Wright Stuff

Wright Stuff is a Division C build event. Before the tournament, a team of up to two students builds a free-flight, rubber-powered Airplane, flies it in test sessions, records the data, and uses that data to tune the plane for the longest possible time aloft. On tournament day the team gets a single 10-minute Flight Period in an indoor space, makes up to two official flights, and is scored on the better one, multiplied by a bonus for a good Flight Log. There is no written test. The event is won at the building board and in the test hall.

The 2027 rules change what limits the plane's size. Instead of a wingspan or chord limit, the assembled plane has to fit inside a lidless Measurement Box whose outside dimensions are capped. Combined with a minimum airframe mass and a maximum motor mass, that box sets the whole design space. Everything below is written to the 2027 rules manual (Division C, Wright Stuff, sections 1 to 7); read those pages yourself before you build.

Event format

The 2027 event text does not name a calculator class, a notes allowance or an eye-protection category for Wright Stuff. The general rules and the eye-protection policy on soinc.org still apply to every event, so follow them and any instructions from your tournament.

What the rules cover

The table below paraphrases the 2027 construction and competition rules. The rules give one set of requirements for every level; tournaments differ only in the room they choose and the supervisor's decisions about practice flying.

The Measurement Box and flight configuration

The Measurement Box is the 2027 size limit, so design it before you design the plane. The box has no lid, and the limit applies to its outside: the whole box, including handles, latches, corner braces or anything else sticking out, must fit inside a 32.0 × 24.0 × 47.0 cm rectangular prism. The plane must then sit entirely inside the box while fully assembled. At check-in the supervisor measures the box and watches the plane go in. You may not bend, twist or squash the plane to make it fit; the only adjustment allowed is turning the propeller to a convenient angle. The supervisor can also ask you to slide the plane out and back in to show its shape does not change, and can ask you to repeat the fit check after your flights.

Wall thickness costs you interior space twice on the length and width (two walls each) but only once on the depth, because a lidless box has a floor and no top. Pick a thin, stiff wall material and work out the interior before you choose a wingspan.

The box shapes the airplane in a few concrete ways:

• Span versus length. The 47.0 cm side is the obvious place for the wing. The fuselage, the motor stick and the tail boom then have to fit in the other horizontal dimension or be angled. Many designs trade a little span for a longer tail moment, because a longer tail improves pitch stability (see the stability section).
• Dihedral and fin height. Dihedral raises the wing tips, and a vertical fin rises above the stabilizer. Both use depth. A plane whose tips rise 3 cm and whose fin stands 6 cm tall needs that height free above the floor of the box.
• Propeller diameter. The prop can be rotated, so a large prop can be turned to lie along a long axis, but its diameter still has to fit somewhere in the box with everything else.
• Orientation. The rules require the plane to fit fully but do not dictate how it lies. Placing the wing on a diagonal of the box would allow a longer span than the straight interior length.

The flight configuration rule is the second half of the size limit. Whatever goes into the box must be the plane that flies: same span, chord, length and lifting area, from the box to the floor. A wing that is removed for transport and refitted after check-in, or tip panels that clip on after measurement, would break the rule. The rubber motor is the exception: it does not have to be on the plane or wound when it goes in the box, which is convenient because the supervisor collects the motors at check-in anyway.

The physics of an indoor rubber-powered airplane

A Wright Stuff plane is an indoor duration model. The rubber motor turns the propeller for most of the flight, often for two minutes or more, so the plane is a slow powered flyer rather than a glider with a short boost. Four forces act on it, and most design work is about balancing them at the lowest possible power.

• Weight (W) pulls the plane down. With the 2027 minimum of 8.0 g for the airframe plus up to 1.5 g of rubber, a plane built to the minimum flies at about 9.5 g with a full-mass motor. The motor stays attached for the whole flight, so the flying mass does not drop as the rubber unwinds.
• Lift (L) is the upward force from the wing. It grows with wing area, air speed and angle of attack, and it comes from the wing turning the airflow downward.
• Thrust (T) comes from the propeller, which turns the motor's torque into a push.
• Drag (D) resists motion. At the very low speeds of indoor flight, most of it is induced drag from making lift, plus friction drag on the wing, tail and structure, and the propeller's own losses.

