has been variously defined as yaw opposite the direction of turn, or yaw opposite the direction of roll. ### Aileron Deflection When rolling into or out of a turn, the downward deflected aileron increases the effective camber of that wing section, increasing lift and increasing drag. The increased drag results in yaw opposite the direction of the roll. ### Change in Relative Wind When Rolling Lift is always defined as being perpendicular to the relative wind. As the airplane rolls, the down-going wing experiences a change in relative wind that tilts the lift vector forward. The up-going wing experiences a change in relative wind that tilts the lift vector rearward. The changes in lift vectors result in yaw opposite the direction of the roll. Additionally, this results in a change in wing angle of attack that resists rolling moments and contributes to lateral stability. ![[A4NA adverse yaw.png]] ### Wing Speed Differential During a turn, the outer wing travels a greater distance than the inner wing. This results in a higher airspeed on the outer wing, more drag being produced, and yaw opposite the direction of the turn (slipping). This wing speed differential is related to radius of turn, and also results in an overbanking tendency. ### Factors Affecting Adverse Yaw Aircraft Design Factors - increasing wingspan results in greater wingtip speed differential, longer lever arm for ailerons - shorter tail section results in shorter lever arm for vertical stabilizer High Angle of Attack - increases in drag coefficient are proportionally greater at high lift coefficients than at low lift coefficients Slow Speed - less control effectiveness, greater control deflections required - reduced directional stability - decreased radius of turn, greater wing speed differential High Roll Rate - greater forward/rearward changes in lift vectors - greater aileron deflections required High Bank Angle - decreased radius of turn, greater wing speed differential (up to a point) - usually associated with greater control deflections and roll rates