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How do Airplanes Fly?

People have got so used to watching the skies filled with jet trails that we never stop and realise its truly magic that hundreds of tonnes of metal with 500 people aboard can hop across the Atlantic and in a fraction of a day you could be waking up to a new language, new culture or lost in the middle of nowhere!

So how is this even possible? Just a little bit over a hundred years back we were barely experimenting with wooden planes that flew for a few meters up and forward before crashing right back to the ground!

It is easy to take the physics of flight for granted, as well as the ways in which we exploit them to achieve flight. We often watch an aircraft in the sky with no greater understanding of the principles involved than with a caveman.

To answer this question, we have to understand the world of fluid mechanics. Basic aerodynamics means that air is just like a fluid; a matter that has weight and occupies space. The entire atmosphere in which planes fly or propel through is a massive fluid layer. We achieve a certain amount of forces by the use of jets and propellers that thrust the aircraft forward. To achieve flight, we exploit four main aerodynamic forces: Lift, Weight, Thrust and Drag. These are the four forces constantly attached to an aircraft but in different strengths and directions.

The image below here shows these four basic forces and the direction in which they act in.

Thrust is what's produced by the aircrafts propellers or jet engines. It is the key requirement if the aircraft's is going to move or go anywhere! This thrust increases the aircrafts forward moving velocity e.g. taking off on the runway. The next key element in the force is Lift. This is achieved due to the curved cross-section shape of the wing as seen in the image. This curvature is important as to play with the airflow both underneath and on top of the wing. As the aircraft moves fast enough forward on the runway, air starts to flow and gets split on contact with the wing. Some of it flows over and some underneath the wing.

The other two forces are Drag and Weight. Drag is what causes the air pushing against the aircraft to reduces its efficiency to move faster through the air. In order to even move and start creating enough airflow over the wings, the thrust will need to be much higher than the drag. This of course is achieved through powerful engines fitted on the aircraft. That is why they use close to maximum engine power for takeoff and the reason why living near an airport can be noisy! Once the aircraft's thrust has overcome drag and it is blasting forward at high speed, the differential air flow pressure over the wings starts to generate lift.

Due to the increased curvature on the top side of the wing, the air tends to flow much faster compared to the flow underneath. This difference in airflow speed creates a significant pressure difference with high pressure below and low underneath the wing aerofoil (See Image below), and therefore causing the wings to lift upward. This gets the airplane airborne as the lift then overcomes the weight of the aircraft and 8 hours later you are sipping on a coffee across the Atlantic!


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