Ping Pong Parachute

Ping Pong Parachute is a build event. Before the tournament your team designs and builds up to two bottle rockets made from plastic soda bottles. At the event, each rocket is pressurized with air only (no water) on a launcher the Event Supervisor provides, and it carries a ping pong ball taped to a small parachute. The goal is simple to state: the ball and its parachute should stay in the air as long as possible. The best single launch decides your rank.

Divisions B and C run the same event under the 2027 rules, with the same numbers, procedures and penalties, so this guide covers both at once. There is no written test. What separates strong teams is understanding: how pressure turns into height, why a tall ceiling is both an opportunity and a trap, how parachute size and mass set the descent speed, and how to keep a practice log good enough to justify the pressure you choose on the day. The rules make that log part of the score, so testing is not optional.

The physics is ordinary mechanics: forces, momentum, gas pressure and air drag. You do not need calculus. You do need to work with units (the rules mix pounds per square inch, feet and seconds), and you need to be able to explain your numbers to the Event Supervisor.

Event format

The design questions come from the general Building Policy on soinc.org, which applies to every build event. In practice the supervisor asks one or both partners how the rocket was built and how it works, often while inspecting the rocket. Both partners should be able to answer.

What the rules cover

The 2027 rules for Divisions B and C are the same, and none of the rules is limited to one tournament level, so everything below applies from invitationals through Nationals. The rules are short; the table summarizes each area in plain language, with the section of the 2027 rules manual where it lives.

Several points are printed in bold in the 2027 manual, which is how Science Olympiad marks rules that changed or deserve attention. They are: the launcher-width and leak rules, the early notice of ceiling height, the request to reduce drafts, the explicit ban on water, the ban on Mylar and ultrafilm, the design-question requirement, the use of the log to justify pressure (with a capped pressure for teams without a complete log), and the full list of penalty multipliers. If you learned this event from older notes, check those items first.

The rocket: construction rules explained

The pressure vessel

Your rocket's body is one plastic bottle that originally held a carbonated drink, 1 liter or smaller. Carbonated-drink bottles are made to hold internal pressure; bottles for still water or juice are thinner and are not allowed. The bottle's label has to be presented at inspection, which is how the supervisor confirms what kind of bottle it is, so keep it (or keep it with the rocket) rather than peeling it off and throwing it away.

The opening must be a standard soda-bottle neck: inside diameter about 2.2 cm and a neck height under 1.6 cm measured from the flange (the plastic ring below the threads) to the opening. That geometry is what lets the bottle seal on the launcher. Odd bottles with wide mouths or tall necks will not fit.

You may not change the bottle's structural integrity. Cutting, sanding, heating, gluing with hot glue or super glue and spray painting are all named as examples of damage. The reason is safety: a scratched or heat-softened bottle can fail at a lower pressure, and a bottle that bursts on the pad sends fragments outward. Treat the bottle as a pressure vessel you are borrowing, not a craft material.

The nose

The rocket flies with the bottle opening down, so the bottle's flat or domed base becomes the front. Most teams add a nose cone or cap to that end. The rules require the tip to be rounded or blunt, and they give a simple test: set a standard bottle cap (about 3.1 cm across and 1.25 cm tall) upside-down on the nose like a thimble. If the nose pokes up far enough to touch the inside top of the cap, it is too pointed. In other words, the tip must be wider than a bottle cap or flattened enough that the cap rests on its rim. This rule protects people and ceilings; it also suits the event, because a blunt nose makes a good seat for the payload.

Fins and attachments

Fins and other parts are attached to the bottle with tape only, and no glue of any kind may touch the bottle. Fins must start at least 5 cm above the level of the bottle opening. That bottom 5 cm is a no-fin zone so the neck can slide onto the launcher and the launcher's clamp or collar can reach it. Measure from the opening itself, not from the shoulder of the bottle.

No metal is allowed anywhere on the rocket or the payload system. That rules out staples, paper clips, wire, metal washers as nose weight, and metal-foil tapes. Mylar and ultrafilm (thin metallized or plastic films sold for model aircraft) are banned from both the rocket and the parachute. Common legal materials are corrugated plastic, foam board, cardstock, plastic sheet, packing tape, electrical tape and modeling clay for nose weight. If you are unsure about a material, ask before the tournament.

Energy source

All energy has to come from air pushed in by the pump through the launcher. Water is not allowed. Other gases, explosives, liquids, chemical reactions, pyrotechnics, electrical devices, elastic assists, throwing devices, remote controls and tethers are prohibited at all times. A rocket that violates any construction rule (3.a to 3.g) or the payload attachment rule (2.b) is not launched at all.

