Steering the air

A car steers by twisting its tyres against tarmac. An aircraft has nothing to push on but the air itself — so every turn, climb and wobble-correction is done by reshaping wings mid-flight. The tools are small hinged flaps, and the logic is everything you already know: change a surface's camber or angle, change its lift. That is the entire secret of flight control.

Three axes, three surfaces

An aircraft rotates about three axes, each owned by one set of surfaces. Roll (one wing down, one up) belongs to the ailerons, out near the wingtips: they move in opposition, one deflecting down (more camber → more lift) as the other rises (less), rolling the aircraft on its long axis. Pitch (nose up or down) belongs to the elevator on the tailplane — and pitch is really the angle-of- attack control from lesson 4, which is why it is the most important surface on the aircraft. Yaw (nose left or right) belongs to the rudder on the fin — less for steering than for keeping the nose honest during rolls and crosswinds.

How an aircraft actually turns

Here is the counter-intuitive part: the rudder is not the steering wheel. To turn, a pilot rolls into a bank — and then the wing's own lift does the turning, because tilted lift has a sideways component that pulls the aircraft around the corner exactly as a banked velodrome pulls a cyclist. The steeper the bank, the harder the turn — and the more total lift the wing must make (back-pressure on the stick, more angle of attack), because part of the lift is now busy turning. At 60° of bank the wing must lift twice the aircraft's weight; passengers feel it as 2g. Turning, it turns out, is mostly a lift-management problem.

From cables to computers

For decades, control surfaces were moved by cables and muscle, then by hydraulics. Modern airliners and every fighter since the 1980s are fly-by-wire: the stick talks to computers, and the computers — consulting the aerodynamics hundreds of times a second — decide the surface deflections, quietly refusing commands that would stall or overstress the airframe. It is lesson 4's stall protection built into the machine's reflexes. The site has a full laboratory on it: