Regional Gliding School l Lift l Weight l Thrust l Drag

Regional Gliding School

Lift Weight Thrust Drag


The upward force that sustains the aircraft in flight.


Newton’s Three Laws of Motion For every action there is an equal and opposite

reaction An object when in motion tends to remain in motion An external force must be applied to alter that state

of uniform motion


Bernoulli’s Principle The total energy in any system remains

constant. If one element increases, another must decrease to counter balance it.


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.


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.


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.

Regional Gliding SchoolNOTE: You must use the buttons in the Confirmation Stage


A

B

C

D

Lift

Weight

Drag

Let's try a few review questions on Theory of Flight:

Question #1 - Which is not a force acting on a aircraft?

Torque

Theory of FlightTheory of FlightFour Forces Acting on a AircraftFour Forces Acting on a Aircraft

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Flying Scholarship Program


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That answer is correct.

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Lift

Weight

Thrust

Drag


A

B

C

D

Newton

Bernoulli

Coriolis


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.”

Ventri



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Bernoulli’s Principle The total energy in any system remains

constant. If one element increases,another must decrease to counterbalance it.


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


The effect is the same whether the thrust is produced by a propeller moving a large mass of air backward at a relatively slow speed or by a jet moving a small mass of air backward at a high speed.


Resistance an aircraft experience when moving forward through the air.


There are two main types of drag they are:

1 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.)


Parasite drag may be divided into two components:

I. 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.



II. 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.



2 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.


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.


NOTE: You must use the buttons in the Confirmation Stage


A

B

C

D

Induced & form

Induced & parasite

Parasite & form


Question #3 - What are the two main types of drag?

Parasite & skin friction



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1 Parasite Drag

2 Induced Drag


A

B

C

D

Parasite

Induced

Skin friction


Question #4 - Name the drag that refers to the shape of a body.

Form



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I. 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.


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!


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Regional Gliding School l Lift l Weight l Thrust l Drag