# Day THREE

Webpages/Articles found:

http://discovermagazine.com/2001/apr/featphysics#.UYm894IU5BR

This article gives interesting insight on what causes lift for an airplane. The well known theory of Bernoulli’s principle works on the idea that as a wing passes through the air the its shape make the air travel more over the top of the wing than beneath it. This creates a higher pressure are beneath the wing than above it. The pressure difference cause the wing to push upwards and lift is created.

However, there is a new  theory to lift, which is based primarily on Newton’s laws and the Coanda Effect. The theory is that lift is a reactive force. As air travels over the wing, air is bend down because of the tendency of the air to stick to the surface it is traveling over (Coanda Effect). To bend the air down, the wing exerts a force on the air. There is an equal and opposite reaction to this force: the air exerts an upward force on the wing. A pilot can increase this lift force by traveling faster or by increasing the angle of attack (explained below) which both divert more air downward,increasing lift due to Newton’s three laws.

http://howthingsfly.si.edu/aerodynamics/alternative-theories-lift

Another site,however, says that the downward push on the air results from air pressure differences on the wing “it is an effect of lift, not the cause of it”.

Take off:

The relationship between angle of attack and lift:

angle of attack is the angle between the direction of the wind and the direction the wing of the airplane is pointed in.

At a small angle, most of the lift comes from the coanda effect and newton’s three laws. As the angle increases, some of the air is deflected downward off the bottom of the wing, which causes lift because of equal and opposite forces (newton’s laws). There is a critical angle of attack where the air stream begins to separate from the surface of the wing and starts a swirling motion which decreases lift and the airplane might stall.

Turns during flight:

Airplanes must be banked to make a turn because the lift force is also used to make the airplane turn. This is similar to normal force on a banked surface. When the wings are level, lift acts directly opposite to gravity. However,when the airplane is banked, gravity acts in vertically, but now the lift has a horizontal component.

Different parts of an airplane that affect lift:

http://www.grc.nasa.gov/WWW/k-12/airplane/airplane.html

WInglets are on the end of each wing on modern airplanes and these are put in place to decrease drag. High pressure on the lower surface creates a natural airflow that makes its way to the wingtip and curls upward around it. When flow around the wingtips streams out behind the airplane, a vortex is formed. These twisters represent an energy loss and are strong enough to flip airplanes that blunder into them. Flaps are deployed downward on takeoff and landing to increase the amount of lift produced by the wing. As the flaps are extended, the curvature of the wing is increased. Due to the coanda effect and newton’s laws, more air is bent downward, which causes a greater lift force.  Slats, like flaps, are used at takeoff and landing to produce additional force and are on placed on the front of the wings. The spoilers are mechanisms that disrupt the airflow over the wing to decrease lift and increase drag.

Summary of Learning:

From my research today I learned a great deal about lift, the effect of the angle of attack, the process of turning an airplane, and the different mechanics of an airplane which allow it to take off, fly, and land. I still need to learn more about the mechanics to allow a plane to cover its journey from the ground to the air and back to the ground.

percent: 45-50%

Misconceptions/surprises:

The biggest misconception I had today was that the air travels faster over the top of the wing to cover the same distance air travels at the bottom of a wing. I thought because of this the greater velocity of the air and the lower pressure, lift occurs because of the pressure difference. This is confusing because in essence the work done by the plane allows it to fly, which is wrong. Newton’s laws better explains the lift force that allows planes to fly. However, i am still confused because other sources say that the air that is pushed down from the top of the wing that creates an equal and opposite force that creates lift is caused by a difference in air pressure. So it might be that both Bernoulli’s principle and newton’s laws cause lift.