Section 2 EO M231.02 – DESCRIBE THE PRODUCTION OF LIFT BY AN AIRCRAFT WING
Resources needed for the delivery of this lesson are listed in the lesson specification located in A-CR-CCP-802/PG-001, Chapter 4. Specific uses for said resources are identified throughout the Instructional Guide within the TP for which they are required.
Review the lesson content and become familiar with the material prior to delivering the lesson.
Create presentation slides or handouts of Figures A-1, A-2, B-1 and C-1.
N/A.
An interactive lecture was chosen for TP1, TP2 and TP4 to introduce the production of lift and give an overview of it.
An in-class activity was chosen for TP3 and TP5 as it is an interactive way to provoke thought and stimulate interest among cadets.
Review for this lesson is from EO M231.01 (The Four Forces That Act Upon an Aircraft). Review the four forces that act upon an aircraft and the condition of equilibrium.
By the end of this lesson the cadet shall be expected to describe the production of lift by an aircraft wing.
It is important for cadets to learn about the production of lift by an aircraft wing so that they can develop an understanding of subsequent and related principles of flight.
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Teaching point 1
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Explain That Air Acts Like a Fluid Insofar As It Has Inertia, Speed, and
Pressure
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Time: 5 min
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Method: Interactive Lecture
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Air follows Newton’s laws of motion:
Newton’s first law predicts that air, being a gaseous fluid, tends to remain in motion when it is moving.
Newton’s second law of motion requires that a force must be applied to change the air’s motion.
Newton’s third law of motion allows the aircraft wing, by applying a force that changes the motion of air, to develop lift through an opposite and equal reaction.
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The fact that air has mass is very important in aviation. Even though air’s mass is less than the mass of most solids, its mass is still great enough to allow an aircraft to fly and to allow the aircraft to control its own flight. |
How does air follow Newton’s first law of motion?
How does air follow Newton’s second law of motion?
How does air follow Newton’s third law of motion?
When in motion, air tends to remain in motion.
When in motion, a force must be applied to change air’s motion.
When air’s motion is changed, an equal and opposite reaction results.
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Teaching point 2
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Introduce Bernoulli’s Principle, Which States That a Liquid’s
Pressure Drops When Its Speed Increases (Venturi Effect)
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Time: 10 min
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Method: Interactive Lecture
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To develop the equal and opposite reaction described by Newton’s third law of motion, the wing is given a shape that takes advantage of Bernoulli’s Principle to make the air change direction. Air behaves like a fluid since it has pressure and speed. As airspeed increases, its pressure drops. A wing uses Bernoulli’s Principle to deflect air, which causes an equal and opposite reaction.
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Show the cadets a slide or handout of definitions of Bernoulli’s principle shown in Figure A-1. |
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One part of Bernoulli’s Principle that is very useful to remember is that if air speed increases, pressure decreases and if speed decreases, pressure increases. This is an inverse relationship between airspeed and air pressure. This part of Bernoulli’s Principle is often referred to as the venturi principle. The shape of the wing is carefully calculated to decrease pressure above while increasing pressure below. |
What relationship exists between air speed and air pressure?
What is the wing’s connection between Newton’s third law and Bernoulli’s Principle?
What is a wing’s shape calculated to do?
An inverse relationship: as speed increases, pressure drops and as speed drops, pressure increases.
A wing uses Bernoulli’s Principle to deflect air, which causes an equal and opposite reaction.
A wing’s shape is calculated to decrease pressure above while increasing pressure below.
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Teaching point 3
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Have the Cadets Explore Bernoulli’s Principle
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Time: 10 min
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Method: In-Class Activity
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The pressure of moving air can be examined by blowing gently over a small piece of curved paper. The air does not push the paper down as might be intuitively assumed. Instead, the paper behind the curve rises toward the moving air. This happens because the air pressure drops over the paper due to the air’s increased speed – this would seem to match the description of speed/pressure relationship. The curvature in the paper enhances the effect of the lowered air pressure.
A similar effect can be observed when air moves past any object that is light enough to be affected by the drop in air pressure associated with movement. A balloon is light enough to show this effect clearly.
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Show the cadets a slide or handout of Figure A-2. Have one half of the class duplicate this paper airfoil activity at their desks while the other half of the class performs the following activity with balloons. Then, have the groups switch and repeat. |
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ACTIVITY
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Time: 5 min
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The objective of this activity is to have the cadets reduce the air pressure over a sheet of paper and observe the results.
Paper 8 1/2 x 11, and
Pencil.
N/A.
1.Tear a sheet of paper 8 1/2 x 11 vertically, into two pieces.
2.Curve one end of the sheet gently over a pencil as shown in Figure A-2.
3.Blow gently over the paper as shown in Figure A-2.
4.Observe that the paper rises into the moving air.
N/A.
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ACTIVITY
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Time: 5 min
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The objective of this activity is to have the cadets see the action of air pressure.
Balloons, and
String.
Hang two long well-inflated balloons at the front of the classroom so they are at shoulder height, hanging 15 centimetres apart. This must be in a draft-free area. The balloons must hang very still so that the effect is clearly visible.
