Chapter 3 of 4
A car steers by pushing on the road. A plane has no road — so it steers by reshaping itself. Every hinged panel on a wing or tail is doing the same trick as chapter 1’s whole wing: turning air, harvesting the reaction. Three small surfaces give command of three axes, and a fourth set exists only to cheat the stall on landing.
A plane can rotate three ways: roll (one wing dips), pitch (nose up or down) and yaw (nose left or right). Each gets its own surface. Ailerons — small flaps at the wingtips, always moving in opposition — make one wing lift more than the other: roll. The elevator on the tail pushes the tail down or up: pitch. The rudder on the fin nudges the tail sideways: yaw. Every aircraft from the Wright Flyer to an A350 hangs on those three handles.
Here is the part that surprises car drivers: the rudder does not turn the plane — not really. To turn, a pilot rolls into the corner. Banked over, the wing’s lift leans sideways, and the sideways slice of it pulls the aircraft around the arc — the wing does the cornering, exactly as it does the carrying. The rudder’s real job is tidying: keeping the nose aligned with the curved path so the aircraft doesn’t skid through its own turn. A coordinated turn feels like nothing at all; your coffee never knows.
Chapter 1 left a problem open: a wing sized for economical cruise is starved for lift at landing speed. The fix is a wing that transforms. Flaps slide back and curl down from the trailing edge, adding area and camber — a bigger, more aggressive wing for slow flight. Slats extend from the leading edge to coax the airflow around the steeper angles without letting go. Watch a wing during landing and you will see it come apart into a machine of sliding panels; that is the wing buying itself thirty knots of slower, safer approach.
The deepest design choice is invisible: a conventional plane is built to fly itself straight. The tail sits like feathers on an arrow — disturb the nose and the tail generates exactly the push that swings it back. Dihedral (wings angled slightly up) gently levels an uncommanded bank. The Wright brothers, remarkably, built their Flyer unstable on purpose, reasoning a rider balances a bicycle; a century later, fighter jets returned to instability for agility — but only because computers now do the balancing, hundreds of times a second.