Pat Symonds
Indianapolis presents the race engineers with a unique challenge, that of what we might call the schizophrenic circuit. With a layout comprising the longest flat-out section of the year, at 23 seconds, and some of the season's slowest corners through the infield, the track effectively demands two contradictory sets of capabilities from the car: for the best time through the infield, the ideal set-up is high downforce and high drag for better braking and traction, while the opposite is true for the remainder of the lap. Managing this contradiction is an interesting challenge for the engineers.
When preparing for a race, one of the primary things to be done by simulation is to decide what wing settings to use. This is done by feeding the lift and drag figures for each setting and wing type, into a sophisticated simulation programme which represents the car doing a lap of the track in question. One might think that it is then easy to choose the setting that gives the best lap time and adapt the set-up of the car to suit this. However, it is not always so simple: on some circuits, with long straights and good overtaking opportunities, it can be necessary to sacrifice ultimate lap time to protect yourself from being overtaken or, to put it more aggressively, to allow the driver to overtake others on the straight. Indianapolis - much like Interlagos - is a circuit that makes this compromise even more interesting as it is in effect a schizophrenic circuit, in that the long final corner and pit straight are extremely fast while the infield is extremely slow. What makes this circuit particularly interesting, though, is that within a reasonable range, the overall lap time varies by only a small amount irrespective of the wing settings used.
There is a clear trade-off between the time spent in the two parts of the circuit depending on the car's downforce level - essentially, the trade-off to be made between top speed and downforce - and the straight line indicating the optimum lap time for the circuit. In terms of preparation, mathematics can only take the engineers so far, and one of the challenges is adapting to the situation that competitors may place us in. For example, the ultimate lap time is achieved with a top speed of 335 kph, but if we find that our true rivals are running a top speed 15kph higher than us, then it becomes necessary to alter the compromise in favour of matching their top speed, even at the expense of lap time. The unique nature of Indy means, though, that achieving this additional 15 kph will only slow the lap time by 0.1 seconds, a relatively small amount for a significant increase in speed.
One might think that in making this compromise the car would become very tricky in slow corners, but in reality this is not really the case as many of the infield turns are extremely slow and, as the downforce produced by an F1 car is proportional to the square of its speed, the absolute amount produced in the slow corners is also low. The loss from the reducing wing setting will be approximately a fixed % and therefore the total lost, if one thinks in terms of kg of force on the car, will represent a fixed % of a small number. Indeed, the increased speed means parts of the car such as the floor and diffuser actually produce more downforce, in large part compensating that lost from the wings. Furthermore, the car becomes less critically sensitive to ride height change and pitch angles with less downforce. Instead, where the driver will really feel the effect of the changes will be much more under braking and the late acceleration phases, during which the downforce levels are much more significant than at the corner apex.
While the race engineer needs to decide on the correct compromise to make, it is sometimes difficult to know how to tackle this. Before the significant change in rules for last year, it was always possible to run the configuration that gave the ultimate lap time for your qualifying run, and then reduce drag levels even at the expense of lap time, if it was felt this would provide a better compromise for the race. Under current rules, we can no longer make any adjustments after qualifying and hence this judgement needs to be made well in advance. At first sight, it may seem this is in fact easier as under the old rules, everyone was trying to second guess on Saturday what settings the competition might adopt for Sunday. However, the single engine rule for 2004 has added a new dimension to the art of second-guessing the competition. With the need to have absolute reliability from the engine over a much greater distance than previously, all teams have adopted an approach where they run their engines with reduced rev limits throughout Friday and Saturday mornings, and only use it at full potential during qualifying and the race. This means that assessing relative speeds during practice can be misleading, so we must make an informed judgement from our knowledge built up during the races so far, in order to assess exactly how we balance the compromise that must be made.
Denis Chevrier
Indianapolis is a much bigger challenge for engine performance than Canada, and the reason for this is the long main straight. When we look at the percentage of the lap spent at full throttle, it is actually less than we see at Canada - 56.6%. However, the singular characteristic of Indianapolis is that much of this time comes in one single burst - the 22 second full throttle period from the exit of Turn 11 to braking for Turn 1. Whereas in Canada, the three sectors of the circuit resemble each other, in Indianapolis, each sector is very different. Effectively we must cope with two circuits in one, and this has serious implications for the engine builder.
For an F1 engine, the longest single period spent at full throttle is the most punishing characteristic at any circuit, rather than the overall percentage of the lap during which the engine is at full load. The challenge is essentially one of heat evacuation, and the area of the engine on which it has the biggest impact is the pistons. When a driver is accelerating through the gears, the engine is not actually at maximum revs for very long, and braking means that the moving parts are given respite from the load they are under, and heat is evacuated. However, for a continuous period at full throttle, there is no respite, and no opportunity for this energy to be lost.
