Parachutes have made safe escapes from crippled aircraft a reality-but it's not always easy to jump out after a mid-air collision, or after the pilot has lost control of the plane and gone into a spin. So a company in the US has decided that it's time for stricken planes to be lowered to the ground safely, using a large parachute attached to the fuselage.
Cirrus Design of Duluth, Minnesota makes the SR20 light aircraft-the first plane to have a built-in parachute system to be licensed for sale by the Federal Aviation Administration. The parachute Cirrus has developed works at altitudes of less than 300 metres with the aircraft in a full spin. It will allow the plane to land the right way up-but as it comes to earth at 17 miles per hour, it uses the landing gear as an elaborate shock absorber. When it touches the ground, the undercarriage shoots through the wings-writing off the plane but leaving the fuselage and its passengers intact.
The parachute is activated by pulling a lever. A rocket is fired from the rear of the fuselage to project the chute to a safe distance from the plane while it is still in its bag.
"A normal parachute would then open all at once, which is fine at low speeds," says Paul Johnston, chief engineer on the project. But, he says, at high speeds the load force be so great the parachute would not work. "The force would tear it to shreds." Either that, or it could be ripped away from the plane. To avoid this, the parachute uses a cloth slider to control the rate at which it opens. The slider slithers down the cables, letting air into the canopy so that the stricken aircraft slows to a safe speed before the parachute can fully open.
Three straps connect the plane to the parachute, one from the rear and two from the front part of the fuselage (see Diagram). The two front straps run along the side of the vehicle and are contained within it, moulded into the fuselage during manufacture. Once deployed, they are ripped out of their casings, which are jettisoned.
Rae Willis of Morristown, New Jersey, has flown light aircraft for 40 years. He says that pilots are most likely to go into a spin below 300 metres when turning into their final approach to land. "The key is that it's a last resort, which is probably more use at higher altitudes. Yank the handle and cross your fingers," he says.
Cirrus has more than 250 advance orders for the plane and expects to deliver its first parachute-equipped aircraft in early April. But tragedy struck the company last week when one of the firm's test pilots, Scott Anderson, 33, was killed while flight testing the SR20. He crashed while attempting an emergency landing. The test aircraft was not fitted with the parachute system-though it's unclear if it would have helped in this case.
Author: Duncan Graham-Rowe
New Scientist issue 3rd April 1999
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