A flight is steady when lift balances weight and thrust balances drag. The motor's output is not steady, so a typical flight has three phases. In the climb, the high torque of a fully wound motor gives more thrust than drag and the plane gains height. In the cruise, torque settles to a slowly falling level, thrust roughly matches drag, and the plane circles slowly under power near its highest point. In the descent, the torque becomes too small to hold height and the plane sinks to the floor. A good indoor plane reaches the top of its climb just below the ceiling, then spends most of the motor run cruising, and lets down slowly at the end.

The example shows the central trade of the 2027 event. Because the airframe cannot go below 8.0 g, you cannot win by building lighter than everyone else. The levers left are wing area (limited by the box), the airfoil and its lift coefficient, the efficiency of the propeller, and how well you spend the fixed energy in a 1.5 g motor.

The airframe under an 8.0 g minimum

The airframe mass is measured at check-in without the motor, and it must be 8.0 g or more. The supervisor's scale may read slightly differently from yours, and the rules let you add ballast you brought (modeling clay, tape) to make up that difference. That leads to a simple plan: build the plane so it weighs just under 8.0 g on your own scale, then add a small piece of clay at a balance-neutral point so it reads a little over 8.0 g, and bring extra clay to the event.

Because the minimum is fixed, there is no prize for a frame lighter than 8.0 g. If your structure comes out at 6.5 g, you have 1.5 g of mass that will be added anyway, as ballast or as material. Material is usually the better use: thicker wing spars, a stiffer motor stick, a stronger tail boom or a tougher covering keep the wing from warping and the motor stick from bending under a fully wound motor. Ballast is dead weight that does no structural work, and placing it in the wrong spot shifts the balance.

Weight placed far from the balance point matters most. A heavy tail needs extra mass at the nose to balance it, and a heavy nose needs a longer tail to stay stable. Put structural mass where the plane needs strength (wing root, motor stick) and keep the tail light.

Wing area, aspect ratio and the airfoil

Within the box, a larger wing gives more lift at low speed and lowers the flying speed, which reduces power. Aspect ratio (span squared divided by area) also matters: a long, narrow wing makes less induced drag for the same lift. The box caps the span, so the remaining choice is chord. A wider chord adds area and lowers wing loading but lowers aspect ratio. Most indoor designs land somewhere in the middle and test both directions.

The airfoil changes the lift coefficient and how the wing behaves near stall. Thin, cambered airfoils are typical for slow indoor models because they make useful lift at small angles with little drag. Camber is the curve of the wing's mean line; a cambered wing lifts even at zero angle of attack.

Angle of attack and lift

When the wing meets the air at an angle, it deflects air downward, and the reaction to that downward push is lift. Lift rises with angle of attack until the flow separates from the upper surface and the wing stalls: lift drops and drag climbs. A slow indoor plane flies close to its best lift-to-drag angle, which sits below the stall, so trim that pushes it a little too nose-up will cost it far more than trim a little nose-down.

Stability on three axes

No one controls a free-flight plane once it leaves the hand (the rules ban steering of any kind), so it must be stable on its own.

• Pitch (nose up or down). Keep the center of gravity ahead of the neutral point, which is the aerodynamic center of the whole plane (wing plus tail). If a gust raises the nose, the stabilizer then makes a restoring force. A longer tail moment (distance from wing to stabilizer) gives more restoring force for the same stabilizer area, which is why many box-limited designs trade a bit of span for a longer boom. A tail-heavy plane stalls and loops; a nose-heavy plane dives.
• Roll (wings rocking). Dihedral, the upward angle of the wing panels, gives roll stability. When one wing drops, the plane slips toward it and the lower wing meets the air at a larger effective angle, makes more lift and rises. Remember that dihedral also takes up box depth.
• Yaw (nose left or right). The fin resists sideslip and keeps the nose pointed along the flight path. Indoor planes are deliberately trimmed to circle, so the fin size and any tilt set how tight that circle is.

