Sports Car International - Feb/March 1996
The Black Art
By Sam Low
The date is May 23, 1993 : With less than a minute left on the last day of qualifying for the Indy 500, Bobby Rahal sits strapped into his car. Moments earlier he was bumped from the bubble by driver Eddie Cheever, and this is his last chance to regain a spot on the starting grid.
As Rahal moves onto the track, I hear the crowd chanting. "Rahal, Rahal..." they're calling, more than 200,000 strong, in a wail like a Roman Coliseum mob demanding the death of a Christian.
On his first timed run, Rahal flashes past the pits. The deep voice of the announcer booms, "now here's the word on Bobby Rahal: His speed is 217.3 miles an hour, just fast enough."
Again the roar of his engine. On the second lap, he is down to 216.8, just four-tenths of a mile an hour too slow. But two more laps remain.
In the car, Rahal scans a computer readout that flashes his average speed. Through Turns One and Two it looks good, but he's worried about Turn Four, where he lost speed on the second lap. "The car is beginning to push," he thinks.
Exiting Turn Three, he keeps his foot into the throttle. He has exactly one second in the short chute to align for Turn Four, and here, as he turns into the corner, the chassis shudders slightly, almost imperceptibly. Rahal relaxes his foot on the throttle, but the slide continues. The rear end hangs out, Rahal turns into the imminent skid, the car wiggles, moves closer to the wall, seems to kiss it, and then continues on down the straight. He's made it through the turn, but the damage has been done: Bobby Rahal, the reigning IndyCar champion, has failed to qualify for the Indy 500.
Rahal has been defeated by an invisible force that all modern racedrivers and their engineers must contend with—the force of the wind. In 1995, this same force also defeated Al Unser Junior, Emerson Fittipaldi and the winningest team in Indy history—Team Marlboro Penske.
Fury of the Wind
"In a real sense, (these Indy) cars are more complicated than the space shuttle, because the environment they deal with is more complex," says Tony Cicale, the race engineer for 1995 IndyCar champion and 500 winner Jacques Villeneuve. "A vehicle running on the road has more complex aerodynamic forces acting on it than a vehicle operating in free air or in space."
Taming the force of the wind by applying the black art of aerodynamics has led to astonishingly high average speeds at Indy, where the current lap record stands at over 232 miles an hour. But the voyage to this pinnacle of speed required 31 ¼2 decades of painstaking evolution in racecar design. In 1960, Eddie Sachs sat on the pole at Indianapolis in a Dean Van Lines Special roadster with a qualifying speed of 146.59 mph. In the ten years that followed, speeds increased only 23.7 mph despite radical design changes including the switch to mid-engines. But in just two years, between 1970 and 1972, speeds jumped an astounding 25.7 mph!
The new ingredient was aerodynamic wings—a design innovation that changed the face of racing forever.
But the winged era did not come without trial. "You know, the new drivers today just don't know what went on when wings first came out." Al Unser is reminiscing in his motorhome at the Speedway . "I think it was in 1971 when we went to Michigan to do a test, and I was having a hard time getting the car going to what we thought should be the speed. So we decided to put a set of wings on it—just on the front, because I was only having trouble with the front. And I had never run wings before on any part of the car. They made a big set of wings and the mechanics put them full tilt, all the way down at an angle. Well, they told me to take it very easy, and I said, ‘well, okay.' So I take off, I warm up the car, and go down the back straightaway.
"Now, going down the straightaway, you have to hold the throttle wide open. So when they say ‘take it easy,' that means take it easy through the corner. So I'm getting close to Turn Three, and I lifted to go in easy. And that car just spun! I mean, it spun about eight times! I didn't hit the wall, thank goodness, but when I got out of that car, my knees were knockin'! We really didn't understand what wings were about yet, and it took me probably another half a year before I'd put them back on."
Al pauses for a moment, chasing an elusive thought. "You know, they can show you two different wings, or bodies, and they can say, ‘this one works, and this one doesn't. And you just say, ‘well, gee whiz this one over here looks pretty, why didn't it work?' You can't see the air, but the air is so critical, so very critical."
