field guide
Quadcopter Flight Physics Overview
The fundamental physics of quadcopter flight - forces, stability, and the torque and yaw control principles that control theory and simulation build on.
Fundamental physics of quadcopter flight covering the forces, stability mechanisms, and control principles behind multirotor operation. Introductory-level but provides the physical intuition that control theory and simulation build on.
Core forces
| Force | Direction | Cause |
|---|---|---|
| Lift/Thrust | Upward (perpendicular to rotor plane) | Propellers push air down → equal/opposite reaction upward (Newton’s Third Law) |
| Weight | Downward | Fg = mg, gravitational pull on drone mass |
| Drag | Opposite to motion | Air resistance proportional to velocity and cross-section |
Equilibrium conditions
Hover (static equilibrium): Lift = Weight. All forces balanced, no net acceleration. Propulsion force is purely vertical.
Forward flight at constant velocity (dynamic equilibrium): Propulsion force tilted forward. Vertical component balances weight; horizontal component counteracts drag. No net force.
Accelerating forward: Horizontal propulsion component exceeds drag → net force → acceleration according to F = ma.
Torque-based yaw control
Each spinning propeller generates reaction torque. Adjacent propellers rotate in opposite directions (CW and CCW) to cancel torque: - Balanced speeds → net torque = 0 → no yaw - Speed up CW pair, slow down CCW pair → net torque in desired direction → yaw
Wake turbulence
Propellers generate spiraling airflow that interferes with nearby objects or other drones. Factors: propeller size/shape, rotational speed, air density, environment. Critical for swarm operations and close-proximity flight. Managed via CFD simulation (ANSYS) for propeller design optimization.
Stability mechanisms
Gyroscopes detect orientation changes; accelerometers detect motion. The flight controller adjusts individual motor speeds to maintain balance — this is the hardware layer that complementary-filter operates on, fusing gyro and accel data into usable attitude estimates.
See also
- complementary-filter — Sensor fusion for attitude estimation (the algorithm)
- accel-roll-pitch-derivation — How accelerometer readings become roll/pitch angles
- thrust-vector-from-attitude — Converting attitude to thrust components
- rotating-coordinate-frames — Body vs. inertial frame kinematics
- torque-yaw-control — Agent note on torque-based yaw