Elastic Launch Glider

Elastic Launched Glider is a Division B build event. Before the tournament your team of up to two builds a small free-flight glider, flies it many times, records what happens, and tunes it for the longest possible time in the air. At the tournament you launch it indoors from a hand-held launch handle with an elastic loop, and timers record how long it stays up. There is no written test. Your score comes from your three best timed flights, multiplied by a bonus if you bring a proper Flight Log. This guide explains what the 2027 rules require of the glider, the handle and your log, walks through the scoring math, and then teaches the physics and trimming practice that turn a legal glider into a long-flying one.

Event format

Because this is a device event, the Science Olympiad Building Policy applies, and either partner may be asked how the glider was designed, built and operated. Both of you should be able to explain the trim, the launch technique and the log.

What the rules cover

The table summarizes the 2027 Division B rules (pages B22 to B24 of the 2027 rules manual). The rules do not change by tournament level: Regional, State and National use the same device limits and scoring. What does change from site to site is the room, so the announced ceiling height and floor size matter to your trim.

Key definitions

The rules define a handful of terms, and several of them decide whether a flight counts.

• Elastic launched glider: a heavier-than-air aircraft held up only by aerodynamic lift on its wing or wings. It has no motor; all of its starting speed comes from energy stored in stretched elastic.
• Launch handle: a rigid hand-held handle with an elastic loop. Neither the handle nor the elastic is part of the glider, so neither counts toward the 3.5 to 10.0 g window.
• Flight configuration: the glider fully assembled and ready to fly. Span, chord, length and total lifting area may not change between the moment it leaves the box and the end of the flight. Folding wings, telescoping booms or anything that unfolds after launch are therefore out.
• Trim flight: a practice flight inside your Flight Period that does not count for score.
• Steering: any way of controlling direction after release, such as poles, balloons, rods or blowing air. It is not allowed.
• Ballast: material such as clay or tape added for balance, stability or control.

The glider: legal limits and what they mean for design

Mass window: 3.5 g to 10.0 g

Both limits are strict, so a glider weighing exactly 3.5 g or exactly 10.0 g is illegal. The phrase that the mass must hold throughout the flight means nothing may fall off: a nose weight that pops out, a wing tip that breaks away or tape that peels off on landing can make a flight illegal. Glue ballast in place rather than pressing it on.

Most competitive designs will sit toward the light end, because a lighter glider climbs higher on the same launch energy and sinks more slowly (both shown below). Do not build right at 3.6 g, though. Scales differ by a few tenths of a gram, and the rules let you add your own ballast at check-in to correct for that. A target of about 4.0 to 5.0 g leaves room on both sides. Bring a small piece of clay so you can add mass if the supervisor's scale reads you low.

Size: the Measurement Box

Your glider must fit, fully assembled and in flight configuration, inside a box you supply with no lid. The outside of that box, including handles, latches or anything else that sticks out, must fit inside a 32.0 × 24.0 × 47.0 cm prism. Because the limit is on the outside, wall thickness eats into the space available: a box with 0.5 cm walls, open on one of its 32 × 24 cm faces, has about 31 × 23 × 46.5 cm inside (the open side does not add a wall).

At check-in the supervisor checks the box and watches the glider go in. You may not bend, twist or squeeze the glider to make it fit, and its overall dimensions must be the same when it comes out. The supervisor can test this by sliding it in and out. Two consequences:

1. Span is set by the box. A wing laid flat across the long dimension can be at most about the inside length. A glider can sometimes fit at an angle, using a diagonal, but only if it does so without flexing. The longest straight line through a 32 × 24 × 47 cm prism is $\sqrt{32^2+24^2+47^2} \approx 62$ cm, and real gliders use much less because the fuselage and tail also need room.
2. Nothing may change shape after the box. Wings must not be detachable or folding for transport, and a wing that warps between the box and the launch is technically a change in flight configuration as well as bad for trim.

Teams from the same school may share one Measurement Box, which saves building effort but means both teams must design to the same internal space.

