Many rookie pilots may be surprised at how their aircraft reacts when they engage the ailerons during a turn. If they are making a right, they may wonder why the aircraft suddenly pivots to the left at first. To understand why this happens, this blog will cover adverse yaw in detail, allowing you to become familiar with this phenomenon.
Adverse yaw is defined as the tendency of fixed-wing aircraft to move or “yaw” in the opposite direction as you roll into a banked turn. For instance, if you roll your aircraft to the left, it will automatically make an unintended yawing motion to the right. It is important to note that adverse yaw exists in varying degrees on all fixed-wing aircraft, but it is less pronounced on airplanes that fly at higher speeds and with shorter wings.
You may ask yourself: “What causes adverse yaw?” Adverse yaw is the result of a lift and drag differential between your two wings. To achieve a right banking turn, you must roll the aircraft to the right. First, you must raise the right aileron and lower the left aileron. By raising an aileron, both lift and drag are decreased. Lowering an aileron, on the other hand, generates more lift and more induced drag. This creates more lift because it alters the chord line and increases the AOA (angle of attack). At a higher AOA, more lift is produced. When lowering the left aileron, the left wing will lift.
If drag decrease was balanced on both wings, the airplane could roll without yawing. In real life, however, there is a drag differential between the two wings. A drag differential happens because the raised aileron is deflecting into lower pressure airflow and the lowered aileron is deflecting into higher pressure airflow. If the amount of deflection is equal, then the lowered aileron’s drag will be greater than it is on the higher aileron. This makes the aircraft yaw in the direction of the lowered aileron which is the opposite of your roll.
There are two main types of ailerons, both of which are intentionally designed to counter and minimize adverse yaw. Frise and differential aileron designs can be utilized solo or alongside one another, providing a tandem hybrid configuration. Since adverse yaw is the result of a drag differential between the up and the down aileron, a frise aileron is intended to create more drag on the up aileron. This aids in balancing the higher degree of drag experienced by the lowered aileron. Increased drag is obtained by setting the aileron hinge point backward. Meanwhile, when the aileron is raided, a portion of it sticks out lower than the bottom of the wing to generate extra drag when air hits.
On a differential aileron design, adverse yaw is decreased by limiting the aileron’s downward range of motion. When one aileron is fully raised and the other is fully lowered, the raised aileron will move up further than the other. As the range of motion of the lowered aileron is decreased, the amount of generated drag is also reduced so it matches the drag of the raised aileron. This decreases the amount of drag differential and the severity of the adverse yaw.
Frise and differential aileron designs help minimize adverse yaw, but there are other actions pilots can take to smooth out their rolls. For example, polishing your coordinated turns with properly timed and controlled rudder inputs is optimal. Generally, adverse characteristics present themselves differently in different aircraft, so you must become familiar with your model’s needs.
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