Trim is the fine adjustment of incidence (the wing's angle to the fuselage), stabilizer tilt, and thrust line that sets the climb, the cruise and the circle. Changes are small, often a millimetre of shim or a fraction of a degree, and the plane's response is often larger than you expect.

Circling inside the announced room

The tournament announces the room's approximate length, width and ceiling height and any known air currents before the competition day. That information is a design input. An indoor plane flies in steady circles, so the circle has to fit inside the room's width with room to spare, and the climb has to top out under the ceiling. A flight ends the moment any part of the plane touches the floor, or when the plane lands on something (a girder, a basketball hoop, a light fixture) so that its wings no longer carry its weight. A plane that drifts into the bleachers or hangs on a beam is finished, however much motor it has left.

Circle size is set mainly by the rudder or fin offset, wing tilt and the motor's side thrust. A plane that circles left under power and a little tighter as the torque falls is the common indoor pattern, but test it: some designs circle right. Log the circle size you see in each test hall so you can predict how the plane will behave in a narrower room.

The propeller and thrust line

The propeller turns the motor's torque into thrust. The rules let you carve your own or buy a pre-assembled prop with shaft, hanger and thrust bearing, but any mechanism that actively changes the prop's diameter or blade angle during flight is banned. A fixed-pitch prop, or one whose blades are simply flexible, is the safe choice.

Pitch is the distance a blade would move forward in one turn if it were screwing through a solid. Diameter sets how much air the prop moves. A large, high-pitch prop takes a big bite of air each turn: it turns slowly, uses the motor's torque over a longer time, and usually suits a slow indoor plane, but it needs more torque to turn and must still fit in the box. A small prop spins faster for the same flight speed and usually wastes more energy in the slipstream.

The thrust line is the direction the prop pushes. If it points above or below the drag line, the plane pitches up or down under power. Downthrust (prop tilted slightly down) tames the steep climb of a fully wound motor; side thrust (prop tilted slightly to one side) shapes the circle under power. Both are adjusted at the prop hanger, and both belong in your log.

The rubber motor under a 1.5 g cap

The motor is a loop (or loops) of rubber strip, wound by turning it with a winder. Twisting stores elastic energy; the unwinding drives the prop. The 2027 cap of 1.5 g covers the whole motor or motor set, including O-rings or any other attachment, and it is checked separately from the airframe. Unlike the airframe minimum, there is no ballast fix for an overweight motor, so build every motor a little under the cap.

The stored energy of a motor is roughly proportional to the mass of rubber that is wound, at the same fraction of its breaking point, so the 1.5 g cap is an energy cap. The design question is how to spend that mass:

• A thicker, shorter motor gives high torque but takes fewer turns. It suits a larger, higher-pitch prop or a plane that needs a strong climb.
• A thinner, longer motor gives lower torque but takes many more turns, which stretches the motor run. It suits a plane that cruises at low power, but it may not turn a large prop fast enough.

Matching the motor to the prop is the main tuning job, and the right answer is found by testing, not guessing.

Turns, torque and a torque meter

Winding is done with a geared winder. Count winder cranks and multiply by the gear ratio to get motor turns. A torque meter (usually a torsion wire with a pointer and a dial) tells you how hard the motor is pulling. The rules let you record torque in arbitrary units if your meter is not calibrated, as long as you use the same meter every time.

Torque is a better guide than turns. Two motors from the same strip wound to the same turn count can give different torque because rubber varies and warms up with use. Many teams wind to a target torque, then let off ("back off") a set number of turns so the launch torque is just what the room's ceiling needs.

Six motors at check-in

You may check in up to six motors (or six sets for a multi-motor plane). The supervisor keeps them until your Flight Period begins, and you may lubricate them before or after check-in. Use the six slots to bring a spread: your main motor, a duplicate in case one breaks, and options for a lower or higher ceiling than expected. If you fly a multi-motor plane, keep each set together; motors cannot be moved between sets after they are massed.

