TECHNOLOGY – AEROBYTES
Simon McBeath offers aerodynamic advisory services under his own brand of SM Aerotechniques – www.
sm-aerotechniques.co.uk. In these pages he uses data from MIRA to discuss common aerodynamic issues faced by racecar engineers
Produced in association with MIRA Ltd
Mirror image W
e conclude our studies this month on the Zytek Z11 SN LMP2 Sports
Prototype of Greaves Motorsport with a look at the effects of the mandatory increase in mirror size, and summarise the overall effect of the 2012 modifications. The team evaluated every
configuration across a range of yaw angles from zero to six degrees, the latter representing the slip angle at which the tyres generate their maximum grip. How, then, would the 2012 mirrors, whose mandatory viewing area had been increased from 100cm2
to 150cm2 , affect
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the aerodynamics over the working yaw range? For the record, drag was very similar with the 2012 mirrors across the yaw range tested, but downforce and balance were affected to an extent. The change in total downforce is also fairly easily explained. With the 1600mm span rear wings now in use on LMP cars, when the car was at zero yaw the wakes of the mirrors essentially passed outboard of the ends of the wing. However, when at yaw the wake of the ‘upwind’ mirror did impinge on the rear wing, and we can see from figure 1 the effect on reducing downforce was increasingly apparent as yaw angle increased. Indeed, the
Figure 1: the larger 2012 mirrors had no effect on straight-line performance, but did affect downforce when the car was at yaw
The last in our series on the Greaves Motorsport Zytek Z11 SN LMP2 Sports Prototype
data on front and rear downforce suggest there was no change in front downforce levels, within the bounds of repeatability, but rear downforce was reduced by about
one per cent at six degrees yaw. Figure 2 suggests there was a small difference in aerodynamic balance, expressed as ‘% front’, with the gap between the two
Figure 2: the effect of 2012 mirrors on aerodynamic balance
The 2011 specification mirror
The 2012 mirrors have a 50 per cent larger viewing area Le Mans •
www.racecar-engineering.com
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