Mini Project 2
INTRODUCTION
The Full Story
What is a Glider?
A Glider is a special kind of aircraft with no engine. The most obvious examples are paper planes, but gliders can come in a wide variety of sizes. The Wright brothers perfected the design of the first airplane and gained piloting experience through a series of glider flights. These aircraft were similar to modern hang-gliders and were launched by running off a hill. More sophisticated gliders are launched by ground based catapults or are towed aloft by a powered aircraft then cut free to glide for long distances and for a long period of time before landing. The Space Shuttle flies as a glider during reentry and landing (the rocket engines are used only during liftoff).
As part of this Mini Project, our team has carried out extensive research to build a glider with a target of landing inside a circle of radius 1 m after a descent down the monumental steps in the Campus Instructional Facility of the University of Illinois. A detailed description of the challenge can be found here.
The three axes of Rotation
Axes of a Glider
A Glider has three axes of Rotations and six degrees of freedom. The diagram above shows the three axes of rotations - Yaw, Roll, and Pitch.
Stabilities of a Glider
The above diagram shows the three stabilities of a glider. We always want the glider to have positive or neutral dynamic stability. If the glider has a pilot, he can maneuver the glider depending on the winds to increase the stability of the glider and the time of flight.
Some Glider Design Choices
Nomenclature of Design Parameters of a Glider
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Streamlined Fuselage - The surface of a glider's fuselage is designed to be as smooth as possible, allowing the plane to fly through the air with little parasitic drag. Today, many advanced gliders are constructed from seamless materials like fiberglass and carbon fiber.
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High Aspect Ratio Wings -The slenderness of a wing is expressed as the aspect ratio, which is calculated by dividing the square of the span of the wing by the area of the wing. FORMULA . Glider wings are very long and thin, which makes them efficient. They produce less drag for the amount of lift they generate.
Aspect Ratio of a Glider
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Control Surfaces - Gliders use the same control surfaces (movable sections of the wing and tail) that are found on conventional planes to control the direction of flight. The main parts include -
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Ailerons - Ailerons are movable sections cut into the trailing edges of the wing. These are used as the primary directional control and they accomplish this by controlling the roll of the plane (tilting the wing tips up and down).
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Elevator (horizontal stabilizer) - The elevator is the movable horizontal wing-like structure on the tail. It is used to control the pitch of the plane, allowing the pilot to point the nose of the plane up or down as required.
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Rudder (vertical stabilizer) - The rudder is the vertical wing-like structure on the tail. It is used to control the yaw of the aircraft by allowing the pilot to point the nose of the plane left or right.
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Control Surfaces
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Glider Takeoff Mechanisms-
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Aero-Tow - A powered airplane tows a glider into the air using a long rope.
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Winch Launching: An engine on the ground powers a winch, connected to a cable launch system. The glider is pulled along the ground at high speed toward the winch and takes off. When the glider reaches the desired height, it releases the winch line before continuing flight.
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Glider Flights Mechanisms -
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Thermals - This refers to the rising air created by the heating of the earth’s surface
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Ridge Lift - This occurs when wind blows against mountains, usually on the windward side of mountains.
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Wave Lift - this is created on the leeward side of the mountain, when winds pass over the top of a mountain.
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Lifts of a Glider
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Landing - Compared to landing in a powered airplane, there are a few key differences when flying a glider. First, gliders cannot add power if they won't make the touchdown zone. The landing itself isn't too different from that in any airplane, you flare until lift reduces, and try to touch down lightly. Since gliders have one wheel, it's a bit of a balancing act to keep the wings off the ground as long as possible.
How does a Glider fly?
Forces on a Glider
In order for a glider to fly, it must generate lift to oppose its weight. To generate lift, the glider must move through the air. But the motion of the glider through the air generates drag. In a powered aircraft, the thrust from the engine opposes drag. The glider, however, has no engine to generate thrust. With the drag unopposed, the glider quickly slows down until it can no longer generate enough lift to oppose the weight..
How does a glider then generate velocity? It trades altitude for velocity as a glider converts its kinetic energy to potential energy during descent to gain velocity.
In real life, a full scale glider with a pilot in it can stay aloft for multiple hours, because they are designed for very high efficiency and if the pilot can locate updrafts (Pockets of rising air), the glider can gain altitude. But for our purpose, we are designing a glider that constantly descends at a rate determined by us, to correctly land inside the desired target area.
Some glider formulas
Below are the basic formulas we use while doing glider calculations
Glide Angle of a Glider
Lift-to-Drag Ratio and Glide Angle Correlation
For a detailed overview of the calculations, please click here.
References
Akhtar, Zaki, et al. “Design of A Micro-Aircraft Glider.” WPI Major Qualifying Project.
Waltham C 1999 The flight of a balsa glider Am. J. Phys. 67 620–3.
Wu, W., Chang, D., and Zhang, F. (2013). Glider CT: Reconstructing flow fields from predicted motion of underwater gliders. In Proceedings of the Eighth ACM International Conference on Underwater Networks and Systems, 47.
“Aviation Instructor's Handbook.” Aviation Instructor's Handbook | Federal Aviation Administration.
Sancha, David Perez. “CFD Analysis of a Glider Aircraft.” Linköping University | Applied Thermodynamics and Fluid Mechanics (MVS), 2019.
“Calculating Best Glide Quantities.” Calculating Best Glide Quantities - MATLAB & Simulink, https://www.mathworks.com/help/aerotbx/ug/calculating-best-glide-quantities.html.
“Effect of Size on Drag.” NASA, NASA, https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/sized.html.
Demircali, Ali Anil, and Huseyin Uvet. “Mini Glider Design and Implementation with Wing-Folding Mechanism.”
MDPI, Multidisciplinary Digital Publishing Institute, 3 Sept. 2018, https://www.mdpi.com/2076-3417/8/9/1541.