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Dropping to safety.

One day in 1975, Boris Popov was hang-gliding when the glider's frail airframe collapsed, dropping him 400 feet into the water. Amazingly, Popov survived his plunge with only a bruised kidney and some missing fillings. He had time to throw a parachute out, he recalls, if only there were one for hang gliders back then.

Soon afterwards, Popov started work on a parachute-based safety system that could save the pilots of stricken hang gliders. By the late 1970s, Popov and his company, Ballistic Recovery Systems Inc. (BRS) in South St. Paul, Minn., had successfully produced a rocket-deployed parachute system for disabled hang gliders, powered ultra-lights, and small experimental planes. Since 1981, more than 10,000 BRS systems have been sold and have been credited with saving 84 lives.

Ten years ago BRS began developing a larger ballistic parachute system for general-aviation (GA) aircraft. Every year about 1000 people die in GA accidents, and BRS claims that 60 percent of them could be saved using whole-aircraft parachute recovery systems. BRS eventually developed the GARD-150, the first such device fully certified by the Federal Aviation Administration for use in a GA airplane - the Cessna 150/152 series, the most popular flight-training aircraft in the world.

One of several major challenges in designing a recovery system for faster, heavier aircraft was ensuring consistent deployment in unpredictable environments and aircraft attitudes throughout the flight envelope. "Particularly difficult was developing a system that operates appropriately in a very wide speed range," said Tony Kasher, BRS project engineer.

A parachute must open quickly with minimal altitude loss if deployed at low airspeeds, which often means low altitude. At the same time, the inflation loads transmitted to the opening canopy must be limited to a tolerable level if it is deployed at high airspeeds to prevent rupturing the seams. Also, the human occupants must not be jolted too much.

The GARD-150 accomplishes this feat with a patented annular slider reefing system that automatically reacts to the speed of the aircraft, opening the parachute rapidly at slow speeds and slowly at high speeds. The system, which is designed for 120-knot (maximum) deployments, was successfully test-deployed in spins and flat spins as well as from inverted attitudes.

The slider is a simple flat doughnut of standard nylon ripstop parachute fabric with metal grommets inserted around the perimeter - one for each suspension line, and reinforcing tape sewn around the edge. If airplane speed is low, the slider is ineffective, enabling the main canopy to open almost immediately. Low speed and low altitudes demand a fast-opening canopy. If the speed is very high, this simple second parachute is more effective than the main canopy, so it flies right at the main canopy's skirt. Because the slider is smaller than the main chute, it restricts the amount of air that can ram into the latter chute.

The airplane then makes its descent at 21 feet per second, dangling horizontally below the 40-foot-diameter main canopy. The ground impact is said to be similar to what someone would experience when jumping from a height of 7 feet. "Saving the aircraft is not the objective of the BRS units," Popov said. "Our goal is to prevent injury to the occupants."

To engage the GARD-150, the pilot reaches overhead, removes the handle cover, and pulls the handle. This cocks and fires a solid-propellant rocket. "The rocket provides a very positive extraction," Kasher said. "A pilot or drogue chute could get entangled." Two-tenths of a second after ignition, the rocket motor extracts the canopy and suspension lines.

When the main canopy hits the relative wind 0.9 seconds after ignition, it begins to fill, starting the plane's deceleration. "The slider, which is pulled up to the main-chute skirt when packed, limits the diameter of the inflating parachute," Kasher said. "This limits the surface area presented to the relative wind, which in turn limits the drag or load on the system."

When the velocity slows to the point that the GARD system can withstand the applied forces, the annular slider moves down the suspension lines toward the aircraft, allowing the canopy to open to full diameter.

The system weighs 43 pounds and fits into a box the size of a large briefcase. The device attaches to the forward and rear spar carry-through structures of the plane at center of the wings. The GARD-150, which sells for about $5500, is intended for cases in which the pilot is incapacitated or the aircraft fails. It could also be used in an emergency over hostile terrain with no landing area available or at night in bad weather.

BRS is refining its parachute technology for heavier and faster planes, maybe even airliners, Popov said. The company is developing a GARD system for Cirrus Design Corp. in Duluth, Minn. The SR20, a single-engine, composite four-place airplane, is the first new-generation GA aircraft to exploit the BRS unit. In addition, BRS recently received a NASA grant to develop a lower-density parachute cloth that could cut the weight of a canopy by almost half.
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Title Annotation:innovative parachute system
Author:Ashley, Steven
Publication:Mechanical Engineering-CIME
Date:Mar 1, 1996
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