O
n the face of it, there is little difference between the 2011 and 2012 Le Mans
Prototypes. Most of the cars on the grid in the World Endurance Championship have been around for a long time with many, such as the Pescarolo, Lolas and Dome, dating back to 2007 and 2008. But a significant set of regulation changes has seen these designs substantially revised for the new season. Immediately obvious are the bodywork revisions, many aimed at keeping the cars on the ground in yaw at high speed. The large dorsal fins appeared on some cars in 2011 but became mandatory for all LMPs in 2012. More significant from an aerodynamic standpoint are a set of holes above each of the wheels. When the decision to
carve holes in the bodywork was announced, Audi’s Dr Martin Mühlmeier criticised
the changes: ‘I am always happy to see the safety of the vehicles being increased,’ he said. ‘But checks need to be carried out to determine how much safer they are, and whether there are actually any safety improvements at all. The fin dimensions are only being marginally changed, but the openings that now have to be above the wheels are a lot more serious. They are supposed to prevent a vehicle from losing contact with the ground on one side when the vehicle is at a large heading angle and therefore spinning. This is certainly the right idea in theory. But these openings unfortunately reduce the vehicle’s stability on the straight because its c of g shifts forward, thereby increasing the likelihood that the driver will oversteer. In other words, the risk of the vehicle spinning out of control is actually increased.’ The FIA refers to these holes as air extractors in the technical regulations, and place
a limit on their dimensions – each wheelarch must have a hole of between 7500mm2 and 9500mm2
at the front
and between 1000mm2 1200mm2
and at the rear, leaving only the tyre visible from above.
AEROBYTES Racecar Engineering has already investigated the influence of these air extractors in some detail as part of the Aerobytes / MIRA wind tunnel programme, and found they do indeed move the car’s balance rearward, as predicted by Mühlmeier. In our tests, they also increased drag by 2.6 per cent (see RE V22N5). The way teams and manufacturers have dealt with this challenge is fascinating, and a wide variety of solutions are currently on display (see sidebar on p10). ‘On the subject of the holes,
there is not a design consensus at the moment, but I think in two or three years you will see the concepts converge, as
that tends to be the way that motorsport goes,’ explains Julian Sole, chief engineer at Lola. ‘The regulation change for the holes came so late that it didn’t really give us any time to develop. So, at the moment we are still experimenting, but you are always managing a loss to some extent, and are always trying to find a gain at the same time. By just opening up a hole, it will certainly be worse but you develop, until you get to the point where you are managing a gain. We have not made an overall gain yet but we have managed the losses.’ The impact of the holes can
be felt significantly on other parts of the car too and, if a manufacturer should get the shape of the holes wrong, it could have a detrimental impact on the rear of the car, especially the rear wing. To mitigate this effect, some manufacturers, including Audi, Pescarolo (Oak) and ORECA, have added small ridges to the bodywork around the holes.
“On the holes, there is not a design consenus at the moment but it think in two or three years you will see the concepts converge”
July 2012 •
www.racecar-engineering.com 9
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