Secondary flight controls help pilots fine tune an aircraft after the main controls have set its basic motion. While ailerons, elevators, and rudders create primary roll, pitch, and yaw, secondary controls make the airplane easier to manage, slow, or descend. Trim tabs, spoilers, and speed brakes are especially important during long flights, approaches, landings, and steep descents.
Understanding them helps students see how aircraft balance lift, drag, and pilot workload.
Key Facts
- Trim tabs reduce the force a pilot must hold on the control yoke or stick.
- Spoilers rise from the wing to reduce lift and increase drag.
- Speed brakes increase drag so an aircraft can slow down or descend more steeply.
- Lift decreases when airflow over the wing is disturbed: lower effective lift means less upward force.
- Drag force increases with speed: D = 1/2 rho v^2 Cd A.
- Roll is rotation around the longitudinal axis, and spoilers can assist roll by reducing lift on one wing.
Vocabulary
- Trim tab
- A small movable surface on a larger control surface that helps hold the aircraft in a desired attitude with less pilot force.
- Spoiler
- A panel on the wing that rises into the airflow to reduce lift and increase drag.
- Speed brake
- A surface used mainly to increase drag so the aircraft can slow down or descend without gaining too much speed.
- Lift
- The aerodynamic force that acts mostly upward and supports an aircraft in flight.
- Drag
- The aerodynamic force that acts opposite the aircraft's motion through the air.
Common Mistakes to Avoid
- Confusing secondary controls with primary controls: primary controls directly command roll, pitch, and yaw, while secondary controls mostly fine tune handling, lift, and drag.
- Thinking trim makes the airplane fly by itself: trim reduces control pressure, but the pilot or autopilot must still monitor and control the aircraft.
- Assuming spoilers only slow the airplane: spoilers also reduce lift, which is why they help with descent, landing rollout, and sometimes roll control.
- Using speed brakes as if they create lift: speed brakes increase drag and often reduce performance, so they help slow or descend rather than support the aircraft.
Practice Questions
- 1 An aircraft is descending at 250 knots and the pilot deploys speed brakes. If drag increases from 18,000 N to 27,000 N, by how many newtons did the drag increase?
- 2 A spoiler reduces lift on one wing from 52,000 N to 46,000 N while the other wing remains at 52,000 N. What is the lift difference between the two wings, and which wing will tend to drop?
- 3 During a long cruise, a pilot must constantly pull back slightly on the control yoke to keep the nose level. Explain which secondary control should be adjusted and why it reduces pilot workload.