The blunt nose rule

Elastic-launched gliders leave the handle fast, so the rules require a blunt nose. The test is pass/fail: insert the front of the fuselage into a lip balm cap with an inside depth of about 1.57 cm and an inside width of about 1.37 cm. A rounded or flat nose wider than the cap stops before it touches the bottom and is legal. A pointed or narrow nose that reaches the bottom is illegal. Build the nose as a block of balsa or foam at least a little wider than 1.4 cm, round its front edge, and test it with a real cap during construction.

Materials and kits

Every material except boron filament is allowed, so balsa, foam, carbon rod, paper, plastic film and tissue are all options. Kits are allowed, but only if you do the gluing and covering yourself. A ready-to-fly foam glider from a toy store does not qualify if its parts arrive already joined or covered.

The launch handle

The launch handle replaces the bare rubber band or launching stick used in many hobby catapult gliders. The 2027 rules set five conditions:

The supervisor collects the handle at check-in and gives it back to start your Flight Period, and may inspect it again afterward.

The elastic usually loops over a small hook or notch under the glider's fuselage, about at the wing's leading edge. The student holds the handle in one hand, pinches the glider's tail in the other, pulls back to stretch the loop, aims and lets go. The glider accelerates while the elastic contracts and leaves the loop when the elastic reaches its relaxed length.

Flight procedure and timing

Before your Flight Period

The tournament chooses an indoor room and announces its approximate length, width and ceiling height in advance, and the organizers try to limit drafts. On the day, the supervisor decides whether more than one team may fly at once and whether practice flights are allowed outside Flight Periods. Practice always gives way to official flights, and there is no practice in the last half hour of the final time block. Some tournaments run an optional self-check station where you can test your box and glider before check-in; you can still make changes after using it.

Once you enter the roped-off flying area, nobody outside may hand you materials, help you or talk to you, and only the two participants may touch the gliders until the event ends. Breaking this ranks your team below every other team, which is harsher than the usual violation tier. Coaches and parents sit in the spectator area.

Check-in

1. Present your gliders in the Measurement Box(es), plus the launch handle and Flight Log.
2. The supervisor checks the box's outside dimensions and that each glider fits without being reshaped.
3. Each glider comes out and is weighed. You may add your own ballast to correct for scale differences.
4. The supervisor holds the launch handle until your Flight Period starts.

During the Flight Period

The 6-minute clock starts when the supervisor gives the handle back. Within it:

• Before every launch, tell the timers whether it is a trim flight or an official flight. If you say nothing, the flight is official.
• You may adjust, repair and trim-fly as often as time allows, but the clock does not stop for repairs or for walking to fetch a glider.
• You may make at most 5 official flights in total, using either or both gliders.
• A flight launched before the 6 minutes expire flies to completion.
• If your glider collides with another team's glider, you may choose to re-fly, and you may decide after it lands. A re-flight is outside the 6-minute limit. Timers can also hold your launch to avoid a collision.

How a flight is timed

Timing starts when the glider leaves your hand and stops when any part of it touches the floor, or when the lifting surfaces stop carrying its weight (for example, it lands on a beam, a light fixture or a basketball hoop), or when the supervisor otherwise rules the flight over. The rules do not list touching a wall or the ceiling as a stop condition, but it usually costs height or speed.

Supervisors are strongly encouraged to use three timers. The official time is the median of the three, not the mean, recorded to the precision of the stopwatches.

After the Flight Period, the supervisor may ask you to show again that each glider fits in the box and may re-check the launch handle and glider mass. A glider that grew, bent or lost mass during your flights can create a violation after the fact, so repair carefully. If your team files an appeal, your gliders, launch handle, boxes and log have to be left behind in the event area.

The Flight Log bonus

The Flight Log is optional, but it multiplies every flight score, so it is the cheapest points in the event. A complete log needs:

• data from 10 or more test flights made before the competition;
• at least 4 parameters: the three required ones plus at least one you choose;
• units on every numeric value (units in the column headers are fine).

The three required parameters, in our wording, are the peak height the glider reached after launch (estimated or measured), the relaxed length of the launch elastic, and the flight time. Your extra parameter can be anything you vary or measure; the rules suggest examples such as launch pitch angle, launch roll angle or how far you stretched the elastic. Good extra choices are the ones that actually explain your results.

