How planes stay in the air

In brief

• Understanding how planes work can help some nervous flyers
• Planes stay in the air by achieving a balance between four fundamental aerodynamic forces: lift, weight, thrust, and drag
• The lift generated by the wings balances the plane’s weight, while thrust from the engines overcomes drag
• Airplanes have multiple safety systems in place to ensure a safe and smooth flight

Science of flight

Planes weighing hundreds of tonnes can stay in the air because the lift that’s generated by the wings balances the aircraft’s weight. The thrust from the engines overcomes drag. It’s not something magical, but precision engineering.

We’re not saying that understanding the science of flight will cure your fear of flying. It probably won’t. But understanding how planes work, how they can stay in the air, and why flying is safer than driving might just help you the next time you fly.

The physics of flight

We’re not going to go too deeply into the science, but a basic explainer can help. Aircraft fly because they achieve a balance between four fundamental aerodynamic forces: lift, weight, thrust, and drag.

Here’s how they work together:

• Lift: This is the upward force generated by the wings as air flows over and under them
• Weight: This is the downward force caused by gravity acting on the mass of the aircraft
• Thrust: This is the forward force provided by engines that propel the aircraft through the air
• Drag: This is the resistance or backward pull caused by air friction as the aircraft moves forward

Lift, needed to take off, is generated by a combination of factors, including:

• Airfoil shape: Curved wings (airfoils) guide airflow over the wing, creating a pressure difference that creates lift
• Angle of attack: The angle between the wing’s chord line and the oncoming air. Higher angles increase lift (up to a point)
• Circulation theory: This describes how air flows around the wing, creating pressure differences that generate lift

To ascend or descend, pilots change the angle of attack using control surfaces. This changes the airflow. As the engines propel the plane forward, a small change in the angle of attack and airflow generates enough lift for takeoff.

You can test this principle yourself by putting your hand out of the window of a moving car. When your hand is flat and level, the air flows over and under it. If you lift your fingers slightly, it’ll lift up into the air.

At cruising altitude, when the plane is at level flight, the balance of forces looks like this:

Lift = Weight
Thrust = Drag

Aircraft safety systems

Aircraft are incredibly complex machines. There are over 300 miles of wiring in the A380 super jumbo aircraft.

Modern aircraft are built with several layers of redundancy. In simple terms, this means they have backups for their backups. If one system fails, another takes over. This applies to:

• Engines: Twin-engine aircraft can fly (and land) safely with one engine. ETOPS regulations (Extended-range Twin-engine Operational Performance Standards) require aircraft to be able to reach a diversion airport even if an engine fails mid-flight.
• Hydraulics: Most aircraft have at least three independent hydraulic systems to operate the flaps, brakes, landing gear, and flight controls.
  Electrical systems: If the main generator fails, the aircraft can draw power from auxiliary systems, including the ram air turbine (RAT). This is a small windmill that deploys mid-flight to provide emergency power.
• Avionics: Flight computers, autopilot and navigation systems have double or even triple redundancy. That means if one system fails, there’s another – and potentially two – more that can step in if required.

Materials and fatigue testing

When you fly, the aircraft is exposed to rapid and repeated pressurisation, freezing temperatures, and turbulence (even if it’s so small you never even notice it). Most commercial aircraft will manage thousands of safe takeoffs and landings over their lifespan.

Planes are built from incredibly strong materials and are tested to extremes. Aircraft airframes are made from aerospace-grade aluminium alloys, carbon fibre composites, and titanium. These materials are all chosen for their strength-to-weight ratio and resistance to fatigue and stress.

All critical components used in a plane are put through non-destructive testing (NDT). Engineers use X-rays, ultrasonic pulses, and dye penetrants to detect microscopic cracks in plane structures.

Every aircraft type must pass “wing flex” tests, where wings are bent upwards by several metres. For example, a Boeing 787 wing can flex up to 8 metres without breaking.

You can see this video to understand the extreme forces wings are exposed to during testing and certification.

Trust the system

When planes are in the sky, they’re doing what they were designed to do. You don’t need to understand how planes stay in the sky to understand that they’re safe – and you are when you travel on them.

If you want some practical ways to deal with fear of flying anxiety, check out the Help Desk and download our Calm Flight Toolkit.

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