Part 22 (1/2)

At intervals round the edge are fastened twenty-four V-shaped tapes.

These are only a few feet long and the lower end of each V-shaped pair is attached to a long main tape. There are twelve of these main tapes, and their lower ends unite in a metal disc from which is suspended the sling and harness by which the man is supported.

[Ill.u.s.tration: THE ”GUARDIAN ANGEL” PARACHUTE.

(1) Shows the airman in the harness by which he is attached to the parachute. By means of the star-shaped buckle he can instantly release himself. (2) Shows the parachute two seconds after the airman has jumped from the aeroplane. In (3) he is seen nearing the ground.

(_By permission of E. R. Calthrop, Esq._)]

So the twenty-four short tapes form twelve V's to the points of which are attached the twelve long tapes which support the man. The reason why tapes are used in this particular parachute and not cords will be referred to later.

In the crown of the silk body there is the usual hole for the purpose of forming the air-rudder to steady the parachute in its descent.

And now we can consider the first great feature of this wonderful invention and ask ourselves these questions: ”By what means is it made to open?” ”What makes it more reliable than others?”

To answer that we must first see why the others sometimes refused to open. In whatever way an ordinary parachute may be packed it must, when coming into use, a.s.sume the state of a shut umbrella with a hole in the top.

In this condition it is a.s.sumed that as it falls the air will find a way in through the lower end and will blow the parachute open in precisely the same way that a strong wind will sometimes blow out the folds of an umbrella.

But, as a matter of fact, the loose folds of a parachute, when the edge of the gussets is gathered in, are sure to overlap and enfold each other more or less. Thus, when in the shut-umbrella state, it sometimes happens that air which is inside can escape upwards through the hole more easily than fresh air can get in from below. The parachute, in such a state, is, let us imagine, falling rapidly through the air. The result is just the same as if it were still and the air were rus.h.i.+ng upwards past it. And the upward rush past the top hole tends to _suck air out_ through the hole faster than fresh air can find a way in at the bottom.

This is the principle of the ejector, which engineers have put to many uses. For example, the vacuum brakes employed on many large railways owe all their power to stop a train to a vacuum caused by an ejector. There is a short tube or nozzle, placed in the centre of another tube through which steam blows. The action of the steam in the outer tube as it rushes past the end of the inner tube drags after it the air which is in the inner tube so effectively as to produce quite a good vacuum. And in precisely the same way, the upward rush of air past the parachute, or what is just the same, the falling of the parachute through stationary air, can suck the air from inside the latter and create a vacuum in it if the gussets gathered together at the mouth unfortunately overlap one another and are thus locked together by the pressure of the air striving to get in. Thus, instead of the downward fall causing the ordinary parachute to open, as in most cases it will do quite well, the fall under these particular conditions actually binds its folds together and prevents it from opening. It is true this does not often happen, but the risk is _always_ present at every drop, and this unreliability has cost the lives of brave men and women, and the knowledge of this constant risk has led others to write down the parachute a failure, by reason of its known unreliability to open instantly. Even when it does open the depth it falls before it opens is so variable, by reason of the fight between vacuum and pressure, that it may be one hundred feet one time and one thousand feet next time with the same parachute.

Now the ”Guardian Angel” is designed so that those conditions cannot occur. Its silken covering is first laid out on the ground and into the centre is introduced a beautifully-designed disc of aluminium, somewhat like a large inverted saucer, of exceeding lightness but of ample strength for what it has to do. Then the silk body is pleated and folded back over the upper part of this launching-disc and gradually packed so that it occupies but a very small s.p.a.ce upon the upper surface of the disc. It is so folded that its edge comes in the topmost layer and also in such a manner that on the tapes being pulled the silk unfolds easily and regularly, flowing down as it were over the edge of the disc almost as water flows if allowed to fall from a tap upon the centre of an inverted saucer. After the folding is complete another aluminium disc is placed above the packed silk body which s.h.i.+elds it from the enormous air pressure when it is being released from an aeroplane flying at top speed. The upper and lower fabric covers are then superimposed and sealed and the ”Guardian Angel” parachute is ready for use.

The tapes, likewise, are folded up, in a special way upon the bottom cover, which is sprung over the bottom of the disc. The bottom cover with the tapes upon it, is pulled away by the weight of the airman as he makes his jump to safety, and the tapes are so arranged that a pull upon them causes them to draw out steadily and smoothly, almost like water falling from a height.