Lessons Learned: Preventive Maintenance Keeps Skydivers Flying

Visual inspections, multiple electrical tests, and infrared inspections of the electrical system for a vertical wind tunnel help avoid costly downtime.

iFLY Seattle, the world's first all-glass vertical wind tunnel, is an engineering marvel. This indoor skydiving thrill ride lets participants float on a column of air for a minute or longer in a tube measuring 14 feet in diameter and 90 feet top to bottom. And just like industrial systems, its fans and motors need to keep turning. So iFly owner Bill Adams relies on preventive maintenance inspections of the electrical systems to keep flyers flying, and avoid costly downtime.

"If one of the fans goes down, I can't make a penny," said Adams. "I'm a military guy, and proactive maintenance is the kind of maintenance that you want to be doing to prevent the catastrophic event of fan failure, which would leave me making no money until you get it right."

The trampoline-like floor of the flight chamber, which is the enclosed section of the tunnel you step into, is aircraft-quality stainless steel. Powerful, high-efficiency axial fans mounted in the upper leg of the tunnel generate wind from above. The wind is channeled and directed down the sides of the tunnel, underneath the flight chamber, and then up through the floor of the flight chamber to lift flyers into the air. The fans move more than two million cubic feet of air per minute to create the wall-to-wall vertical cushion of air.

The four turbine-like fans above the flight chamber are each attached to a purpose-built, air-cooled 400-hp Reliance Electric AC motor rated at 900 rpm and capable of bursts to 600 hp and 1,125 rpm. Although most flying happens at 90 to 150 mph wind speeds, these motors can draw air up past the flyers at speeds up to 230 mph.

When a company testing vibration in the four fan motors identified a vibration signal possibly caused by an electrical anomaly, Adams called in electrical contractor Keithly Electric to examine the system, including supply circuits, harmonic filter, variable frequency drives (VFDs), and motors.

In that inspection, a scan with an infrared camera from Fluke revealed that increased resistance at a loose terminal at a fuse block inside the power filter was heating the block to 139 °F
 (59 °C), noticeably more than the reading of less than 100 °F
 (37 °C) for blocks nearby. Re-torqueing the screw showed it to be a half-turn too loose.

"The solution was simple," said Keithly Project Manager Zach Bryson. "We removed power from the line filter, and the terminal was tightened. It was just a torque issue, but the bigger issue is that whole fuse holder probably would have burned up, and then it would have been a lot more work than five minutes of torqueing a terminal. It would have meant removing an entire fuse holder and re-wiring that back into the cabinet. Preventive maintenance was the ounce prevention that removed the pound of cure."

Infrared cameras also help the potentially problematic aluminum—rather than copper—power cables. Aluminum expands more than copper when it heats up under load, which means connectors can loosen over time—increasing resistance, and the potential for trouble.

"What happens with aluminum conductors is they heat and cool with much more thermal expansion," Bryson said. "They are able to work themselves loose, and that's where your torque issues typically will come in. With each of these motors, you have the potential for huge thermal expansion problems. You have to be much more careful that you're

The Keithly Preventive Maintenance Program for iFLY includes visual inspections, multiple electrical tests, and infrared inspections, according to Bryson. The facility even has to pass a “smell test,” Bryson said. As they run their other tests, Keithly technicians are on the alert for the unmistakable scent of burned electrical components.

Read this article online (http://awgo.to/484) for a step-by-step look at what the Keithly team does to test the iFLY systems.

Video: See iFLY owner Bill Adams and his friends in action.

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