Today’s Indy cars look drastically different than those that ran in the first Indianapolis 500 in 1911, and that has a lot to do with the series’ aerodynamic advancements. The Verizon IndyCar Series has a video showing just how much slipperier cars have become throughout the decades, and take this as a warning: nerdy Computation Fluid Dynamics lies ahead.
The Automotive Research Center, or ARC, in Indianapolis decided to run some Computational Fluid Dynamics simulations (used to predict fluid behavior) on four Indy cars—a 1911 Marmon Wasp, a 1955 Kurtis Kraft 500C, a 1965 Lotus 38 and a 2011 Dallara—to see just how much better the newer cars are in the wind tunnel versus their predecessors.
Here’s how they stack up:
1911 Marmon Wasp
The winner of the first ever Indy 500 in 1911 was Ray Harroun in a Marmon Wasp. The car was impressive, but it was also a bit of a brick aerodynamically. Of course, designers back then didn’t have the tools we have today to simulate fluid flow, so we can’t be too hard on the engineers.
What they devised was a car with sharp edges around the radiator and exposed suspension components, both of which created massive turbulent vortices and lots of drag.
IndyCar’s technical expert and former IndyCar driver Jon Beekhuis, “Professor B.,” says the rear suspension of the Wasp accounts for a whopping 41 percent of the aero force resisting forward motion. He also says the rear of the car makes no downforce at all, and that the front actually produces lift!
Harroun’s famous mirror—the one that vibrated so much over the Indianapolis Speedway’s brick surface that it was rendered essentially useless—appears to actually have served a purpose, as Professor B. points out that the mirror deflects airflow up and over the driver’s head, decreasing overall drag.
1955 Kurtis Kraft 500C
The ARC also ran CFD simulations on a 1955 Kurtis Kraft 500C, the car that Bob Sweikert piloted to win the Indy 500 in 1955. The rounder Kurtis Kraft was found to make 22 percent less drag than the Wasp, due in large part to its “tidier” suspension (IndyCar makes no mention of the difference in frontal area between the two).
That tucked-in suspension accounts for only 9 percent of the car’s drag, according to simulations, which is similar to the contribution modern IndyCar suspensions make to their overall drag figures.
The biggest factor in the Kurtis Kraft’s aero drag is the wheels, which account for 51 percent of overall drag.
1965 Lotus 38
British driver Jim Clark drank the milk at the brickyard in 1965 after taking the checkered flag in a Lotus 38. That car’s tiny frontal area was a godsend for drag (drag is directly related to frontal area), and a dual windshield also helped keep the fluid boundary layer attached and drag figures down.
Unfortunately, the long suspension arms blocked airflow and hurt the vehicle’s aero properties. Even worse was the fact that the suspension was offset (i.e. the car doesn’t sit at the midpoint of the track width) with longer suspension arms on one side; this supposedly offered better handling for oval tracks.
But that meant there were more aerodynamic forces working against one side than the other, giving the car a tendency to yaw to the right—not exactly what you want to do when you’re turning left. The car also produced zero downforce, which could make cornering a bit hairy.
Still, with 10 percent lower drag than the Kurtis Kraft, it’s safe to say the Lotus was a step in the right direction.
The final simulation the ARC ran was of the modern Dallara design. The car, unlike its predecessors, is designed to produce massive quantities of downforce. In fact, it is capable of producing an incredible 2,000 pounds of the stuff, with the bottom of the car acting like an upside down airfoil sucking the car to the track.
Despite having a larger frontal area than the Lotus, the Dallara makes 29 percent less drag, showing just how valuable modern Computational Fluid Dynamic simulation tools can be in optimizing vehicle shape.
The biggest contributor to the modern IndyCars’ drag is the wheels, which account for 51 percent of the 2011 vehicle’s drag. The following year, 2012, brought that figure down to 48 percent, though, and IndyCar says the Honda and Chevy aero kits are even more aerodynamically efficient.
From no downforce to 2,000 pounds of it, and from blunt-nosed cars that tapered in the back to pointy-nosed cars with huge rear wings, Indy cars have made some huge strides in aerodynamics. It should be exciting to see where they go next.
source: gizmodo.com by David Tracy