated with the vertical loads imposed on the engine at such high engine speeds, we succeed in reducing them to such an extent that the engine can cope.
However, it would be untrue to suggest that this opening 22 second portion is the only severe section of the circuit for the engines. At approximately 100 seconds, Spa is the longest lap of the year, and it also requires a very wide operating range from the engine: the drivers need good low-speed performance on the exit of the hairpin and the Bus Stop chicane, but also high top speeds on the two long full throttle sections (La Source to Les Combes, and Stavelot to the Bus Stop chicane).
This demand for comprehensive engine performance throughout the rev range means in practical terms that we need as much available torque as possible throughout the rev range. This includes acceleration from the slow corners, as previously mentioned, but also in-gear acceleration at higher revs: Spa sees the drivers at full throttle for 65% of the lap, one of the highest values of the year aside from the exceptional case of Monza.
Furthermore, unlike more modern circuits such as Hockenheim, these accelerations often follow fast third or fourth gear corners rather than slow first or second gear hairpins, and consequently place different demands on the engine's performance.