Overbanking tendency refers to the aerodynamic effects of turning flight overcoming the natural lateral (roll) stability of the airplane, causing it to roll into a progressively steeper bank angle. ## Wing Speed Differential In turning flight, 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 lift differential, and a rolling moment in the direction of the turn. If this rolling moment overcomes the natural lateral stability of the airplane, it will roll into a progressively steeper bank angle without pilot intervention. The speed differential is determined by [[Radius of Turn]] and bank angle, and also produces a drag differential that creates [[Adverse Yaw]]. ![[A4NA turn radius modified.png]] ## Turn Radius and Bank Angle Maximum wing speed differential will exist at a **minimum turn radius**, and a **minimum bank angle**. Radius of turn is determined by bank angle and true airspeed; **increasing bank angle** and **decreasing airspeed** reduce the radius of turn. At very steep bank angles, wingtip turn radii converge, and wing speed differential **decreases**. If the bank angle were to reach 90 degrees, the wingtips would be traveling in the same radius, and have the same local airspeeds. ![[GFH bank angle vs wing speed differential modified.png]] ## Factors Affecting Overbanking Tendency For a particular model of airplane, overbanking tendencies will appear at **lower bank angles at lower airspeeds**, and **higher bank angles at higher airspeeds**. ### Aircraft Design - longer wing spans produce greater wing speed differential - less lateral stability will resist overbanking tendency less ### Airspeed - lower airspeed decreases radius of turn for a given angle of bank, and increases wing speed differential ### Bank Angle - higher bank angle decreases radius of turn for a given airspeed, and increases wing speed differential, up to a point ## Additional Information For additional information, see *Level Turns* (pgs. 3-11 to 3-17) in the *Airplane Flying Handbook*, and *Radius of Turn* (pgs. 5-39 to 5-40) in the *Pilot's Handbook of Aeronautical Knowledge*. # 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)]() ### By Kevin Sakson