<< Page 45 Page 46: Page 47 >>   Gliders Workshop This is an activity that can be done with kids age ~10 to ~20 and that teaches many of the most important principles of aeronautical engineering in a way that is fun and memorable. To read about the origins of this activity, please go here and scroll down to the last paragraph. Purpose and Scope This document describes an activity to be done with children, ideally aged 10-20. The purpose of this activity is to introduce children to some of the most basic and most important concepts of aircraft design, such as maximizing lift, minimizing drag, and correctly placing the center of gravity. Each of these three things has a direct and easily observable impact on the performance of a glider. For this reason, these concepts are very well illustrated by making and testing gliders. By the end of this activity, the students should be able to recognize many key features in airplanes that cause them to have optimal balance, low drag, and high lift. In the process of designing and building gliders, students will encounter many of the decisions faced by engineers when a new aircraft’s configuration is first designed or later refined: The exchanges between stability, performance, manufacturability, and cost (use of resources). This activity is also fun and memorable, and the children get to keep the aircraft they designed and made – one which, if made in accordance with the principles discussed here, should be able to glide quite far and in a straight line. Duration Ideally three hours. By skipping most of the historical information about gliders, by not expecting that students have time to color/decorate their gliders, and by and having lots of adults (one adult for every 4 students or so), the activity can be done in about two hours. Materials - This outline. - A copy of the Gliders Handout document for each student. - A Gliders Powerpoint file to be projected at the beginning of the activity The three files listed above can be downloaded as a single .ZIP file here. Ideally, each student should get to build a glider. If the budget for the activity is more limited, students may have to team up to build their gliders, in groups of two to four. For each glider to be built: - One sheet of foam core, about 24” by 36” - A small amount (<2 oz) of Plasticine, Play-Doh, or other similar modeling clay - One (but ideally two or three) pins (or thumb tacks, needles, or other similar sharp pointy objects) - A pencil or two, and a couple of sheets of paper (for design & planning) The following should also ideally be available for each glider that is to be built. But if the budget is limited and/or if the students are too young to handle box cutters or hot-glue guns, then maybe the following supplies can be had in smaller quantities, with their use supervised by an adult each time a student wishes to use it: - One hot-glue gun (may be shared or supervised) - Scotch tape (may be shared or supervised) - A box cutter (may be shared or supervised) - A ruler or yardstick (for drawing straight “cut lines” on the foam, and possibly measuring them) - Markers with which to color the gliders (may be shared) Also, some balloons for the gliders to be aimed at. (Scotch tape, thumb tacks, string, etc, may be used to attach the inflated balloons to a wall). Depending on how “easy” you want the target to be, this will involve up to three or four balloons per glider (assuming that every glider hits the target and the target consists of three or four balloons). And finally, a prize or two for the students/groups who design the best gliders (miss their target least often, or have highest glide ratio). Outline At the beginning of the activity, a copy of the Gliders Handout is given to each student. Students are told that all the relevant information from the activity is summarized onto those handouts, but that they may feel free to write on the handouts any extra information they might like to remember. Students should also be encouraged to ask questions about aviation history and technology (if the person running the class is knowledgeable about these topics, which ideally should be the case). The activity starts with a Powerpoint presentation. The "script" for what should be said by the presenter is included as the Notes for each slide. So make sure that, when preparing for this presentation, you can see the Notes for each slide, not just the slide itself! With these Notes, the presentation can be given (and the entire activity can be led) by any teacher, not necessarily just by aeronautics experts. The presentation explains what gliders are, why they have been and continue to be very important in the development of aviation technology, as well as their other uses such as recreation and as military transports during World War II. Students should then be told to pay special attention to the following part of the presentation, since they will need to use these concepts in designing their glider, and they will then compete for a prize and find out whose glider is best. Winning the prize depends on how well students apply the following ideas. The presentation then goes into glider performance. A shallow glide slope is most important, since it maximizes the distance traveled given the starting altitude. (Well, to most recreational gliders, a slow descent rate is most important, since it maximizes the time in the air given the starting altitude, but that is a detail that does not need to be brought up, since lowering the flight speed is a complicated requirement we will not burden the students with at this level). The presentation shows that a shallow glide slope is the consequence of a high lift-to-drag ratio. We then cover what design features lead to high lift and low drag. Finally, the presentation covers the concepts of balance and stability – where the center of gravity should be placed, and what the angle of incidence of the tail should be, in order to allow for stable straight-line flight while not increasing