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The sum of the total reactive aerodynamic forces acting on an aerofoil is called (1) _____ and acts through the (2) _____.
• A
(1) Total reaction; (2) Centre of Pressure
• B
(1) Total reaction; (2) Centre of Gravity
• C
(1) Lift; (2) Centre of Pressure
• D
(1) Lift; (2) Centre of Gravity

Refer to figures.
The sum of all the reactive forces on an airfoil is known as the “Total Reaction”, which acts through a point called "Centre of Pressure" at 90º to the chord line.

When an Angle of Attack of a symmetrical airfoil greater than zero exists, the Total Reaction tilts backwards and is split into two elements:

• Lift, which is defined as the proportion of the Total Reaction perpendicular to the Relative AirFlow (RAF).
• Drag, which is the proportion of the Total Reaction which is parallel to and in the same direction with the RAF.

Centre of Gravity is the point of a body through which the sum of the forces of all masses of the body (weight) is considered to act.

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