The parachute payload system

Each payload is one unaltered standard ping pong ball with a parachute attached by tape. Unaltered means you may not drill, fill, cut or paint the ball. A standard 40 mm ball has a mass of about 2.7 g, and that mass is fixed, so everything you control is in the parachute.

The parachute rules are short. Tape is the only allowed connection to the ball; the canopy must not contain Mylar or ultrafilm; and because metal is banned on the payload system, no wire hooks or metal swivels. There is no size or mass limit written for the parachute, so the practical limits are physics (a heavier chute falls faster unless it is also bigger) and packing (the chute must ride on or in the rocket and open after separation).

Light canopy materials include thin polyethylene film such as a produce bag or thin trash bag, and tissue paper. Polyethylene has a density of about 0.92 g/cm³, so a film 12 µm thick weighs about 0.92 × 12 ≈ 11 g per square meter. A 50 cm diameter circle of that film has an area of π × 0.25² = 0.196 m² and weighs only about 2.2 g. Tissue paper is about as light but porous, which lets air leak through and lowers its drag. Shroud lines of light thread, taped to the canopy edge and to the ball, finish the payload.

Physics of a launch

The flight has three stages: a very short powered phase on the launcher and just after it, a coast upward against gravity and drag, and the payload's descent under the parachute. Time aloft starts when the rocket leaves the launcher, so it includes the ascent, but most of it comes from the descent.

Pressure, gauge readings and force

The launcher's gauge reads gauge pressure, the amount above the surrounding air. Physics formulas for gases use absolute pressure:

The push on the rocket at the moment of release comes from the pressure difference acting over the nozzle opening. A first estimate of the starting thrust is that difference times the nozzle area. For compressed air rushing out of a nozzle the true value is somewhat higher, because the escaping air also carries momentum, but the simple product gives the right scale.

That huge force does not last. An air-only rocket carries very little propellant. Using the ideal gas law (ρ = p/RT with R = 287 J/(kg·K) for air at 293 K), 1 L of air at 60 psi gauge (74.7 psi or 515 kPa absolute) has a mass of only about 6.1 g, and roughly 1 to 2 g of it is still inside when the bottle has emptied to room pressure. Only a few grams of air are thrown out, and the thrust is gone within a fraction of a second. This is why air-only bottle rockets reach heights in the range of an indoor gym rather than the much greater heights of water rockets.

From pressure to height

After the thrust ends, the rocket coasts. Ignoring drag, a rocket that leaves its powered phase at speed v₀ rises to

The launch speed comes from the impulse of the escaping air (average force times the time it acts), divided by the rocket's mass: v₀ ≈ J ÷ m. Put that into the height formula and you get h ≈ J² ÷ (2 g m²), which leads to two useful conclusions:

• Height rises steeply with pressure. More pressure means more air mass, faster exhaust and longer thrust, so the impulse grows with pressure, and the height grows faster still. Your log will show this as a curve that climbs quickly.
• Rocket mass matters a lot. At a fixed impulse, height scales roughly with 1/m². Adding 10% to the rocket's mass costs about 17% of its no-drag height (1 ÷ 1.1² = 0.83). Extra mass is not always bad, though, because you will be throttling the rocket with pressure anyway; a heavier, sturdier rocket simply needs a little more pressure to reach the same height.

Do not try to predict your flight heights from first principles to the foot. The thrust phase depends on valve release, launcher friction and the gas cooling as it expands, and drag depends on fin and nose shape. Instead, use the physics to understand the trend and use your log to calibrate it. That is exactly what the rules ask you to do.

Stability on the way up

A rocket flies straight when its center of gravity (CG, the balance point) is ahead of its center of pressure (CP, the point where the overall aerodynamic force acts). If the rocket tilts, the aerodynamic force at the CP, being behind the CG, swings the tail back into line, the same way a weather vane points into the wind. Fins move the CP rearward; weight in the nose moves the CG forward. Model rocketeers aim for the CG to be about one to two body diameters ahead of the CP.

For this event a stable rocket matters for two reasons. An unstable rocket tumbles, losing height and possibly hitting walls or lights, and a wobbling rocket throws the payload off at an unpredictable time and angle. A simple check: tie a string around the rocket at its balance point and swing it in a circle. A stable rocket flies nose-first in the airflow; an unstable one tumbles or flies sideways. Remember the 5 cm no-fin zone above the opening when you place fins, and use clay rather than metal for nose weight.

