How does a plane fly?

This is a very fundamental question that a newbie will ask. Lets discuss the forces that acts on an aircraft during flight.



A = Lift, B = Thrust, C = Weight, D = Drag

So in order for an aircraft to have a level flight, this relations must comply.
A = C
B = D

If A greater C then aircraft will climb but if A lesser C the aircraft will descend. When B greater D the aircraft will speed up but if B lesser D then it will slow down. Therefore it is important to understand how all four forces work, then of course you need to understand how lift is created too.

While I have done some research on the internet for the 2 theories, I found out 2 that is used today are the Bernoulli explanation and the Newtonian explanation. Both contribute to an intuitive understanding of how lift is created.

Here is an excerpt from "How Stuff Works" site on Bernoulli

The Longer Path explanation (aka Bernoulli) holds that the top surface of a wing is more curved than the bottom surface. Air particles that approach the leading edge of the wing must travel either over or under the wing. Let's assume that two nearby particles split up at the leading edge, and then come back together at the trailing edge of the wing. Since the particle traveling over the top goes a longer distance in the same amount of time, it must be traveling faster.

Bernoulli's equation, a fundamental of fluid dynamics, states that as the speed of a fluid flow increases, its pressure decreases. The Longer Path explanation deduces that this faster moving air develops a lower pressure on the top surface, while the slower moving air maintains a higher pressure on the bottom surface. This pressure difference essentially "sucks" the wing upward or pushes the wing upward.

Here is another on Newtonian

Isaac Newton stated that for every action there is an equal, and opposite, reaction (Newton's Third Law). You can see a good example of this by watching two skaters at an ice rink. If one pushes on the other, both move -- one due to the action force and the other due to the reaction force.



In the late 1600s, Isaac Newton theorized that air molecules behave like individual particles, and that the air hitting the bottom surface of a wing behaves like shotgun pellets bouncing off a metal plate. Each individual particle bounces off the bottom surface of the wing and is deflected downward. As the particles strike the bottom surface of the wing, they impart some of their momentum to the wing, thus incrementally nudging the wing upward with every molecular impact.

Then again "How Stuff Works" has another explanation on Lift is generated.

Pressure Variations Caused By Turning a Moving Fluid
Lift is a force on a wing (or any other solid object) immersed in a moving fluid, and it acts perpendicular to the flow of the fluid. (Drag is the same thing, but acts parallel to the direction of the fluid flow). The net force is created by pressure differences brought about by variations in speed of the air at all points around the wing. These velocity variations are caused by the disruption and turning of the air flowing past the wing. The measured pressure distribution on a typical wing looks like the following diagram:



A. Air approaching the top surface of the wing is compressed into the air above it as it moves upward. Then, as the top surface curves downward and away from the airstream, a low-pressure area is developed and the air above is pulled downward toward the back of the wing.
B. Air approaching the bottom surface of the wing is slowed, compressed and redirected in a downward path. As the air nears the rear of the wing, its speed and pressure gradually match that of the air coming over the top. The overall pressure effects encountered on the bottom of the wing are generally less pronounced than those on the top of the wing.

C. Lift component

D. Net force

E. Drag component

When you sum up all the pressures acting on the wing (all the way around), you end up with a net force on the wing. A portion of this lift goes into lifting the wing (lift component), and the rest goes into slowing the wing down (drag component). As the amount of airflow turned by a given wing is increased, the speed and pressure differences between the top and bottom surfaces become more pronounced, and this increases the lift. There are many ways to increase the lift of a wing, such as increasing the angle of attack or increasing the speed of the airflow.

Confused already? Why not try this experiment. While driving or someone else is driving, stick your palm out (Make sure there are no other cars in the opposite direction). Place it horizontal like a wing on an aircraft, while the car is still moving change the angle of your palm. You will realise that your palm will be push up or down when you change the angle of your palm, it something quite similar to the expalnation above.

Though it is not the best experiment, but it will give you a rough understanding how would a wing work. Also by trying out the different angles of your palm, you realised that different attack angles push your palm up or down.

Happy Experimenting.