The rules do not define what makes a log "partial" (×1.1) rather than "complete" (×1.2). A log with fewer than 10 flights, a missing required parameter or missing units is likely to be judged partial, but the supervisor decides. Avoid the question by exceeding every requirement: log 20 or more flights, every required column, units everywhere, and keep the log neat enough to be read in a minute. The supervisor returns logs after inspection and reviews your recorded competition data with you at the end of your time.

To estimate peak height in a gym, compare the glider's top point against known heights: the basketball rim is 3.05 m above the floor, and the room's ceiling height is announced. Two people watching from the side give better estimates than the launcher looking up.

Scoring math

Because every flight gets the same multiplier, the Final Score equals $B$ times the sum of your three longest official flight times. Ties are broken by the longest official flight score that did not count, which is your fourth-best official flight if you flew at least four.

How the launch stores and releases energy

Stretching the elastic does work on it and stores elastic potential energy. On release, the elastic contracts and accelerates the glider, turning that energy into the glider's kinetic energy. During the climb, kinetic energy becomes gravitational potential energy (height), minus what drag takes. During the glide, the glider spends that height slowly to stay in the air.

Real rubber does not follow Hooke's law closely. Its force rises unevenly with stretch, and it gives back less energy on contraction than it took to stretch (the difference becomes heat, called hysteresis). The useful energy is the area under the measured force–stretch curve on the way back. You can measure it at home with a luggage scale and a meter stick: record the force every few centimeters of stretch and add up force × step. The relaxed length, a required log parameter, sets where that curve starts, so changing to a longer or shorter loop changes the energy at the same pull-back distance.

Energy, mass and climb height

That is the strongest reason to build light. It is also why the minimum mass exists: without it, the event would reward ever more fragile gliders.

Matching the launch to the ceiling

Indoors, height is capped. A launch that would reach 9 m in a room with a 7 m ceiling either hits the ceiling or must be aimed lower, wasting energy. The best launch puts the glider near, but safely below, the ceiling with the speed bled off and the glider level. This is why the log tracks peak height alongside elastic length: they are the two numbers that let you tune launch energy to a known ceiling.

Use the announced ceiling height to plan before the tournament. If your practice gym is 8 m and the tournament gym is 6 m, shorten the stretch or angle the launch less steeply, and practice that setting at home.

The climb and transition

A catapult-launched glider flies in three phases:

1. Climb. It leaves the handle fast, nearly vertical or angled, with the wing producing little lift because the angle of attack is small at that speed.
2. Transition. As it slows near the top, it must roll level and settle into gliding speed without stalling or looping.
3. Glide. It descends slowly in a wide circle until it reaches the floor.

The transition decides most flights. A glider that loops at the top loses its height in a dive. One that rolls the wrong way can spiral down. A good launch adds a small bank (the launch roll, a natural extra Flight Log parameter) so that the glider climbs in a gentle curve, then the wing's lift and the trim bring it level at the top.

What keeps a glider in the air

In free flight three forces act: weight $W = mg$ down through the center of gravity, lift $L$ perpendicular to the oncoming air, and drag $D$ along the oncoming air, opposing motion.

Speed, wing loading and sink rate

The event scores time, not distance, so the number that matters is sink rate, how fast the glider descends.

Sink rate falls when wing loading $W/S$ falls and when the wing flies efficiently (low $C_D / C_L^{3/2}$). Large, light wings are the recipe, within the box and the minimum mass.

Forty meters is longer than most gyms, which is why indoor gliders are trimmed to circle.

Turning costs sink rate

In a banked turn at bank angle $\phi$, the lift must tilt to provide the turning force, so the wing must make more total lift.

Reynolds number: small gliders are different

For the example glider, $Re = 2.75 \times 0.045 / (1.5 \times 10^{-5}) \approx 8 \times 10^{3}$, hundreds of times lower than a light airplane. At such low Reynolds numbers air separates easily from thick, blunt airfoils. Thin, slightly curved (cambered) wings, or flat sheets with a sanded, rounded leading edge, work best for small gliders. A smooth surface helps, but a very thin, light structure helps more.

