1. Four Forces Acting on an Aircraft
Four Forces Acting on an Aircraft

2. The Four Forces
Acting On An Aircraft
In Flight Are:
Lift
Weight
Thrust
Drag

3. Lift
The upward force that sustains the aircraft in flight.

4. How Lift is Created: Newton’s Three Laws of Motion
An object in motion stays in motion and object at rest stays at rest, unless acted upon by an outside force. Also known as the Law of Inertia.
F = ma. Force and acceleration are directly proportional according to mass.
For every action, there is an equal and opposite reaction.

5. Bernoulli’s Principle
How Lift is Created:
Bernoulli’s Principle
The total energy in any system remains constant. If one element increases, another must decrease to counter balance it.

6. How Lift is Created:
Air flowing over the wing’s upper surface accelerates as it passes through the constricted area just as it does in the venturi tube (Newton’s Laws of Motion and Bernoulli’s Principle). The result is a decrease in pressure on the upper surface of the wing that results in the phenomena known as lift.

7. Downwash
Downwash is the flow of air downward towards the trailing edge of the wing. Also, the airflow passing under the wing is deflected downward by the bottom surface of the wing. The wing receives an upward force, therefore, downwash contributes to lift.

8. Weight The downward force due to gravity, directly opposed to lift.
The weight of an aircraft acts through the Centre of Gravity (C of G).
It is the point through which the resultant of the weights of all the various parts of the aircraft pass in every attitude it can assume.

9. NOTE: You must use the buttons in the Confirmation Stage

10. Four Forces Acting on a Aircraft
Theory of Flight
Four Forces Acting on a Aircraft
Let's try a few review questions on Theory of Flight:
Question #1 - Which of the following are not one of the 4 main forces? A
Lift B
Weight C
Torque D
Drag

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13. Four Forces Acting on a Aircraft
Theory of Flight
Four Forces Acting on a Aircraft
Let's try a few review questions on Theory of Flight:
Question #2 - Name the scientist who theorized “The total energy in any system remains constant. If one element increases, another must decrease to counter balance it.” A
Newton B
Bernoulli C
Ventri D
Coriolis

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16. Thrust
The force exerted by the engine and its propeller which pushes air rearward with the object of causing a reaction, or thrust, in the forward direction.

17. Thrust
Propellers move a large amount of air back at a relatively slow speed.
Jets move a small amount of air back at a relatively fast speed.
The effect is the same!

18. Drag
Resistance an aircraft experiences when moving forward through the air.

19. Types of Drag: There are two main types of drag they are:
Parasite Drag
is the term given to the drag of all those parts of the aircraft which do not contribute to lift (e.g. the fuselage, wheels, antennas, etc.)
Induced Drag
is caused by those parts of the aircraft which are active in producing lift (e.g. the wing). Therefore, it is always present and cannot be eliminated.

20. Parasite Drag: Parasite drag may be divided into two components:
Form Drag
refers to the drag created by the form or shape of a body as it resists motion through the air. Streamlining the exterior components of the aircraft helps reduce this type of drag.

21. Parasite Drag: Parasite drag may be divided into two components:
Skin Friction
refers to the tendency of air flowing over a body to cling to its surface; dirt, mud or ice that has accumulated on the aircraft contributes to skin friction.

22. Types of Drag: Induced Drag
The greater the lift, the greater the induced drag. Airflow over the top of an airfoil tends to flow inward, airflow under the bottom of the wing tends to flow outwards, at the trailing edge, small eddies are created. These tend to move to the tips resulting in wing tip vortices which are the chief contributors to induced drag.

23. NOTE: You must use the buttons in the Confirmation Stage

24. Four Forces Acting on a Aircraft
Theory of Flight
Four Forces Acting on a Aircraft
Let's try a few review questions on Theory of Flight:
Question #3 - What are the two main types of drag? A
Induced & form B
Induced & parasite C
Parasite & skin friction D
Parasite & form

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27. Four Forces Acting on a Aircraft
Theory of Flight
Four Forces Acting on a Aircraft
Let's try a few review questions on Theory of Flight:
Question #4 - Name the drag that refers to the shape of a body. A
Parasite B
Induced C
Form D
Skin friction

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30. Four Forces Acting on a Aircraft
Theory of Flight
Four Forces Acting on a Aircraft
Congratulations!!
You have now completed the Four Forces Acting on a Aircraft lesson of the Theory of Flight Module. Of course, this lesson is always available to you for future reference if required.
You are now ready to move along to the next Theory of Flight lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam.
Good Luck!