Forces of Flight and Stability Quiz Review

Four forces on an aircraft in flight:

Weight:   Gravitational attraction of the Earth.

Lift:   Created by the effect of airflow as it  

passes over and under the wing.

Thrust:   Forward-acting force which opposes drag.

Drag:   Acts in the opposite direction of flight.

Force is what type of quantity? Vector

What is a vector quantity?

• Quantity that has both magnitude and direction

• Represented by arrows

• Length of arrow is the magnitude

• Orientation of arrow is the direction

What is the resultant force?

When two or more forces are applied to an object, the resulting force is called the resultant force.

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When opposing forces have the same magnitude and opposite directions, the resultant is zero and the object is in static equilibrium.

• Center of gravity must be located within a manufacturer’s determined range

• Inside the range, aircraft is controllable

• Outside the range, aircraft is unsafe

• Must calculate and adjust weight pre-flight

Moment = Force x distance

Distance (d) is called the moment arm. It must be measured perpendicular to the line of action of the force.

M = F (d)

Bernoulli's Principle

• More camber along upper airfoil.

• Fluid cross section is reduced.

• Low pressure above airfoil.

• High pressure below airfoil.

• Pressure differences causes upward force.

Circulation

• Fluid flow direction changed above and below airfoil

• Flowlines more curved on upper surface than lower

• Results in a greater pressure gradient across upper streamlines

Deflection

• Newton's Third Law of Motion

  • For every action there is an equal and opposite reaction.

• Downward deflected air produces an upward reaction force

Coanda Effect

• Fluid flow pulled toward the solid surface (airfoil)

• Flow accelerates over the airfoil top surface

• Most pronounced on high angle of attack slow fluid flow