How does an airplane fly?

We all know that an airplane is heavier than air, so how does that 500,000 pound metal object fly?

Grade 8: Topic Choice 1

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y!

The answer is FORCE

Remember, Force = mass x acceleration, and is the capacity to do work or cause change

It actually has real applications, and explains how an airplane can fly!

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Four Forces Affecting an Airplane in Flight

When forces are balanced, the airplane is moving at a constant speed and altitude. If we change any force, we change the motion of the aircraft.

Click on a force to

learn more about it

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Lift

• Lift is the force that pushes an airplane up into the air

• It is caused by the shape of an airplane’s wings, and the air flowing over the wing.

• Lift is the most complex of the 4 forces because it cannot be created without forward motion of the airplane.

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• Picture the air going over the wing as paired particles.

How do we create lift?

1

2

2

Notice the distance the red partner has to travel from 1 to 2 versus the distance the blue partner travels

airflowfrontback

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• The particles going over the top of the wing (red) have to travel a further distance than their partners (blue) on the bottom of the wing.

• This means the air on top of the wing is moving faster than the air on the bottom of the wing because speed = distance/time

Fast moving air = less pressureSlow moving air = more pressure

Increased pressure on the bottom of the wing and decreased pressure on the top of the wing creates LIFT

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If we increase lift,

the plane will go up, or ascend/climb.

Lift

Drag Thrust

Weight

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If we decrease lift,

the plane will go down, or descend.

Lift

Drag Thrust

Weight

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How might we change lift?

• Change the angle of the wing to change the airflow pattern.

(Click screen to find out)

• Increase speed to increase the airflow over the wing, further decreasing the pressure above the wing, and increasing lift.

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Thrust

• Thrust is the force that pushes an airplane forward

• It is produced by propellers or jet engines

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If we increase thrust,

the plane will speed up, or accelerate.

Lift

Drag Thrust

Weight

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If we decrease thrust,

the plane will slow down, or decelerate.

Lift

Drag Thrust

Weight

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How might we change thrust?

• Increase power, and therefore speed (accelerate)

(Click screen to find out)

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• Decrease power, and therefore speed (decelerate)

Drag

• Drag is the force that slows the airplane down• It is similar to friction

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If we increase drag,

the plane will slow down, or decelerate.

Lift

Drag Thrust

Weight

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If we decrease drag,

the plane will speed up, or accelerate.

Lift

Drag Thrust

Weight

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How might we change drag?

• Change the shape of the wing to interfere with airflow

(Click screen to find out)

• Put landing gear down, which will interfere with airflow and slow the plane down.

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Weight

• Weight is the force of a mass being attracted to another mass

• With airplanes, this force is the mass of the plane times acceleration, in this case, gravity

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If we increase weight,

the plane will go down, or descend.

Lift

Drag Thrust

Weight

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If we decrease weight,

the plane will go up, or climb/ascend.

Lift

Drag Thrust

Weight

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How might we change weight?

• Add cargo or passengers to increase weight– Is this something we can do in flight?

• Decrease cargo or passengers to decrease weight.– Think skydiving or food/supply drops

(Click screen to find out)

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Remember how balanced forces do not cause a change in motion?

• Lift and Weight• Thrust and Drag

If the forces are balanced, the airplane is no longer changing speeds or altitudes (height from the ground). It is cruising at a constant speed and altitude until one of these forces is manipulated.

(Click screen for answer)

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How do the forces affecting an airplane balance? What are the pairs of opposite forces?

Just to introduce the idea:• Lift is a more complex force and one that can only be created by

wind/air going over the wing.• This means that thrust must be occurring in order to produce

lift.• As the plane accelerates (increased thrust), lift increases as well

because air is moving faster over the wing, creating a lower pressure above the wing and therefore increased lift.

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When discussing these forces on airplanes, they are somewhat intertwined and not as clear cut as

previously presented. However, for this lesson we have been, and will continue to, focus on the primary

reaction to increasing or decreasing the four forces.

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Let’s Play!

Thrust

Lift

Drag

Weight

Click the purple arrows to increase or

decrease the force and see what

happens!

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Activity!

Increase Lift

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Decrease Lift

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Increase Weight

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Decrease Weight

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Increase Thrust

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Decrease Thrust

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Increase Drag

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Decrease Drag

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Quiz

• If you are ready to take the quiz, click– In the quiz, click on your answer choice to see if

you are correct.

• If you would like more review, click

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Question 1

The four forces acting on an airplane are _____________________.

a) lift, gravity, drag, frictionb) drag, thrust, gravity, climbc) lift, thrust, weight, dragd) lift, friction, gravity, weight

Correct! Great Work!

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Try again…that was a tough one

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Question 2

Which force could be increased to result in the airplane descending?

a) Liftb) Dragc) Weightd) Thrust

Correct! Great Work!

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Try again…that was a tough one

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Question 3

If you decrease thrust, what will happen to the airplane?

a) Speed up (accelerate)b) Slow down (decelerate)c) Climb (ascend)d) Descend

Correct! Great Work!

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Try again…that was a tough one

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Question 4

Which forces must be equal and opposite to balance an airplane?

a) Drag & Weight, Lift & Thrustb) Lift & Drag, Thrust & Weightc) Lift & Weight, Thrust & Drag

Correct! Great Work!

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Try again…that was a tough one

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YOU ARE FINISHED!!!

You are now ready to move on to more complex force applications for airplanes!

Next time someone asks how or why an airplane can fly…you have the answer!

DONE!