Deakin Communicating Science 2016

EES 200/101

Applied Physics: Flight

Welcome back to applied physics, this week we will look at the basic principles of flight.
So the practical uses for flight are rather obvious, you slap wings on a big thing full of people and you can fly… right? That is a rather blunt way of putting it but the incredible thing about flight is flight itself as it gives us the ability to travel such great distances in a relatively short time. So we all know what flight is used for but how exactly does the phenomenon occur?

So there are a couple of properties of motion that we need to go over as we explore flight and the first one is that any object will at all times be subjected to 4 forces which are push, pull, gravity and normal.

balancedforces

 

Now some people may think or ask if an object is not moving how is there any force on it? A reasonable question – if it’s not moving how is there force acting? The answer is quite simple though, if an object is at rest it doesn’t mean no forces are acting it means that the net force is equal to zero meaning that the forces cancel each other out leaving the object at rest. Now the same thing that applies to a block on the ground applies to a plane in the air, though some of the forces change their name. The 4 forces that act on a plan are thrust, wind resistance, lift and gravity with the key force being lift. Now that we have identified lift as our key force lets go into how it is achieved on a large/heavy metal object.

 

So the other property of motion that we need to go through is Bernoulli’s principle as it is how we will achieve our desired lift. Bernoulli’s principle states “that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy” (Clancy,L J 1975) so there is an inverse relationship between the velocity and  pressure. An example of how this works is a chimney, the top of the chimney has faster moving air going across the top than the air at the bottom so the air at the top is low pressure relative to the chimney as such the air will move to reach equilibrium and force itself up the chimney.
slide_20

 

So how do we apply this to making a plane fly? To utilise Bernoulli’s principle, planes are designed in a way as such the wings are what we call an aerofoil which are specially designed shapes to make air flow faster over the top of the wing and slower directly underneath. This as we just learned makes the air rush towards the low pressure zone (on top of the wing) pushing up on the underside of the wing, this is how lift is achieved. The important thing to note here is that the lift generated needs to be equal to or greater than the force of gravity (weight force) acting on the plane to achieve flight.  So in order to create enough air flow (and in fact move the plane in a “forwards” direction) we need to create thrust, this is done by either a propeller or multiple jet engines depending on the size of the plane. It is also noteworthy that the size/wingspan of the wings determines how much lift you can achieve however there is a size vs weight ratio that needs to be considered. With enough lift and thrust to move the plane forwards and up flight is achieved.

That’s all for this week hopefully everyone knows a little bit more than they used to after reading this, if you have any questions/feedback please feel free to leave me a comment.

 

Clancy, L J (1975). Aerodynamics. London, Pitman Publishing Limited, pg16-32

Mrsciguy.com. N.p., 2016. Web. 8 May 2016.

Mrsciguy.com. N.p., 2016. Web. 8 May 2016.

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This entry was posted on May 8, 2016 by in Uncategorized.

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