If you look at the trailing edge of an airplane’s wings, you’ll probably notice they aren’t completely flat. Most feature hinged flight control surfaces. Known as ailerons, they allow the airplane to roll. When the pilot turns the yoke, the aileron on one wing will deflect upward, while the aileron on the opposite wing will deflect downward. This opposing action will roll the airplane.
What Are Frise Ailerons?
Frise ailerons are designed to address the issue of adverse yaw. Like all ailerons, they are found on the trailing edge of an airplane’s wings and allow banking. Frise ailerons, however, are a specific type of aileron that feature a unique shape to minimize adverse yaw.
Understanding Adverse Yaw
In aviation, adverse yaw is a phenomenon that involves an airplane’s nose moving in the opposite direction of an intended turn. The nose will essentially swing toward the outside of the turn.
A pilot, for instance, may turn the yoke to the right. The left aileron will then deflect downward, and the right aileron will deflect upward. The downward-deflected aileron will produce more lift and drag than the upward-deflected aileron.
This difference in drag causes the airplane’s nose to move toward the opposite direction of the turn, a phenomenon known as adverse yaw. It’s not a mechanical issue. Rather, adverse yaw is simply a phenomenon that pilots must account for when controlling the airplane.
How Frise Ailerons Reduce Adverse Yaw
Frise ailerons leverage a unique shape to reduce adverse yaw. The front surface, or leading edge, is shaped so that when the frise aileron deflects upward, a small section of the front protrudes below the wing. It may look like a design flaw to an unsuspecting person. After all, the protruding section of the frise aileron will produce additional drag — but that’s exactly what it’s supposed to do.
The additional drag created by the protruding section of a frise aileron minimizes the total drag difference between the opposite aileron. This section will only protrude when the frise aileron is deflected upward; the aileron on the opposite wing won’t protrude. The end result is a smaller drag difference and, thus, less adverse yaw.
The shape of frise ailerons must be carefully designed. If the upward-deflected frise aileron produces too little drag, it won’t be effective at minimizing adverse drag. If it produces too much drag, on the other hand, it will make the airplane more difficult to control. Therefore, engineers must walk a fine line when designing frise ailerons.
