Helicopter

Helicopter is a build, test and fly event. Each team builds up to two rubber-powered, free-flight helicopters, tunes them with test flights, records the data, and then flies for as long as it can during a 10-minute flight period. Your score is your best official flight time multiplied by bonuses for a complete flight log and for two-bladed rotors. The best teams are not simply the ones whose helicopter stays up longest. They are the ones whose builders can explain why the rotor makes lift, how the rubber motor delivers its torque, and what their test data show.

Event format

The competition area is cordoned off once you enter it. From then on you may not receive outside materials, help or communication, and only participants may handle the helicopters until the event ends. Spectators wait in a separate area.

What the rules cover

This guide follows the 2026 Division B and Division C manuals (2025-26 season), the most recent ones for this event. They have the same sections, and the text is the same in substance. You do not need separate study tracks for the two divisions. Neither manual marks any item as State & National only. The table below summarizes each section. Read the manual's own section numbers (cited in the first column) when you need the exact wording.

The manual is about building, testing, flying and explaining. It does not ask for the history of aviation or for memorized aircraft specifications. Its one knowledge requirement is in section 3.h: you must be able to answer questions about design, construction and operation, with reference to the Building Policy on soinc.org. In practice that means you must understand every choice you made on the helicopter.

The physics of a rotor

A helicopter rotor is a set of rotating wings. Almost every idea in this event comes back to three quantities: how much air the rotor pushes, how fast it moves that air, and how much energy the motor spends doing it. The sections below build those ideas in order.

Lift is a pressure difference that grows with speed squared

A rotor blade is an airfoil: a shape with a curved upper surface, a leading edge that meets the air first, and a trailing edge where the flow leaves. The straight line from leading edge to trailing edge is the chord. The angle between the chord and the oncoming air is the angle of attack (AoA). A cambered (curved) blade at a small positive AoA deflects the air downward, and the pressure under the blade ends up higher than the pressure above it. That pressure difference, acting over the blade's area, is the lift.

Two explanations describe the same effect. Bernoulli's principle connects faster flow over the top surface with lower pressure there. Newton's third law connects the downward push on the air with an upward push on the blade. Use the lift equation to do calculations:

Two consequences matter most. First, lift grows with the square of speed, so doubling the blade's speed quadruples its lift. Second, the speed of a blade section depends on its distance from the hub. A point at radius $r$ on a rotor turning at angular speed $\omega$ moves at $\omega r$, so the outer part of the blade (the tip region) does most of the lifting and sets the tip speed limit.

This gives the central cause-and-effect chain of the event:

↑ motor torque → ↑ rotor angular speed → ↑ blade speed (ωr) → ↑ lift (∝ v²)

When the motor unwinds, its torque falls, the rotor slows, lift falls, and the helicopter sinks. Every tuning decision you make is a decision about where on this chain you want the helicopter to be at each second of the flight.

Angle of attack controls the lift coefficient only up to a point. As AoA rises, the air eventually separates from the upper surface. This is stall: lift drops sharply and drag rises. Small rotors fly at low speeds where air is more easily disturbed, so a blade that stalls near its tip costs lift exactly where lift is most effective. The standard remedy is washout, a gradual twist that makes the tip's AoA lower than the root's. Washout keeps the tip flying clear of stall at the cost of a little lift near the hub. Figure 1 labels the parts of an airfoil, and Figure 2 shows lift and drag relative to the oncoming air.

Disk size and hover power

In hover, the rotor must produce a thrust $T$ equal to the helicopter's weight $W$. The rotor does that by accelerating a column of air downward through its disk, the circle swept by the blades. Momentum theory gives the power needed for that thrust in the ideal case. The formula below is the lower limit on induced power, the power spent pushing air down. Real helicopters also spend power on blade drag, so the true number is higher, but the trends hold.

The formula says three things. For a fixed weight, the power falls as the disk area grows, because a larger disk moves more air more gently. The power rises steeply with weight, because $T^{3/2}$ grows faster than $T$. And denser air helps, because it carries more mass through the same disk, so the air needs to be pushed less hard for the same thrust. Designers use disk loading, $W/A_{disk}$, as the summary measure: lower disk loading means less power per gram.

