# How do Planes Fly

When we finally made the pivotal breakthrough, man-made flight took off in a hurry.

In 45 years, we went from the Wright Brothers’ beach hops to businessmen harassing stewardesses at 20,000 feet and test pilots moving faster than sound. Each leap forward came from ever-greater feats of engineering.

For millennia, would-be aviators knew bird flight had something to do with wing structure, but were clueless regarding the details. As it turns out, the shape of a wing is optimized to generate lift, an upward force caused by manipulating airflow. Awing has a rounded leading edge with a slight upward tilt, a curved topside, and a tapered trailing edge pointing downward. This shape alters the flow of air molecules into a downward trajectory. This results in – as Newton put it in his Third Law of Motion – “an equal and opposite reaction.” When the wing pushes the air molecules down, the molecules push the wing up with equal force. The airflow also creates a lower pressure area above the wing, which essentially sucks the wing up.

Constructing wings is the easy part. To fly, you need to generate enough forward force – or thrust – to produce the necessary lift to counteract gravity. The Wright Brothers finally accomplished this by linking a piston engine to twin propellers. A plane propeller is simply a group of rotating wings shifted 90 degrees, so the direction of lift is forwards rather than upwards. In 1944, engineers upgraded to jet engines, which produce much greater thrust by igniting a mixture of air and fuel, and expelling hot gasses backward.

A pilot controls a plane by adjusting movable surfaces on the main wings, as well as smaller surfaces and a wing-like rudder on the tail. By changing the shape and position of these structures, the pilotvaries the lift force, acting on the different ends of the plane to essentially pivot the plane along three axes: its pitch (up or down tilt of the nose), roll (side to side rotation), and yaw (turn to the left or right).

For the sake of efficiency, engineers keep planes as light and aerodynamic as possible. The first planes -sparse wooden frames covered in fabric – were lightweight and open, which minimised drag, the backwards force of air resistance.

But the structure was only strong enough to handle low speeds. ‘Hot-rod’ a Wright Brothers’ plane with a jet engine, and the extra thrust would tear it apart. Along with more powerful fi^ engines, engineers had to develop stronger metal frameworks and streamlined aluminium alloy surfaces.

Modern fighter jets are manufactured from super-strong, lightweight composite material, applied in layers to form precise, aerodynamic shapes. This helps them get up to more than twice the speed of sound.

## How does the pilot make a plane climb?

Imagine a straight line going through the middle of a wing. The angle of attack is the angle of this line relative to the direction of rushing air. As you increase this angle, you boost the air pressure under the wing, resulting in greater lift. Pilots increase the angle of attack in order to climb, and decrease it to level out or dive.

Channel your inner seven-year-old, and try it yourself. Carefully, stick your hand out the window of a moving car with your palm down, and your thumb side tilted slightly up. Tilt the thumb side up, and your hand directs even more air downward, and you feel a greater upward push. If you keep pivoting your hand, however, you’ll reach a point where air can’t flow easily around it. The lift drops suddenly, and your hand flies straight back. In aeroplanes, this is called the stall point, and it’s usually bad news for pilots.

## What forces act on the airfoil?

More than a century after the Wright Brothers, physicists are still debating exactly how wings work. Accessible explanations for the rest of us can’t help but leave things out, and some common answers are flat-out wrong.

The crucial thing to understand is that air is a fluid, and that wings alter the flow of that fluid. The top and bottom of the wing both deflect air molecules downwards, which results in an opposite upward force. In the typical airfoil design, the top of the wing is curved. Flowing air follows this curve, causing it to leave the wing at a significant downward angle. This also generates a low-pressure area above the wing, which helps pull it up.

Long, skinny wings are more efficient because they produce minimal drag proportional to lift. But they’re also fragile and slow to manoeuvre. In contrast, stubby wings offer high agility and strength, but require more thrust to produce lift.

Lift –  The air flowing over the top has further to go, so must travel quicker to keep up with the air below.

Airfoil- The airfoil is thin at the front, thicker in the middle and thinner again at the rear end.

Drag – Air resistance pulls the aircraft in the opposite direction.

## What happens during takeoff and landing?

1. Acceleration – To generate adequate lift from the ground, the pilot increases the size and camber (top curvature) of the wings by extending flaps at the back, and slats in the front.

2. Take-off – The pilot raises the tail elevators, and rushing air pushes the tail down. This raises the nose up, and increases the wings’ angle of attack, producing enough lift for takeoff.

3. Flight – Inflight, the pilot retracts the flaps and slats, and continually adjusts the ailerons, rudder and elevators to manoeuvre the plane.

4. Landing – The pilot reduces thrust to slow the plane and extends the landing gear, flaps and slats. When it touches down, the pilot extends spoilers on top of the wing to quickly decrease the lift.