Vertical currents—columns of ascending air—are frequently encountered in unexpected places and have more or less tendency, according to their strength, to make it difficult to keep the machine within a reasonable distance from the ground.
These vertical currents are most generally noticeable in the vicinity of steep cliffs, or deep ravines. In such instances they are usually of considerable strength, being caused by the deflection of strong winds blowing against the face of the cliffs. This deflection exerts a back pressure which is felt quite a distance away from the point of origin, so that the vertical current exerts an influence in forcing the machine upward long before the cliff is reached.
CHAPTER XV. THE ELEMENT OF DANGER.
That there is an element of danger in aviation is undeniable, but it is nowhere so great as the public imagines. Men are killed and injured in the operation of flying machines just as they are killed and injured in the operation of railways. Considering the character of aviation the percentage of casualties is surprisingly small.
This is because the results following a collapse in the air are very much different from what might be imagined. Instead of dropping to the ground like a bullet an aeroplane, under ordinary conditions will, when anything goes wrong, sail gently downward like a parachute, particularly if the operator is cool-headed and nervy enough to so manipulate the apparatus as to preserve its equilibrium and keep the machine on an even keel.
Two Fields of Safety.
At least one prominent aviator has declared that there are two fields of safety—one close to the ground, and the other well up in the air. In the first-named the fall will be a slight one with little chance of the operator being seriously hurt. From the field of high altitude the the descent will be gradual, as a rule, the planes of the machine serving to break the force of the fall. With a cool-headed operator in control the aeroplane may be even guided at an angle (about 1 to 8) in its descent so as to touch the ground with a gliding motion and with a minimum of impact.
Such an experience, of course, is far from pleasant, but it is by no means so dangerous as might appear. There is more real danger in falling from an elevation of 75 or 100 feet than there is from 1,000 feet, as in the former case there is no chance for the machine to serve as a parachute—its contact with the ground comes too quickly.
Lesson in Recent Accidents.