Flight controls, trim & flaps

Primary flight controls

Definition

An airplane moves about three axes, and each has one primary control surface. The elevator controls pitch about the lateral axis (nose up and down). The ailerons control roll about the longitudinal axis (wings banking). The rudder controls yaw about the vertical axis (nose left and right). In normal flight you use them together — especially in turns, climbs, slow flight, and crosswinds.

Explanation

Each axis runs through the airplane's center of gravity. Longitudinal is nose-to-tail (roll), lateral is wingtip-to-wingtip (pitch), vertical is straight up-and-down through the CG (yaw). The control that produces each motion is the one whose surface is farthest from that axis — ailerons out on the wings for roll, elevator back on the tail for pitch, rudder on the tail for yaw.

Figure 6-4. Airplane controls, movement, axes of rotation, and type of stability. — Figure 6-4 · FAA-H-8083-25C, Pilot's Handbook of Aeronautical Knowledge (p. 151)

Why it matters

Every maneuver you'll fly is some combination of these three. Knowing which control commands which axis is the foundation for coordinated flight and for the checkride oral.

From the Right Seat

Ailerons bank the airplane; they don't turn it by themselves. The rudder keeps the turn coordinated and counters the yaw that aileron drag and propeller effects create — that's why we say 'step on the ball.'

A DPE might ask

What are the three axes and the primary control for each?
Which control produces roll? Pitch? Yaw?

PHAK ch. 6 — Flight controls & the three axes

How the controls move

Definition

The cockpit controls move the surfaces through a mechanical system — cables, pushrods, torque tubes, or a combination. The control wheel or stick works the ailerons and elevator; the rudder pedals move the rudder, and the toe brakes on top of the pedals work the wheel brakes. Different airplanes use different hardware, but the aerodynamic job is the same.

Explanation

Because it's a mechanical linkage, your flight-control preflight checks three things: the surfaces move in the correct direction for the input, they move fully and freely with no binding, and everything is secure. Look at the surface while you move the control — don't just feel the yoke.

Why it matters

A control rigged backwards or binding is a killer that a proper preflight catches on the ground. 'Free and correct' isn't a slogan — it's you looking at the surface as you move the control.

Safety

Actually watch each surface during the control check. Reversed aileron rigging after maintenance has caused fatal accidents — the yoke feels normal; only looking catches it.

A DPE might ask

How do the cockpit controls connect to the surfaces?
What are you checking during the flight-control preflight?

PHAK ch. 6 — Control systems & preflight

Trim

Definition

When you've established the attitude and power you want, trim changes the aerodynamic force so you no longer have to hold a large control pressure. Trim relieves the pressure — it does not replace flying the airplane. If you change power, speed, configuration, or attitude, expect the trim requirement to change too.

Explanation

The sequence matters: set the attitude, set the power, then trim off the remaining pressure. Trim is the last step, not the first. Chasing the airplane with trim — trying to trim your way to an attitude instead of establishing it first — is one of the fastest ways to get behind the airplane.

Why it matters

Good trim technique makes every phase of flight easier and more precise; bad trim technique (leading with trim) makes you fight the airplane. Examiners watch for attitude-power-trim, in that order.

Common error

A common mistake is using trim to establish the attitude — cranking trim to get the nose where you want it. That leaves you chasing the airplane. Trim is for relieving the control pressure after you've already set the attitude with the yoke and the power.

You want to establish a climb. What's the correct role of trim?

A DPE might ask

What does trim actually do?
What's the correct order: attitude, power, and trim?

PHAK ch. 6 & AFH ch. 3 — Trim & basic flight maneuvers

Flaps

Definition

Flaps are a secondary control. Extending them increases the wing's camber and usually increases lift at a given angle of attack — but it also increases drag. That combination lets you fly a slower approach and descend more steeply without gaining airspeed. Every airplane has flap-speed limits and approved settings in its POH.

Explanation

The trade is lift and drag together: partial flaps mostly add lift (useful for takeoff in some airplanes), while full flaps add a lot of drag (useful for a steep, slow final approach). Because flaps change lift and pitch, expect a trim change when you extend or retract them — and never exceed the white-arc flap-limit speed.

Figure 6-17. Five common types of flaps. — Figure 6-17 · FAA-H-8083-25C, Pilot's Handbook of Aeronautical Knowledge (p. 157)

Why it matters

Flaps are how you fly a stable, slow approach into a normal runway. Using them within their speed limits and expecting the pitch/trim change is basic airplane control and a checkride staple.

From the Right Seat

Flaps aren't a fix for a fast or high approach. Get stabilized first, then use the configuration your POH teaches — don't dump full flaps to salvage a bad setup.

A DPE might ask

What do flaps do to lift and drag?
Why do we use flaps on approach, and what limits their use?

PHAK ch. 6 & AFH ch. 9 — Flaps & approaches and landings