The science of flight — how a metal tube weighing 200 tonnes lifts itself off the ground
Four invisible forces decide whether something flies or falls
A Boeing 747 weighs about 400,000 kg fully loaded — that's heavier than 60 African elephants. Gravity wants to pull it straight down. Yet it cruises at 10,000 metres for hours. How?
The answer is that flight isn't one thing. It's a balance between four forces acting on the aircraft at all times. When the right ones win, you fly. When the wrong ones win, you crash.
Try this: take a sheet of A4 paper. Hold it just below your bottom lip and blow across the top of the paper (not into it). What happens?
The paper rises. You didn't blow underneath it — you blew over it. That tiny demonstration contains almost everything you need to understand how a wing works. We'll get there in the Lift section.
Every aircraft in flight has exactly four forces pushing on it:
They come in two pairs that fight each other:
If lift = weight AND thrust = drag, the plane flies in a straight line at constant speed and altitude. This is called level cruise — what airliners do for most of a flight.
Change the balance and the plane responds:
Lift is made by the wing (also called an airfoil). A wing isn't flat — it's curved on top and flatter underneath, like this:
Air splitting around the wing has to travel further over the curved top than under the flatter bottom — so it moves faster on top. And here's the key idea:
So under the wing the pressure is high, and above the wing the pressure is low. High pressure pushes up into low pressure — and that push is lift. The faster the wing moves through air, the bigger the pressure difference, and the more lift you get.
Wings also produce lift by deflecting air downward. If something pushes air down, that air pushes the wing up (Newton's third law: every action has an equal and opposite reaction).
The angle between the wing and the oncoming air is called the angle of attack. Tilt the wing up slightly → more air gets shoved down → more lift.
Air isn't nothing. As the plane shoves itself through the sky, the air shoves back. That backward push is drag, and it comes in two main types:
Together they form a U-shaped curve: drag is high at very slow speeds and at very fast speeds. Most airliners cruise at the speed where total drag is lowest — that's their most fuel-efficient point.
Thrust is generated by the engines. There are three common ways:
All of them work by the same trick: throw mass backward, get pushed forward. That's Newton's third law again. The faster and the more mass you throw, the more thrust you get.
The pilot doesn't grab the plane and turn it. Instead they move small flaps on the wings and tail called control surfaces. Each one changes the airflow in a specific way to rotate the plane around one of its three axes.
To turn a plane, you usually combine roll and yaw — bank the wings into the turn with the ailerons, and gently push the rudder the same way. The lift, which used to point straight up, now points slightly sideways and pulls the plane around the curve.
Now you can read a takeoff in physics:
Eight quick questions on the Four Forces, Bernoulli's principle, and control surfaces. Pick an answer for instant feedback.
Walk around a plane: every bit of metal does a specific job
A modern airliner has roughly 3 million individual parts. But almost all of them are doing one of six jobs: hold the plane together, make lift, make thrust, steer, support it on the ground, or keep the people inside alive.
In this topic we'll walk around a typical airliner and name the big pieces. Once you know the parts, the news ("a hairline crack was found near the wing root") starts making sense.
The fuselage is the long tube in the middle. It carries the passengers, the cargo, the cockpit and the fuel. It also acts as the spine that everything else (wings, tail, gear) bolts onto.
Airliner fuselages are pressurised — at 35,000 ft the outside air is too thin to breathe, so the fuselage is sealed and pumped up to roughly the pressure of being on top of a moderate mountain. That's why a fuselage is essentially a thin metal balloon.
The wings are where lift comes from (see Forces of Flight). But they do much more:
The tail — properly called the empennage — does two jobs: keep the plane pointing the right way, and give the pilot controls for pitch and yaw.
It has two main pieces:
Hold a feather by its base and toss it — the feathered end always ends up trailing behind. That's passive stability: the surfaces at the back make sure the front (the nose) leads. A plane's tail does the same job. If a gust pushes the nose sideways, the tail acts like a weathervane and swings the plane straight again.
Look at a wing during takeoff and landing — bits stick out, panels droop, flaps extend. Each one has a name and a job.
