Welcome aboard Collected Wisdom Airlines. If you look out the window, you'll see that we are flying through a humungous thunderstorm. But don't worry, this state-of-the-art, coal-powered Stratocruiser is completely sa …
How are aircraft protected from lightning strikes? Hector McNeill of Lindsay, Ont. (a nervous flier) wants to know.
Lightning strikes on commercial aircraft are rare and generally harmless, writes Michael Lennick of Toronto, writer-director of the Discovery Channel series Rocket Science. However, under certain conditions, lightning strikes can be dangerous, and aircraft travelling through U.S. airspace are required to have static-discharge wicks to minimize any damage.
“The outer skin of most airplanes is made of aluminum,” he says, “a very good conductor of electricity. Thus a variety of conditions, from flying through storm clouds to simple air friction, can cause static charges to build up on the outer surface of the aircraft.”
Discharge wicks were first introduced in 1945, Mr. Lennick adds, and are designed to provide a continuous low-resistance path from the aircraft to the surrounding air. (On most commercial jets, they're the thin rods you can spot extending from the main wings' trailing edges.)
“While the wicks won't prevent lightning strikes, they'll direct the charge to travel along the outer body of the craft and dissipate in the atmosphere. Because the most powerful lightning strikes tend to seek ground, an ungrounded aircraft, with its exterior surface well insulated from its interior, is not generally in danger, although there have been exceptions.”
Perhaps the most famous lightning strike came during the U.S. moon landings when Apollo 12 launched during a downpour on Nov. 14, 1969. “Less than a minute into the flight, lightning twice struck the rapidly ascending rocket, riding the Saturn V's ionized exhaust plume all the way down to ground itself on the launch tower. The charge overloaded the command module's main power and instrumentation, leaving the vehicle roaring toward orbit in near-darkness.”
After some initial confusion, lunar-module pilot Alan Bean flipped the necessary switch to bring the systems back on line. NASA never again tried launching during a thunderstorm.
Bill Barr of Edmonton wonders why headlights on many vehicles have three or four small bumps on them.
“Typically this is so the headlights can be aligned,” says Peter Clarkie of Ottawa. The bumps fit into a machine, “and the mechanic is informed by computer which adjusting screws need to be advanced or retarded. This is a lot easier than the old way, where a car was placed on level ground, at night, with the lights pointed at a garage door 30 feet away. The mechanic would then aim the lights by hand until the pattern on the door looked good.”
- “When I take a bath, the parts of my body above the water sweat,” writes Alain Gingras of Notre-Dame-de-la-Salette, Que. “What about the parts in the water? Do they sweat? If not, why not?”
- Robert Findlay of Toronto asks: If black and grey squirrels are from the same family, why aren't their numbers approximately the same? The black squirrels always seem to be in the majority.
- Why are beer cans 355 millilitres but beer bottles only 341 millilitres? Mike Maher of Montreal wants to know.
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