Alternatively, for more visual effect, this can also be done with helium-filled balloons with strings weighted to the floor, floating a metre high.
Have each cadet approach the balloons slowly, one at a time, and blow gently between them. The cadet will observe that the balloons move toward each other, not apart.
If a single balloon is used, the cadet can simply blow beside the balloon and the balloon will move toward the moving air.
N/A.
Why does the paper airfoil rise when a cadet blows over it?
Why do balloons move toward moving air?
Why was the paper deliberately curved before blowing over it?
Air pressure over the paper drops as the air moves, so the still air below the paper pushes it up.
Moving air pressure is lower, so still air pushes the balloon into the moving air.
The curvature in the paper enhances the effect of the lowered air pressure.
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Teaching point 4
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Introduce Angle of Attack
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Time: 5 min
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Method: Interactive Lecture
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An aircraft wing is an airfoil because of its cross-sectional shape. The top surface is curved outward (convex curvature). Therefore, the air flowing over the top has further to go, over the curve, and so it must move faster which, as we know, will result in lower pressure. This happens above the wing.
Below the wing, the air is deliberately slowed to increase its pressure. This is done by curving the surface slightly inward (concave curvature) and by sloping the wing so that it is slightly higher at the front (leading edge) than it is at the back (trailing edge). This angle of the wing’s under-surface, which encounters the moving air, is called the wing’s angle of attack.
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Use a model aircraft to demonstrate to the cadets that the wing’s angle of attack increases when the aircraft’s nose is raised during flight. |
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The greater the wing’s angle of attack, the more air the under-surface of the wing will encounter, thereby generating more lift. This is a direct relationship between angle of attack and lift. Increasing the wing’s speed will also cause it to encounter more air, thereby generating more lift. This is also a direct relationship between speed and lift. |
There is a limit to the amount of lift that can be produced by merely increasing the angle of attack. Long before the wing becomes vertical, it stops generating lift above and this often happens abruptly. The wing “stalls” and stops generating lift when this happens.
Which surface of an aircraft wing is curved outward (convex)?
What shape is often given to the underside of an aircraft wing?
What happens to air pressure under a wing as angle of attack increases?
The top surface of a wing is curved outward.
A slight inward, or concave, curve is often given to an aircraft wing.
The pressure increases as angle of attack increases.
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Teaching point 5
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Have Each Cadet Create and Fly an Airfoil
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Time: 25 min
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Method: In-Class Activity
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The objective of this activity is to have the cadets see an airfoil lift itself in a stream of moving air.
Index cards,
Tape,
Hole punch or sharp pencil,
Scissors,
Plastic drinking straw,
Bamboo skewers or large straightened paper clips,
Base that the skewers can stick into (Styrofoam or corrugated cardboard), and
Hairdryer or fan.
This activity may take place at the cadets’ desks/tables.
Give each cadet an index card to fold into an airfoil shape with mounting holes for the launching skewers. The cadets will:
1.Fold the card in half. Tape the top of the card down to the bottom half of the card so that about 6 mm (1/4 inch) of the bottom shows, leaving the top in a curve and the bottom flat. This will produce a cross-section airfoil shape.
2.Use the hole punch (or a sharp pencil) to put two sets of holes in the thickest part of the airfoil.
3.Cut the straw so you get two pieces 5 cm (2 inches) long. Fit these mini-straws through the holes in the airfoil.
4.Set the airfoil on the base and slip a skewer or unbent paper clip through each of the mini-straws and into the base.
5.Use the hairdryer or fan to move air over the airfoil to create lift. Try it both ways—with the flat side of the airfoil on the bottom and with the flat side on the top. Note which position the airfoil is in when it climbs best.
N/A.
The cadet’s participation in creating and flying an airfoil will serve as the confirmation of TP5.
How does the top surface of a wing generate lift?
How does the under-surface of a wing generate lift?
What determines how much lift is produced by a wing at a given speed?
The top surface of a wing generates lift by lowering air pressure over the wing.
The under-surface of a wing generates lift by raising air pressure under the wing.
The angle of attack will determine how much lift is produced at a given speed.
N/A.
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There are other methods of producing lift, such as rocketry, but airfoils are by far the most common, not just because of their elegance, but because they are best suited to prolonged horizontal flight.
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C3-017 (ISBN 1-895569-23-0) Schmidt, N. (1998). Fabulous Paper Gliders. New York, NY: Sterling Publishing.
C3-058 (ISBN 1-4027-3034-9) Schmidt, N. (2005). Paper Creations Paper Airplanes. New York, NY: Sterling Publishing.
C3-091 (ISBN 1-55652-477-3) Carson, M. K. (2003). The Wright Brothers for Kids: How They Invented the Airplane. Chicago, IL: Chicago Review Press.
C3-116 A-CR-CCP-263/PT-001/(ISBN 0-9680390-5-7) MacDonald, A. F. and Peppler, I. L. (2000). From the Ground Up: Millennium Edition. Ottawa, ON: Aviation Publishers Co. Limited.
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