The Streamlining Era
In the late 1950s, it was still an item of faith that a car had to slip smoothly through the air with as little drag as possible. In sports-car racing, this tenet led to the sensuous shapes of the early Ferrari Testa Rossas, the Costin Lister-Jaguar, the Aston Martin DBR2—the sort of curves that still inspire a passionate love for racecars of that era.
But in the early 1960s, as engines began producing staggering amounts of horsepower and sports-car speeds approached 200 miles per hour, these slick shapes also exhibited a dangerous tendency to lift off the track—to fly. The dark side of the air's fury was revealed for all to see.
"Lift is a function of surface area," explains longtime racing designer Peter Brock, "so with open-wheelers like the prewar Mercedes GPs, where the body is just a little cigar, even though they were going maybe 180-200 miles per hour, body lift wasn't a real problem. The wheels themselves were the biggest source of lift and drag. But then in the late '50s, early '60s, you started getting fendered cars going that fast at Le Mans and places like that. Then you had a real problem."
One of the racers encountering this problem was Jim Hall, a maverick driver and racing designer from Midlands , Texas . Trained as an engineer, Hall contracted with Troutman and Barnes to build his first racecar in 1961 and named it after a bird common to his home in the prairies—the chaparral cock, or roadrunner. Two years later, he decided to construct his next Chaparral himself.
Hall's Chevrolet-powered Chaparrals were engineered to be light yet stiff, and soon they sported radical innovations like an ingenious 3-speed automatic gearbox. They were blindingly fast. But they were also dangerous. "When we built the first Chaparral it had a tremendous amount of lift in the front end." Hall makes two fists and raises them to shoulder level, gripping an invisible steering wheel which he saws back and forth. "In fact, on the straightaway, I could take it above 150 mph and turn the wheel from side to side like this and it wouldn't even effect the car. The car would just go straight on."
It was a common problem, one also experienced by Mario Andretti, who drove everything from stock cars to open-wheelers and sports cars in those days. "We were getting a lot of lift," says Andretti. He runs his hand over an imaginary shape, tracing the smooth, flowing lines of a mid-'60s sportsracer. "In terms of aerodynamic design, it was kind of a ‘it-looks-good' type of thing."
But Jim Hall realized that lift was actually caused by the streamlined shape of these sports cars, which at high speeds acted like an airfoil to lift them off the track. Like others in the early 1960s, he was already using angled trim panels—spoilers—to generate pressure at the front and rear of the body and therefore combat lift. This solution only came at an increase in drag that Hall deemed unacceptable, however. His alternative solution, developed and worked out with covert engineering assistance from Chevrolet, debuted at Bridge- hampton in 1966. Jim Hall affixed a real airfoil—an inverted wing—to stilt-like struts and attached these directly to the car's rear-suspension uprights. He had already learned that attaching a major source of downforce to the body dictated uncomfortably stiff springs to hold the car up. Putting this pressure directly onto the unsprung suspension components obviated the problem.
On the straight, the wing of his radical Chaparral 2E was set parallel to the pavement, allowing the wind to flow over it smoothly. In the corners, it was tilted down, deflecting the force of the wind to push the car onto the track. "In a general way," Hall explains, "what you're trying to accomplish is to load the car down into the ground. That allows you to corner and stop more quickly, because the tires have more friction with the road. And when we started putting downforce on the cars, the science was different. Now, you could press them down and the cornering speed was tremendously higher. It changed the whole concept of a racecar."
Hall certainly wasn't the first person to recognize this solution. "For example, Erwin Komenda," says Peter Brock, "put airfoils—plain upside-down wings—on the Mercedes T80 speed-record car before the War. That had a full body and those big, narrow tires, so he knew lift and traction were gonna be real problems. The Germans were just decades ahead of everybody else on this, but you know, they just got bombed out of business."
Swiss engineer Michael May also put an inverted, strut-mounted, variable-angle airfoil very much like Hall's on his Porsche 550 Spyder at the Nürburgring in 1956. It worked: "A corner I could usually take at 70 mph or so," May explains in Karl Ludvig-sen's Porsche: Excellence was Expected, "I took with the wing at over 100 mph." The ADAC sanctioning group, however, banned the device as dangerous and demanded its removal before the race. May complied.
