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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


New vs old W


e start another new project this month, again on a current specification racecar


from a leading international formula - the Fortec Motorsport Formula 3 Dallara F312. For comprison, Fortec also brought along a 2011-specification F308. Our feature in last month’s Racecar Engineering described the F312 in full but, in short, the F312 featured cleaner bodywork with less aerodynamic paraphernalia, a higher nose, a larger front wing and a sharply terminated engine cover with a gearbox top shroud below. We knew, with the F3 car’s


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ultra-low front ground clearance (typically 10mm to the front splitter under the driver), that MIRA’s fixed floor would not enable fully realistic data to be generated, especially on downforce from the floor, and to a lesser extent from the front wing. But we would still be able to compare the 2011 and 2012 cars and examine the relative effects of configuration changes. We have used aerodynamic coefficients throughout, calculated at a nominal frontal area value to preserve some semblance of confidentiality. So the coefficients here should not be taken as absolute.


Both cars were brought to the wind tunnel with maximum front and rear wing settings. And during the cars’ set up, each was fitted with ‘trip strips’ on the tyres to better simulate rotating wheels, these angled aluminium strips cause flow separation on the tyres closer to where it would naturally occur if the wheels were rotating (the flow stays attached further around a stationary wheel and creates a different flow field downstream). The baseline aerodynamic data on the two cars is shown below in table 1. The differences (∆ values) between the two cars are given in ‘counts’ where 100 counts = a coefficient difference of 0.100.


The brand new Dallara F312 comes under the wind tunnel spotlight, with the old F308 for comparison


So, with maximum wing angles and the same chassis rakes, both cars generated much the same drag level, but the new car generated 111 counts (7.5 per cent) more overall downforce, with 140 counts more on the front end. Given that exactly the same adjustment ranges were provided on the wings of both cars, the new front wing is clearly a more potent device. According to Andi Scott, Fortec’s chief race engineer, the static weight split of the old car of around 41-42 per cent on the front meant it was always hard to generate enough front-end downforce to obtain an aerodynamic balance. It would appear that the F312 will not have this problem.


Table 1: the baseline aerodynamic data on the 2011 and 2012 Dallara F3 cars, with maximum permitted wing angle front and rear


CD -CL -CLf -CLr %front -L/D


2011 car 0.637 1.480 0.571 0.909 38.6 2.323 2012 car 0.630 1.591 0.711 0.880 44.7 2.525 ∆ (Delta) -7 +111 +140 -29 ∆ (%)


-1.1% +7.5% +24.5% -3.2% CD -CL -1 -CLf +6


+6.1 +202 -


Table 2: aerodynamic data on the 2011 and 2012 Dallara F3 cars with similar aerodynamic balance


-CLr %front -L/D


2011 car 0.637 1.480 0.571 0.909 38.6 2.323 2012 car 0.614 1.479 0.577 0.902 39.0 2.408 ∆ (Delta) -23 ∆ (%)


-7 -3.6% -0.1% +1.1% -0.8%


+0.4 +85 -


+8.7%


+3.7%


The 2012 Dallara F312


The 2011 Dallara F308 July 2012 • www.racecar-engineering.com 51


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