Adverse yaw is a type of aerodynamic coupling. When an airplane is rolled in flight, a yawing moment is induced in the **opposite direction**, left or right. In some contexts, adverse yaw is also used to refer to a yawing moment experienced in the opposite direction of a turn. ## Aileron Deflection When rolling into or out of a turn, the downward deflected aileron on the rising wing increases the effective camber of that wing section, increasing lift and increasing drag. The increased drag produces a yawing moment opposite the direction of the roll. This effect can be minimized with **differential** or **frise** type ailerons, or with spoilers that produce **proverse yaw**. ![[PHAK adverse yaw.png]] ## Rolling Motion The lift vector of a wing is defined as the aerodynamic force **perpendicular** to the relative wind. When an airplane is rolled in flight, 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. These changes in lift vectors produce a yawing moment opposite the direction of the rolling motion. This also 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 Once established in a turn, the outer wing travels a greater distance than the inner wing. This creates a speed differential between the wings; the outer wing experiences a higher local airspeed, while the inner wing experiences a lower local airspeed. This speed differential produces a drag differential, and a yawing moment in the opposite direction of the turn, or a tendency to [[Slip]]. The speed differential is determined by [[Radius of Turn]] and bank angle, and also produces a lift differential that creates an [[Overbanking Tendency]]. ![[A4NA turn radius modified.png]] ![[AFH differential drag modified.png]] ## Factors Affecting Adverse Yaw For a particular model of airplane, adverse yaw will be greatest with large aileron deflections, at low airspeeds, and high angles of attack. ### Aircraft Design - longer wing spans produce greater wing speed differential, and generally longer aileron arms - less directional stability (ie shorter tail, smaller vertical tail surfaces, etc) will resist adverse yaw less ### Angle of Attack - higher angle of attack will produce more adverse yaw; increases in drag coefficient are proportionally greater at high lift coefficients than at low lift coefficients ### Airspeed - lower airspeed reduces control effectiveness and requires greater aileron deflection - lower airspeed decreases directional stability - lower airspeed decreases radius of turn and increases wing speed differential ### Roll Rate - higher roll rate results in greater change to relative wind and lift vectors - higher roll rate requires greater aileron deflection ### Bank Angle - higher bank angle decreases radius of turn and increases wing speed differential, up to a point - higher roll rates and greater control deflections are typically used with higher bank angles ## Additional Information For additional information, see *Adverse Yaw* (pgs. 6-3 to 6-4) in the *Pilot's Handbook of Aeronautical Knowledge*, *Level Turns* (pgs. 3-11 to 3-17) in the *Airplane Flying Handbook*, and *Adverse Yaw* (pgs. 291 to 293) in *Aerodynamics for Naval Aviators*. # References - [[faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf](https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf)]() - [[Airplane Flying Handbook (FAA-H-8083-3C)](https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/00_afh_full.pdf)]() - [[00-80T-80.pdf](https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/00-80T-80.pdf)]() ### By Kevin Sakson