Even as well-known a machine as Dan Gurney's Ford-powered Lotus 19 wore a small strut-mounted airfoil over its front axle-line by 1964. Meanwhile over at Shelby American, Peter Brock had created a prototype Group 7 entry around the deck-mounted airfoil that Shelby 's reluctance had kept him from installing on the Cobra Daytona Coupes.
But while a number of such tentative examples were already in existence, Hall was undoubtedly the first person to put all the pieces together and see them to their conclusion. "There's no question that Jim Hall was the first to study the situation methodically," asserts Andretti. "He started coming out with actual airfoils when everybody else...was just messing around with trim tabs and so forth. Aerodynamically, there was a period when the Chaparral was head and shoulders above everything else."
Common fendered racing cars had finally reached the speeds where issues of downforce could no longer be ignored: So many qualifiers at the 1966 Can-Am opener in St. Jovite , Quebec had crashed after becoming airborne that competitors started an unofficial "Can-Am Flying Club." But it was equally critical that in Jim Hall, auto racing had a man who truly understood the importance of aerodynamic balance.
Hall shaped the nose of his Chaparrals to create a given amount of downforce on the front tires, then he balanced those forces by varying the size and angles of the wing at the rear. "What you like in a racecar," the Texan elaborates, "is for it to go through the corner without the tail sliding too much and without the front pushing off too much. We balanced the car with the wing so that it took a 4-wheel slide through the corner and gave us a very secure feeling."
But in spite of the obvious advantages offered by his wings, there in plain view for all to see, Hall's early experience was just like May's: None of his competitors adopted them. "Well the first reaction we got was a kind of hee-haw," Hall recalls. "‘What are you guys doing? This wing looks like a signboard!' It was kind of a scoffing at our idea. It was something new, and they weren't used to it. They said, ‘well, gosh, it's in the way, it blocks our vision, it's going to fall off and hurt us.' I guess it surprised me that our competitors didn't realize the value of it at first."
"Sometimes the more sophisticated people think they are, the more conservative they are," responds Mario Andretti. "You see something that's smoking your butt, and it's right in front of you, and why don't you copy it? You just have to go through a period of time before you are totally convinced. Plus, the other designers gave a lot more credit to Hall's mechanical innovations than the aerodynamic ones; nobody had a gearbox like they did, for instance. And Hall's drivers were mum about the aerodynamics, because you know, they were enjoying it. I think they just had a period there where they had everybody snookered." By 1968, however, the racing world had finally realized that to win, you had to first defeat the air around you. Almost all Formula One cars adopted stilt-mounted wings by this point and, perhaps inevitably, they pushed the envelope too far. At the 1969 Spanish Grand Prix, the wings on the Lotuses of Graham Hill and Jochen Rindt failed, causing spectacular crashes.
Jim Hall still blames these failures on improperly designed attachments rather than the concept itself, but the F1 sanctioning body banned stilt-mounted airfoils outright. Sports-car rulemakers soon followed suit, and Hall's existing Chaparrals were suddenly regulated into obsolescence.
Into The Vacuum
Disinclined to relinquish his advantage so easily, Hall's next innovation would be even more radical. In 1970, he introduced the brick-shaped Chaparral 2J, which he named the "Ground Effect Vehicle." It astounded and infuriated his competitors. Hidden inside the ungainly body were two snowmobile engines attached to fans that evacuated the air from underneath the car. This produced a vacuum that sucked the car to the pavement, providing incredible amounts of downforce and traction for unheard-of cornering speeds.
The idea for this radical design came from Hall's collaboration with Chevrolet's engineers and was inspired by the Hover-craft. Hall explains: "You see, a Hovercraft has fans that blow air under the machine. It's got a skirt around the perimeter to keep the airflow under it, so the trapped air picks the Hovercraft up and it moves around almost frictionlessly. We just turned that system backward; we sucked the air out, and then ran a skirt around the bottom to maintain a low-pressure area.
"I remember the first few times I drove it. You'd go into the corner and apply the brakes and think, ‘Gee, I'm too slow.' And you'd go around the next lap and come up to that same corner and take it deeper, and you'd go ‘again, I'm too slow!' You just couldn't believe how fast the car would stop and corner. It was a different order of magnitude from what I was used to."
It was also a completely different order of magnitude from what Hall's competitors were used to. A chorus of protest was raised about the 2J, claiming it was dangerous. The complaints said the 2J's fans sucked dust from the track and spit it out the rear, obscuring the vision of the other drivers— most of whom, not coincidentally, were behind the fast-moving machine. The Chaparral 2J raced only a partial 1970 season before before it, too, was banned from Can-Am competition. "I had a period where I felt singled out entirely," Hall remembers, "because the development that we did during the '60s with high-mounted wings was disallowed after the fact, and then the vacuum car was banned before it ever won a race! So I felt like the things that I had been doing for the last ten years were wasted, basically."
Chapman and Andretti
Licking his wounds, Jim Hall retired from racing for a time. But his achievements had already brought the game to a new level of aerodynamic consciousness. He popularized the two most basic innovations: downforce produced by airfoils and downforce due to a vacuum under the car. The arena now shifted to F1, where another maverick designer would up the ante. Mario Andretti sat in for this hand of the game as a Lotus team driver for Colin Chapman.
"Sometimes it takes a maverick to try something new," recalls the driver today. "I mean, to roll the dice you have got to believe in something. That's why I loved Colin Chapman. Here was a guy that by hook or by crook was always looking for that elusive ‘unfair advantage.' And he got it several times! There wasn't a conservative bone in his body."
In 1976, the unfair advantage—or any advantage, for that matter—was eluding Chapman. Lotus was struggling mightily with it Type 77 GP car, and at the season's third race, Long Beach , the situation looked dire. Misfortune also struck Andretti that weekend: With a year and a half left in his contract to drive for the Vel's Parnelli Jones team, the outfit folded. This set the scene for a momentous partnership.
"At that time, I was in shock for one reason and Colin was in shock for another," continues Andretti. "And so we were having breakfast at the Hilton in Long Beach . I remember those things as vivid as could be. And I joined the table with him, and we looked at each other and were just chatting and this idea came on. We just said, ‘We should get together. This time, we should really get together.'
"So we teamed up. There was a lot of work to do with the car—it was really a piece of crap. But by the end of that year, from the Italian Grand Prix on, we were competitive, and we won in Japan ." Lotus had improved the Type 77 mechanically and had developed a better understanding of surface aerodynamics— the use of airfoils to create downforce. Like so much in car design, it was a process of evolution. But what happened next was revolutionary—the first effective example of a car that was sucked to the track like Hall's Chaparral 2J without the use of fans.
The true era of ground effects was about to be launched. "When the ground effects started, we had no idea what we were achieving. It just all came about by accident," Mario recalls.
Chapman had convened his engineers and drivers at Ketteringham Hall in Norfolk , England . Mario remembers it as if it happened yesterday: "‘Okay, as a driver what are you looking for?' Chapman asked me. I said, ‘Okay, it's downforce with no penalty.'"
"‘Ha ha ha ha,' the others were all laughing. But Colin wasn't laughing. ‘How are we going to achieve that?' he said.
"So I gave him something. I said, ‘You know, when I drove for March there were some interesting things happening there.' The March in 1970 had airfoil-shaped fuel tanks in between the wheelbase—saddle tanks, like. The car had some downforce, but since the downforce acted on a point that was right before the center of gravity, we had more downforce on the front than the rear. It was not balanced downforce.
"So I said, ‘what if we just build this type of sidepod but have it with the center of pressure behind the center of gravity? Then we will have the type of downforce we can trim with our front wings.'"
Chapman and Andretti were on exactly the same wavelength: What the driver didn't know was that Chapman had already begun serious experiments using information gleaned from that earlier March racecar. Tony Rudd, Chapman's team manager, had hired Peter Wright as Lotus' aerodynamicist in 1974, and Wright had previously worked in the composites shop of Specialized Mouldings, where the March's airfoil-section sidepods had been fabricated. He came to Lotus with the intention of probing the relationship of the car and the ground it traveled over, and he came with those sidepods in mind.
The March Hare
"In 1975, Tony Rudd was given a folder to rethink the GP car," Wright recalls. "We used the moving-road wind tunnel at Imperial College , where we started a fundamental program to look at the relationship of the car to the ground." Most importantly, the engineer adds,"We were using the right equipment and looking in the right area."
A standard wind tunnel is good for simulating a body moving through free air, but a moving-road tunnel—one in which the test subject sits on a conveyor belt moving at the same speed as the wind—is much better at modeling a body moving through the air and over the ground. Pioneered to study the performance of aircraft wings at extremely low altitudes, the moving-road tunnel also revealed the true nature of ground effects for the first time.
"For the Type 78, we experimented with housing the radiator and the fuel tanks in the sidepods to reduce drag, but at first we didn't realize the potential of this for creating downforce," Peter Wright remembers. "We were concentrating on the nose and the front wings at the time. Then one day the model produced tacky results; we got variable downforce. The model was made of wood and plasticine and cardboard all held together by tape, and as the windspeed in the tunnel increased, the sidepods sagged. As the did, they cut down the gap between the road and the car and produced some downforce; then they sagged even more, because the downforce was increasing. We saw what was happening, and so we reinforced the model and used cardboard as skirts. Bingo—it was all history after that."
The Lotus team had stumbled upon a way to harness a basic principle of physics first discovered in the 16th century by a scientist working in Italy , G.B. Venturi. When air is sped up by forcing it into a constricted air is sped up by forcing it into a constricted space, a partial vacuum is created. Today, this is known as the Venturi Effect. Rather than working effectively as a wing section, the model's sidepods were constricting air between themselves and the track. When that air escaped again behind the constriction, a significant pressure drop ensued.
The Lotus team decided to improve the vacuum under their car by containing it. Mario remembers the next step vividly. "We were in Hockenheim , Germany , and we sent the chief mechanic, Bob Dance, into town to just buy all the strips of plastic he could find at a hardware store. And we closed up the space under the car with skirts to trap the air. All of a sudden the car sucked. Oh man! I could really feel it. The downforce just stuck the car to the ground. So we said, ‘Now we've got to learn how to handle it.'"
Design for the Lotus Type 78 actually began in 1975, before the team really understood the effects of the vacuum created below the car. Thus, Lotus had neither the time nor the experience to perfect the design for the use of ground effects. "The car was built in 1976," Wright remembers, "ran tests at the end of that year and raced in '77. We spent the entire year developing skirts. We first used brushes, then hinged plastic strips, but the vacuum sucked them inward and we lost downforce. Then we designed springs to keep them from being sucked in, and used ceramic on the tips to keep them from wearing away."
Using lessons learned in the windtunnel and tested on the easily modified Lotus Type 77, the Type 78 would almost certainly have won the 1977 Formula One championship if not for some ill-timed mechanical failures. Still, the Type 78's downforce surfaces were far from perfect, and the design created a lot of drag, limiting the car's straightline speed.
So for the succeeding Type 79, "...they cleaned everything up," remembers Mario Andretti. "The body was a clean silhouette, and also they narrowed the tub so that you could get a much better airflow underneath. It was just a series of developments that brought the car to the next dimension. The Type 79 was really a peach of a car, much more aerodynamic in every way."
In 1978, driving the Lotus 79, Mario won the World Championship with what one writer referred to as "insolent ease." But the following year, the team was hampered by Colin Chapman's Achilles heel—the reverse side of his maverick genius. "The biggest problem was that the new Lotus Type 80 had more downforce than we could use. What was overlooked was that the more downforce you have, the stiffer everything must be to hold the car up off the track. With surface aerodynamics, if you have a flexi-flyer car, you can handle it. But with a high-ground effects car, when it flexes, forget it! You have a demon on your hands! The car will not repeat its performance from one turn to the next.
"For two years after that, we kept begging Colin to put a collar around the cockpit of the Lotus to reduce its flexing," says Andretti. "We still had a cockpit with a big opening, and the thing was awful—the more downforce we got, the more it was detrimental! We couldn't use it! But with Colin, you had to be there for the kill when he was really on to a new idea. You look at Colin's career, and it's just peaks and valleys. He's either on or off. Fortunately, I was with him in one of the peaks."
