Mulsanne's Corner: The new LMP aero regulations have been introduced in light of improving safety through reduced yaw sensitivity. There are those who advocate doing away with downforce generation all together as a means of reducing lap times and improving racecar safety. What are your thoughts about the relationship between downforce and safety?
Peter Elleray: I think downforce itself is not necessarily ‘unsafe’ – but loosing it can be, particularly if this happens in a way that the driver can't control. Perhaps there is an analogy to the flight envelope of an aeroplane – if the pilot strays outside of it then the aerodynamics of the plane can play nasty tricks on him. In our case we are talking about a situation in which the car’s aero platform is potentially unstable within the cars operating envelope, and as a result, the dynamics of the car as a whole become unstable, or divergent – the Mercedes incidents being the ones that stay in everyone’s mind but there were others.
When you think that this happened to a manufacturer backed operation that was well resourced and funded then it perhaps highlights that harnessing aerodynamic downforce is still not an exact science.
I think that the changes have been introduced based on the principle that we need to produce cars which have aerodynamic characteristics that the driver can sense and understand and react to – in other words the car wont react in a highly non linear manner or play tricks on him. On track he should never be placed in a situation where the car is outside of those boundaries. I think the perception was that the old cars did stray outside of them and I think that’s what the new regs have sought to achieve. For instance, Its generally accepted that you will loose downforce – and more particularly front downforce - if you follow the car in front closely, say less than 1 car length. That might be deemed acceptable but if the result of doing so is that you take off and land in a pine forest then it wouldn’t.
I’m glad that there wasn’t the sort of knee jerk reaction to this problem that we might have seen in the past – the FIA’s subsequent study and revised regulations were backed up by detailed research.
It would have
been quite naive anyway to
think that you could ‘ban downforce’ – even if you banned
Designers and Engineers had figured out how to generate some downforce
on Sports racing cars before they ran separate wings or tunnels and it
would be very difficult to legislate that out without going to a
formula. I hope nobody wants that.
MC: There seems to be some contention as to what the new regulations will do to aero forces. The ACO indicated a desired 10% increase in drag for a 25% reduction in downforce. Interestingly enough, in Dome’s press release for their hybrid S-101hb they claim the 10% ACO drag increase but for a 20% gain in downforce. Most puzzling, Laurence Pearce indicated that the hybrid Lister LMP would have “less drag”. Realistically, what do you think the new regulations will achieve?
PE: If you look at the individual changes that the regulations have introduced then it’s not easy to say.
The new underbody has its flat section further forward and has larger tunnels with an exit that is almost 50% bigger. That would move the centre of pressure forwards and increase the level of downforce from the floor. However, that flat area is now narrower, the sides are inclined upwards and radiused (which means that they are acting as lateral intakes) and there is the 20mm plank in the middle. This means that dynamic front ride height will be increased for most people reducing that downforce, although it would appear, from what I’ve seen so far, that dynamic rake can be reduced as a result of the increased tunnel area and roof rake.
There is also the 50mm rule that governs the front diffuser middle section. In reality I think many diffusers were already raised above the bottom of the car – on the Bentley this would have meant lifting it between 35mm and 40mm. At the same time the car itself is running higher because of the plank. So you would expect to loose peak performance from the diffuser, but not necessarily the same amount under heavy compression of the front springs and high rake, where the old diffusers tended to stall out.
At the rear the overhang is down from a potential maximum of just under 1100mm to only 750mm – that’s a lot of rear wing leverage lost. The wing itself is down to a 300mm chord, but in fact we ran a 310mm 2 piece section on the Bentley in 2002 and for Sebring 2003 and you can get plenty of efficient downforce from that size of wing. So it’s the leverage that’s the issue.
You can see how the basic changes place more emphasis on the floor (within the wheelbase) and less on the extremities – exactly what was planned, My understanding is that people are doing quite a bit better than the 25% loss that you mention at whatever ‘datum’ ride height they run in the tunnel, and that downforce levels are not very different once the car is in balance – but to be honest its pretty meaningless if you are just looking at one ride height, the whole aeromap needs quantifying to try and draw a comparison.