Indoors there is little wind, so the main disturbances are the launch itself and drafts from vents. The rules encourage officials to reduce air flow, but they cannot remove it, so build a rocket that recovers from a small push.

Physics of the descent

Drag and terminal velocity

Once the payload separates and the parachute opens, the ball falls under two forces: its weight, pulling down, and drag, pushing up against the motion. At these speeds drag grows with the square of speed:

As the payload speeds up, drag grows until it equals the weight. From then on the payload falls at a steady terminal velocity:

For a flat circular canopy, published drag coefficients based on the flat area are roughly 0.75 to 0.8; a canopy that inflates into a dome can do a little better. A crumpled, half-open or spinning canopy does much worse, which is why deployment and stability matter as much as size.

The figure shows how a falling object approaches terminal velocity. A light parachute gets there quickly: the time scale is about v_t ÷ g, which is under a tenth of a second for a payload falling at 0.6 to 0.8 m/s. That is why descent time is close to height divided by terminal velocity once the canopy is open. The slow part in real flights is the canopy opening, not the speeding up.

How big should the canopy be?

Terminal velocity depends on the ratio m ÷ A. The ball's 2.7 g is fixed, but canopy mass grows with area. If the canopy material weighs σ grams per square meter, then the payload mass is about 2.7 g + σA (plus tape and lines), and

v_t² ∝ (2.7 g + σA) ÷ A = 2.7 g ÷ A + σ

As the canopy grows, the first term shrinks and the descent slows, but the improvement levels off: a giant canopy can never fall slower than its material alone would. With 11 g/m² film, going from 40 cm to 60 cm diameter helps a lot (the ball term drops by more than half), while going from 80 cm to 100 cm helps much less. The lighter your material, the larger the canopy worth building. Very large canopies have real costs: they are harder to pack, slower to open, more likely to tangle, and more likely to drift into a wall or catch on a light.

Stability under canopy

A canopy that swings back and forth or spins loses drag and time. Two common fixes are a small spill hole at the center of the canopy (a vent that lets air escape steadily instead of spilling from one edge at a time) and evenly spaced shroud lines of equal length. Lines roughly as long as the canopy's diameter are a common starting point; test shorter and longer. Keep the ball centered under the canopy and the tape joints symmetric.

Separation and deployment

The payload must separate from the rocket. If it does not, timing ends when any part of the rocket touches the ground, and that launch is multiplied by 0.90. Because a rocket falls much faster than a parachute, a stuck payload usually also means a short time, so the real loss is far bigger than 10%.

After you place the payload on or in the loaded rocket, nobody may touch it, and the rocket carries no electronics or timers. Separation therefore has to be passive, driven by the flight itself. Think through the forces at each stage:

1. Powered phase. The rocket accelerates upward hard, so the payload is pressed down onto the nose. Anything resting on top stays there.
2. Coast. Both the rocket and the payload slow down. The light payload, with its bundled canopy, has a larger drag-to-mass ratio than the rocket, so on its own it would slow faster. The rocket therefore keeps pushing it from below, and it stays seated.
3. Near the peak. The rocket's speed falls toward zero, it begins to tip over, and the push stops. A payload sitting loosely on top now slides or falls off, and air flowing past it starts pulling the canopy out.

Designs that work with this sequence include a payload sitting in a shallow cup or collar on the nose, a canopy loosely folded around the ball, or a short tube on top that the ball and folded canopy sit in, which empties once the rocket turns over. Designs that fight it include tight wraps that do not open, canopies packed so they catch air during the climb (which costs height and can pull the payload off early), and anything that could snag on fins.

Opening height matters as much as peak height. If the canopy needs a meter of free fall to open, that meter costs you about a second of descent time at 0.7 m/s (1.4 s of canopy descent replaced by roughly 0.45 s of free fall). Watch your test videos for where the canopy actually becomes fully open.

The practice log and choosing pressure

What the log must contain

At inspection you present a flight log from at least 10 test flights made before the competition. Each flight must record at least five parameters:

Then add at least two more parameters you choose. The rules give number of fins and parachute diameter as examples. Others that are useful: rocket mass, payload mass, canopy material, fold method, whether the payload separated, separation height, and ceiling height of the test site.

A log is incomplete if any flight is missing a required or chosen parameter, or if it has fewer than 10 flights. Every row needs every column filled.