Pilots don't reach out and grab the ailerons. They move a yoke (or sidestick) and rudder pedals. Cables, hydraulics or fly-by-wire signals move the surfaces.
The landing gear (or undercarriage) holds the plane up on the ground, steers it on the runway, and absorbs the bump on touchdown. Most airliners use a tricycle arrangement — one nose wheel, two main gear bogeys under the wings.
The gear retracts after takeoff (huge drag reduction) and extends again for landing. The reassuring "clunk" you hear on approach is the gear locking down.
The engines provide thrust. We'll go deep on how they work in Jet & Rocket Engines. The shorthand:
Eight quick questions on the parts of an aircraft.
From bird-watchers in the 1500s to half a million people in the air right now
People have wanted to fly forever. Around 1500, Leonardo da Vinci sketched designs for ornithopters (flapping wings), parachutes and a helicopter-like aerial screw. None of them worked — but they were the first serious engineering attempts.
The first humans actually left the ground in 1783, when the French Montgolfier brothers sent a sheep, a duck, a rooster and then (a few weeks later) two humans up in a hot-air balloon. Balloons drift with the wind, though — you can go up, but you can't choose where you go.
The Wright brothers ran a bicycle shop in Dayton, Ohio. They spent four years (1899–1903) building wind tunnels, testing wing shapes, designing their own lightweight petrol engine, and inventing the world's first practical aircraft controls.
On 17 December 1903, at Kitty Hawk in North Carolina, Orville flew Flyer I for 12 seconds and 36 metres. By the end of the day they had a 59-second flight covering 260 metres. It was the first sustained, controlled, powered flight by a heavier-than-air machine.
Between the two World Wars, aircraft transformed. The biplane fabric-and-wire designs of WWI gave way to all-metal monoplanes with enclosed cockpits, retractable landing gear and engine cowlings. Speed records doubled, then doubled again.
This era produced cultural icons:
The jet engine was invented in parallel by Frank Whittle (Britain) and Hans von Ohain (Germany) in the late 1930s. Jets flew in combat by 1944 (the Me 262), but they really came of age in the 1950s.
Concorde was retired in 2003 — too expensive, too noisy, too fuel-thirsty. The modern airliner is the opposite: huge, slow-ish (Mach 0.85), very fuel-efficient, and almost absurdly safe. A 2020s airliner like the Airbus A350 or Boeing 787 uses around half the fuel per passenger-mile of a 1970s 747.
Today around 500,000 people are airborne at any moment. The dream Da Vinci sketched in 1500 has become so routine we complain about the snacks.
Eight questions on aviation history.
All thrust comes from the same trick: throw mass backward, get pushed forward
Every engine that makes thrust — propeller, jet, rocket — uses the same fundamental rule:
That's it. The only thing that changes between engine types is what the mass is and how it's accelerated. A propeller throws air. A jet throws hot air. A rocket throws hot combustion gases — and crucially, it carries its own oxygen so it works in space.
Two ways to get more thrust:
Different engines pick different trade-offs:
A piston engine is essentially a car engine — pistons moving up and down in cylinders, driven by exploding fuel/air mixture. The crankshaft turns a propeller, which is just a set of small spinning wings.
Each propeller blade has the cross-section of an aerofoil. As it spins, it produces "lift" — but pointing forward instead of up. That forward lift is thrust, and it pulls (or pushes) the plane through the air.
Propellers hit a wall as the aircraft approaches the speed of sound. The blade tips spin so fast that they reach supersonic speed, even when the plane isn't moving very fast — and the airflow gets messy and inefficient. Above about 700 km/h, propellers run out of road.
To go faster, you need a different kind of engine.
Engineers solved the propeller-speed problem by burning the fuel inside the engine itself, and using the expanding hot gas as the exhaust. There are four steps — easy to remember:
The plane is shoved forward by the mass of hot gas being thrown backward.
A pure turbojet sends all the air through the combustion chamber. It's fast but noisy and thirsty. Most modern airliners use turbofans instead.
