Undrstanding the Aerofoil

8/13/2019 Undrstanding the Aerofoil

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Understanding the Airfoil

Mr. Presti

Northport Middle School Technology
http://www.mae.ncsu.edu/research/flight_Research/F18/pictures/f18tkof2.gif


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What is aerodynamics?

The word comes from two Greek words:aerios = concerning the air.dynamis = meaning powerful.

Aerodynamics is the study of forces andthe resulting motion of objects through theair.


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4 Forces of Flight

1. Gravity (Weight) : Pulls the plane down.

Gravity pulls everything near or on Earthtowards the center of Earth.

2. Drag : Holds the plane back. Drag is theresisting force called friction. Friction willcontinue to push against objects until itstops. Water and air cause friction.


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4 Forces of Flight (Continued)

4. Thrust : Pushes the plane forward. Forwarddriving force of a propeller attached to anengine, or the forward force produced by gasesescaping rearward from a jet or rocket engine.

3. Lift : Pushes the plane up. Slower air on

the underside of the wing creates more airpressure than the upper curved part of thewing (faster moving air)creating lift.


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Forces Acting on a Plane


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Tests the EffectsTo test the effects of pressure andairspeed, take a regular piece of

notebook paper and hold it up like thegirl at the left.

Blow over it and watch what happens.

When you blow across an airfoil youare increasing the speed at which theair moves across the top of the airfoil.This decreases the pressure andcauses lift.


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Straight and Level Flight

In order for an airplane to fly straight and level, the

following relationships must be true:

Thrust = Drag

Lift = WeightQ1 - What would happen if Drag is greater than Thrust?

Q2 - What would happen if Lift is greater than Weight?


8/23

A Few Words About Fluid A principal concept in aerodynamics is the idea that air

is a fluid (like all gases, air flows and behaves in a

similar manner to water and other liquids).

Basic aerodynamic tests are sometimes performedunderwater.

Lift and Drag can exist only in the presence of amoving fluid ( object is stationary and the fluid ismoving OR fluid is still and the object is movingthrough it ).


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A Few Words About Fluid

Consequently, neither liftnor drag can be createdin space (where there isno fluid). This explainswhy spacecraft don'thave wings unless thespaceship spends at leastsome of its time in air.
http://travel.howstuffworks.com/category.htm?cat=Spacehttp://travel.howstuffworks.com/category.htm?cat=Space


10/23

Whos Theory on Lift Is Correct?

1. Bernoulli Focused his studies on the curvature of the wing, andthe differing air pressure over the top and bottom of the wing.

2. Newton Focused his studies on the deflection of air or fluid on anobject and its reaction. (Newtons 3 rd Law)


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How Lift is Created (Bernoulli)

The Longer Path Explanation: holds thatthe top surface of a wing is more curved thanthe bottom surface. Air particles thatapproach the leading edge of the wing must

travel either over or under the wing.


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Let's assume that two nearby particles split up at theleading edge, and then come back together at the trailingedge of the wing.

Since the particle traveling over the top goes a longerdistance in the same amount of time, it must be travelingfaster.


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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 onthe bottom surface.


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Why i s i t no t en t i rely c or rec t? (HAND-OUT) (Bernoulli)

There are several flaws in this theory, although this is a verycommon explanation found in high school textbooks and evenencyclopedias:

The assumption that the two air particles described above rejoineach other at the trailing edge of the wing is groundless. In fact,these two air particles have no "knowledge" of each other'spresence at all, and there is no logical reason why theseparticles should end up at the rear of the wing at the samemoment in time.

For many types of wings, the top surface is longer than thebottom. However, many wings are symmetric (shaped identicallyon the top and bottom surfaces). This explanation also predictsthat planes should not be able to fly upside down, although weknow that many planes have this ability.


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How Lift is Created (Newtonian)

Newtons 3 rd Law: For every action there is an equal,

and opposite, reaction.

You can see a good example of this by watching twoskaters at an ice rink. If one pushes on the other, bothmove -- one due to the action force and the other due

to the reaction force.

Wing

Air Particles


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How Lift is Created (Newtonian)

Each individual air particle bounces off the bottomsurface of the wing and is deflected downward.