Why the log controls your pressure

The log must justify the pressure you choose. Teams without a log, or with an incomplete one, may not pressurize beyond a safe pressure that the supervisor sets so that rockets will not reach the ceiling. That capped pressure is the same for every such team. On top of that cap, their score is multiplied: 0.70 with no log and 0.85 with an incomplete log. So a missing log costs twice: a lower pressure (less height and less time) and a multiplier.

Measuring height

Indoors, the simplest method is a wall with tape marks every foot, filmed from a distance so the camera sees the whole flight. Parallax is the main error: if the rocket flies a meter in front of the wall, it looks higher or lower depending on where the camera is. Film from as far back as you can, with the camera level and roughly at the mid-height of the flight.

The second method is an angle measurement. Stand a known distance from the launcher, sight the highest point with a clinometer (a phone app works), and use trigonometry:

Turning the log into a pressure choice

Plot estimated peak height (y-axis) against pressure (x-axis) for every flight of the same rocket. The points will scatter, but they show a trend. Then:

1. Mark the competition ceiling height, which tournaments announce in feet as early as they can.
2. Choose a target peak below the ceiling with a margin larger than your scatter. If flights at the same pressure vary by ±2 ft, a target only 1 ft below the ceiling will hit it often.
3. Read the pressure for that target off your trend, and check that you have actual flights near it. A pressure you never tested is hard to justify.

Because the gym you test in may be lower than the competition venue, include flights at several pressures. A log that only covers 20 to 30 psi cannot justify 50 psi on the day.

The competition

You arrive with eye protection on and rockets ready to inspect. The supervisor checks the rockets against the construction rules and checks your log. Then you have 5 minutes for two launches, which can use the same rocket twice or one of each.

For each launch:

1. Connect your pump (if you brought one) and load the rocket on the launcher. These connections are made before the timer starts.
2. With the rocket loaded but not yet pressurized, place the payload on or in the rocket. From then on it may not be touched.
3. Pump to your chosen pressure. The supervisor checks the gauge to confirm it matches the pressure your log supports.
4. When the supervisor confirms three timers are ready, a team member calls out a loud "3, 2, 1, LAUNCH!" and releases the rocket.
5. Recover the rocket and get ready for the second launch.

If a rocket will not hold pressure on one launcher, you may move to another launcher (if one is there) with the clock stopped. Launchers with slightly different connection widths, around 21.5 to 22.0 mm, are encouraged for exactly this reason. If a rocket fails to leave because of a problem with the supplied launcher, the launch did not happen and you may restart it.

Timing starts when the rocket separates from the launcher and stops when the payload lands. Each of the three timers records to hundredths of a second, and the middle value (the median) is official. All times are recorded because the second launch breaks ties. If you file an appeal, you must leave your rockets, payloads and log in the event area.

The ceiling rule

If any part of the rocket or payload touches the ceiling, or anything attached to it such as a rafter, light or basketball hoop, while going up, timing stops at the moment of contact and the launch is multiplied by 0.25. A ceiling hit therefore gives you a short time and then cuts it by three quarters. The rule names the ascent only.

Scoring

High score wins. Your rank comes from the greatest time aloft from a single launch, with any penalties applied to that launch. The other launch breaks ties: if two teams have the same best time, the team whose other launch was longer ranks higher. A team whose rocket cannot make any launch receives participation points only, and rockets or payloads that break the construction rules (3.a to 3.g) or the tape-only payload rule are not launched.

Estimating time aloft from your design

Putting the pieces together, a good flight's time is roughly the time to rise plus the time to fall from the separation height:

The best single launch counts, which changes the strategy. Fly the safe plan first. Once you have a good time on the board, the second launch can take more risk, because a bad second launch only weakens your tiebreak. A slightly higher pressure is reasonable on the second launch only if your log supports it.

Design and testing practice

Build two rockets, not one. The rules allow two, and a spare protects you against a leak, a crushed fin or a failed inspection. Make them as similar as you can so one log covers both, or log them separately and say which is which.

Change one variable at a time. A good test session fixes the rocket and pressure and varies only the canopy, or fixes the canopy and steps the pressure. Fly at least three flights per setting; a difference smaller than the scatter between repeats is not real.

Time the way the supervisor does. Use three timers and take the median. A large spread among your timers means your timing method needs work, not your rocket. A phone video at 30 or 60 frames per second gives times to about 0.02 to 0.03 s and settles disputes.

Record the test room. Ceiling height, drafts and whether vents were on all change results. A canopy that drifts into a wall in your gym may land cleanly in a larger venue.

