Definition
The angular movement of the rudder away from its neutral (streamlined) position, produced by pilot input on the rudder pedals. Rudder deflection creates a sideways aerodynamic force on the vertical tail, which yaws the airplane around its vertical axis. The amount of deflection is limited by mechanical stops and, at low airspeeds, by how much pedal force the pilot can apply.
Plain English
How far the rudder is moved left or right from its straight-back position when the pilot presses a rudder pedal. The more the rudder is moved, the stronger the sideways push on the tail that swings the nose left or right.
Context Anchor
Seen in discussions of engine-inoperative flight in multiengine airplanes, where the pilot may need rudder deflection to keep the airplane’s nose from turning toward the failed engine.
Derivation
‘Rudder’ comes from Old English rōther, meaning a steering oar on a boat. ‘Deflection’ comes from Latin deflectere, ‘to bend away.’ Together the term literally means ‘bending the steering surface away from straight,’ which is exactly what the pilot does with the pedals.
Why Pilots Care
The amount of rudder deflection available directly determines whether directional control can be maintained at low airspeeds after an engine failure.
Grounding Statement
Picture the rudder centered, then moved left or right; the amount it moves is the rudder deflection.
Intuition Check
Do not read “deflection” as the rudder being bent or damaged. Here it means the rudder’s normal movement away from center.
Example Sentence 1
As airspeed decreased toward VMC, full rudder deflection was required to keep the nose aligned with the runway heading.
Example Sentence 2
Above VMC, less rudder deflection is needed because higher airspeed produces greater rudder effectiveness.