DARPA’s Adaptive Landing Gear Is Cool But…

There’s been some breathless coverage of a Defense Advanced Research Projects Agency experiment with what look like mechanical insect legs to replace the usual wheels or skids helicopters land on. One article called the Adaptive Landing Gear nothing short of “incredible.” The video DARPA publicized is certainly fun to watch (see above), but there’s a lot less utility there than meets the eye — at least for now. “The only thing that I can see it would have an advantage over what we have in a skid is on a slope,” said retired Army Maj. Gen. Patrick Brady, who won the Medal of Honor and a ton of other decorations for saving more than 5,000 wounded in more than 2,500 combat missions as a rescue helicopter pilot in Vietnam. The Encyclopedia of the Viet Nam War calls him the conflict’s top helicopter pilot. “Looks like a big grasshopper,” Brady said of the leg-like landing gear, developed by the Georgia Institute of Technology on a roughly $1 million DARPA grant. Another Vietnam vet, retired Army Lt. Col. Bob Greene, who logged 1,900 combat hours flying South Vietnamese and U.S. troops into action in UH-1 Hueys, said the idea is “interesting” but that’s about all. “I love DARPA,” Greene said, “but this is probably not one of their better things.” The goal is to make it possible to land on slopes or uneven or rocky terrain of the sort combat helicopter pilots often confront and end up hovering over instead of landing on or to put a bird down safely on a rolling ship deck. DARPA program manager Ashish Bagai explained in a briefing to the American Helicopter Society International’s yearly conference last May that, “The feet have tactile feedback; they have pressure feedback. Each foot is individually operated. When you encounter an obstruction, the foot that first contacts the obstruction allows the leg to bend until everything else has contacted terra firma.” Roger Connor, rotorcraft curator at the National Air and Space Museum, called the concept interesting. “You only have to Google ‘dynamic rollover’ to understand why this would be of value,” Connor said, referring to the risk posed by a helicopter’s high center of gravity. But Connor said the benefit probably wouldn’t be worth the added weight, complexity and cost for combat aircraft. Mark Costello, the Georgia Tech aerospace engineer and professor of autonomy who has led the project over the past two years explained that the version in the video relies on eight electric motors to activate four joints — two hips and two knees. When a special film on the bottoms of the “feet” is subjected to pressure by the foot touching an object, the resistance of the electric circuit changes, activating the joints to bend and equalize the pressure on all four feet. “It’s electricity that makes it move,” Costello said. His team calculates that replacing skids with adaptive landing gear in small to medium-class helicopters would reduce their payload by about 7 percent. Replacing wheels would be about an even weight trade, he said. DARPA’s Bagai said pneumatic and hydraulic versions of the four-legged gear have been studied, too, and would be necessary for aircraft much heavier than the 250-pound Rotor Buzz used in the video. Veteran combat pilots Brady and Greene questioned how a helicopter equipped with DARPA’s landing legs would do in a “running” takeoff or landing, a maneuver required when helicopters of the sort they flew suffer hydraulic failures, which bullets can cause.“I would wonder how robust that puppy would be,” Greene said. “I’m suspicious of mechanical devices that have to go up and down. When you add mechanical things, the opportunity for failure presents itself. And what happens if one side fails? You could conceivably hit the ground with your rotor.” Bagai said the critics “make very good points” but he and Costello emphasized that the project is simply exploring the possibilities. Adaptive landing gear, perhaps coupled with a deck lock system, could greatly increase the sea state levels at which helicopters can land aboard ships, Bagai said, or make it possible for a helicopter to take off and land from a moving trailer in a convoy. Costello added that, “Our analysis suggests that pilots will be able to land in complex situations faster with lower pilot work load.” But not any time soon. “This is … in the spirit of DARPA investigation and technology development,” Bagai said. “This is the first step to recognizing a potential improvement.” Connor said DARPA’s gear might work just fine on a light, unmanned helicopter and be especially helpful for one flying autonomously. It’s generally much easier for a human being than a computer to detect obstacles in a landing zone. “This is a technology that…allows helicopters to operate in situations where you would normally have to have a very skilled pilot,” Connor said. “Amazon, I would think, would be very interested in this technology if they’re serious about delivering packages in certain locations.”

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DARPA’s Adaptive Landing Gear Is Cool But…

Posted on October 30, 2015

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