February 22, 2007
Daredevil’s fall re-enacted in UW’s water tunnel
In a tank on the south campus, a Superman figure dangles from a plastic airplane wing. He swings helplessly as fluid rushes past his body creating tendrils in his wake. The only thing missing from this dramatic re-enactment is a crowd of 70,000 onlookers, watching the stuntman from hundreds of feet below.
Bob Breidenthal and Joe Giordano in the Aeronautics & Astronautics Department constructed the scale model for a show airing this week on the Discovery Channel. The UW’s water tunnel makes fluid dynamics visible, helping to study turbulence. This unusual experiment was done for an episode of a new television show, Survive This! that looks back on extreme events.
“We begin every story with a piece of dramatic video tape that covers a disaster, an accident, a crime, or something of an extremely violent and scary nature, that leaves the viewer wondering how the subject at the center of it all could possibly have come out alive,” said producer Keith Cornell. Afterward, Survive This! calls on experts who can explain what happened during the disaster. For this episode, they wanted to know how much aerodynamics had hampered a stuntman’s ability to climb back onto an airplane wing once he’d slipped.
Initially the producers approached the manager of the UW’s wind tunnel. But to actually see turbulence it’s more instructive to do the experiment in water. Dye, in this case food coloring, tracks the flow better than the smoke commonly used in wind tunnels.
Few people know the UW’s water tunnel better than Joe Giordano, who graduated last year with a master’s degree in aeronautics. Giordano returned to the lab from his current job at Boeing to create a scale model of the air show incident. First, he watched video footage of the original accident to build a model; past experience with remote control planes helped him build the foam-core wing. He found a Superman action figure for the stuntman and positioned the apparatus in the fluid tank for the re-enactment.
Since the 1920s people have gaped at the antics of wing walkers, aerial daredevils who walk or hang from the wings of moving airplanes. At the Oregon International Airshow in 1991, stuntman Lee Oman had a bad day. He was hanging from the wheel axle and trying to swing his legs up to dangle upside-down when he slipped and fell.
Luckily, Oman was wearing a safety harness. “So he wasn’t a guy falling from a plane, he was a guy hanging from a plane,” Giordano noted. Still, things weren’t going well. The safety rope was a bit too long, so Oman was dangling out of reach of his handhold. And as the wind whipped past his body at 70 mph, he tried and failed to climb back up the rope.
The ground crew scrambled to think of a rescue. The plane couldn’t land because Oman was below the wheel base. They eventually devised a makeshift plan. Two pickup trucks drove along the runway. One was directly below the plane to catch Oman. The other drove alongside, so the pilot could watch it and gauge his speed to match that of the truck. The entire convoy moved at 70 mph. Crew members didn’t need a doctorate in fluid dynamics to tell them that if the plane slowed down too much, it would lose lift, and thus altitude.
Oman spent 10 wind-whipped minutes hanging in the air but survived the accident. Afterward he told reporters he planned to repeat his stunt the next day. “Only this time we’ll do it the way we planned,” he said.
In the UW laboratory in late December, the tunnel showed that vortices spinning off the Superman figure buffeted him back and forth. Giordano is an expert on this type of turbulence — he used the water tunnel in his research to study vortices that can affect jet engines’ efficiency. The Superman’s rocking motion would likely be representative of what happened during the accident, he said, given the density of air and the speed of the plane.
Breidenthal, a professor of aeronautics & astronautics and Giordano’s former advisor, calculated the total drag force on Oman’s body as he struggled to climb back up the rope.
“One of the issues was: How important was aerodynamics in this guy’s dilemma?” noted Breidenthal. He made some calculations and found that at these speeds drag probably wasn’t a huge factor. “I’m not saying that it was necessarily a pleasant experience,” he added, “especially when you’re contemplating your mortality.”
The on-camera event provided a rare spotlight on the UW’s fluid tunnel, which is temporarily housed in the Harris Hydraulics Lab during Guggenheim Hall’s renovation. The tunnel was originally built in 1986. It has been used to test telescope enclosures, the F22 fighter plane and more recently another aeronautics research product, RoboFish.
The episode showing Breidenthal and the fluid tunnel is scheduled to air on the Discovery Channel at 10 p.m. Tuesday, Feb. 27.
