Once all manufacturers have officially presented their new cars for 2017 WRC season, except Volkswagen (who finally renounced to participate due to the dieselgate), it’s time for comparison. Higher power means higher downforce required at car rear to improve car handling, so all manufacturers have designed bigger wings, up to the limits fixed by the new regulations. That is, an extra 30 mm overhang, in addition to the 55 mm increase in car width, which is supposed to make cars more spectacular and effective.
The picture above shows the rear view of the five cars’ wing, in order of appearance in the tests, that is, VW Polo, Hyundai i20, Citroen C3, Ford Fiesta and Toyota Yaris.
Assuming they have the same width, as limited by 2017 regulations, the following characteristics can be identified:
- All of them include two central planes, upper and lower.
- The angle of attack of upper wing is very similar in all cases. For the lower plane, Hyundai’s is almost flat, Ford, Citroen and VW use a similar angle of the upper wing, while Toyota’s angle is very aggressive, with an angle higher on the lower plate.
- Upper wings end up with open ends on both sides for the Polo, i20, C3 and Toyota, while Ford and the Finn/Japanese team have closed end plates with an additional side, smaller wing.
M.Østberg/T.Eriksen, Ford Fiesta WRC, Rally Catalunya 2017, 5th
- Ford is the only one to use vertical endplates, thus increasing aerodynamic efficiency by keeping the pressure difference between upper and lower planes. Wings without endplates are supposed to be less effective, because they have a higher probability of vortices generation, as a consequence of air from upper plate trying to move downwards to lower pressure side.
- Toyota’s upper plate takes a descending, vertical shape on both sides, thus acting as an endplate, also minimizing entrance of high-pressure air into the low-pressure side.
E.Lappi/J.Ferm, Toyota Yaris WRC, Rally Catalunya 2017, ret.
- The upper plate is flat, except for the C3, which presents a complex, irregular design.
K.Al Qassimi/C.Patterson, Citroen C3 WRC, Rally Catalunya 2017, 17th
- Lower wing width is limited to windscreen width in all cases except for the Toyota, where lower wing also have side arms descending in parallel to upper wing.
- The clearance between wings is similar in all of them but higher in the i20 and smaller in the C3.
- All except Ford use swan neck supports. This is done to avoid having structures interfering with the pressure gradient below the wing, which may lead to downforce loss due to boundary layer separation. A good explanation can be found in this video from Kyle.Drives.
- Swan neck supports used are very thin, to minimize drag effect. All of them are located close to wing extremes, except Toyota, who has placed them in a more centered position.
- Ford’s wing is the only supported by side endplates.
- All use small Gurney flaps on the rear end of the wing, in order to help air flow upwards while leaving the wing, which contributes to generating additional downforce, with very low impact on drag. Again Kyle.Drives explains this effect in this video.
J.M.Latvala/M.Anttila, VW Polo WRC, Test in Spain (Gratallops), September 2016
Hyundai i20 Coupe WRC. Picture by Eric Rochette
Citroen C3 WRC
Toyota Yaris WRC
J.Hanninen/K.Lindström, Toyota Yaris WRC, Rally Catalunya 2017, ret.
Toyota and Ford have added smaller side wings to even increase downforce, showing that these two cars had a bigger deficit compared to the others. In both cases, wings have the same length as the central wing. Also, Toyota is the only one to insert small vertical fins.
S.Ogier/J.Ingrassia, Ford Fiesta WRC, Rally Catalunya 2017, 2ond
Hyundai introduced some lids on both ends of upper and lower wing, with the intention of moving air into the most efficient direction.
Late in October 2017, Hyundai used one of their jokers to modify rear wing, by introducing new, stronger supports, and larger end plates, with reduced end lips.
A.Mikkelsen/A.Jaeger, Hyundai i20 Coupé WRC, Tests in Spain (Colldejou), September 2017
Toyota introduced their new design very late in the preseason, and still some tests carried out days before Montecarlo Rally by Jari Matti Latvala were still done with original wing. Maybe a sign that there was still debate about which design was better, or maybe trying to generate confusion on the other teams?
Design of this wing is very similar to the final design used by Ford, with the main difference on the presence of fins in the upper wing.
O.Tänak/M.Järveoja, Ford FiestaWRC, 2017 Rally of Poland, ret.
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