four forces of flight bird
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The four forces of flight

You may be asking yourselves “Why is he talking about this?” Well, the four forces of flight affect us all. It surrounds us and provides us! 

Just sit in a garden and watch what is just around you. Nature shows us the FFF. It could be the leaf falling from the tree or birds gliding to the feeding table. The ability of a bird to fly is a scientific phenomenon known as the Four Forces of Flight.

So what are the four Forces of Flight?

The FFF is all around us and are:

  • Thrust
  • Gravity
  • Lift
  • Drag
four forces of flight wing aerofoil pressure
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The force which pushes an object forwards or backwards. This force could be that Rolls Royce jet engine or the wings of a bird pushing air backwards.

The force known as THRUST is equal to the exit mass times the exit speed less the free stream mass flow rate times the free stream velocity.

‘Thrust (F) = momentum thrust + pressure thrust’


The mathematician Sir Issac Newton is an iconic and influential scientist. We have all been told of his discovery of Gravity when the apple fell from the tree. To be honest Issac never discovered gravity as it was always there he just acknowledged it. 

‘F = G*((m sub 1*m sub 2)/r^2)’


The wing as we see on an aircraft has an aerofoil cross-section. Modern jet planes have a complex system but the principle is simple. The lift is created because of the difference between high and low pressure. The air which the wing travels through starts at the leading edge and has to leave at the trailing edge at the same time. But an aerofoil section has a curved top and a flat bottom and so the top has a longer distance. So if the air has further to travel over the top it stands to reason it has to travel faster so to meet the trailing edge at the same time. This addition speed of travels increases the air pressure. In short, the air travelling over the top of the aerofoil section is a high pressure and the uninterrupted air travelling across the bottom is low pressure. This difference in air pressure causes lift.

‘L = Cl * A * .5 * r * V^2’


Drag is a force, with units of pounds. If you fall through the air the resistance that comes from the friction is the force of drag. Bigger the object in relation to the trust put upon it increases drag. 

As an example: jump out of a plane without opening your chute and the result is the drag is purely upon your body and you fall fast! Open that parachute and the resistance is almost equally balanced against the force of gravity. Drag is increased thus saving your life.

‘D = Cd * A * .5 * r * V^2’

So in conclusion of The Four Forces of Flight

We can invent a variety of calculations to perform different scientific tasks, lets leave that for the scientists. In practice, the force of Thrust is met with an opposite force, Drag. The force of Lift is contained by the force of Gravity

About the Author

Hi, there I’m Marcus and we thank you for reading our blog on this aerodynamic phenomenon. This subject has always interested me as an aeromodeller designing and building radio-controlled gliders. I also feel tranquil while watching the bird flight as its form is what has shaped our aeronautical sciences. In nature and its forces contained within evokes query and quandary.  

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