2009 Acura ARX-02a
Images copyright Martin Spetz and  Michael J. Fuller
Text copyright Michael J. Fuller
Acura ARX-02a, Sebring WDWT 2009Acura's interpretation of the '09 specification rear wing.  The result of the reduction in span from 2 meters to 1.6 was significantly reduced rear downforce.  Indeed, Acura suffered somewhat given that very late-hour regulation change as the car was designed around a slight front biased weight distribution.  And the reduction in rear downforce meant the new ARX-02a suddenly had a mid-corner snap oversteer issue.  In fact, the ARX-02a was described as a "dog" in the first back-to-back test with the new rear wing.  Ultimately this problem was mollified by shifting that slight front weight bias rearwards.  But naturally this meant that because of that late regulation change the ARX-02a was forced to move away from the hard wired design solution and was less optimized initially.
Acura ARX-02a, Sebring WDWT Test 2009It's hard to overlook the rear wing mounts.  The "swan necks" mount to the less sensitive, less important, high pressure side of the wing freeing up low pressure side wing area and reducing airflow disruption.  

This all came about becuase the reduction in chord from 300 mm to 250 mm for '09 (in addition to the span reduction) led to the use of wing profiles with increased camber.  These more aggressive profiles were inherently more sensitive to wing disruptions and tended to result in very large flow separations when run at higher and higher angles of attack (given the desire to try and recoupe lost downforce).   The Acura's rear wing mounting solution was designed to reduce these surface disruptions as much as possible.

For the record, the rear wing mounts on the Acura are actually referred to as "Quillars", which is an amalgamation of "Question Mark Pillars."  
Acura ARX-02a, WDWT Test 2009Naturally the ARX-02a's rear end is much more aggressive than the ARX-01a/b.  We also suspect additional development work was carried on the rear end since the car initially rolled out in order to reclaim back some of the lost rear downforce.  Note that the diffuser strakes come all the way out to the trailing edge of the diffuser.
Acura ARX-02a, WDWT Test 2009At the Wheels Down Winter Test the engine cover trailing edge had a full length gurney.
Acura ARX-02a, Sebring 2009At the 12 Hours of Sebring, the full width gurney was replaced with a center gurney.
Acura ARX-02a, Sebring 2009Starting at Sebring the rear diffuser strakes were trimmed back from the trailing edge of the diffuser.

ęCopyright 2009, Michael J. Fuller