Page:Popular Science Monthly Volume 92.djvu/914

 Parachute Safety Device for Airplanes

A new attempt to revive the late Sir Hiram Maxim's idea of twenty years ago

OF his first machine Sir Hiram Maxim said, over twenty years ago, that, completely stalled in the air, it would "pancake" down with the velocity of a fall of four feet. But these old machines were loaded barely more than one pound to the square foot, and their center of gravity was far below their carrying surface. The arrangement, as we know now, prevented easy flight, but it made them good parachutes. The more perfect and efficient the modern airplane became, the more it lost its former likeness to a parachute.

The wings of modern airplanes bear a load of five to seven pounds to the square foot and the center of gravity has been raised. Stalling and pancaking are nowadays considered worse than upsetting and "looping the loop"; yet pancaking, that is, descending like a parachute, is obviously the safest way to land on badly broken, mountainous ground.

Very interesting is a revival of Maxim's parachute idea in modified form, by Gerrit Van Daam, because it aims at making safe not only stalling but also landing on the worst ground. It is not feasible with heavily loaded biplanes, since in their case one wing surface blankets the other; but with lightly loaded monoplanes of the Bleriot type the plan may work out satisfactorily. What such monoplanes lack in surface for a parachute-like descent, the inventor makes up, more or less, by turning the wings into true, highly-arched parachutes of increased air-resistance.

A parachute is tightly folded over the whole upper surface of each wing, being held in place by a netting. When needed, this netting is instantly loosened, and at the same time a long slot opens along the center line of each wing, admitting the air from below into the spacious pocket formed by the distending parachute, now held only by the margin of the wing.

By releasing the parachute and opening long slots in the wings through which the air rushes under the parachute, the descent of the airplane is made safe

Smoothness of the wing tops in flight is absolutely essential; so the folded parachute and the netting will have to be covered, while not in use, by a smooth light shell firmly secured to resist the air suction, yet easily removed when necessary. Of greater importance is a device that will keep the pancaking airplane on an even keel during descent. That is not so easy with a machine of the Bleriot type. In that machine, the tail makes an excess of surface toward the rear, while the advanced center of gravity, balancing the equally advanced center of lift, gives an excess of weight in front. The only remedy would seem to be control independent of the machine's headway, or adjustable rudders with a circular motion of their own, which remain efficient in a stalled machine.

Numerous attempts have been made in the past by inventors in many countries to utilize the principle of the parachute in safety devices, but the success has not been encouraging. Parachutes have been found useful and fairly reliable for dropping from observation balloons, but have failed to give satisfaction as a safe means of escape in practically all other cases. They have not been used extensively for military purposes; but perhaps this new device may solve a hitherto battling problem and thus add to the balance of safety in the aviator's favor.

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