The Physics of Winning
What Reno air race winners know that losers don't.
- By George C. Larson
- Air & Space magazine, January 2007
Richard Vander Muelen
(Page 2 of 2)
When a pilot pulls a 70- to 80-degree bank in turns, the Gs scrub off speed the way the friction of the front tires does on cars. To pull those Gs, pilots are pulling the stick back, pitching the nose up toward the inside of the turn and increasing the angle of attack of the wings to increase their lift and counter the centrifugal force that can make a 200-pound pilot
feel as though he weighs 800 pounds.
In the 1990s, Bill “Tiger” Destefani flew the modified P-51 Strega to victory against competitors with more horsepower. He explains his advantage in terms of pulling Gs: “You’ve got to get through the turn with the least amount of Gs. Gs equal drag. We’ll put enough weight in the tail so if you’re pulling up to 4 Gs in a turn, the tail-heavy airplane goes faster.” Flying Strega was all finesse, he says. “No rudder in the straights. In the turns, just a liiii-tle bit.” His team went to great efforts to remove every last bit of trim pressure that would be exerted at top speed. Even a small surface like a trim tab or a tiny control deflection adds drag.
Steve Potter, vice president and general manager at Lime Rock Park, a race track in Connecticut, says his first experience in a race car was very different from how he’d imagined it, and he’s spent years thinking about the challenge of driving at speed—and about the line.
“In the entire span of nature’s time, until an eye-blink ago, humans lived in a 20-mile-per-hour world. All of our sensory systems have evolved to live with that. The trick is to slow the world, when you’re in a vehicle, down to 20 mph. Look out a side window, and at 50 mph, the guardrail is a blur. If you look far enough down the road, things are not approaching very quickly. To follow the line around a race track, it’s critical to learn to look far ahead and ignore what’s close.”
All well and good when you have a track to yourself at the Indianapolis 500 time trials or you’re just running practice laps at Reno. In real-world racing, you can find yourself in traffic or in somebody’s prop wash. And you can’t expect to enter every turn at precisely the right point. Racers learn to compensate when they can’t follow the ideal line or when they make a mistake and have to correct for it. On the track, drivers are trained to make optimum use of the tires’ grip by using part of their adhesion for braking, part for cornering, and part for acceleration out of the turn—all influenced mightily by the line through the corner.
A driver has the right to defend against being passed, and swinging wide in a turn is one way to block. That happened to Mary Dilda when she was trying to pass a competitor in 2005’s T-6 Gold race: “When he would roll into a turn, he was delaying the roll and hoping I was [flying as if in formation]. I flew my own line a little higher.” Although that gain in altitude might have forced her to expend energy, she says, “I didn’t have the G forces that he had to pull. He had to pull harder through the turn.” She got her spent energy back coming downhill after she passed the competitor’s T-6 handily.
“Sometimes in traffic, you get away from the optimum [line],” says Shelton. “You go outside somebody because of traffic or prop wash. Prop wash can whip you past vertical [90-degree bank] and really gets your attention. The wing can get stuck in the vortex and it won’t come out. Then it whips out, and it’s really a violent thing. Then you’ve got to settle back in.”
Though altitude gain and prop wash are alien to race car drivers, air racers and auto racers still have a lot in common. Shelton sums it up: “I’ve gone to the Motorsports Hall of Fame and talked to the auto, motorcycle, boat guys, and others, and we all talk the same language.”