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Transcript of Airplanes
Angle of Attack
Newton's Laws and Lift
The wing as a Pump
-In aerodynamics, angle of attack specifies the angle between the chord line (the line between the leading and tail edges of the wing) of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere
-To understand lift, one must understand Newton's 1st and 3rd laws.
-The wing pushes down lots of air (downwash) to generate lift.
How Airplanes Work
-The popular explanation of lift is a result of Bernoulli's principle: as air speeds up, pressure is lowered. So a wing generates lift because the air goes faster over the top of the wing, creating a region of low pressure.
- Why does air travel faster over the top? Many have resorted to the argument that the distance the air traveled is directly related to its speed. A common claim is that when the air splits at the leading edge, the top and bottom parts must converge. This is called the "principle of equal-transit times".
-However, the air at the top of the wing gets to the trailing edge considerably before the air under the wing.
-Angle of attack cannot be strictly defined on an airplane, because the wing can bend.
-The popular explanation also implies that inverted flight is impossible.
It also does not address acrobatic airplanes, which have symmetric wings
(top/bottom are the same shape).
-Angle of attack effects the lift constant, as seen in this graph:
-The popular explanation also has another shortcoming: it ignores
the work that's done. Lift requires power, which is change in work/change in time
Newton's First Law: A body at rest remains at rest, or a body in motion remains in motion, and at a constant velocity, unless acted upon by a force.
Newton's Third Law: For every action there is an equal and opposite reaction.
Jets and Jet Planes
-Jets help to propel an aircraft forwards, lift and AOA keeps the aircraft flying.
A masterpiece by:
-In order to generate lift, the wing must do something to the air. What the wing does to the air is the action while lift is the reaction.
-This allows for airplanes to be more efficient and faster.
This figure shows streamlines, as they should be drawn. The air passes over the wing and is bent down. The bending of the air is the action. The reaction is the lift on the wing.
-To an observer on the ground, this downwash goes straight down, generating lift. The lift of a wing is equal to the rate of change in momentum of the air it is diverting down.
-Using F=ma (Force = mass x acceleration, Newtons law) a wing can generate a lot of lift, especially when used with a jet engine to increase acceleration.
- Even though they are thin, wings divert air