Soaring and Gliding
Soaring and gliding is the flying of manned heavier-than-air gliders, which are motorless aircraft. The activity involves soaring, or using up-currents in the air that make sustained flight possible, and gliding, or coasting, on an inclined plane of air in steady downward flight. The glider, a monoplane, has been used in military aviation and for meteorological research, but most motorless flying is done for sport.
Types of Gliders
Gliders are made of wood, lightweight metals, or plastics. There are two general types. The sailplane is a one- or two-seater, high-performance, streamlined monoplane, requiring experienced pilots. The utility, often a two-seater, is a simpler craft used for soaring and glider training. During the 1920's and 1930's a low-performance craft called a primary glider was used for training purposes.
The sailplane's wings are long and tapered and generally extend across the top of an enclosed body, or fuselage. The utility glider has an enclosed body, and its wings are braced to the body with streamlined struts. The primary glider had a short untapered wing secured to an open-braced framework fuselage with an open seat at the front on which the pilot sat unprotected.
Gliders have a hinged control surface, or aileron, on each wing. With one aileron raised and the other lowered, the plane tilts toward the side with the raised aileron. On the tail section are hinged elevators, which swing up and down and make the craft nose up or down, and a hinged rudder, which swings sideways and helps in turning. Foot pedals operate the rudder, and a stick or wheel controls the ailerons and elevators. Flight instruments include altimeters, airspeed meters, turn-and-bank indicators, and a variometer. The variometer shows the rate of ascent or descent and helps the pilot find rising air currents which enable him to sustain flight. A retractable wheel in advanced sailplanes, under and behind the cockpit, aids in takeoff and landing, and glide-angle control for landing is attained by* use of lift spoilers or dive brakes in the wings.
Modern gliders are a far cry from the early hang gliders, which had no fuselage. A hang glider had a hole in the wing, and the pilot thrust his head, arms, and shoulders through this hole and grasped the aircraft by handles mounted on the wing's upper surface. He used his legs both for a landing gear and to help gain flying speed.
The most common method of launching is by airplane tow. A 200-foot (61-meter) rope with a steel ring at each end connects the towplane with the sailplane. The two aircraft generally climb together to an altitude 2,000 feet (610 meters) higher than the takeoff point before the sail pilot releases the towline. This method minimizes strain on the sailplane structure. The sail pilot gets a graphic indication of lift and sink by observing the climb and descent of the towplane ahead of him.
Another method is to tow the sailplane with an automobile, using a rope from 500 to 2,000 feet (152 to 610 meters) long. As the car accelerates, the sailplane becomes airborne. Sometimes a winch is used with its drum geared to a powerful motor. The sailplane gains height as the engine reels in towline at a speed varying from 20 to 60 miles (32 to 97 kilometers) per hour, depending upon the type of craft and speed of the wind. With either method, the pilot disengages the towline by a release mechanism operated from the cockpit.
An older method of launching is by bunjee, or rubber shock-cord. A crew of men run down a hill stretching a long rubberized rope attached to the nose of a sailplane, which is held back manually. On the plane's release, it quickly gains flying speed, catapulted forward as from a slingshot, then starts down the hill into a valley for a straight glide.
Types of Soaring
Before 1930, pilots practiced ridge, or slope, soaring almost exclusively. First they had to find a strong upward current above a ridge or hill. Then, after launching, the pilots flew in the rising air current on the windward slope. Ridge soaring was done at low speed, and sailplanes could stay aloft in very light winds.
An increased knowledge of meteorology in the 1930's led to thermal soaring. Thermals are large bubbles or columns of heated air that rise from the ground through an unstable atmosphere. Given sufficient moisture, the thermals condense on reaching the cooler upper atmosphere, forming cumulus or cumulonimbus clouds. Pilots look for these clouds and continue flight by circling and gaining altitude in these currents. On distance flights, pilots usually soar on thermals.
A recently exploited source of lift by air currents is orographic—that is, by means of waves of air that rise on the lee side of mountains facing a strong wind. Pilots undertake wave soaring for very high altitude flights. The world altitude record is 46,000 feet (14,000 meters).