For a plane of many tons to take off from the ground, maintain itself in the air, and cover hundreds of kilometers seemed impossible until the Wright brothers flew the first controlled flight back on December 17th, 1903.
There are numerous factors that come into play when discussing the reasoning behind why an airplane can fly. Amongst them are aerodynamics and other physics, the human factor, very precise engineering, and many more.
Throughout our airplane pilot courses, you will study everything that is related to the flying of airplanes in depth, but we want to give you a short preview on this topic and briefly explain how planes fly and what are the main factors that contribute to maintaining such a vehicle, capable of transporting passengers and all sorts of cargo, in the air.
Why do planes fly? Here’s some physics: The forces that act on an airplane to make it fly.
To see how planes can fly we have to look at the physics behind it all, specifically the forces that act on the wings and the airframe as a whole, allowing them to soar in the skies.
Primarily, there are four basic forces that come into play that allow the aircraft to ‘float’ and move forward in the air:
The drag component acts opposite to the direction the aircraft is moving in, as if trying to hold it back. This force can be caused by numerous factors, the shape of the airframe, the smoothness of the skin, and as a product of the lift being generated by the wings. Drag tends to slow the aircraft down.
Thrust is a reactive force produced when an object, in this case the engine, accelerates or expels a mass (air) in the opposite direction. Thrust counteracts the force of drag, and acts in the direction of the moving aircraft, allowing it to move forward and reach high speeds.
A force like weight is a product of the aircraft’s mass and the earth’s gravitational pull. This force acts vertically towards the ground, and to stabilize it, aircraft are equipped with horizontal and vertical stabilizers, allowing the aircraft to return to a stable position after any disturbance.
Possibly being the most important of the four, lift acts perpendicular to the airflow moving across the wing. This occurs when air moves over and below the wing, caused when an aircraft advances through an airmass. Lift occurs on the wings and depends on the aircraft’s speed and the wings’ angle of attack, the angle formed between the relative airflow and the wing.
The main goal is to achieve the most lift with the least drag, and an airplane attempts to achieve this thanks to the aerodynamic profile of the wings, also known as airfoil.
How does an airplane work? How can it stay in the air?
The wings of an airplane are essential for said aircraft to remain ‘afloat’ in the air, given that these are the structures where lift occurs and therefore allow the aircraft to fly. Additionally, although this does not apply to all aircraft, the engines are mounted below the wings, thanks to which the airplane can propel itself forward.
How is lift produced in the wings?
As mentioned, the force of lift is the force that is primarily responsible for flight.
The airfoil design of the wings depends on characteristics like what the aircraft will be used for, the speed which it will fly at and so on. This shape allows for the divergence of the air to the top and the bottom of the wing, creating a pressure difference. This difference in pressure results in low pressure forming on top of the wing, therefore pulling it up, and a high-pressure sector below the wing, keeping it afloat. This aerodynamic force is known as lift.
You can test out this phenomenon yourself while driving down the road, if you stick your hand out the window and change its pitch (which also changes your hand’s angle of attack), you will feel it wanting to fly up with a positive pitch and dropping with a negative pitch. The faster the vehicle, the easier it will be to keep your hand in the air. This is possibly the most basic way to see lift occurring.
The same theory applies to airplanes, the faster the air flows around the wing, the greater the lift. This is primarily why airplanes need a long enough runway to reach a speed at which the lift produced can carry the aircraft off the ground.
Another one of the basic factors that contribute to lift being generated in the wings is the angle of attack. Returning to the example of you sticking your hand out the window, as mentioned, you will notice that with an increasing pitch, your hand will want to rise, up to a certain point where it would simulate a stall and therefore fall abruptly.
The same occurs in the wings, when the pitch of the aircraft changes, or when the speed is modified keeping a constant nose pitch, the angle of attack is impacted, directly affecting the coefficient of lift.
The importance of the engines for aircraft in flight
The main purpose of the engines is to provide thrust which is transformed into forward speed for an aircraft.
Currently, modern aircraft models feature turbofan engines, similar to previous jet engines, carrying out compression, combustion, expansion, and exhaust.
The process of air going through the engine is as follows: Initially, air enters the engine and is pushed back through the various stages of compressor blades, this compresses the air and increases its temperature. The following step will carry the air through the combustion chamber where it is mixed with fuel and ignited, drastically increasing its temperature and pressure. The flow of air then passes through the turbine stages, expanding and cooling itself, the turbines move a shaft that is directly connected to the compressor at the front of the engine. Lastly, the expanded and cooled down air, although still hot, is rapidly expelled through the back of the engine, resulting in the necessary thrust to move the aircraft forward.
