Lightning Experiment May Help Better Protect Airplanes

Sources: Martin Uman, (352) 392-0913, uman@ece.ufl.edu; Vladimir Rakov, (352) 392-4242, rakov@ece.ufl.edu

GAINESVILLE, Fla. --- An experiment aimed at gathering new information about what occurs at ground zero of a lightning strike may lead to more effective lightning protection for airplanes, University of Florida researchers say.

While lightning rarely causes plane crashes, it is not unheard of, and the Federal Aviation Administration plans to use the information to update its tests for new airplanes to ensure they are adequately protected against lightning, the researchers say.

"We may determine some of the parameters in the FAA's lightning test standards do not represent what's going on when lightning strikes and should be modified according to our measurements," said Vladimir Rakov, professor of electrical and computer engineering.

Rakov, who recently returned from a conference in France on lightning and airplanes, said lightning destroyed a glider in Europe recently and has brought down several helicopters in England and Scandinavia in recent years. On average, lightning strikes a commercial jet once for every 10,000 hours in the air, but most strikes cause no significant damage because the lightning current flows harmlessly across the metal skin of the aircraft, he said.

"However," Rakov said, "once in a while, the consequences of a lightning strike can be very, very dramatic, even catastrophic."

In perhaps the most famous lightning-related crash in the United States, lightning brought down a Boeing 707 in Maryland in 1963, killing all 81 people aboard. Since then, lightning has been implicated in a handful of jet crashes worldwide, Rakov said. An increasing reliance on composite materials in aircraft construction creates the potential for additional problems because the composites can allow a connection between lightning and airplane electrical circuits, he said.

The experiment got under way earlier this summer at UF's International Center for Lightning Research and Testing near Starke. Located on an isolated tract of land on the Camp Blanding National Guard base, researchers at the center rely on a time-tested method for studying lightning: They trigger it using wire-trailing rockets shot toward storm clouds.

While the researchers often launch rockets from a tall tower, the launch pad for the experiment is located in a pit in the ground. Surrounding the pit is a thick 70-by-70-meter metal mesh buried an inch or so beneath the topsoil.

Martin Uman, chairman of the electrical and computer engineering department, said the rocket launcher and other equipment are below ground to eliminate interference when the bolt arrives. The wire mesh will prevent the lightning from arcing. The setup is designed to create the perfect environment to measure the electromagnetic fields, currents and shockwaves near a lightning strike -- information the FAA then may use to modify the tests now in use to ensure airplanes are protected, Uman said.

The data gathered in the experiment also are expected to shed light on the physics of lightning strikes, Uman said.

"We're going to settle lots of problems that exist in the scientific literature about this issue with this superior experiment," he said.

The FAA and the National Science Foundation are sponsoring the two-year experiment, each contributing $150,000 to $200,000 annually.

In another experiment at the lightning center this summer, researchers are testing two different power lines to determine how and why lightning damages them. One of the lines routinely sustains less damage from lightning strikes than the other, and Florida Power & Light Co., which is sponsoring the experiment, wants to know why, Uman said.

"Lightning is a leading cause of outages in the summer, and year-around it's a major cost to power companies," he said. "FP&L is hoping to find out how to improve their lines so they can reduce their damages and keep their customers happy."

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