Aspect ratio and induced drag

At the wing tips, high-pressure air below leaks around to the low-pressure side above, forming tip vortices and induced drag. Induced drag is largest when the wing works hard at low speed, which is exactly a slow glide.

The example wing has $AR = 0.36^2/0.0162 = 8$. A wing of the same area with a 0.25 m span would have $AR \approx 3.9$ and noticeably more induced drag. The box limits span, so within it, choose the longest span you can make stiff enough to survive a launch load of about 13 times its weight without flexing.

Angle of attack and stall

The angle of attack is the angle between the wing chord and the oncoming air. Lift rises with it until the air can no longer follow the upper surface; then lift drops and drag jumps: a stall. Gliding slowly means flying close to the stall angle, so a good trim keeps a small margin.

Stability: why gliders loop, dive and spiral

A glider rotates about three axes through its center of gravity, and each needs its own stabilizer.

• Center of gravity (CG). The CG must sit ahead of the neutral point (the combined balance point of wing and tail). Free-flight gliders with a large stabilizer often balance somewhere around the middle of the wing chord, farther forward with a small stabilizer; treat that only as a first guess and find the final spot by test glides. Too far back gives a pitch-up and stall; too far forward gives a dive.
• Dihedral. Wing tips angled up from the root. When the glider banks it slips toward the low wing; the low wing meets that sideways flow at a higher angle of attack and makes more lift, rolling the glider back. Polyhedral (only the outer panels tipped up) does the same with a flatter center section.
• Fin. A vertical fin keeps the nose pointed into the airflow. A slightly offset fin, or a small rudder tab, is the usual way to set the turn direction for circling.

Too much dihedral couples roll to yaw strongly and causes slow weaving; too little lets the turn tighten into a spiral dive. A small fin with generous dihedral tends to give a stable, wide circle.

Design principles

1. Light, then stiff. Aim for 4 to 5 g total. Spend mass on the launch hook, wing root and nose block, which take the launch load, and save it everywhere else.
2. Use the box. Lay out the glider so the wing spans the long direction of the box. Plan the inside dimensions before cutting a wing, then build the box and the glider together.
3. Thin, flat or lightly cambered wing with a sanded leading edge and a crisp trailing edge, for the low Reynolds number.
4. Generous tail. A horizontal stabilizer of roughly a quarter to a third of the wing area, set well behind the wing, gives pitch stability through the large speed change from launch to glide.
5. Blunt, solid nose. A balsa or foam block wider than 1.4 cm passes the cap test and doubles as nose weight.
6. Fixed geometry. Glue the wing and tail permanently. The flight configuration rule makes removable or folding parts a liability.
7. Repeatable launch hook. A firm notch or hook at a fixed spot under the fuselage gives the same release every time.

Trimming a glider

Trim a finished glider in order, and fix each step before the next.

1. Check symmetry. Both wing halves should have the same incidence, dihedral and shape; the fuselage and fin should be straight. Most bad flights start with a warp.
2. Set the CG. Balance the glider on two fingertips, mark the CG, and adjust with ballast in the nose block.
3. Hand glide. Toss it gently and level at walking pace. Watch for stall-dive cycles (CG too far back or too much tail nose-up), a steady dive (too far forward) or a turn.
4. Fix pitch with small CG or stabilizer changes.
5. Set the turn. Choose a direction, then add a small fin offset so the glide circles widely.
6. Low-power launches. Launch with a short stretch and a modest pitch. Watch the climb and the transition. If it loops, reduce nose-up trim or launch pitch; if it rolls into the ground at the top, change the launch roll or turn direction.
7. Raise power step by step toward the height your ceiling allows, re-checking trim each time.
8. Log every flight, including failures, so a teammate can reproduce the setting.

