Happy landings

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Aircraft are notorious for not failing safe. If anything goes wrong, it can be a terrible task to keep the plane in the air until it can land at an airport. Ideally, aircraft should be fitted with parachutes for safe descent; but a chute big enough to support a plane would occupy almost its whole interior. Daedalus now has a way out.

A parachutist hauls on the webs of his canopy just before hitting the ground. As a result, the parachute descends a little faster, and the man beneath it a little slower, at the crucial moment of impact. DREADCO engineers are now taking this strategy to extremes. They are devising a small but very strong parachute, to be deployed from an aircraft in distress, from a door in the top of the fuselage. Its horizontal flight will be checked below stalling speed, and it will plummet towards the earth, suspended in a horizontal attitude beneath its chute. The chute, however, is attached to the plane not by a simple anchorage, but by a winch. As the plane falls, the winch unwinds rapidly, paying out the parachute on many hundreds of metres of cable. But just as the plane is about to hit the ground, the winch is powered in reverse, and winds the cable forcefully in again. This hauls the parachute downwards far faster than its terminal velocity. So the parachute exerts a powerful upward force on the plane, which slows at the last minute and hits the ground quite gently.

A reliable safety system must be as simple as possible. As the parachute unreels, Daedalus wants it to wind up a spring on the winch, whose tension will wind it in again when the craft is about to hit the ground. This moment will be determined by a weighted cable lowered from the craft, which will go slack when its far end touches the ground. This purely mechanical system will have no vulnerable electronics or powered units.

At last the worry of flying will be relaxed. In case of decompression, engine failure, hi-jacking or structural fatigue, a plane will be able to drop safely out of the sky onto the friendly land. By angling the plane on its tether, the pilot could even ‘glide’ it towards the best landing site, as human parachutists do. Even if the plane hit the sea, the gentle impact would leave it undamaged. It would float until rescue arrived.

The further Inventions of Daedalus (Oxford University Press), 148 past Daedalus columns expanded and illustrated, is now on sale. Special Nature offer: m.curtis@nature.com

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Jones, D. Happy landings. Nature 402, 477 (1999) doi:10.1038/44988

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