Imitating the Way of Birds
By “Awake!” correspondent in Japan
“I want to fly like a bird, float on the blue sky, touch the white clouds.” Is this the faraway fantasy of long ago? Perhaps. Man’s dreams of becoming airborne go back to the ancient Greek myth about the inventor Daedalus. He fashioned wings of feathers and wax, which enabled him and his son Icarus to fly like the birds. But because the heat of the sun melted the wings, Icarus plunged to his death.
However, in 1680, the impossibility of this kind of flight was recognized. The calculations of the Italian mathematician Giovanni A. Borelli showed that, if man were to depend on the strength of his arms flapping like a bird in order to fly, he would never get off the ground.
It was not until 1783 that the first bird’s-eye view of terra firma was enjoyed by two Frenchmen. They sailed over Paris in a linen balloon. Years later, experiments with kites and gliders led to the marvels of powered flight.
Common today are jet planes carrying almost 500 passengers or 100 short tons (90 metric tons) of cargo and traveling at speeds of 600 miles (966 kilometers) per hour. Speed records in excess of 2,000 miles (3,200 kilometers) per hour have been set, and nonstop distance flights of over 10,000 miles (16,000 kilometers) have been made. Although many stand in awe of these advances in aviation, others find contentment and much enjoyment in noiseless flying at low altitudes (2,000 to 3,000 feet; 600 to 900 meters) and at low speed. This is the world of gliding.
Use of Gliders
Gliders were first used for flight experimentation and have since been utilized for training, transport, combat, research and sport. Gliding for sport is very popular in the United States, Germany and Australia, where glider records have been set. For example, the world altitude record of 46,267 feet (14,102 meters) was set in 1961 in the United States; the longest nonstop straight-line distance of 907.7 miles (1,460.8 kilometers) was attained in Germany; and the fastest speed, 87.43 miles (140.7 kilometers) per hour, over a triangular course of 500 kilometers (311 miles) was achieved in Australia.
In Japan, there are close to 3,000 gliding enthusiasts, half of whom are students. According to a newspaper report back in 1975, two experienced pilots were training to launch an advanced type of glider from the summit of 3,776-meter (12,388-foot) Mount Fuji for a trans-Pacific flight. Some believe that, if needed oxygen and food could be carried and adequate altitude could be attained, theoretically a trans-Pacific flight would be possible. However, plans for such a flight have been abandoned. Because government regulations limit the flight ceiling to about 450 meters (1,470 feet), no world records are being set here. Nevertheless, training and pleasure flights are continuing at a gliderport in Kambara, a small fishing town nestled between the mountains and the sea near the base of Mount Fuji. Would you like to make an armchair visit to this gliderport and find out just how these motorless planes continue to give man his closest approach to imitating the birds?
Visiting the Gliderport
On our first look into the hangar, we see two single-engine airplanes, to be used for towing the gliders into the air, and two motor gliders—each having a small 25-horsepower engine that can be turned off when the plane is airborne. Where are the other gliders? We crane our necks as the doors of the second story are opening and see them lined up inside. Due to their weighing only 250 to 350 kilograms (550 to 770 pounds) each, they can be lifted by power hoists and lowered to the ground. They are pushed to the runway by hand. To one who may be accustomed to the noise and bustle of a modern big-city airport, this gliderport may not be too impressive. The narrow runway is gravel and the radio tower is mounted on the roof of a van that is driven to the runway area. But the excitement of taking to the air with the birds is just the same, if not greater, because the thrills of gliding are enjoyed in silence.
As we look around, we notice gliders of various shapes. Some look rather cumbersome, whereas others are sleek and streamlined. What accounts for the differences? Primary gliders are just that—gliders. They have larger wing surfaces, but their design and weight permit them only to glide back to earth once they are released from the tow plane. The sleek sailplanes, however, are designed to soar. That is, to gain altitude, they can utilize winds blowing up the slopes of mountains, as well as rising columns of warm air called “thermals.” It is this type of soarplane that can travel great distances and stay up in the air for hours at a time.
Just what enables these man-made birds to float in the sky? A basic understanding of the principles of flight will help us to understand.
Principles of Flight as They Affect Gliders
There are four forces that act on an airplane in flight: (1) gravity (the natural force acting on its weight to pull it to the ground), (2) lift (opposite of gravity and produced by the design of the wings or updrafts of air), (3) drag (air resistance opposing forward movement), (4) thrust (forward power to overcome drag and propel the airplane forward). To get a glider off the ground, the initial thrust is provided by either towing it with a car or an airplane or pulling it with a winch and cable mounted at the far end of the runway. Once it is separated from this source of power, lift and the glider’s aerodynamic design counteract gravity and drag, keeping the glider in the air. Lift is provided by (1) the curved design of the wings and (2) the rising currents of air.
From studying the shape of birds’ wings man came to recognize that a curved shape would provide lift. Just what is involved in the design of the wing? The bottom surface of the wing is flat and the top surface curved, tapering toward the back or trailing edge. When a glider is stationary, the air pressure on the top and the bottom of the wing is the same. But when it moves forward, only the air pressure on the bottom of the wing stays the same. The air across the top curved surface has to travel a greater distance in the same time that it takes the air to pass by the underside of the wing. Hence, the air passing over the top of the wing moves faster and is thinned out, causing the pressure to drop. As high-pressure air tries to fill the void in a low-pressure area, the air under the wing tries to force itself to the area of low pressure above the wing. But the wing is in the way and the result is a lifting force being applied to the underside of the wing.
