Gliders and How They Fly
Simply put, a glider is an unpowered aircraft, or an aircraft without an engine. Although many of the same design, aerodynamic, and piloting factors that apply to powered aircraft also apply to gliders, the lack of an engine inevitably changes a great deal about how gliders work. There are many different types of gliders. For the purposes of this blog, we will cover how sailplanes work.
Type of Gliders Work
Gliders have the same basic parts of an aircraft: fuselage, wings, control surfaces, and landing gear. However, there are many differences between these parts on a glider and a conventional aircraft. The fuselage of a glider is designed to be as small and light as possible. As there is no engine taking up space, gliders’ sizes depend on the cargo they carry - usually one or two people. Their skins are designed to be as smooth as possible, allowing the glider to slip through the air with minimal resistance. Most modern glider fuselages are made from fiberglass and carbon fiber, as these allow designers to create seamless and rivet-less structures.
When it comes to wings, there are significant differences between gliders and conventional aircraft. Glider wings are much longer and narrower than conventional aircraft wings. They have very high aspect ratios, meaning their span is much longer than their width. The higher aspect ratio a wing has, the more efficient it is. The control surfaces of a glider are the same as those on a conventional aircraft: ailerons, elevator, and rudder. Each of these functions the same way on both types of aircraft. However, the landing gear of gliders differs from that of conventional aircraft. On a glider, the landing gear is typically a single wheel mounted below the cockpit.
So, without an engine, how do gliders work? Without an engine, the first problem is getting the glider off the ground and up to altitude. The most common launching method is aero-tow. In this, a conventionally powered aircraft tows the glider into the sky using a long rope. Once at the desired altitude, the gilder pilot releases the rope and the two aircraft turn in opposite directions. The glider is now in flight, and the other aircraft can return to the ground. To stay in the air, the glider’s wings must produce enough lift to balance the weight of the glider. The faster a glider flies, the more lift is produced. If the glider flies fast enough, the wings will produce enough lift to keep it in the air. However, the wings and fuselage also produce drag, which also increases with the glider’s speed. Since there is no engine, and therefore no thrust, the glider must overcome this drag another way. Angling the glider downward trades altitude for speed but allows the glider to remain in flight.
Landing a glider is very similar to landing a conventional aircraft, apart from the aforementioned differences in landing gear. Glider wings are very strong and have reinforced wingtips to prevent damage if they scrape along the ground during landing. Still, pilots are usually able to keep both wingtips off the ground. During landing, it is critical that the pilot be able to control the glide path (the rate of descent vs. distance traveled) in order to bring the glider down in the right location. The pilot must reduce the amount of lift produced by the wings without altering the speed or altitude of the glider. This is done by deploying spoilers on each wing. The spoilers disrupt the airflow over each wing, reducing lift and increasing drag, helping the aircraft come back down to ground.
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