Helicopter

Overview

Indoor helicopters seek maximum duration via efficient rotor aerodynamics, tuned rubber motors, and meticulous trimming.

Rotor aerodynamics (qualitative)

• Lift and drag: lift ∝ velocity² and blade area; induced drag rises with lift; profile drag rises with speed and angle of attack (AoA).
• Pitch and washout: set AoA for low Reynolds numbers; add washout (lower AoA near tips) to mitigate tip stall and improve efficiency.
• Planform: larger disk area lowers induced power; weight and structural stiffness limit radius.

Rubber motor tuning

• Torque–turns curve: high torque initially, decays as unwinding; match rotor load to torque profile for steady climb and slow descent.
• Lubrication and braiding: reduce hysteresis; store energy safely; track maximum safe winds.
• Motor selection: length, width, and density; batch variability requires testing; record temperature/humidity.

Trimming and flight strategy

• Climb phase: manage torque burst to avoid ceiling bumps; reduce pitch or turns to moderate initial climb.
• Cruise/descend: aim for slow, stable rotation without stall; lateral stability via slight tilt or fin/rudder if allowed.
• Ceiling interactions: plan for controlled brushes if venue permits; otherwise reduce initial torque to avoid contact.

Structure and mass

• Keep center of gravity aligned; minimize parasitic mass; ensure straight shafts/booms; balance blades to reduce vibration.
• Joints: cyanoacrylate with reinforcements at high‑stress points; avoid warps.

Calibration and logs

• Flight logs: winds at launch, peak height, duration, ceiling contacts; motor logs: length, mass, max winds, wind‑down profiles.
• Environmental conditions: temperature/humidity influence rubber and air density; adjust wind counts accordingly.

Worked micro‑examples

1. Disk loading

• For constant mass, increasing rotor radius reduces disk loading (W/Area), improving duration until structural/venue limits.

2. Torque matching

• If initial climb is excessive, reduce initial winds by 10–15% or lower pitch by ~0.5–1°; verify with climb rate logs.

3. Washout effect

• Introducing 2–3° washout at tips reduces stall and improves late‑flight stability; observe smoother descent.

Pitfalls

• Excess pitch causing tip stall; unbalanced blades inducing wobble and energy loss.
• Over‑winding beyond safe turns; failing to re‑lube consistently.
• Inconsistent launch techniques; poor documentation.

Practice prompts

• Design a test plan to select motor dimensions for a given rotor load; include log templates.
• Measure and adjust blade pitch/washout with simple jigs; correlate with duration changes.
• Plan a torque‑matching strategy across low/medium/high ceilings.

References

• SciOly Wiki – Helicopters: https://scioly.org/wiki/index.php/Helicopters