CPL Aerodynamics & Flight Controls
In-depth study guide on boundary layer physics, aerodynamic stalls, load factors, flight control surfaces, adverse yaw remedies, and high-lift devices.
Interactive Turn Load Factor & Accelerated Stall Calculator
Formula: Load Factor n = 1 / cos(θ) | Accelerated Stall Vs = Vs0 × √(n)
A stall is an aerodynamic phenomenon where airflow separates from the upper wing surface when the Critical Angle of Attack (typically 14° to 20°) is exceeded, causing a sudden loss of lift and surge in pressure drag.
At high AoA, air must flow from low pressure at the suction peak towards higher pressure at the trailing edge. When the boundary layer loses kinetic energy, flow stops and reverses, causing total separation.
Stall Recovery: Reduce Angle of Attack immediately by relaxing back pressure on control column, level wings, and apply full throttle smoothly.
When an aircraft rolls, the down-going aileron increases camber and lift, creating more induced drag on that wing. This causes the nose to yaw away from the turn (Adverse Yaw).
- Differential Ailerons: The up-going aileron deflects farther upward than the down-going aileron deflects downward, equalizing drag.
- Frise Ailerons: The leading edge of the up-going aileron protrudes below the wing lower surface into the airflow, creating parasitic drag to counter yaw.
- Rudder Coordination: Pilot applies coordinated rudder into the turn to neutralize adverse yaw.
The Piper PA-28 Archer III DX utilizes an all-moving horizontal tail called a Stabilator, pivoted near its aerodynamic center.
Because an all-moving stabilator is highly sensitive to pilot input, an anti-servo tab is hinged to its trailing edge that deflects in the SAME direction as the stabilator. This creates an opposing aerodynamic moment, providing tactile resistance, preventing pilot-induced oscillations (PIO), and doubling as pitch trim.
Flaps increase both wing camber and maximum lift coefficient (CLmax), reducing takeoff and landing stall speeds.
When the PA-28 slotted flap deploys, a duct opens between the wing lower surface and the flap. High-energy, high-pressure air rushes from the bottom of the wing through the slot to re-energize the slow boundary layer over the upper flap surface, delaying airflow separation and allowing steeper approach angles without stalling.