(by Mark Vaughn autoweek.com 3-2-12)
Sometime around 11 a.m. on Thursday, March 1, the twin-cowled, triangulated DeltaWing race car took its first lap around a race track. The car that could either revolutionize open-wheel racing across the globe or become an historical oddity akin to the six-wheeled Tyrrell Formula One car drove onto the Cal Club's track at Buttonwillow Raceway Park in California, at about half speed for its first shakedown runs.
And? The car some thought would flop over on its side because of its seemingly unstable needle nose, actually took corners at what appeared to be normal speeds.
“They weren't going fast, but they went around the track a few times,” said one race fan who watched the test.
The car was back out after lunch, and this time opened up a little more, hitting what sounded like a rev limiter on the engine--the supplier of which remains unknown--before it went back into the garage for the day.
The main thing is it worked, turning corners with remarkable stability. So far, so good.
Two days before the test, Autoweek visited All American Racers, Dan Gurney's engineering and speed emporium in Santa Ana, Calif., where the car was built. We got some background on the project, or as much as the team could reveal before a couple of sponsorship deals go through and all is made public. First up, how exactly does this thing go around corners?
“Well, it is counterintuitive,” said chief designer Ben Bowlby, formerly of Lola Cars. “For a long time, we all believed that the world was flat, because it's counterintuitive to think that it's round, or spheroid or whatever.”
Before he described how the DeltaWing turns, Bowlby started out describing the basic concept and the physics behind it. The craft is both simple and at the same time somewhat delicate.
“In this case, the tire capacity, the mass distribution and the aero distribution are all in harmony,” Bowlby explained. “The result is that the car is actually balanced.”
Given that it's a rear-wheel-drive configuration, Bowlby said the DeltaWing is extremely well-balanced, with the optimum distribution for traction and braking.
“With a two-wheel-drive car, you put the majority of the tractive capacity at the end that's going to have the weight transfer and acceleration,” he explained. “But equally interesting is braking stability, which is also a function of trying to have more than 50 percent of the braking behind the center of gravity. This is perhaps one of the most unique aspects of the DeltaWing, that from a racing-car perspective it does have more than 50 percent of the braking behind the center of gravity.”
So no matter how much force you apply, there's a self-correcting stability. Like an arrow, sort of.
“It's a combination of factors, and really it's a result of throwing away the rule book,” Bowlby continued. “Racers have become constrained by regulations, and so by throwing away the rule book and saying, ‘Hey let's do something that is in line with our times, which is to get more for less, right?' That's what we did.”
The idea is that with less aerodynamic drag, less car and less weight, you can drive the same race distance as everyone else, using less fuel.
But that still doesn't explain how the car turns.
“Well, obviously, the front wheels steer, and the front wheels have a very long lever arm to the center of gravity and the amount of mass, the amount of weight, on those tires means that the contact-patch pressure load, per square inch if you like, is the same at the front as it is at the rear,” he said. “So it's all in tune. So the result is that the front has the ability to cause the car to change direction very quickly. But then, somewhat unique to here, the majority of weight transfer, like 97 percent, occurs across the widely-spaced rear tires.
“Obviously, the center of gravity has to be between the widely spaced rear tires, otherwise you have a completely unstable device that will fall over. Essentially a delta-plan-form car, otherwise known as a tricycle gear, has to have the weight distribution very carefully observed. There isn't a huge latitude to where you put it. In a conventional rectangular layout, you have the ability to put the center of gravity in a lot of places, and it stays stable. In a delta-wing form you have to observe it very carefully. So you don't want the weight distribution 5 percent further forward, and you don't want it 5 percent further back. You have one spot. In racing, you can control that and end up with a very optimum tire utilization and light weight.”
Bowlby said that there is almost no torsional loading on the chassis, because there is not a pair of axles with their own stiffness.
“Three points makes a plane no matter where you put them. So the result is the chassis is under a very small amount of load. And there isn't a balance effect of different roll stiffness distributions. The car always has an intrinsic balance as a function of its mass, tire capacity and aerodynamic distribution.”
The differential has capacity for vectoring torque to either wheel (or for remaining open), but the car is stable without that torque vectoring.
“Our intention is to make the tuning of the car's balance driver-adjustable,” Bowlby said. “That's a slightly lofty goal at the moment, but all of our simulations have been done without torque vectoring.”
The DeltaWing is a collaborative effort between American Le Mans Series founder Don Panoz, Highcroft Racing, Ganassi Racing and Gurney's All American Racers. The Automobile Club de l'Ouest, the Le Mans organizer, has agreed to let the DeltaWing run as part of its Garage 56, the 56th entry in the field at the June race this summer. The idea is to promote innovation.
The car was, of course, offered up originally as an alternate to the traditional Izod IndyCar Series chassis but rejected by IndyCar in favor of a more conventional design from Dallara. Where it goes after Le Mans is anyone's guess. But just seeing it run laps around a track was a big step.
“It's more than three years that we've been waiting,” said Bowlby. “I have to say that without Dan, it would not have been possible. He knows the process of idea to race track and realized that if we don't start now, it ain't gonna happen, so let's get going.”
