Forces of Flight and Stability Quiz Review

Center of Gravity

Interactive Study Guide

Forces on an Aircraft

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.

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Forces 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

Forces of Flight

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.

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Multiple Choice

What is the resultant force on the aircraft? (magnitude with units and direction ex. 10 N left)

• 30 N Left

• 60 N Left

• 60 N Right

• 0 N the aircraft is in static equilibrium

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Weight and Balance

• 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 Review

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)

Multiple Choice

The co-pilot weights 235 lbs. and is seated 32 in. from the airplane's center of gravity. Calculate the moment created by the pilot. (Show your work and include units in your answer)

• 235+32 = 267 in-lbs

• 235-32 = 203 in-lbs

• 235*32 = 7,520 in-lbs

• 235/32 = 7.34 in-lbs

Multiple Choice

An airplane's weight and moment is graphed below. Based on the given center of gravity moment envelope, is the airplane's center of gravity safe?

• Yes, the weight and moment fall within the boundaries for the airplane to be controllable.

• Yes, the weight is above 1,750 lbs. which guarantees the airplane to be controllable.

• No, the weight and moment don't fall within the boundaries for the airplane to be controllable.

• No, the weight is below 2,000 lbs. which guarantees the airplane to be uncontrollable.

Multiple Choice

An airplane's weight and moment is graphed below. Based on the given center of gravity moment envelope, is the airplane's center of gravity safe?

• Yes, the weight and moment fall within the boundaries for the airplane to be controllable.

• Yes, the weight is above 1,750 lbs. which guarantees the airplane to be controllable.

• No, the weight and moment don't fall within the boundaries for the airplane to be controllable.

• No, the weight is below 2,000 lbs. which guarantees the airplane to be uncontrollable.

Lift

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.

Lift

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

Lift

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

Lift

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

Multiple Choice

Which type of lift creation is being shown in the picture?

• Bernoulli's Principle

• Circulation

• Deflection

• Coanda Effect

Multiple Choice

Which type of lift creation is being shown in the picture?

• Bernoulli's Principle

• Circulation

• Deflection

• Coanda Effect

Multiple Choice

Which type of lift creation is being shown in the picture?

• Bernoulli's Principle

• Circulation

• Deflection

• Coanda Effect

Multiple Choice

Which type of lift creation is being shown in the picture?

• Bernoulli's Principle

• Circulation

• Deflection

• Coanda Effect