Flight Phase (Aerial Phase)

The part of a gait where every foot is off the ground at once and the body is airborne.

Legged locomotion breaks down over time into phases: a foot bearing weight on the ground is in stance phase, a foot swinging through the air is in swing phase, and if there's a stretch where no foot touches the ground at all, that's the flight phase. It's the key distinction between walking and running: in walking, at least one foot is on the ground at all times, while running includes a flight phase. For a robot, gravity is the only force acting during flight, so the center of mass follows a parabolic arc, and the controller can no longer use ground forces to change the robot's overall momentum — it can only adjust leg posture to prepare for landing, and must then absorb an impact the instant it touches down, which is why running, jumping, and parkour are so much harder than walking. Raibert's hopping robots split each cycle into a stance phase and a flight phase with separate control, choosing a foot placement by swinging the leg during flight; quadruped bounding and galloping gaits, and humanoid running and flips, all include a flight phase.

ExampleIn a humanoid robot's jog, the brief moment after one foot pushes off the ground and before the other foot lands is the flight phase — the only thing the policy can do during it is adjust the swinging leg's posture to prepare for the next landing.

Also called

Aerial Phase, Flight Period

Related

Stance Phase / Swing Phase · Gait · Gait Cycle and Duty Factor · Spring-Loaded Inverted Pendulum · Bound Gait · Gallop Gait

Sources

Running - Wikipedia
Legged robot - Wikipedia