In a turbofan, the giant fan at the front does two jobs: some air goes through the engine core (suck-squeeze-bang-blow), but most of it bypasses the core entirely and is just blown backwards by the fan. This "cold" air provides most of the thrust on a modern engine — and it's much quieter and more efficient than blasting everything through the core.
A jet engine sucks air from outside. That works great in the atmosphere — but stops working completely in space, because there's no air to suck.
A rocket carries its own oxidiser (often liquid oxygen, "LOX"). It mixes fuel and oxidiser inside a combustion chamber, burns the result, and blasts the exhaust out a shaped nozzle. Because the rocket doesn't need atmospheric air, it works anywhere: in dense atmosphere, in near-vacuum at the edge of space, or in deep space.
The Shuttle famously used both: the two white solid rocket boosters provided huge thrust to escape Earth's gravity quickly, while the orbiter's three main engines burned liquid hydrogen and oxygen from the big orange tank.
Eight questions on engines and how they make thrust.
Six machines that changed what flight meant
The plane that started it all. A biplane built from spruce and muslin, weighing 274 kg, powered by a custom 12-horsepower petrol engine driving twin propellers via bicycle chains. Top speed: about 50 km/h.
The original Flyer was so unstable it took a skilled pilot to keep it airborne for even seconds. But it had every feature of a modern aircraft: wings, a tail, an engine, three-axis control, and a pilot. Everything since has been refinement.
The aircraft that made commercial air travel pay for itself. The DC-3 carried 21 passengers, cruised at 333 km/h, and was so reliable that airlines could finally make money on tickets alone — without subsidies from carrying mail.
Over 16,000 were built. In WWII the military version (C-47 Skytrain / Dakota) dropped paratroopers on D-Day, flew "the Hump" over the Himalayas, and basically carried the Allies' war.
Britain's iconic WWII fighter. Designed by R. J. Mitchell, the Spitfire combined an elliptical wing (low drag, high lift) with the powerful Rolls-Royce Merlin V12 engine. It cruised around 580 km/h and could reach 9,000 metres.
In the Battle of Britain (1940), Spitfires and Hurricanes turned back Germany's Luftwaffe in what was probably the most consequential air battle in history. Without the Spitfire, the UK might have been invaded.
Built in the depths of the Cold War as a spy plane. The SR-71 flew at Mach 3.3 (around 3,500 km/h) at 25,900 metres — three times the speed of sound, higher than any other operational aircraft. If a missile was fired at it, it simply outran the missile.
It was so fast that aerodynamic heating made the skin reach 300 °C in cruise. The titanium fuselage was designed with deliberate gaps that closed up as the plane heated and expanded — meaning the SR-71 leaked fuel on the ground but sealed tight in flight.
A joint Anglo-French project to build a supersonic airliner. Concorde cruised at Mach 2.04 (around 2,200 km/h) at 18,000 metres. London to New York took 3 hours 20 minutes — less than half the time of a normal jet.
It had a droop nose that lowered for takeoff and landing (so the pilot could see the runway over the long pointed fuselage) and used afterburners on takeoff to climb to supersonic speed quickly.
Concorde was technically brilliant but commercially difficult. It was loud (banned from supersonic flight over land because of the sonic boom), thirsty (one tonne of fuel per passenger across the Atlantic), and expensive. After the Paris crash in 2000 and a downturn in air travel, it was retired in 2003.
The opposite philosophy from Concorde. Where Concorde was fast and small, the Boeing 747 was slow (Mach 0.85) and enormous. The original "Jumbo Jet" carried 400+ passengers on two decks — more than double anything before it.
The 747 made long-haul flying affordable for ordinary people. By spreading the fuel cost across hundreds of passengers, ticket prices dropped dramatically. The world's middle classes started flying for holidays in numbers that simply weren't possible before 1970.
Over 1,500 were built across 50+ years of production. The final 747 rolled off the line in 2023. Many remain in service as cargo aircraft (UPS, FedEx) and as Air Force One.
Eight questions on these six famous aircraft.