Two practical limits stop you from simply making the rotor as large as possible. The first is the box. Your helicopter must fit into a measurement box no bigger than 32.0 cm × 24.0 cm × 47.0 cm, counting protrusions, and the rules control what can change after the helicopter leaves that box. The second is structure: a longer blade bends more under load and changes its shape in flight. The flight-configuration rule helps with the box. Parts that rotate in flight may be turned to fit the box, but chord, span, length and total lifting area may not change after the helicopter leaves it. So you can turn a rotor so its blades lie along the box's longest dimension at check-in, but you cannot fold, bend or collapse a blade. The helicopter must be assembled and ready to fly in that box, although the rubber motors need not be installed or wound.

Energy budget: flight time is stored energy divided by power

Flight time is an energy budget problem. The motor stores energy when you wind it. The helicopter spends that energy at a rate equal to the power the rotor and airframe require. If the average power is $\bar{P}$ and the stored energy is $E$:

This is why the event rewards both sides of the budget. A team can store more energy, with a longer or wider motor and more turns within the safe limit. A team can also spend less power, with a larger rotor disk, less weight, a cleaner airframe and blades that stall late. A good design balances the two. The mass floor in section 3.g applies to the airframe alone, excluding the rubber motors. A heavier motor therefore does not violate the mass rule, but its weight is still in the helicopter for every second of the flight.

Rubber motors: storing and releasing energy

A rubber motor is a bundle of elastic strands that you twist, or wind, with a winding tool. Winding stores elastic energy, and the motor turns the rotor as it unwinds. The energy you store is the work you do while winding, which is approximately the area under the torque-turns curve. Some of that work comes back as heat when the strands flex, so the energy released is a little less than the energy stored.

Torque is not constant. A wound motor delivers its highest torque at the start and the torque falls as it unwinds. The shape of that curve, not just its total energy, decides how the helicopter climbs and descends. A steep early torque produces a fast, high climb that can strike the ceiling. A torque that falls too quickly leaves the rotor too slow to sustain lift and the helicopter sinks early. Matching the motor's torque profile to the rotor's load is the core motor-tuning task.

Several practical factors govern the motor.

• Lubrication. Lubricant reduces friction between the strands, so less of the stored energy is wasted as the strands rub. The manual does not specify a lubricant, so test any product you use and record it in your log.
• Safe turns. Overwinding can break strands, and a broken motor ends the flight. Find the maximum safe number of turns for each motor size, and record it.
• Temperature and age. Rubber stiffens or softens with temperature and changes as it ages. Record the room temperature and humidity during tests, since you cannot control them at the tournament.
• Batch variability. Two motors from the same package can differ. Test each batch before the tournament and keep your best motors matched to your best flights.
• Timing of winding. The Event Supervisor returns the motors to your team at the start of your flight period, so you cannot pre-wind for your official flights. Plan your winding routine in advance and practice it.

Stability, trim and the ceiling

You cannot steer the helicopter after release (section 4.e.ix, and section 7.f defines steering), so its stability must come from the design. A helicopter that flies in a predictable way, with a steady climb and a slow descent, is a product of four choices. Keep the center of gravity on the rotor axis, so the helicopter does not tilt. Balance the blades, because an unbalanced rotor wobbles and wastes energy. Keep shafts and booms straight, because a bent part changes the lift on each side. Set blade pitch and washout so that no part of the rotor stalls during the long, slow part of the flight.

The trim flight is the event's tuning tool. Section 4.e.iv requires you to tell the timers before each launch whether the flight is official or trim, and a flight you do not announce counts as official. Trim flights are practice and do not score. Use them to find the torque profile that gives you a steady climb, to measure how far the helicopter drifts in the room's air currents, and to test your winding routine under time pressure.

The ceiling is part of the flight. Section 3.b requires a flat balsa disc at the uppermost point, large enough to cover a dime, with its face being the part that contacts the ceiling. The rule fixes which part touches first, so every helicopter meets the ceiling in the same way. A flight also ends the moment the helicopter lands on a girder or a basketball hoop, or any time the lifting surfaces stop supporting its weight. Use the room announcement (section 4.a) to choose a torque profile. In a low room, you want an early climb that is gentle, so the helicopter does not strike the ceiling and spend its energy on a bounce. In a tall room, you can use more torque early, but a strong early climb uses energy that the rotor could have spent on flight time.