Check the rules on every change. After repairs, look again for metal, glue on the bottle, fins within the 5 cm zone and the nose cap test. A rocket that fails inspection is not launched.

Protect the bottle. Store rockets so the bottle is not dented or creased, do not leave them in a hot car, and replace a bottle that has been damaged or has flown many times. A replacement must also be a carbonated-beverage bottle of 1 L or less, presented with its label.

Strategy: splitting work and preparing

One partner can own the rocket (bottle, nose, fins, stability, launcher fit) and the other the payload (canopy material, size, lines, fold, separation). Both should own the log and both should be ready to answer design questions, because the supervisor may ask either of you. Practice a short explanation of why your rocket is stable, why you chose your canopy size and how your log supports your pressure.

Rehearse the launch sequence until it is calm and quick. Five minutes covers two launches, recovery of the rocket after the first one, payload placement and pumping. Decide in advance who loads the rocket, who places the payload, who pumps and who calls the countdown. Pack spare payloads already folded and taped, since you may not adjust a payload once it is placed.

Before the tournament, find out the venue's ceiling height (it is supposed to be given in feet as early as possible) and pick your target pressure for each rocket from your log. Bring the log in a form that is easy to read, with all columns complete and the pressure-height trend visible, so the supervisor can see at a glance that your chosen pressure is justified.

Common disqualifications and penalties

• Wrong or damaged bottle. Non-carbonated bottles, bottles over 1 L, missing labels, and bottles that are cut, sanded, heated, glued or spray painted are not launched.
• Pointed nose. A nose that touches the inside top of a bottle cap fails the nose rule.
• Glue or metal. Any glue on the bottle, or any metal anywhere on the rocket or payload (staples, wire, foil tape, metal weights), fails inspection.
• Mylar or ultrafilm. Banned in the parachute and the rocket.
• Fins too low. Any fin or part within 5 cm of the bottle opening.
• Payload joined without tape. The parachute must be attached to the ball with tape only.
• Water or another energy source. Air from the pump through the launcher is the only legal energy.
• No eye protection. You must arrive ready to launch with Category B (Z87+) eye protection.
• Penalty multipliers. No separation × 0.90; incomplete log × 0.85; no log × 0.70; ceiling strike on the ascent × 0.25.

Common pitfalls

How tournaments test this

The site's archive and question bank contain no tagged written questions for Ping Pong Parachute, which fits the event: under the 2027 rules there is no written test. The event tests three things instead:

• Flight performance, through the time-aloft scoring and multipliers.
• Rules compliance, at inspection: bottle type and label, nose cap test, tape-only attachment, no glue on the bottle, no metal, no Mylar or ultrafilm, the 5 cm fin zone and air-only power.
• Understanding, through the design questions and the log. Supervisors may ask why your rocket is stable, how the payload separates, what limits your descent speed and how your data supports your pressure. Teams that can explain their trend line and their margin below the ceiling have the easiest time defending their pressure choice.

Test yourself

There are no archive questions for this event, so this section uses original practice questions written for this guide. They are not official tournament questions. Work them on paper before reading the answers.

1. A gauge reads 45 psi. What is the absolute pressure in psi and in kPa?
2. Estimate the starting force on a rocket with a 2.2 cm nozzle at 30 psi gauge.
3. A team's timers read 7.88 s, 8.21 s and 8.02 s. What is the official time?
4. A payload has a mass of 4.5 g, a canopy area of 0.20 m² and C_d = 0.8. What is its terminal velocity?
5. A log estimates a peak of 15 ft. Ignoring drag, what was the rocket's speed leaving the powered phase?
6. A team's best launch is 9.40 s, but its log has only 9 flights. What is its score?
7. True or false: a ceiling hit by the parachute on its way down receives the 0.25 multiplier under the 2027 rules.
8. Name three materials or items that would fail inspection even if the rocket flew well.

References and further reading

• Science Olympiad (soinc.org): the 2027 rules manual, the Ping Pong Parachute event page, the Building Policy and the eye protection policy.
• NASA Glenn Research Center, Beginner's Guide to Rockets: thrust, stability (center of gravity and center of pressure) and flight of model and bottle rockets.
• NASA Glenn Research Center, Drag Equation: the drag formula and the drag coefficient.
• NASA Glenn Research Center, Terminal Velocity: the balance of weight and drag.
• OpenStax University Physics, Volume 1: kinematics, Newton's laws, impulse and momentum, drag, and the ideal gas law.
• SciOly Wiki: community notes on past bottle rocket events. Use them for context; the 2027 rules manual is authoritative.