Building for repeatability

• Build both allowed gliders to the same plan. One is your spare on the day, and comparing them shows which results come from the design and which from build variation.
• Weigh parts as you go. Glue and tape add mass fast. Keep a running total against your 4 to 5 g target.
• Keep wings flat. Humidity and heat warp thin balsa and foam. Store gliders in their Measurement Box, re-check shape before every session, and keep the box out of a hot car.
• Reinforce the launch zone. The hook, nose and wing root see the highest loads.
• Replace elastic on a schedule. Rubber weakens with use and ages in light and heat. Keep the relaxed length the same when you replace it, since the log depends on it.

Strategy

• Finish the Flight Log early. It is worth 20% of every flight. Log flights all season, not the week before.
• Plan the 6 minutes. A typical plan is one or two declared trim flights to check trim in the new room, then official flights spaced so you can retrieve the glider and adjust between them. Retrieval time counts, so let your partner fetch while you prepare the next launch.
• Split the jobs. One partner launches and the other watches the flight path and the timers, announces trim or official before each launch, and keeps track of the count of official flights.
• Know when to stop. Once three good flights are in, a fourth official flight only matters as a tiebreaker. A fifth risky flight cannot lower your score, so experiment with the last ones if time allows.
• Use the room information. Practice in a space with a similar ceiling height, and check for vents, open doors, hanging lights and basketball hoops on arrival. Plan the launch direction so the glider circles over open floor.

Competition day checklist

1. Weigh each glider and measure the box at home; confirm the nose with a lip balm cap.
2. Pack both gliders in the Measurement Box, the launch handle, spare elastic of the same relaxed length, glue, tape, clay ballast, a ruler and the Flight Log.
3. Wear Category B eye protection and bring a spare pair.
4. On arrival, look at the room: ceiling, beams, vents, hoops, doors.
5. At check-in, have ballast ready if the scale reads under 3.5 g.
6. Announce trim or official before every launch.
7. After your period, keep the gliders intact until the supervisor confirms the post-flight box and mass check.

Common pitfalls

• Building to the edge of the mass window. A 3.6 g glider can read 3.4 g on a different scale. Leave a margin and carry ballast.
• Forgetting the mass must hold for the whole flight. Loose clay or tape that falls off on landing can make a flight illegal.
• Measuring the box on the inside. The 32.0 × 24.0 × 47.0 cm limit is on the outside, including latches and handles.
• Flexing the glider to fit the box. The supervisor can check that it slides in and out without changing shape.
• A pointed nose. It fails the lip balm cap test.
• Metal in the elastic, or a handle 1 m long. The handle must be under 1 m in every direction, and the elastic must be non-metallic.
• Elastic that pops off the handle. If it leaves the handle, timing ends for that flight.
• Forgetting to declare trim flights. Undeclared flights are official.
• Planning for a 10-minute flight window. You have 6 minutes of Flight Period; a flight launched inside it may finish after.
• Logging only flight times. A complete log also needs peak height, relaxed elastic length, one more parameter and units.

How tournaments test this

Elastic Launched Glider has no written exam, and the archive has no tournament questions for it, so there is no question-type data to report. The tournament tests three things:

1. Compliance: the box, the glider's fit and shape, its mass window, the nose, the launch handle and the elastic, checked at check-in and possibly again after your flights.
2. Performance: up to five official flights in six minutes, timed by the median of three timers, three longest summed.
3. Documentation and understanding: the Flight Log for the bonus, and questions under the Building Policy about how you designed, built and flew the glider.

Prepare for the third by being able to explain, in a sentence each, why your CG is where it is, how you chose the elastic length and stretch, and what your extra log parameter showed.

Test yourself

There are no archived tournament questions for this event yet, so these practice problems were written for this guide.

References and further reading

• Science Olympiad, 2027 Division B Rules Manual, Elastic Launched Glider (pages B22 to B24), and the Building Policy and eye-protection rules at soinc.org.
• National Free Flight Society (the event sponsor), freeflight.org, for catapult and hand-launched glider plans and trimming advice.
• NASA Glenn Research Center, Beginner's Guide to Aeronautics, for lift, drag, glide ratio and stability.
• OpenStax, University Physics Volume 1, for work, elastic energy and circular motion.
• SciOly Wiki event page for Elastic Launched Glider, for orientation only; the rules manual is the authority.