Two days of running last week at the Indianapolis Motor Speedway left the NTT IndyCar Series with a number of aerodynamic configurations to consider for use at next years Indy 500.
Amid frigid temperatures spread across Wednesday and Friday, entries from Andretti Autosport, Arrow McLaren SP, Chip Ganassi Racing, Ed Carpenter Racing, Rahal Letterman Lanigan Racing, and Team Penske assisted the series with sampling new or familiar aero components. The test was focused on improving stability at the front of the cars in turbulent air which, in turn, would improve the odds of making successful passes.
With a number of aero pieces readied for the drivers to use that increase downforce with the Dallara DW12’s underwing, drivers Takuma Sato, Josef Newgarden, Scott Dixon (photo above), Pato O’Ward, Ed Carpenter, and Ryan Hunter-Reay were put to work in lead-follow sessions led by IndyCar aerodynamic director Tino Belli.
“We managed to keep everything pretty much to plan,” Belli told RACER. “The first day was a Dallara day, with just Sato and Newgarden, and the cars were instrumented up a little bit extra. We did some straight-line running to get aero numbers with the cars on their own just to validate that to the wind tunnel. But we also did phase one of our attempt on traffic study, and we actually equipped the cars with a radar in the nose, and that was to measure directly and provide feedback to the driver directly of their following distance.
“What we’re doing with Dallara is CFD studies of two cars at specific distances, so we studied the second car running 40 meters back (131 feet), 20 meters back (66 feet), 10 meters back (33 feet), and one and a half meters, offset (five feet). So from the GPS that we have off the car, we plotted the typical overtaking trajectory. And the main reason for the Dallara day was to acquire the forces and surface pressures on the underwing and the front wing of the following car in those positions to correlate to CFD (computational fluid dynamics software). So as you could imagine, simulating two cars in CFD is very, very computer intensive. It takes a long time. It’s just massive. It needs loads and loads and loads of CPU time.”
Along with the time needed to validate real-world lead-follow data with the Dallara’s CFD findings, Belli used the Wednesday outings to start the long list of two-car test runs.
“The whole idea is obviously we want to try and get the computer time down as low as we can and still get realistic results, so we did four outings,” he said. “The first outing had a little bit of a communication problem with a radar in one of the cars that was overloaded. The second one was a repeat of basically the 2020 configuration, and then we ran through a couple of the possible 2021 configurations, where we did… the leading at the different meter interval, then swapped Sato and Newgarden, and ran them again. Our guys are very, very, very happy with that.”
Rain on Thursday gave Belli and Dallara time to process a lot of the testing information which helped refine Friday’s six-car session. More cool temperatures delayed the start of on-track activity.
“The new requirement is 45-45 now; 45 Fahrenheit ambient and 45 track surface, and I don’t think we got running until 12:15, which basically gave the teams two hours to run through the 2020 baseline and three configurations, which we came up from Wednesday,” Belli said. “So the configurations ended up with was obviously the 2020 race package, which is our baseline. Then the upper and lower infills on the outer edges of the floor, with a 15-mil wicker on the trailing edge. Then the upper and lower infill without the wicker, the bargeboard, and the Z30’ strakes from the original DW12. The Z30 is 30 millimeters above the bottom of the skid, so we ran the Z30, which is typically all we’ve ever run on ovals in the past. The last time that would have been used with that Pocono last year.”
Armed with a wide array of combinations it could try with the aforementioned pieces, the various increases in underwing-based downforce produced mixed responses from the drivers polled by Belli and IndyCar’s Bill Pappas.
“The whole concept behind it was to back out the front wing angle, create the front downforce from the leading edge of the underwing, and after that, all you’re doing after that is tuning downforce levels,” he said. And so we didn’t have too many hiccups. For sure, there is a difference of opinions among the drivers. But in general, all solutions did what we expected them to. And after that, the difference in opinions really becomes how easy the car should be to drive. And I think we have that same difference in opinions, even within our fan base. And that’s going to be the complicated one.
“So as you could imagine, certainly those leading-edge solutions that we came up with allowed us to run significantly reduced amounts of front wing. Which we think is good and I think most of the drivers thought was good. Then the window that opens up with us is obviously when you put the strake in and make more rear downforce, it tends to add a bit of front back in to rebalance the car with the strake. The strake is really just pure downforce, very efficient downforce, very little drag induced by it. And then it really becomes, whether you want the cars to be easier to drive or not. And that’s where there’s a big disparity among the drivers of how easy the cars should be to drive.”
The next steps will be for IndyCar and its paddock to decide how many of the aero options to allow next May.
“From an aerodynamic point of view, I think we filled our toolbox, and have the parts and the knowledge of what to do with them,” Belli said. “It’s just a decision of how much to do. We have to decide how much downforce we need to be giving the drivers, and mustn’t underestimate how difficult a decision that is.”