Elastic Launched Glider

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Elastic Launched Glider
Engineering & Build Event
Forum Threads 2014 2013 2012 (from Helicopter forum)
2012 (trial)
There are no tests available for this event
Images Images (needs submissions)
There are no question marathons for this event
This event was not held last year in Division B
Division C Champion Poudre High School



Contents

General

Elastic Launched Glider was a 2012 Division C trial event at the National Tournament. It has been a full-fledged Division C event since 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:

  • Aileron: In short, the back edge of a wing of a glider (The edge closest to the tail). They can bend up or down to alter the glider's flight. The most distinct example of what it is is on the Time Machine model from the AMA site.
  • 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.


Plane.jpg

Construction

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

Because of 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.

Wood.jpgBalsa Log.JPG

Incidence

A very major part of the construction of the elastic launch glider is the "incidence" (see terms above). In this scenario, 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 adjust 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 re-glued 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.

How to Angle the Glider and Launch Handle

As stated in other parts of this article, the launching of the glider into the air is ballistic, not aerodynamic; i.e. the glider is not flying to the ceiling, you are throwing it there. However, it is very important to note that aerodynamics are involved in the ascent. If the glider were to be simply launched into the air without any thought, it would likely stall and fall back to the ground. Instead, what you want to do is launch it in such a way that it aerodynamically corkscrews to the ceiling without stalling. The spiral will only contain a small number of rotations; maybe 1 to 1.5 turns (this is why it might be hard to observe in videos). Now, as each glider is different, the exact angle of launch will be different for suc cess, but in general it goes like this:

1. Hold the launcher in one hand and glider attached to the elastic loop in the other.

2. Stretch the elastic the desired amount, and hold the system vertically. The elastic loop should be in a vertical line.

3. Move the glider a small distance horizontally away from the launch handle. This way, when you the glider is less likely to hit the handle.

4. Tilt the system so that it is not vertical but 70 to 80 degrees in respect to the ground. This is so the the glider does not go straight up and thus can transition into its glide.

5. Roll the glider (rotate it about the axis of the fuselage) about 45 degrees. Make sure to roll the launch handle (i.e. rotate your wrist of the hand with the launch handle) the same amount! This is what gives the corkscrew ascent.

6. Launch and pray.

How to Control the Launch Height

A question you may (and should, if you do not already know) be asking is "How do I control how high my glider goes when I launch it?" What you definitely should NOT do in a competition is pull your elastic back a probable amount and just wing it (pun entirely intended), hoping that this random launch will get your glider close-ish to the ceiling. This method leaves far too much room for error on the day of the competition.

A far better method of controling the launch height is a process called "shortening". What you do is start with a relatively loose loop of elastic that, when stretched as far as your arms will allow, does not get the glider all the way to the ceiling. Once you are at the competition area, test-launch by pulling this loose loop back as far as you can, and launching the glider. If the glider does not make it as high as you want it to, shorten the elastic, perhaps by looping it around the launch handle, and launch the glider again by pulling the elastic back as far as your arms allow. Repeat this process until the glider ascends to the desired height.

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 to 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.

Roll

Tilting of the glider to the left and to the right about the axis of the fuse would be classified as roll. The part of the glider that controls roll is the ailerons. Altering the ailerons most directly effects the glider's roll.

Pitch

Tilting of the nose of the glider up or down is what would be called pitch. Pitching of the glider in the air is most directly controlled by the glider's elevator. If the glider is pitching upwards and stalling, or pitching downwards and nosediving, the best way to fix it would probably be to adjust the elevator.

Yaw

Turning of the glider towards the right or the left in air is yaw. This is a very important part of this event, because, as it is indoors, the glider needs to circle downwards, and this circling is yaw. The main control for yaw on the glider is the rudder. As you will compete is different sizes of rooms, and you want to have as large a circle for your descent as the room will allow, you must be very proficient in adjusting your rudder to change the magnitude of the yaw.

In Conclusion

Once you have developed good launching technique, this freeflight trimming is very important. Your goal is to have your glider fly steadily but also slowy, in a large spiral to the ground. It will take some adjusting of the parts which controlroll, pitch, and yaw, but if you know which parts these are, which you now should, it becomes a matter of simple diagnosis of the problem and editing of your glider until the descent is to your standards.

Troubleshooting

When it comes to freeflight trimming, it is oftentimes quite difficult, especially as a beginner, to determine exactly why your glider is not gliding properly, and what you can change, either about the glider or about your launch method to fix it. Below is a list of various problems you might be having, and potential solutions to them.

My Glider...

  • Nosedives immediately after its transition: This is probably an issue with incidence. Try bending the trailing edge of the elevator upwards a little (be careful, though...too much bend and the glider will loop backwards instead). Try this
  • Flips backward it its transition and loops backward before going into a glide (or doesn't make it into a glide at all): This is most likely an incidence problem. Try bending the trailing edge of your elevator downwards a little (be careful, though...too much bend and the glider will nosedive instead, which is generally more likely to cause damage to your glider). Another thing that might help is simply launching the glider at less steep an angle.
  • Is not turning properly (it flies straight in its glide instead of gliding in circles): To fix this, the easiest thing to do is probably going to be to carefully remove your glider's rudder, and reglue it at more of an angle. To get it to turn in a left-hand circle, glue it so that the front end of the rudder is further to the left than the back end. Reverse this if a right-hand circle is desired.

Resources

One incredibly helpful website which covers almost all aspects of this event can be found here (this is the aforementioned AMA glider website). 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. Also do check out http://www.grc.nasa.gov/WWW/k-12/airplane/short.html. Its superb for understanding the what happens during flight and you need a middle school level of algebra to understand what they're talking about.

Kits

Two kits which are relatively easy to build, fit the 2012-2013 specifications, and will produce decent to very good gliders (depending on the build itself) are:

Plans

2012 National Tournament Trial Events

Division B: Helicopter Egg Drop | Division C: MagLev ยท Elastic Launch Glider