Definition
A crosswind control input in which the pilot turns the control yoke or stick toward the wind, raising the aileron on the upwind wing and lowering the aileron on the downwind wing. This input counteracts the wind's tendency to lift the upwind wing and roll the airplane during ground roll and the early stages of takeoff in a crosswind.
Plain English
Turning the yoke into the wind during a crosswind takeoff so the wing facing the wind doesn't get lifted up. The aileron on that wing tips upward, which helps hold the wing down on the runway.
Context Anchor
Used during crosswind takeoffs and landings, especially while the airplane is still rolling on the runway and the wind can lift one wing more than the other.
Derivation
"Upwind" means the side facing into the wind. "Aileron" comes from the French for "little wing," referring to the hinged control surface on the trailing edge of each wing. "Deflection" simply means moving a control surface away from its neutral position. Together: tilting the control surface on the wind-facing wing to resist the wind's lifting effect.
Why Pilots Care
Keeps the wings level and maintains directional control when a crosswind tries to lift the upwind wing.
Grounding Statement
Picture a wind gust trying to raise the wing on the windward side; upwind aileron deflection is the control input that helps hold that wing down.
Intuition Check
Do not read “upwind” as meaning the airplane is climbing or moving upward. Here it means the side the wind is coming from, and the aileron input is made toward that side.
Example Sentence 1
With a strong crosswind from the right, the pilot held full upwind aileron deflection at the start of the takeoff roll and slowly reduced it as the airplane gained speed.
Example Sentence 2
As airspeed builds the pilot gradually reduces upwind aileron deflection to prevent overbanking once the wings begin to fly.