Build quality

Design sets the plane's potential; construction decides how much of it shows up on the day.

Alignment. Wing, stabilizer and fin must sit square to each other and to the motor stick. A wing set a little crooked makes the plane circle in a way you did not intend, and a twisted stabilizer couples pitch and roll. Check alignment on a flat board before glue sets and again after.

Warps. Thin balsa and film covering move with humidity and after hard landings. Sight along each trailing edge before every flight. Some builders build in a deliberate washout (the tip's angle slightly less than the root's) on the inside wing to stop tip stalls in the circle; whatever you do, make it deliberate and record it.

Joints. Use as little glue as holds the joint, but make high-stress joints (wing mounts, the motor hook and the prop hanger) strong. A fully wound 1.5 g motor puts a large compressive load along the motor stick, and a stick that bows changes the thrust line and can fold.

Covering. Kits must not come pre-covered, so you will cover the frames yourself. A thin, tight, wrinkle-free covering keeps the airfoil true and adds little mass.

Testing and the Flight Log

The Flight Log is optional, but it is worth up to 20% of your score, which is more than most trim changes will ever gain. For the bonus, the log must show data for at least 10 test flights flown before the competition, with 6 or more parameters per flight. Three parameters are required:

1. The motor size before wind-up (for example its mass, length and width).
2. Either the number of turns at launch or the torque at launch.
3. The flight time.

You choose at least three more. The rules give examples such as turns left at landing, peak height (estimated or measured), torque at landing and prop pitch. Other strong choices are the backed-off turns, the room's ceiling height, circle diameter and the trim change made since the previous flight. Every number needs a unit, and putting the unit in the column header is enough. If your torque meter is uncalibrated, label the torque unit as arbitrary. The supervisor inspects the log at check-in and returns it; at the end of your time the supervisor reviews your recorded flight data with you.

A practical log is a table with one row per flight and one column per parameter, plus a notes column for what a number cannot capture: "climbed steeply, stalled once at the top", "circle drifted toward the wall", "motor broke at 1,600 turns".

(The rows above are illustrative, not measured data.)

Use the log to decide, not just to qualify for the bonus. For each setting, look at the mean and the spread of the flight times. A setting with a high mean and a small spread is the one you fly first.

Scoring and tiebreakers

Each official flight is timed from the moment the plane leaves your hand until it touches the floor, comes to rest on a structure, or the supervisor rules the flight over. Supervisors are encouraged to use three timers, and the median of the three times (at the precision of the devices) is the official time aloft, not the average.

Two scoring rules shape strategy. First, only the better flight counts, so once one good flight is on the board the second is a free attempt at a longer time; it can only raise your score, though it also sets your tiebreak. Second, rule violations are ranked, not just penalized: a team that breaks a construction or competition rule without a specific penalty is placed after every team that followed the rules, and a team that takes outside materials, help or communication into the cordoned flying area is ranked below all others.

The 10-minute Flight Period

Time management is the hidden skill in this event. At check-in the supervisor inspects your box and plane, has you take the plane out for massing, inspects the log and collects every motor. Your 10-minute Flight Period starts when the motors are handed back. Inside those 10 minutes you may install motors, wind, adjust, repair, make trim flights and make up to two official flights. Any flight launched before the 10 minutes run out may finish, but you get no extra time for recovering or fixing the plane.

Before every launch, tell the timers whether the flight is official or a trim flight. A flight you do not declare counts as official. Undeclared test hops can use up both official flights before you are ready.

Other competition details to know:

• Launch. You must stand on the floor and release the plane from your hand. Nothing may raise your launch height, and no steering is allowed after release.
• Collisions. If your plane hits another plane in the air, you may choose a re-flight after your plane lands. The re-flight is not limited by the 10-minute window. Timers may hold your launch to avoid a collision, so when official flights run at the same time, watch the air before you release.
• Practice flights. The supervisor decides before the first time slot whether official flights may overlap and whether practice flying is allowed during the event. Practice must yield to official flights, and there is no practice in the last half hour of the final period, though a team inside its own Flight Period can still make a declared trim flight.
• Cordoned area. Once you enter the flying area, no outside help, materials or communication (unless the supervisor allows materials), and only the two participants handle the plane until the event ends.
• After the flights. The supervisor may ask you to show that each plane still fits in its box in flight configuration (motor on or off) and may weigh it again.
• Appeals. If you plan to appeal, leave your planes, motors, boxes and log in the event area.

