Training Tips: Designs with a twist

June 25, 2013

As your aircraft moves through the air, the angle of attack—that is, the angle between the chord line of its wing and the relative wind—produces lift and drag that the pilot harnesses to achieve the desired flight profile. Student pilots learn that exceeding the critical angle of attack produces an aerodynamic stall; practicing stall recognition, entries, and recoveries is a basic component of primary flight training.

What controllability characteristics does your trainer exhibit as it approaches the critical angle of attack, and during stall recovery? What you experience during practice is the result of how another angle—this one a fixed design feature of your aircraft’s wing—works to affect flight characteristics.

This design feature is the wing’s angle of incidence, defined as “the angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.”

A desirable feature of a wing is for it to stall at the root before the wingtip. Why is that a plus?

This excerpt from an AOPA review of the Piper PA-28-161 Warrior notes how the Warrior’s wing employs “washout” of the wing’s angle of incidence to achieve the desired stall characteristic: “Stand at the wingtip and sight down the leading edge, and you'll notice that the leading edge twists slightly downward near the tip. This decrease in the angle of incidence means that even when the wing root area has stalled, the outer portion of the wing continues to generate lift and the ailerons remain effective. All of that means the airplane is more controllable in an aerodynamic stall.”

Other aircraft get the same result through different means. AOPA reported that the composite Cirrus SR20’s wing incorporates a cuff on the leading edge to influence airflow: “The cuff causes the air flowing over the ailerons to remain ‘attached’ to the wing at very high angles of attack. As a result, the ailerons remain effective even after the inboard portions of the wing have stalled.”

An important tip: Washout, cuffs, or other airfoil designs improve aircraft handling at high angles of attack, but recovering from an inadvertent stall (or spin) may require neutralizing the ailerons to avoid the adverse yaw their deflection produces. Know the recommended procedure for your trainer!