How do aeroplanes fly?

Aeroplanes fly because wings moving through air at a suitable angle of attack generate lift by creating a pressure distribution that turns airflow downwards. Jet engines or engine-driven propellers provide thrust to sustain speed. By managing lift, weight, thrust and drag, the pilot can take off, climb, turn, cruise, descend and land.

In Aviation & Real-World Flying, these are the principles behind conventional fixed-wing aircraft, from gliders and trainers to airliners. Helicopters also use aerofoils, but their rotating wings require a different explanation.

The four forces acting on an aeroplane

Every aeroplane is acted upon by lift, weight, thrust and drag.

In straight, unaccelerated level flight, lift balances weight and thrust balances drag. The aeroplane accelerates, changes direction or changes its flight path whenever those forces no longer balance as vectors.

This is why the familiar four-arrow diagram must not be taken too literally. In a steady climb, lift does not have to exceed weight: lift normally balances the component of weight perpendicular to the climbing flight path, while excess thrust or power supports the climb. In a bank, lift is tilted rather than pointing straight upwards.

On a conventional aeroplane, the engine’s main role is to add energy and maintain airflow over the wings. It does not hold the aircraft up directly. A glider has no engine but keeps flying by trading altitude for forward motion.

What creates lift on an aeroplane wing?

A wing creates lift by establishing a pressure difference around itself and changing the downward momentum of the surrounding air.

These are two descriptions of the same aerodynamic process, not rival theories. The wing’s shape and angle of attack alter the airflow, producing a pressure field around the aerofoil and downwash behind it. The resulting aerodynamic force can then be resolved into lift and drag.

The common claim that air travelling over the curved upper surface must meet the same parcel of air travelling below the wing at the trailing edge is false. There is no equal-transit-time rule, and air over the top commonly reaches the trailing edge first.

A useful lift equation is L = ½ρV²SCL. Lift depends on air density, speed through the air, wing area and the coefficient of lift. Because speed is squared, a change in airspeed has a large effect, but the pilot can also change lift by altering the coefficient of lift.

Angle of attack is the angle between the wing’s chord line and the oncoming relative airflow. It is not the same as pitch attitude relative to the horizon. An aeroplane can be nose-high with a moderate angle of attack in a climb, or nose-low with a dangerously high angle of attack during a steep descent or manoeuvre.

Camber helps a wing produce lift efficiently, but curvature is not an absolute requirement. A symmetrical aerobatic wing and even a flat plate can generate lift at a suitable angle of attack. Flaps and slats change the wing’s effective shape or airflow so it can produce a higher coefficient of lift; our guide to how flap settings affect lift, drag and low-speed handling explains why their use is aircraft- and phase-specific.

Can an aeroplane fly upside down?

A suitably designed aeroplane can fly inverted by holding an angle of attack that produces lift in the required direction.

Symmetrical aerofoils make sustained inverted flight more practical, but wing camber does not make it impossible. Most normal and transport-category aircraft are not approved for inverted flight; their structures, fuel and oil systems, operating limits and control characteristics are not designed for it.

Why does indicated airspeed matter more than groundspeed?

A wing responds to speed relative to the surrounding air, not speed across the ground.

Pilots therefore use the airspeed specified in the aircraft’s operating data for take-off, approach, climb and stall references. Indicated airspeed is not a direct angle-of-attack measurement, and instrument and position errors exist, but it represents aerodynamic pressure far more usefully than groundspeed does.

A headwind means the required airspeed is reached at a lower groundspeed, which usually shortens the take-off run. A tailwind requires a higher groundspeed and normally increases runway distance. The effect of wind on airspeed, groundspeed and runway performance is covered in our practical explanation of wind during take-off and landing.

Air density matters as well. At a hot or high-altitude airfield, an aeroplane needs a higher true airspeed to achieve a given indicated airspeed. Many engines and propellers also produce less thrust in thin air, so acceleration is weaker and the take-off distance increases. This combined performance penalty is why density altitude matters even when the airspeed indicator shows familiar numbers.

How does an aeroplane take off?

An aeroplane takes off by accelerating to the required airspeed and increasing angle of attack enough to establish a safe flying trajectory without stalling.

1. Thrust overcomes resistance. The propulsion system must overcome rolling resistance and aerodynamic drag so the aircraft can accelerate.
2. Airflow builds. Increasing airspeed produces more lift and makes the elevator, ailerons and rudder more effective.
3. The pilot rotates. At the recommended rotation or lift-off speed, if one is specified, a controlled nose-up input increases the wing’s angle of attack.
4. The wheels unload. As aerodynamic forces take over, the runway’s supporting reaction decreases to zero and the aircraft leaves the surface.
5. A stable climb is established. The pilot sets the required pitch, power, airspeed, trim and configuration rather than continuing to pull back.

There is no universal rotation speed or flap setting. The correct figures depend on aircraft type, mass, centre of gravity and configuration. Runway length, slope, surface condition, wind and density altitude affect whether the aeroplane can reach that speed safely.

A mistake we see constantly in simulators is pulling back too early and then holding excessive nose-up input. Pitch attitude cannot replace missing airspeed. The result is more drag, poor acceleration and possibly a stall or tail strike.

How do pilots control an aeroplane in flight?

