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LMP 1 REAR WINGS


assemblies, they stumbled upon one fundamental problem – flow separation in the area of the conventional rear wing mounts. And apparently the solution was a pretty universal one, hence Audi designers using an Italian scale wind tunnel agreed with Acura designers using a virtual wind tunnel.


But in the end, how much


downforce was really lost by the initial span and chord reduction? And how quickly was it gained back? In the winter of 2008 it was obvious that the world economy was in the gutter. Yet the ACO was proposing expensive safety changes for the following season, with the singular objective of slowing the cars down. Surely there were vastly less expensive alternatives? And how effective really were the narrow wing rules in reducing downforce? We’ve assumed they did as intended, but aerodynamicists are a clever lot, and it would be pretty naïve to assume they just accepted the loss.


But what methods could we


The reduction in rear wing span is immediately apparent in these pictures of the 2008 (top) and 2009 (bottom) Pescarolo. And while lap times did slow straight afterwards, other factors came into play at the same time, including the introduction of domed skids beneath the car that increased ride height and improved safety


slow in 2009, but analysing events that ran to full 2009 ACO regulations (Le Mans Series events, Le Mans, in addition to Sebring and Petit), qualifying lap times increased an average of two per cent. But then again, how much of that lap time increase could be attributed to the 10 per cent power reduction the diesels were given for 2009? The narrow span rear wings, coupled with the 20mm domed skids beneath the cars, introduced at the beginning of 2009 as well, did seem to have a cause / effect relationship, in as much as there haven’t been any yaw-induced blow overs since. But what was more influential – the narrow rear wing or the domed skid that increased running heights significantly?


NEW TRENDS In direct response to the changed regulations, two new trends emerged, with one driving the other. First, in order to recoup as much of the lost downforce as possible, aerodynamicists began utilising more aggressive rear wing angles of attack, in addition to more extreme wing profiles and cambers.


respectively, with near identical details in the area of the rear wing. Instead of utilising a conventional bottom rear wing mount, both cars arrived with top mounts for the rear wing, the so-called ‘swan neck’ mounts. But how could two cars with completely divergent design philosophies come to the exact same design execution in such a


“surely there were vastly less expensive alternatives?”


The second trend was


in response to the first, and ultimately was more intriguing, if perhaps only initially. The intriguing bit was that, simultaneously, Audi and Acura debuted their R15 and ARX-02a


74 www.racecar-engineering.com • January 2012


critical area? What was going on here, another Stepneygate? The answer, as it turns out,


was comparatively boring, and quite simple. As aerodynamicists started to go down the route of more aggressive rear wing


use to independently explore the effects of the ACO’s 2009 rear wing regulations? Could we also replicate what was seen in the development of the swan neck rear wing mounts? If the cause and effect was so universal, could they be repeated?


THE CFD OPTION Inquiring with insiders at various LMP manufacturers produced little in the way of concrete answers. Apparently discussions of downforce lost are as short as discussions about downforce gained, even when only looking for a relative answer. This would be telling in hindsight. Short of a good sized budget and a wind tunnel, this investigation was coming to a rapid halt. But, of course, there was CFD. Could these questions be investigated accurately utilising commercially available CFD? Tapping the talents of Racecar Engineering’s Simon McBeath, the CFD option quickly became reality. The only thing required was the time to generate the CAD files on my end, and all the meshing and case running on Simon’s end.


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