The drag, I think, is a bit more difficult to call. One thing I have realized since getting involved with LMP cars other than the Bentley is that whilst the general level of downforce available doesn’t seem to vary dramatically between them, the level of drag at which it is produced does. Some of the open cars were not very efficient. I can understand how they might well be finding that drag has not changed significantly. On the other hand, an efficient open LMP900 would seem to be hurt by the twin roll hoops and the reduction in rear wing leverage. This would imply needing to run more downforce from the wing – and drag – to rebalance the car if you can create as much front as before from the new floor and raised front diffuser.
The coupe is
different again. The
new cab is a little higher – but also potentially narrower.
the potential for a long tail low drag ‘feathered’ wing setup like we
in 2003 has been removed the wing is now over 150mm higher, and that is
significant. So although I’d be quite surprised to see the
drag figures I was used to over the last 3 years, I would still expect
to be able to do a pretty reasonable job with a coupe.
MC: I’ve been somewhat surprised at the pace of the Nasamax hybrid LMP1. Do you anticipate the ACO tinkering with the aero regulations should the LMP1/2s show more speed at a sooner date than anticipated?
Well they have already legislated for rear wing gurneys in 2006 that
not required yet, so it would seem quite possible. I think
Nasamax’s speed is perhaps not quite so surprising when you look at
the 10% larger restrictor does to the top end power, and then look at
significance of that at Le Mans, Monza and even Silverstone.
MC: Prior to the LMP era, sports cars suffered from an archetypal understeer condition. What balance data I have seen of LMP900s would suggest the ability to dial in as much front grip as needed. How do expect the new-regulation LMPs fair in regards to aero balance?
I think that we are very much more attuned to the need for aero and
balance to be in harmony than we were maybe 10 or 15 years ago and that
a great deal of tunnel work will be devoted to making sure that we have
it. As I said earlier, from what I have seen so far there is
a fundamental issue here with the regulations as they are currently
MC: Now that open top cars are mandated to run symmetrical roll over structures, do closed top cars look any more attractive than they did under the old regulations? What are the benefits of running a closed top sports car as compared to an open top car? What are the drawbacks?
PE: I think that the regulations do make the coupe attractive. There were some fairly subtle problems in producing a competitive one that were written into the old regulations and those have all gone. Against that the coupe has lost its theoretical power advantage. That is significant at Le Mans but needs to be looked at carefully – the ability of the older style coupe to get its power down entering the straights was just as important and the new regulations have probably helped it in this area.
The problems with running one are mainly practical. If it’s hot and more particularly humid then it’s a sod to cool the cockpit, and if its wet then the last thing you want the driver to do is switch on the windscreen wiper. We went through hell trying to sort those things out on the Bentley – as well as stopping the inside of the screen misting up. We were more or less there by 2003, but of course the race was dry and it wasn’t particularly hot. The driver change used to be an issue as well but that was more a case of restructuring the sequence of events and again we had that buttoned up so that it was taking less time than refueling in 2003.
There also used to be the worry about extracting an injured driver from one. The new regs have partially addressed that.
well, as I have said the older
style coupe had a pretty good drag figure, and even if the newer one is
not quite at that level it should be possible to produce a pretty
car. At Le Mans that counts for an awful lot.
MC: There still hasn’t been any major announcement from anyone committing to LMP other than Lola and Lucchini. Do you see that as a missed opportunity for a LMP1 given the additional penalties for LMP900s next year?
PE: Yes – it’s a curious situation and perhaps more a function of commercial and political issues rather than technical ones. Although the ACO backed away from introducing a 10mm plank on the LMP900s everything else that they have done plays into the hands of the newer cars. Perhaps they made it a bit too attractive to update an existing car and run it as a hybrid.
certainly be interesting to see
where we are in 12 months time in this respect…
Many thanks to Peter Elleray for taking the time to answer our questions.