Helicopter

Category: Technology & Engineering

Format: Build

Participants: 2

What It Is

Helicopter is a classic endurance flight event. Teams pre-design and construct rubber-band-powered free-flight helicopters and compete to achieve the maximum total time aloft across multiple flight attempts. The event rewards careful aerodynamic design, materials knowledge, and mechanical optimization.

What to Know

Aerodynamics & Flight:

• Rotor blade design: pitch (angle of attack), chord (width), span, planform shape
• Lift generation: how rotating blades create lift (similar to fixed-wing but rotational)
• Torque and counter-rotation: why model helicopters need a tail rotor or contra-rotating rotors to counteract main rotor torque
• Autorotation: after rubber band exhausts energy, the helicopter may glide/autorotate down
• Drag: minimizing parasitic drag on the fuselage and rotor hub

Rubber Band Motor:

• Energy storage: number of winds, rubber band cross-section, and length determine energy stored
• Rubber band materials: competition-grade rubber (FAI-spec) vs. standard rubber
• Winding technique: under-winding (safe), optimal wind, over-winding (risk of breakage)
• Torque curve: how torque varies across the unwind — high initial torque tapers off
• Lubricants: proper lubrication reduces internal friction, improves flight time

Structural Design:

• Materials: balsa wood (fuselage, rotor blades), carbon fiber, tissue paper covering
• Weight minimization: every gram counts — lighter = longer flight
• Rotor hub mechanics: bearing quality, shaft alignment
• Durability: must survive transport and multiple flights

Key Formulas:

• Tip speed ratio, figure of merit (rotor efficiency)
• Rubber band energy: approximately proportional to number of turns × rubber stiffness

Competition Format

Teams launch their helicopter(s) in a designated flying area (gymnasium or outdoor space). Each team gets multiple flight attempts; total time aloft across scored flights determines the score. Timers start at launch and stop when the helicopter lands or touches a wall/ceiling. Rules specify maximum rotor diameter, maximum rubber band mass, and other construction limits.

Notes

• Bring multiple helicopters — crashes happen and spares are essential.
• Practice winding is critical: know exactly how many winds your helicopter's rubber band can handle safely.
• Indoor vs. outdoor flying areas have different air currents — practice in similar conditions.
• Temperature and humidity affect rubber band performance; adjust winding accordingly.
• Rotor blade pitch is one of the highest-impact tuning variables — even small pitch adjustments significantly change flight time.
• Trim the helicopter so it rises in a stable spiral; an unstable climb wastes energy.