The Black Art
One year after Lotus revealed the Type 79, ground effects appeared at Indy when Jim Hall and Roger Penske introduced their new cars. In 1980, Hall's Chaparral 2K won the Indy 500.
Today, after 15 years of aerodynamic evolution and in spite of rules changes limiting the efficiency of aerodynamic wings and underbodies, a modern Indy car develops more than two tons of downforce—enough so that it could literally run upside down if the track were inverted. More practically, this has allowed blinding speed in the corners. In 1972, when Mario Andretti qualified at Indy he hit about 160 mph in the turns. Today, he could do 220 without blinking an eye.
Using the underbody of the car to generate downforce has raised the game to an exquisite new level. The modern Indy car is so complex that tuning it to run at Indy has become a black art—an art that even the best of teams, like Rahal's in '93 and Penske's in '95, can fail to master.
The amount of downforce a car produces and the point at which that downforce acts—its center of pressure—depends on the shape of the venturi created by the car's underbody and the track. But as a car moves, that shape constantly changes.
Approaching a corner, the driver lifts his foot and the nose pitches down. In the corner, the car leans away from the apex. Accelerating out of it, the front rises and the rear squats. All of these motions change the relationship of the underbody to the track, causing the center of pressure to move. This, in turn, changes the proportion of downforce acting on each tire, profoundly effecting the car's balance. And in a 220-mph corner at a place like Indy, a car must be balanced perfectly.
"So you have an aerodynamic device in which the aerodynamics are dependent on the mechanics of the car—the springs, the shock absorbers, the stiffness of the tires. These all relate to the ride height of the car, which interacts with the aerodynamics. You have a loop," says Brian Lisles, chief engineer for the Newman/Haas IndyCar team. "You can't just say that ‘at 200 mph we have this much downforce at this point on the car,' because at 200 miles per hour in a corner you have a different rear and front ride height than on a straightaway. This effects the downforce."
Indy-car engineers control changes in ride height—and therefore the stability of the aerodynamic package—by adjusting springs and shocks. They also adjust the basic ride height of the car off the track. An Indy car is so sensitive to ride height that a common adjustment is called "one flat." It is made by turning a bolt that has six flat sides just 1/6th of a turn—one flat. It's the equivalent of a few thousandths of an inch in the height of the car over the road.
Consider just one more factor—the temperature of the air moving over and under the car. As its temperature increases, the density decreases, which also lowers the amount of downforce. Thus, a slight temperature change can unbalance a modern Indy car at speed.
Nature of the Game
"Designing an Indy car is a 3-dimensional chess game," Alan Mertens, the designer of the car that won the Indy 500 in 1992, once told me. "You have the basic mechanical package of the car, the suspension; you have the aerodynamic forces that work on the car; and you have the changing environment that the car must operate in. It's almost impossible to control all of those variables, because they are all interrelated and they are all changing."
"My dad is an aerospace engineer, and I look at that as the pinnacle of engineering," adds engineer Tony Cicale. "Everything is done theoretically and mathematically with a real understanding of the physics involved. But we don't have NASA budgets, so there's a lot of art in racing-car technology. As well as an engineering, logical approach, we often rely on our instincts and experience and common sense. 'Better' in racing means only that the car is better on this particular track, on this particular day, with this setup and this driver. We could try the same thing on a different day and get a totally different result. That is the subtle nature of the beast we're trying to get at."
So in spite of all the science that is used to design and tune a car, it is still a black art. And as with Mario Andretti and Colin Chapman, it remains an art that depends on a strong partnership between the men who design the car and the human being who must drive it.
"The best ingredients a guy like me can have is good engineers and to work closely with them," says Mario Andretti. "The driver tries to understand the beast just enough, and then you have good engineers that can just go the rest of the way and really make things happen. But even with all the science that you have at your disposal, still, the ultimate thing is that the driver either feels right or wrong. He's the one that gives it the ultimate seal of approval."
Mario rises from his chair and points at his groin. "But instead of being here," he says, and then moves his hand to the side of his head, "it's up here."