Definition
In the context of gyroscopic precession, the reaction of a spinning rotor (such as a propeller or rotor disc) to an applied force, where the effect appears not at the point the force was applied, but 90 degrees ahead in the direction of rotation. The 'resultant action' is the actual response that occurs after this 90-degree shift.
Plain English
When you push on a spinning object like a propeller, it doesn't react where you pushed it. The reaction shows up a quarter-turn later in the spin. That delayed, shifted reaction is the resultant action.
Context Anchor
Seen in discussions of gyroscopic precession, especially when explaining why a propeller-driven airplane may try to swing its nose left or right during pitch changes.
Derivation
Resultant' comes from Latin resultare, meaning 'to spring back' or 'to result from.' Here it means the action that ultimately results from a force, after the gyroscopic shift has been applied — not the immediate reaction you might expect.
Why Pilots Care
It explains the unexpected yaw that occurs when raising the tail on takeoff or changing pitch attitude, requiring rudder correction to maintain directional control.
Analogy
A spinning bicycle wheel can feel like it reacts in an unexpected direction when you try to tilt it. The push is applied in one place, but the strongest effect seems to show up around the wheel from where you pushed.
Grounding Statement
Picture the propeller as a fast-spinning disk: a push on one part of that disk produces its main effect about a quarter turn later.
Intuition Check
Do not read “resultant action” as simply “whatever happens next.” In this context, it means the specific 90-degrees-ahead effect caused by applying force to a spinning object.
Example Sentence 1
When the pilot pushed the stick forward to raise the tail, the resultant action from gyroscopic precession was a yaw to the left.
Example Sentence 2
The pilot applies right rudder to counteract the resultant action when raising the nose during a go-around.