Secondly, there are natural columns of air that the glider may ride. If the glider is lightweight and well designed, it does not take much updraft to keep it afloat. Wind that is deflected upward by hills or mountains can give lift, as can the waves of air produced on the leeward side of high mountains. If cool, heavy air moves into an area of warmer air, the warmer air is forced upward and these “shear lines” can be used for lift. Also, certain land surfaces, such as plowed fields or the asphalt and concrete of cities, absorb heat from the sun, causing warm air to rise. Sailplane pilots look for soaring birds or cumulous clouds, for these often indicate the presence of a “thermal.” By circling in the thermal, the sailplane pilot gains altitude, and then takes off in another direction, looking for another updraft.
Flying the Glider
But what gives the glider maneuverability? How does the pilot control his sailplane? There are three basic movements to a glider: (1) pitch (movement on the lateral axis from wingtip to wingtip), (2) roll (movement on the longitudinal axis running from nose to tail), and (3) yaw (movement on the vertical axis through the center of the fuselage). Pitch is controlled by the up-and-down movement of the “elevator” on the trailing edge of the horizontal piece of the tail assembly. Roll is controlled by ailerons, which are movable parts of the trailing edge of the wings. To roll to the left, the left aileron goes up and the right aileron goes down. Rolling to the right requires just the opposite. Yaw, or left and right movement, is governed by the rudder, the trailing edge of the vertical tail assembly.
This may sound complicated, but a look at the glider cockpit shows us that the operation is relatively simple. A stick coming up from the floor controls the pitch and roll. Push it forward and the nose goes down. Pull it back and the plane starts to climb. Move it to the left and the left wing dips to start a left roll. Moving it to the right causes the ailerons to move in the opposite direction, and the plane rolls right. The left and right movement of the rudder is controlled by the two foot pedals. Push the left one and the glider moves left; push the right one and the glider goes right. A left or right turn, or bank, is made by a combination of a roll and rudder movement in the direction that you want to go.
Also, in the cockpit, we see a knob for releasing the tow rope and a lever for controlling the flaps and spoilers. Flaps are the parts of the trailing edge of the wing nearest the fuselage and are extended downward mainly to reduce speed on landing. Spoilers serve the same function, but rise upward from the center of the top surface of the wings. There are relatively few instruments—an air speed indicator, an altimeter, a compass, and a variometer (a device showing the rate at which the glider is rising or sinking). Most gliders are equipped with a small radio.
How Safe Is Gliding?
The past few years have seen an increase of enthusiasm for gliding, especially in the use of relatively inexpensive kite-like hang gliders. Some of the sailplane pilots that we talked to were quick to distinguish between sailplanes and hang gliders. One pilot, with over 30 years of experience, noted that he could not recommend hang gliding because of the danger involved. He explained that because these gliders lack stability and are controlled by movement of the operator’s body, it is difficult to regain control once it is lost. So the hang glider is vulnerable to sudden gusts of wind and the inability or inexperience of the operator. No doubt this continues to contribute to the toll taken by hang-glider crashes.
What about sailplanes? How safe are they? Design and controllability contribute to the safety of sailplanes. We are told, at a free one-day gliding course sponsored by the Shizuoka Prefecture Aeronautic Association (Japan), that if you lose control of a glider, probably the best thing to do is to let go of the stick and the plane should right itself, as it is designed that way. Also, the president of the association mentioned that he feels safer riding in a glider than he does driving to the gliderport in his car. Gliders are considered by some to be safer than airplanes because they are not dependent on an engine, which can fail. Of course, if a glider pilot gets too far from home and runs out of updrafts, he will have to look for a flat, open area on which to land. A general rule of thumb is that if the gliderport is within a 30-degree radius of the glider, it is possible to get home. This is because the glide ratio, or ratio between how far forward a plane will go as it sinks, is relatively high. In the use of many gliders, for every meter they drop, they move forward 30 meters (98 feet). Some sailplanes have a glide ratio of over 1 to 50, whereas airplanes may have a glide ratio of only 1 to 10.
Glider pilots receive training and must obtain a license before they may fly alone. This takes over 50 hours of flying time. In addition, good judgment contributes to the safety of gliding. When we visited the gliderport, a typhoon was approaching, and when the wind rose notably, flying was stopped for the day. Of course, although gliding is relatively safe, there are certain risks involved, as with any flying. There is always the possibility of structural defects, human error, or unforeseen occurrences. These are the things that must be considered by one contemplating the taking up of gliding.
Reflections on Our Visit
It has been delightful watching these fiber-glass and metal “birds” as they cast shadows across the ground. Then, too, it is interesting to see how, after 70 years of aviation progress, men still find pleasure in the simpler beginnings of motorless flight.
Also, we have learned humility as we have seen how man can learn from the birds. The very design of the sailplane’s wings is but a copy of those of soaring birds. As we look skyward and see the sailplane sharing the same thermal with five buzzards, we feel that no doubt there is yet much to be learned as man imitates the way of the birds.
[Diagram on page 19]
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Controlled by the Ailerons
Controlled by the Rudder
Controlled by the Elevators