Pilots control an aeroplane by changing pitch, roll, yaw, power and configuration while using trim to remove sustained control pressure.

• Elevator or stabilator: changes pitching moment and helps the pilot set angle of attack and flight path.
• Ailerons: create a rolling moment and establish the bank angle.
• Rudder: controls yaw, counters adverse yaw and helps coordinate turns.
• Throttle or thrust controls: change the aircraft’s energy input, affecting acceleration and climb performance.
• Trim: relieves the force needed to hold a chosen condition; it is not an autopilot.
• Flaps, slats and spoilers: alter lift, drag and handling for particular phases of flight.

These controls interact. Adding power can change pitch and yaw as well as speed; pitching up can initially reduce speed rather than create a climb; extending flaps can produce a pitch change alongside extra lift and drag. Our detailed breakdown of the main flight-control surfaces and their aerodynamic effects shows what each surface contributes.

How does an aeroplane turn without losing height?

An aeroplane turns by banking, which tilts the lift vector and creates a horizontal force towards the inside of the turn.

Part of the lift is now acting sideways, so a level turn requires greater total lift to keep the vertical component equal to weight. The pilot normally increases angle of attack with back-pressure and may need more power to offset the additional drag.

This raises load factor and stall speed. In an ideal coordinated 60-degree banked level turn, the load factor is 2g and the stall speed is about 41 per cent higher than its wings-level value in the same configuration. Rudder keeps the turn coordinated; using rudder alone is not the normal way to turn a conventional aeroplane.

Why does an aeroplane not drop when the engine stops?

An aeroplane with no engine thrust normally descends in a glide rather than dropping vertically.

As the aircraft moves forwards and downwards, air continues to flow over the wings and they continue producing lift. Gravity supplies the energy: altitude is exchanged for the forward motion needed to overcome drag.

The pilot’s immediate aerodynamic priority is normally to establish the approved best-glide speed, followed by the aircraft-specific engine-failure procedure. Flying too slowly risks a stall; flying unnecessarily fast usually reduces the distance available. Best glide is intended to maximise distance in still air, while minimum-sink speed maximises time aloft and is not necessarily the same figure.

Wind, aircraft mass, propeller drag, landing-gear position and flap configuration affect the resulting ground range or descent. The correct speeds and procedures must come from the flight manual for that aircraft.

What causes an aeroplane to stall?

An aeroplane stalls when a wing exceeds its critical angle of attack, not simply because the engine stops or the airspeed is low.

Beyond the critical angle, airflow separation increases, the coefficient of lift stops rising normally and drag grows sharply. Depending on the aircraft, the pilot may notice buffet, a stall warning, poor control response, an uncommanded roll or a nose drop.

Low speed makes a stall more likely because the wing needs a higher coefficient of lift to support the aircraft. It is still possible to stall at high airspeed during a hard pull-up or steep turn because load factor increases the lift demand. Published stall speeds apply only to stated masses, configurations and manoeuvring conditions.

The essential aerodynamic action in a stall recovery is to reduce angle of attack. The pilot then manages bank, power and configuration according to the approved procedure. Pulling harder or adding power without reducing excessive angle of attack may delay recovery.

How can I demonstrate lift in a flight simulator?

Use a basic training aircraft, calm weather, plenty of virtual altitude and minimal assistance, then change one variable at a time.

1. Establish level flight. Hold a constant indicated airspeed and altitude, trim the aircraft and note the pitch and power settings.
2. Reduce power. Watch the airspeed decay and observe how pitch must change if you want to hold a chosen speed or altitude.
3. Enter a medium bank. Apply enough back-pressure to maintain height and note the increased angle of attack and drag.
4. Compare flap settings. Extend the flaps in stages within their operating limits and observe the lower-speed capability, pitch change and additional drag.
5. Try an idle-power glide. Hold the aircraft’s recommended glide speed and watch altitude become the source of forward energy.
6. Approach a stall safely. At ample simulated altitude, recognise the warning signs, reduce angle of attack and recover without an abrupt pull.

Auto-rudder, simplified flight assistance, AI control and some stability aids can conceal yaw, trim changes or stall behaviour. Flight models also vary between aircraft, so a simulator demonstrates the principles without proving that a particular add-on exactly matches the real aeroplane. For a familiar practical example, our Cessna 172 cockpit and control walkthrough connects these forces to the controls and instruments a student pilot actually uses.

Why will my simulated aeroplane not take off?

A simulated aeroplane that will not rotate usually has insufficient airspeed, an incorrect configuration or a control-input problem.

• Check that the parking brake is released and the engine or engines are producing the expected thrust.
• Confirm that pulling back commands nose-up elevator movement and that no duplicate or reversed controller axis is cancelling the input.
• Use indicated airspeed and the aircraft’s specified take-off data rather than guessing from groundspeed or outside-view motion.
• Verify take-off trim, flap position, mass and centre of gravity. A heavily loaded aircraft or excessively forward centre of gravity may require more runway and control force.
• Retract spoilers or speedbrakes unless the aircraft’s procedure explicitly requires another setting.
• Check for a tailwind, high density altitude, uphill runway or soft-surface simulation before assuming the flight model is faulty.
• Disable assistance or automatic trim temporarily if it is overriding the pilot’s input.