Flight

       Everyone who has seen birds, it is safe to say, has envied them their power of flight. Few people have ever tried to find out how to fly. And fewer still ever dreamed, until a short time ago, that men would actually imitate them. Yet flying is no more difficult for a bird than walking is for us. Most of us find it almost as hard to explain walking as flying. The reason is that, like the birds, we learned so young and so well that we are unconscious of the skill we employ.

       Let us think a little about both means of travel - bird's and men's side by side, so that we may use the more familiar one to help explain the other. No animal moves without some work on its part. If we were not willing to work in order to move and stand upright, the safest thing for us to do would be to lie flat on the ground like a plank of wood, or other lifeless thing. It costs us muscular effort, in the first place, merely to stand on two legs. We constantly tend to fall over. We only keep from doing so by moving the weight of our bodies so as to preserve our balance. We work more or less steadily at this all day long, and we don't realize what a tiring job it is until we feel the relief of tumbling into bed at night where we are glad to lie until morning with no more trouble about balancing.

       If, in addition to balancing, we want to move around, we must go through other motions. Our weight rests on our feet and our feet are touching the ground. So, in order to move in any direction we may choose, we simply push the ground away from us in the opposite direction. This is called walking.

       Now a bird does pretty much the same thing. He also has the double job of keeping from falling down as well as moving along. It would not do, however, for us to carry the comparison between walking and flying too far, for they are much different. Our weight is always well supported at the point where our feet rest. So, we are able to devote our greatest effort to covering the ground. But a flying bird is resting on air that does not support its weight for a moment if he stops. Consequently, the bird works hardest at keeping afloat. It is not nearly as hard for him to move along through the air as it is for us to travel over the ground, because air is so much more yielding than earth.

       Birds' flight has been likened to swimming or rowing in air. However, even this helpful way of picturing flight does not do justice to the bird, for water supports the weight of a fish or a boat while the air will not support a motionless bird, as aforesaid. Yet, as far as the actual stroke of the wings goes, it is something like a rowing motion, except that it is a down beat instead of a horizontal one.

       The wing is tilted with its back edge up, as the down stroke is made. The effect of the air's resistance to the wing, tipped this angle, is to push the bird upward and forward. In a sense, birds' flight might better be likened to treading water than swimming. It is only because of the tilt of the wing that the bird moves forward by the downward beat. On the return stroke, the wing is folded so as to lessen air-resistance.

       Our city pigeons can glide on outstretched wings for quite a distance without beating the air. But if you watch them closely you will find that they are always nearer the ground at the end of a glide than at the beginning. In other words, they are not beating the game by gliding. True, they can travel quite a way without working their wings, but what they gain in distance they lose in height. They cannot glide far without beating their wings from time to time in order to climb back to a height from which they can start gliding again.

       There is a way, however, by which birds rise without effort. They have learned to make the wind do the work. If a bird, traveling against the wind, holds his wings straight out and slightly tilted up against the breeze, the moving current of air striking the under side of his wings will lift him up. This flying stunt is almost opposite to gliding, for now the bird gains in height while losing in speed and distance.

       Soaring birds, such as the eagle, vulture and albatross, make use of this trick to stay in the air for a long time without moving a wing. The skill of soaring is not thoroughly understood but it is thought that the trick of sailing in the teeth of the wind explains part of it. You have noticed that soaring birds travel in circles. They do that so that they can take advantage, by turns, of the lifting power of a counter-wind, and the pushing power of a wind at their backs. For a while the soarer travels up-wind, losing speed but gaining altitude; then he wheels and sweeps down-wind in a graceful curve gaining speed but losing a little altitude. Cooke.

 How Bird Wings Work by

SmarterEveryDay