Control

Control in Principles of Flight: Managing Lift, Drag, and Stability

In Principles of Flight, “control” focuses on how pilots use aerodynamic devices and control surfaces to manage lift, drag, and pitch/roll/yaw moments to achieve the desired flight path. For ATPL theory (EASA/ICAO-aligned), you must understand how configuration changes—flaps, slats, and spoilers—alter the angle of attack (AoA), lift coefficient (CL), and drag coefficient (CD). For example, extending spoilers at a constant AoA immediately increases CD and reduces CL, reducing wing lift and increasing sink rate. High-lift devices behave differently: extending flaps increases camber and lift; extending slats energizes the boundary layer to increase the critical AoA, delaying stall.

Configuration changes demand correct procedures. In straight and level flight at constant IAS, extending flaps initially boosts lift, but after retrimming, CL eventually returns to the same value (because weight hasn’t changed), now achieved at a lower AoA and with more drag. Conversely, when retracting flaps at constant IAS, you must increase AoA (and often add thrust) to maintain lift; if you hold a constant pitch attitude while retracting, the aircraft will start to sink. Near the stall, wing planform matters: a straight wing typically develops a nose-down tendency just before stall as the center of pressure moves aft, aiding recovery. A swept-back wing without corrective features tends to stall first at the tips, which can shift the center of pressure forward and cause a hazardous pitch-up. The wing wake can also blanket the tail, producing a nose-up tendency and/or reduced elevator effectiveness. With swept wings and a T-tail, this can progress to a deep stall if not prevented by design and strict adherence to procedures.

Control in turning flight is equally critical. In a steady, coordinated turn, the load factor (n) is greater than 1, which increases stall speed (VS) by roughly the square root of n. This is why managing AoA and bank angle is vital at low speeds. Other factors that increase stall speed include a forward CG and reduced thrust. Engine-out behavior also affects roll control: on wing-mounted propeller aircraft, the loss of slipstream over the wing and flaps on the failed-engine side creates a stronger roll toward the dead engine than on comparable jet aircraft. Standard operating procedures (AFM/FCOM) emphasize prompt rudder input, coordinated aileron, and maintaining the correct safety speed during asymmetric flight.

What this question bank covers

• Effects of spoilers on CL and CD, and their use in roll control and descent planning.
• Flap and slat operation: changes to AoA, CL, CD at constant IAS or constant AoA; trim and thrust implications.
• Stall behavior on straight vs. swept wings: tip stall, pitch-up, center of pressure movement, elevator effectiveness, and deep stall risks with T-tails.
• Turning flight: coordinated turns, load factor (n > 1), and increased stall speed.
• Influence of CG position and thrust on stall speed and handling qualities.
• Engine failure roll tendencies in jets versus propeller aircraft and associated control procedures.
• Identification and function of high-lift devices, including the split flap and other flap types.
• ATPL-relevant terminology, procedures, and systems knowledge aligned with EASA aviation regulations and training standards.