Everything has a beat. A rhythm. A frequency at which it likes to shake. You can rock most objects off-beat for as long and hard as you like, and not much will happen (see: the career of John Mayer). But start to push and pull in time with the natural frequency—the “resonant” frequency—of the object in question, and it will quite literally start to fall apart, much like the helicopter in the video below.
I always understood resonant frequencies best by thinking of the old-timey toy the paddleball. This uniquely solitary time-waster—Minesweeper for the Greatest Generation—consists of a bouncy red ball attached by elastic string to a small wooden paddle. Success comes when you hit the ball, the elastic pulls it back to the paddle, and you hit it again. And again and again and again. You quickly notice that there’s only one frequency that works, only one rhythm that prevents you from flailing wildly at the stupid little red ball. This is the paddle’s resonant frequency, and in this case, it’s a good thing.
Not so when dealing with bridges, skyscrapers or helicopters, however. Shake these at their resonant frequency, and the back-and-forth motion spells trouble. Each push adds more and more energy to the object—energy that, if not dissipated, starts to wreak havoc. That’s what happens with our Chinook. The rotating blades begin to shake the airframe at its resonant frequency, and physics takes care of the rest: Because the blades are unable to dissipate the excess energy, the convulsions rend them from the fuselage.
According to PopSci’s aviation expert, Bill Sweetman, helicopters are prone to resonant effects, which is why resonance ground testing (as seen in this video) is a standard part of chopper R&D. If both blades in a twin-rotor helicopter share the same heavy vibration and the engine mounts aren’t rock-solid, the energy generated can actually make the motors start moving around the engine mounts, and the next thing you know, that bird’s goose is cooked.
Sweetman also offered up this anecdotal tidbit: “Little-known fact: Charles Kaman, a U.S. heli designer who was also a bluegrass guitar player, combined his knowledge of acoustics and fiberglass (used in rotor blades) to create the Ovation guitar series.” Cue Patsy Cline’s “I Fall to Pieces”. . . —Michael Moyer
A lucky eBay bidder could walk away with a one-of-a-kind Skycar prototype. Starting bid? Just $1 million
By Eric AdamsPosted 10.09.2006 at 1:00 am0 Comments
Last year, the Skycar was offered for sale on the cover of Neiman Marcus's famed annual holiday catalogue. No buyers. Now it's on eBay. What's next, collect 340 million Pepsi bottle caps, and it's yours?
Sad but true: The lure of being cast into the air by a speeding floatie was so intense that PopSci almost featured the Wego Kite Tube in our magazines Whats New section earlier this spring. We didnt, because it just seemed too dangerous, but heck, we werent the only idiots who thought it looked like a ton of fun. More than 19,000 Kite Tubes were sold this year, and the thing was even named 2006 Sports Product of the Year by the Sporting Goods Manufacturers Association.
But what was everyone thinking? If there were a Darwin Awards for toy manufacturers, these guys would get top honors. The floppy 10-foot diameter discs—brazenly printed with skulls and the slogan Never kite higher than youre willing to fall—were recalled a few weeks ago after causing 39 injuries and two deaths. And were not talking Slip n Slidecaliber injuries. One 29-year-old man broke his neck after falling from a height of 35 feet at 45 miles an hour.
The problem is that the tube provides a means of creating loft (a vertical-pulling mechanism that lifts the front of the disc enough to force air beneath it) but no means of steering once youve gotten off the ground. As aviation writer and resident aerodynamics expert Bill Sweetman puts it, Flight is more than just lift (the bottom of the tube) and thrust (the boat). There is also something essential, which is referred to as control. Without that, you are fish food.
So without further ado, the tasteless feature youve been waiting for: The Wego Kite Tube crash video. —Megan Miller
It floats, it flies, it eliminates enemy targets-meet the water-launched unmanned enforcer
By Bill SweetmanPosted 02.21.2006 at 2:00 am0 Comments
Lockheed Martin's Skunk Works, famed for the U-2 and Blackbird spy planes that flew higher than anything else in the world in their day, is trying for a different altitude record: an airplane that starts and ends its mission 150 feet underwater. The Cormorant, a stealthy, jet-powered, autonomous aircraft that could be outfitted with either short-range weapons or surveillance equipment, is designed to launch out of the Trident missile tubes in some of the U.S. Navy's gigantic Cold Warâ€era Ohio-class submarines.
The A380 is the most massive jetliner ever built, and getting it done was an equally huge undertaking. Here, an exclusive look at the unveiling of Airbus's giant gamble
By Bill SweetmanPosted 03.31.2005 at 2:00 pm0 Comments
There were acrobats from the Cirque du Soleil, a mechanical objet d'art that looked like a mad inventor's spaceship, and a voluble computer-generated wizard that bore a disturbing resemblance to a bathrobe-clad George Carlin-the ceremony in Toulouse, France, that marked the completion of Airbus's first A380 was nothing if not pomp-filled. But when four kids finally tugged on a huge tasseled cord and the curtain fell to reveal the largest jetliner ever built, the spectacle was just beginning.
This morning, October 18, 2002, the Air Force and Boeing unveiled to a small group of selected journalists the Bird of Prey, a previously "black" or ultra-secret airplane prototype that was built and tested in the mid-1990s. The unveiling took place at Boeing's Phantom Works facility in St. Louis.
In our December issue, Popular Science names the 100 best innovations of the year: bombproof wallpaper, self-parking cars, the fastest helicopter, and 97 more. Plus inventor profiles and videos.