the drag any more than is necessary. It is then time to build the gliders. Time permitting, students should be given 5 or 10 minutes to sketch their glider design on a blank sheet of paper. If gliders are being designed and built by groups rather than by individual students, then the group should ideally have 10-15 minutes to design the glider. They should be encouraged to design gliders with mostly-straight, somewhat tapered, slightly dihedral, high-aspect-ratio wings. Students are given a sheet of foam core – this is all the material they will get from which to make the wings and fuselage and tail fins of their one glider. Students should first draw their “cut lines” on the foam, and only begin cutting once the design is complete. If the students are young, cutting should be done under adult supervision, or by an adult. Once the glider parts are cut, they may be attached with tape by the students, or with hot glue by the adults (unless the students are old enough to handle hot-glue guns safely). It is recommended that the tail not be attached too firmly since it might need to be adjusted during test-flying. Unless a lot of hot glue is used, most attachment points (such as where the wing attaches to the fuselage) will need reinforcement in order to hold their angle. This is typically done with a strut (which can be made of tape or foam) or with a small foam triangle glued into the attachment point (e.g. into the “armpit” of the airplane). This can be seen in the illustration below, which is not to scale (the reinforcement triangle should not be this large!) It should then be time for balancing the gliders and ensuring stability – something that is most easily done by test-flying. For best results, the center of gravity (i.e. the lump of modeling clay) should be slightly ahead of the wing. This will cause the airplane to nosedive when thrown. This tendency can be fixed by pitching the tail down into a slightly negative angle of incidence. This way, the airplane in flight is “balanced” on the wings, with the clay weighing down the nose and the horizontal fins pushing down the tail. This is illustrated extensively in the handout and the Powerpoint. Finally, pins or thumbtacks should be attached to the nose of the glider. This is because the gliders will be flown at a target of balloons, and the glider that pops a balloon earns a “hit”. Each glider may get up to three pins to be spread along its leading edges, but one on the nose should be enough. Once the gliders are made – and, time permitting, decorated – it will be time to have them compete! Inflate some balloons and hang them from a wall. Hang them low to the ground so that gliders can be thrown from the other side of the room (the glider will descend during its flight – it might start out at eye level but might end close to the ground). Most of these gliders should fly about 20-30 feet. Set up the competition however your common sense indicates. For example, have all the gliders be flown at the target once. If they all hit the targets, have the next round be thrown from further away, or decrease the target to a single balloon and the pins to only one per glider. But if no one succeeds, thrown the gliders from closer to the target and/or increase the number of balloons and/or of pins. Eventually, add up each glider’s balloon-popping score, and announce a winner. One more competition is the glide ratio competition. This might take the form of a simple distance toss: Have the gliders be thrown by the students and see which goes the farthest. Or have them thrown from a certain height – say, the middle of a set of stairs. It is worthwhile to note that a glider will have a certain terminal velocity. It should not be thrown very fast (this might in fact damage the foam if it is thrown at high speeds and high angles of incidence), but released at a speed similar to the speed it tends to reach given some time in the air. Gliders thrown too fast are also benefiting from momentum rather than from aerodynamics: A dart or arrow could be used instead. The point is not to have something that can be thrown accurately like a dart, but to have a glider that can fly gently and slowly in a straight line. Students should be encouraged to find out their glider’s natural flight speed, and to thrown them at that speed or slightly faster, rather than throwing the gliders like darts. Finally, hand out the prizes, and clean up the bits of foam, glue, modeling clay, and popped balloons from the room. As for helping to decide which student in each group gets to keep the glider… Good luck! It might be worthwhile to try and get the kids to reflect at the end about which gliders did best and why that might have been the case, design-wise. Who had well-balanced gliders? Poorly-balanced? Stable? Unstable? Draggy? Conclusion Hopefully you can see that this is a fun activity, and one that demonstrates some key concepts in aeronautical engineering. Again, if you have any questions, suggestions, or other feedback, please email me! And if you actually did this activity, please let me know! I'm sure I will find that very rewarding. And in case you're just joining us (i.e. if you're not familiar with this website): Students interested in airplane design, or who wish to learn more about why airplanes are designed the way they are, should visit AirplaneDesign.info, a website that lays out the scientific principles behind most features of the designs of different airplanes. Given most modern airliners, fighter jets, ultralights, sailplanes, recreational airplanes, and stealth bombers, anyone should be able to see that there is an enormous variety of airplanes out there – and to wonder why they are each designed as they are. Well, they are designed as they are for very good, interesting reasons, and students should be encouraged to look up this information. AirplaneDesign.info presents this information with lots of pictures and simple graphs, tons of interesting examples, and almost no math. So check it out!