Flight rules that cost points

Most rule violations in this event are about the flight period, not the design. The points below are the ones teams most often lose.

• Build limits. Kits may not contain pre-glued joints or pre-covered surfaces, and boron filaments are banned (sections 3.a and 3.c). Only the rotors may lift: no wings or any other lifting surface (section 3.f). A blade is a single surface that spans no more than 90 degrees around the axis (section 7.d). At check-in you take the helicopter out of the box so its mass can be measured, and the motors are collected until your flight period starts (section 4.d).
• Fit and configuration. The helicopter must fit in its box with the lid off, and its dimensions cannot change after it leaves the box. The Event Supervisor can ask you to show the fit on request (section 4.f), so check it before every flight. Use the optional self-check station if your venue has one (section 4.c).
• Steering. You may not steer a helicopter once it is released. The manual's definition of steering is broad: anything used to control direction after release counts, including balloons, poles, rods and air. What you set before the release is your launch, not steering.
• Launch. The student releasing a helicopter by hand has to be standing on the floor, and no device such as a stand, a chair or a ladder may raise the launch point (section 4.e.x).
• Outside help. After you enter the competition area, outside materials, help and communication are not allowed. Teams that break this rule are ranked below all other teams (section 4.b.ii), which is worse than any penalty in the scoring section.
• Collisions. If another helicopter collides with yours, you may elect a re-flight after landing. Timers can delay a launch to avoid a collision, and the 10-minute flight period does not apply to that re-flight (section 4.e.xi).
• Appeals. A team filing an appeal must leave its helicopters, measurement boxes and Flight Log in the event area (section 4.h).

The time-aloft rule is worth reading closely. Time starts when the helicopter leaves your hand. It stops when any part touches the floor, when the lifting surfaces stop supporting the helicopter, or when the Event Supervisor decides the flight is over (section 4.e.vii). The manual strongly encourages three timers, and the official time is the median of their readings (section 4.e.viii).

Scoring and the flight log

Scoring has three steps. Each official flight gets a flight score, your final score is the larger of your flight scores, and ties are broken by a separate rule.

The two multipliers stack. The largest possible multiplier is $1.2 \times 1.1 = 1.32$. The manual's own example uses this stacking: a flight of 68.00 s with a complete log and two-bladed rotors scores $68.00 \times 1.2 \times 1.1 = 89.76$ points (section 6.c.v).

The Flight Log is inspected at check-in and returned to you afterward. Every numeric entry needs units, though torque may use "arbitrary" units if your torque meter is uncalibrated (section 5.b).

Is the flight log worth the work? It is worth 20% of your score, so a team with a complete log can fly 16.7% less than a team with no log and still tie. The log's real value goes beyond the multiplier, though: the 10 or more test flights it requires before the event, since those flights tune the helicopter. Section 5.a requires at least six parameters, three of them required: motor size before winding, turns or torque at launch, and flight time. The other three are your choice. The manual's examples include turns remaining at landing, an estimated or recorded peak altitude, torque at landing and propeller pitch.

Two-bladed rotors. Using two blades instead of three is worth a 10% bonus. A two-bladed design only pays if it flies at least $1/1.1 = 91\%$ as long as a three-bladed design. Work it out for your own design. If a three-bladed helicopter flies 80.00 s with a complete log, its score is $80.00 \times 1.2 = 96.00$. A two-bladed helicopter with a complete log must fly at least $96.00 / (1.2 \times 1.1) = 72.73$ s to match it.

Ties. Section 6.e breaks a tie using the longest official Flight Score that was not your final score. The manual says Flight Score, so the comparison uses the multiplied score, not the raw time. A strong second flight can therefore decide a tie.

Penalties. A rule violation with no specific penalty ranks your team after every team that did not violate the construction or competition rules (section 6.d). Treat such a violation as a serious problem, even though the manual does not assign a points value.