One of the key factors for aircraft engine manufacturers and airlines is the aircraft’s overall fuel consumption. Due to this, modern engines only use the necessary amount of air to obtain compression, combustion, and expansion, which happens at the core of the engine. The rest of the air is pushed by the forward fan around the core through an area known as bypass, which is also responsible for a significant amount of thrust. This design results in a much cheaper and more efficient way of producing thrust.
How do airplanes take off the ground?
The takeoff process is one of the most technical and important phases of the flight. It is during this time that engines run at full power and every parameter must be correct with everything running to perfection.
The takeoff procedure follows these steps to be successfully completed:
- Preparation: Before takeoff, the pilots taxi the aircraft out to the runway. In the meantime, various briefings and checks are carried out to make sure the aircraft is in a safe state and ready for departure.
- Entering Runway: The aircraft is then lined up on the runway, a long and paved strip specially designed for aircraft operations and where the planes will take off or land onto.
- Engine Thrust Set: The pilots then apply power to the engines, providing the necessary thrust to pick up speed as it travels down the runway. As previously mentioned, the engines work by pushing the air back, making the aircraft move forward.
- Rotation Speed: As the aircraft accelerates it picks up speed. The speed at which an aircraft lifts off depends on its type, size, weight, and other factors like weather conditions. Generally, commercial aircraft reach a speed of around 250 to 300 km/h before the pilots raise the nose off the ground.
- Rotation: When the aircraft has reached rotation speed (Vr), the pilot flying pulls back on the controls and raises the nose of the aircraft off the ground. This is achieved by the movement of the ailerons and elevator, which are located on the wings and the tail of the aircraft, respectively.
- Lift: Thanks to the changing pitch of the aircraft, the airflow around the wings is changed, modifying the angle of attack, and as a result favoring the creation of lift. This force ‘pulls’ the aircraft off the ground, against gravity, allowing it to fly.
- Take off: The combination of speed and angle of attack, the airplane fully lifts off the ground, with the adequate climb angle. This is where the flight begins!
- Retracting the Landing Gear: Following takeoff, once the aircraft is in the air and it is safe to do so, the pilots retract the landing gear, the structure allowing it to move on the ground, where the wheels are mounted. By doing this, drag is significantly reduced, making the plane more aerodynamic.
- Climb-out: After takeoff, the aircraft continues to pick up speed and altitude, while the pilots also adjust the heading to reach their destination. The pilots keep a close eye on numerous parameters and manage the speed, altitude, and heading throughout the rest of the flight, to ensure a smooth and safe operation.
How do airplanes land?
Just like takeoff, landing an airplane is one of the most delicate phases of flight, where pilots demonstrate their technical abilities. During landing, it is crucial to maintain the speed and rate of descent of the aircraft so as to touch down correctly.
These are the steps a flight crew follows to land the airplane:
- Descent: Prior to beginning the approach and landing phase, the airplane begins its descent from cruising altitude. The pilots manage the thrust provided by the engines and angle the aircraft in a way that initiates a descent towards the destination airport.
- Speed and Track Control: The pilots control the plane’s speed and trajectory throughout the descent stage, making use of the controls: ailerons, elevator, rudder, and engines. The objective is to maintain a safe speed and flight path as the aircraft approaches the airport.
- Runway: As the airplane approaches the airport, the Air Traffic Controllers give the pilots directions to guide the aircraft down and adjust its altitude, heading, and speed to adequately align with the runway.
- Landing Configuration: Prior to landing, the aircraft must be prepared and fully configured to carry out said procedure. Among other things, the pilots lower the landing gear and the flaps so that the plane can achieve a lower speed.
- Touchdown: During the final approach to the runway, the pilots precisely maintain a speed and attitude to maintain a trajectory to ensure a smooth and safe landing. The so called ‘pilot flying’ controls the aircraft and flies it down, while the ‘pilot monitoring’ monitors the aircraft parameters for maximum safety during the landing.
- Reverse Thrust: Along with other devices used for stopping, such as spoilers and brakes, the pilots typically activate the reverse thrust, which pushes the airflow from the engines in the opposite direction, helping the plane rapidly slow down.
- Rollout and Taxi: After the landing, the airplane is taxied out of the runway onto a taxiway. From there, it is given instructions to taxi to a ramp or a gate, where the engines are shut down and the aircraft is prepared for deboarding.
- Engine Shutdown and Deboarding: Finally, as the aircraft reaches the gate, the engines are shut down, stairs or an airbridge are attached to the plane, and the passengers can safely exit the aircraft onto the platform or terminal, respectively.
- An engine failure, electrical malfunction, depressurization, or any other problem inside of the aircraft will not stop the wings from working as they should and generating lift.
- Do not forget that in the unlikely event that an aircraft loses all engines, it will not drop like a stone, rather, it will glide down to an airport or a safe area where landing can be achieved. This is thanks to the altitude it flies at and its forward speed, allowing lift to form on the wings despite the loss of thrust, because it is designed to do so.