Competition-day routine

• Before you leave home: two planes, each checked in its Measurement Box; six labeled motors, each just under 1.5 g; lubricant; winder and torque meter; clay or tape ballast; the Flight Log with units in every column; repair kit (glue, spare prop, thin balsa); a stopwatch for your own reference.
• Self-check station: if the tournament offers one, use it. You can still fix the box or the plane before check-in.
• Check-in: present both planes in their boxes and the log. Teams from the same school may share a Measurement Box. Have ballast ready for the mass check. Hand over the motors.
• Flight Period: fly your plan. Declare every trim flight out loud. Bank a safe first official flight before trying anything bold.
• Know your plane. Under the Building Policy, either partner may be asked how the plane was designed, built and trimmed. Answer from the log.

Rules interpretation

Read the rules as two lists: the constraints that can sink a plane, and the choices you optimize. The constraints in 2027 are the box limit (outside dimensions and a fully assembled fit), the flight configuration rule, the 8.0 g airframe minimum, the 1.5 g motor maximum, wing-only lift, rubber-only power, the ban on actively variable props, the boron ban, the kit restrictions, the hand launch from the floor, and the no-steering rule. The choices are everything else: span, chord, airfoil, tail moment, dihedral, prop, motor size, turns and trim.

When a rule is unclear, read the whole section with its definitions, then check the official clarifications posted on soinc.org. If it is still unclear, ask your tournament's event supervisor before the event and keep the answer in writing. A plane designed around an untested reading of a rule should always have a conservative backup.

Common failure modes

Common pitfalls

How tournaments test this

Wright Stuff has no written test, and there are no archived Wright Stuff questions on this site. Your rank comes from your best official flight time multiplied by your Flight Log bonus, with the other official flight as the tiebreak, and from staying clear of rule violations that place a team below every compliant team. The supervisor will check three things in person: the box and the fit, the airframe mass, and the motor mass. Expect to be asked about the plane under the Building Policy and to go over your recorded data with the supervisor at the end of your time.

Spend your preparation on building to the box, testing and logging. Understanding each choice in terms of forces (why the wing has the area it has, why the plane balances where it does, why this motor goes with that prop) is what lets you read a flight and pick the right single change between flights.

Test yourself

No archived or bank questions exist for this build event, so there are no quiz blocks. Answer each prompt in one or two sentences, using the sections above:

1. Your box is built from 0.4 cm board to the full outside limit. What is the longest straight interior dimension, and why is depth reduced by only one wall?
2. Why does the 8.0 g airframe minimum make a 6.5 g structure plus 1.5 g of ballast a poor choice?
3. A 100 cm length of rubber weighs 0.90 g and your O-rings weigh 0.05 g. How long a strip gives a 1.45 g motor?
4. Your first official flight was 112.0 s and your log is complete. What is your score, and what time must the second flight beat to raise it?
5. Why is winding to a target torque more repeatable than winding to a target number of turns?
6. The announced ceiling is lower than your test hall's. Name two changes you could make, and how you would check them inside the Flight Period without using an official flight.

References and further reading

• Science Olympiad (soinc.org) - the 2027 Division C rules manual, official rules clarifications, the Building Policy, and the eye-protection policy.
• National Free Flight Society - the event's sponsor; indoor free-flight resources, rubber and prop information, and contacts for experienced indoor flyers.
• NASA Glenn Research Center: Beginner's Guide to Aerodynamics - lift, drag, thrust and weight explained for students.
• FAA Pilot's Handbook of Aeronautical Knowledge - wing geometry, stability on three axes and propeller basics.
• Related build guides on this site: Boomilever, Hovercraft, Ping Pong Parachute, Elastic Launch Glider.