As the air particles strike the bottom surface of thewing, they impart some of their momentum to thewing, thus incrementally nudging the wing upward with

every molecular impact.

Wing

Air Particles


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Why i s i t no t en t i rely c or rec t? (HAND-OUT) (Newtonian)

The Newtonian explanation provides a pretty intuitive picture ofhow the wing turns the air flowing past it, with a couple ofexceptions:

The top surface of the wing is left completely out of the picture.The top surface of a wing contributes greatly to turning the fluidflow. When only the bottom surface of the wing is considered,the resulting lift calculations are very inaccurate.

Almost a hundred years after Newton's theory of ship hulls, aman named Leonhard Euler noticed that fluid moving toward anobject will actually deflect before it even hits the surface, so itdoesn't get a chance to bounce off the surface at all. It seemedthat air did not behave like individual shotgun pellets after all.Instead, air molecules interact and influence each other in a waythat is difficult to predict using simplified methods. This influencealso extends far beyond the air immediately surrounding thewing.
http://travel.howstuffworks.com/framed.htm?parent=airplane.htm&url=http://www.nadn.navy.mil/Users/math/meh/euler.htmlhttp://travel.howstuffworks.com/framed.htm?parent=airplane.htm&url=http://www.nadn.navy.mil/Users/math/meh/euler.html


18/23

Angle of AttackThe angle of attack is theangle that the wing presents tooncoming air.

This angle controls theamount of lift that the winggenerates (although it is notthe only factor).

What other factors control lift?


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Air Plane Parts


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Problem Statement

To design a model airplane that can fly as

high as possible and indefinitely with aconstant power source.


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Building Your Plane

1. Research (Generate Ideas)

2. Fuselage Construction3. Vertical/Horizontal Stabilizers

4. Motor Mount

5. Airfoil Construction (Wing Design)

6. Control Surfaces

7. Test


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Resources (Links) Airplane Parts with worksheet (quiz).http://www.grc.nasa.gov/WWW/K-12/BGA/Dan/airplane_parts_act.htm

Wing Geometry and Definitionshttp://www.grc.nasa.gov/WWW/K-12/airplane/geom.html

Wing Area Problemshttp://www.grc.nasa.gov/WWW/K-12/BGA/Melissa/wing_area_act.htm

Inventing Flight for Schoolshttp://www.inventingflightschools.org/index.html

Wright Brothers (Simulator, Movie Clips, Story Board)http://dsc.discovery.com/convergence/wright/wright.html
http://www.grc.nasa.gov/WWW/K-12/BGA/Dan/airplane_parts_act.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/K-12/BGA/Melissa/wing_area_act.htmhttp://www.inventingflightschools.org/index.htmlhttp://dsc.discovery.com/convergence/wright/wright.htmlhttp://dsc.discovery.com/convergence/wright/wright.htmlhttp://www.inventingflightschools.org/index.htmlhttp://www.grc.nasa.gov/WWW/K-12/BGA/Melissa/wing_area_act.htmhttp://www.grc.nasa.gov/WWW/K-12/BGA/Melissa/wing_area_act.htmhttp://www.grc.nasa.gov/WWW/K-12/BGA/Melissa/wing_area_act.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/K-12/BGA/Dan/airplane_parts_act.htmhttp://www.grc.nasa.gov/WWW/K-12/BGA/Dan/airplane_parts_act.htmhttp://www.grc.nasa.gov/WWW/K-12/BGA/Dan/airplane_parts_act.htm


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History of Flight (Activity Sheet)1. When did the Wright brothers achieve their historic flight? (be

specific)

2. Where did the historic flight take place?3. Why did they bring their flying machine to this particular site? (3

reasons)4. Describe their flying machine? (size, weight, engine, ect..) 5. How many times were they able to achieve flight that day?6. What was the distance of their first attempt, and how long was it up

in the air for?7. What was the furthest distance they were able to travel that day?

http://sln.fi.edu/flights/first/during.html
http://sln.fi.edu/flights/first/during.htmlhttp://sln.fi.edu/flights/first/during.html

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Undrstanding the Aerofoil

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