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economic climate. A much more cost-effective change would have been the simple implementation of inlet restrictor reductions aimed at bringing engines closer to the proposed 2011 power levels. This would have been a reduction of between 100- 150bhp (from 700 to around 550bhp). The cost would have been negligible and, coupled with a regulation mandating an engine freeze up to 2011, there would have been no


incentive for expensive engine development. According to Engine Developments Ltd’s John W Judd, ‘Changing restrictors is very cheap compared to the change in wing design, particularly as for some teams the first opportunity to test the new design at high speed may be the Wednesday of Le Mans week, three days before the race starts.’ Engines would have needed to be re-mapped, of course, but, as Judd points out, ‘We are used to the restrictor size


changing almost on an annual basis, so the work to optimise the engine for a new restrictor is something we are used to, and wouldn’t be an additional cost to the teams.’ But Zytek’s Tim Holloway


offers a slightly different opinion on the matter: ‘You are right in that they could have proposed a simple, large power reduction, which would have reduced lap times. But, as always, we chassis people would then want to take


drag out of the car… and that would lead to a high cost aero programme. So whichever route you take there is no cheap, simple solution, other than where we started out.’ Perhaps, but the cost burden


would have shifted from a high mandated cost to a more reasonable elected cost. With the way the rules were implemented, the 2009 aero regulations simply became a $240,000 rules compliance fee.


Figure 7: viewed from below, it is apparent that up to a third of the span was affected


Figure 9: the velocity profile in the transverse plane level with the wing’s trailing edge shows two large triangular ‘holes’ in the airflow


Figure 11: set the same as in figures 6-8, using swan neck mounts has eradicated the flow separation, and the wakes from the mounting plates are much reduced


Figure 8: off-surface streamlines show even more graphically how much of the region below the wing was affected


clearly in figure 4. These wakes had only a very minor effect on the pressure distributions on the underside of the secondary flap element. The same was essentially true of the second model, the 1.6m wide wing using the 2008 profile, although there was a slightly greater proportionate effect caused by the effect on the narrower span. However, the third model, which saw increased camber and angle of attack used to try and recover the downforce level of the 2m wing, showed a rather more surprising effect.


Figure 10: the new swan neck mount half model (courtesy M Fuller)


Figure 12: the velocity profile in the transverse plane level with the wing’s trailing edge shows the much less pronounced effect of the swan neck mounting plates compared to figure 9


Figures 6 and 7 illustrate, and the wakes from the mounting plates can be seen to have a much more widespread effect.


configuration. Figure 9 shows the velocity profile across the transverse plane at the wing’s trailing edge, and two large


“The switch to the ‘swan neck’ mounts produced a potent remedial action”


Figure 8 gives a 3D view using off-surface streamlines, and the flow across the whole centre section of the wing has been thoroughly compromised in this


triangles can be seen to have been ‘punched’ in the airflow under the centre of the wing. Reducing angle of attack on the mainplane enabled the


flow to substantially re-attach here, but this still meant that the mounting plates were compromising performance. The switch to the ‘swan neck’ mounts produced a potent remedial action, eradicating signs of flow separation entirely, as figure 11 shows quite clearly. The streamlines show no disruption from the mounting plates at all, and even the transverse plane velocity plot at the trailing edge in figure 12 shows a minimal wake from the swan neck mounting plates. — Simon McBeath


January 2012 • www.racecar-engineering.com 79


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