Elastic Launched Glider

General
Elastic Launched Glider was a 2012 Division C trial event at the National Tournament. It is planned to become a full event for 2013.

The 2012 rules may be found here.

This event is a building event consisting of two parts: a glider made to be launched by the pulling and releasing of a rubber loop, which can be constructed based on plans of the competitor, or from a kit, and a flight log similar to that of other aviation events.

Terms to Know
One important part of this event which may confuse those new to it when reading Elastic Launch Glider threads on the forums is the terminology used, so here is a basic glossary of some terms you may want to know:


 * Roll: The rotation of the glider upon the main axis of the wings that runs through the glider's center of gravity.
 * Pitch: The rotation of the glider about the main axis of the fuse.
 * Yaw: The rotation of the glider about the axis perpindicular to both the axis of roll and the axis of pitch.
 * Fuse: Short for fuselage; the main body of the glider.
 * A-Grain: A type of balsa used in gliders (see below). Its properties include it being softer are more malleable than other balsa.
 * B-Grain: A type of balsa used in gliders (see below).B-grain balsa has a wide range of properties, as it is cut randomly from balsa stock, but in general it has proprties which fall in the middle of whatever range they are in.
 * C-Grain: A type of balsa used in gliders (see below). Its properties include it being harder and more stiff than other balsa.
 * Rudder: See vertical stab.
 * Elevator: See horizontal stab.
 * Stab: This is short for "stabilizer". It can refer to different parts of the glider, depending on who says it. In general, it refers to the whole of the tail of the glider; however, sometimes when someone says it they may only be refering to the horizontal stab or the vertical stab.
 * Horizontal Stab: the horizontal part of the tail of the glider, is also called the elevator.
 * Vertical Stab: the vertical part of the tail of the glider, also called the rudder.
 * Incidence: The angle between the main axis of the wings of the glider and the horizontal stab. When talked about, the incidence is generally given as positive, with the wings tilted upwards when the horizontal stab is parallel with the ground, negative, with the wings tilted downwards when the horizontal stab is parallel with the ground, or 0-0, with the wings and the horizontal stab parallel with the ground at the same time.

Materials
The glider is allowed to be built from any plan, published, student-devised, or otherwise. It can be built from wood, carbon fiber, glue, paper, and plastic flim only, with any non-metal malleable substance able to be used as ballast.

Balsa
Becausef the fact that the Elastic Launch Glider must be able to withstand traveling at a very high velocity, but also must be aerodynamic, different types of balsa may need to be used so that the glider can transition from these two elements of its flight, depending on the design being used. One such type of design is the Time Machine, the plans for which can be found at the AMA glider website linked to below. The three types of balsa used are commonly called A-grain, B-grain, and C-grain. the definitions of these types of balsa are given above.

Basics
In competition, the glider is launched with the elastic loop, fly upwards balistically until it reaches the ceiling (it is an indoor-only event), and transition into a circular glide which maximizes the time taken to descend to the floor; thus, the glider has to be built to be able to do this. Firstly, it has to be able to withstand the initial jolt of the launch, which means the contruction, particularly of the wings, is significantly different from that of the other aviation events. The glider as a whole has to be much more durable but just as aerodynamic as the wings/rotors of the devices of Helicopter and Wright Stuff.

Incidence
A very major part of the construction of the elastic launch glider is the "incidence" (see terms above). In this senario, the angle of incidence is the angle between the plane of the wings and the plane of the elevator (also know as the horizontal stab). Ideally, these two planes would be parallel, having an incidence of 0-0; a negative incidence (when the wings are at a negative angle of attack) leads to the glider taking a nose dive and a positive incidence (when the wings are at a positive angle of attack) leads to the glider flying back to the earth in an inside loop. However, it is incredibly hard to build the glider with enough precision to have the perfect incidence initially; thus, it is best to be able to adust the incidence. The best way to do this is to make sure you glue the elevator to the fuse with CA glue so that it can be dissolved with acetone and reglued at a better angle after having been tested.

The Launch
The launch of your glider is almost certainly the trickiest part of this event. There is a laundry list of things that might go wrong, and, unfortunately, many of these things result in the totalling of your glider. Therefore, you should be very cautious in launching your glider the first few times before you have developed a good technique.

How to Grip Your Glider
One very easy problem to fix, but one that could cause legitimate damge to your glider if not acknowledged, is how to hold your glider in the launch. With the simple simon design, one easy way to hold your glider is by gripping it from the top behind the wings, with your thumb on one side and fingers of the other, with none of your fingers going further than the plane of the bottom of the fuselage. This way, when the glide shoots upward out of your hand, the elevator goes beneath your fingers, and the rudder goes between your fingers and your thumb, and no part of the tail is damaged.

The Flight
Because of how the event is set up, gliders of this event are called "free flight gliders". That is to say, the only control the competitors have in its flight is the launch; after that, the glider is on its own. Therefore, it is good to know wha a flight should look like, and how that translates into the design of the glider.

Flight Outline
As mentioned above, the flight of a glider is largely in two parts: the initial, high velocity ascent, and the descent, which you want to take as much time as possible. The ascent, although largely ballistic, does need to have some aerodynamics involved. If you don't launch your glider in the right way, it will stall and take a backwards loop into the back of your head. More information about how to launch your glider so that it ascends smoothly can be found in this pages "launch" section. The descent of your glider is controlled by three key factors, which are in turn controlled by corresponding elements of the glider's design. For more information on this, read on.

Freeflight Trimming
''There is a wonderful, much-more-in-depth article about this on the AMA website linked to below; please go and check it out. However, here is a decent summary of freeflight trimming:''

As mentioned above, the elastic launched glider is what is known as a freeflight device. Because of this, it is essential to know which parts of the glider control which parts of its flight in what ways so that you can devise you glider t fit your specific demands (which, by the way, will change with the different sizes of rooms you compete in, so make sure you are able to alter the design of you glider slightly after it has been built, perhaps by using glue dissolvable in acetone). The three main movements of the glider are the rotations of roll, pitch, and yaw. The definitions for these terms are given above, but in case you didn't understand them, it helps to think of a x-y-z axis, with the origin point at the glider's center of gravity. If the glider is held parallel to the ground, the z axis runs through the fuse, and the x axis runs through the wings. Rotation about the z axis is roll, rotation about the x axis is pitch, and rotation about the y axis is yaw.

Resources
One incredibly helpful website which covers almost all aspects of this event can be found here. The 2012 Forum thread which can be found here lays down much groundwork for the event. Also, when searching for videos for this type of glider, be sure to try searching "Catapult Launch Glider", which is another name for this project.