Strategy

Split the work by system, then teach each other. One partner usually owns the airframe, including the balsa disc, the box fit, the mass check and the rotor geometry. The other owns the motors, the winding routine, the timing and the Flight Log. Both partners must answer design questions (section 3.h), so every week run a short interview in which each partner explains the other's design in two sentences.

Plan the test program early. The Flight Log requires data from at least 10 test flights before the event. Schedule them in the weeks before the tournament, and record every flight, including failures. A test program that changes one variable at a time gives you data a judge can follow. Changing blade pitch, motor size and wind count on the same day gives you data nobody can use.

Use trim flights, save official flights. You may make up to two official flights, using one or two helicopters. Your final score is the better of those two flights, so a second official flight can raise your score and never lower it. Use trim flights for exploration, and reserve the official flights for the configurations you expect to beat your best test flight. An official flight that you fly to test a new idea wastes one of two chances.

Plan the 10 minutes. The flight period starts when the motors come back. Before you check in, decide the order of your official and trim flights, the winding routine, and the moment you will stop. Keep a spare helicopter ready, but remember that every flight you declare official uses one of your two official slots, whichever helicopter flies it. Repairs and adjustments are allowed during your flight period, but teams are not given extra time to recover a helicopter.

Read the room. The manual requires the room's approximate dimensions and any known air currents to be announced before the event (section 4.a). Use the announcement to choose the torque profile for that ceiling height and air movement. If the room has air currents, a light, slow helicopter can drift into a corner in one flight. Test in a similar room if you can, and log the drift.

Prepare for check-in. Practice fitting your helicopter into its box with the lid off, and practice removing it without changing its shape. Confirm the box's external dimensions against section 3.d before you travel. Bring the Flight Log to check-in, since it is inspected there.

Common pitfalls

How tournaments test this

The question bank holds a small sample of Helicopter questions, and the public archive currently holds none. The numbers below come from the bank only, so read them as a rough profile, not a forecast.

Two patterns stand out. Most questions are free response, so a term alone is rarely enough: the grader rewards a sentence that explains why. The task profile backs this up, with 2 of 9 questions asking you to explain or give a reason, one asking for a calculation and one asking you to pick the correct statement from a list. The remaining five did not match any of the task types the tagger recognizes. Only one bank question asks for a formula rather than a number, and it is the lift question whose key drops the one-half factor (see the pitfalls). No question in the bank asks you to calculate a flight score.

The main test of this event happens in the room, not on paper. Section 3.h says you must answer questions about your design, construction and operation. Section 4.g says the Event Supervisor will review your data with you at the end of your event time. The manual does not attach points to this review, but Section 3.h and the Building Policy require you to answer questions about your device, so be ready to explain every number in your log. Prepare for that review by writing a one-page summary of your best flight, the motor, the turns, the flight time and the conditions, and rehearsing how you would defend each number.

Preparation that follows from this profile is straightforward. Learn the vocabulary of aerodynamics well enough to define it in one sentence: airfoil, chord, angle of attack, stall, lift, drag, disk loading. Be able to state the lift equation and say what each variable does. Practice the scoring arithmetic until you can do it in your head. Then practice the explanations, because that is what the event asks for.

Test yourself

The archive has no Helicopter tests yet, so these three questions come from the question bank. Three other bank questions were left out after review: one lists the same answer twice among its options, one lift-formula key omits the one-half factor, and one asks which vehicle uses Bernoulli's principle "most", which is a matter of opinion. The practice problems below cover the arithmetic the bank does not test.

Test yourselfTest yourself: aerodynamics and air

0 / 0 correct

1. 1

   What is the study of the properties of air and how it moves around objects?

   Show answer

   From: Rickards Science Olympiad Invitational 2022, Division B

References and further reading

• Science Olympiad, Division B and Division C Helicopter event rules, 2026 manuals, on soinc.org. The event pages and the Science Olympiad Store list the current resources and the Building Policy.
• NASA Glenn Research Center, Beginner's Guide to Aeronautics, for lift, angle of attack and stall.
• Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge, for airfoil terms and the forces on a rotating wing.
• OpenStax, University Physics Volume 1, for fluid flow, Bernoulli's principle and the lift and density relationships used here.
• SciOly Wiki, Helicopters. Read it for context; this guide does not reproduce it.