Definition
The reduction in rudder effectiveness during a crosswind landing rollout caused by the upwind wing being lowered, which places the fuselage between the rudder and the relative wind. With the fuselage shielding the rudder from the crosswind, the rudder loses some of its ability to keep the airplane aligned with the runway centerline.
Plain English
When you lower a wing into the wind during landing rollout, the body of the airplane partly shields the tail from the crosswind. That makes the rudder less able to keep the nose pointed straight down the runway.
Context Anchor
Seen during crosswind taxi, takeoff, landing, and landing rollout when the pilot is using aileron into the wind.
Derivation
From 'block,' meaning to obstruct or get in the way of. Here, the fuselage gets in the way of the wind reaching the rudder.
Why Pilots Care
Reduces rudder effectiveness, requiring pilots to use proper crosswind technique such as the wing-low method to maintain directional control.
Intuition Check
Blocking effect does not mean the airplane stops the wind completely. It means one part of the airplane shields another part enough to make the wind forces uneven.
Example Sentence 1
As the upwind wing was lowered during the crosswind rollout, the pilot anticipated the blocking effect and applied additional rudder to hold the centerline.
Example Sentence 2
During the takeoff roll the pilot anticipated the blocking effect and applied extra rudder as the nose came up.