Forces of Flight

Scalar and Vector Quantities

A scalar quantity has only magnitudeA vector quantity has both magnitude and direction

Scalar QuantitiesLength, area, volume, speed, mass, density, pressure, temperature, energy, entropy, work, power

Vector QuantitiesDisplacement, direction, velocity, acceleration, momentum, force, lift, drag, thrust, weight

The Car: A Vector Example

East

• A car drives on a straight road heading due east at 60 mph...

• The speed of the car is 60 mph. This is the first part of the vector.

• The speed tells us the magnitude; size of the vector.

• The direction of travel is due east. This is the second part of the vector.

60 mph

Weight or Gravity

• A negative force• A force always directed towards the

center of the earth• Dependent upon the mass of all the

airplane parts, plus the amount of fuel, plus any payload on board (people, baggage, freight, etc.)

Weight or Gravity

• During a flight, an airplane's weight constantly changes as the aircraft consumes fuel.

• The distribution of the weight then changes, so the pilot must constantly adjust the controls to keep the airplane balanced, or trimmed.

LiftLift: The force that directly opposes the weight

of an airplane and holds the airplane in the air.

Simplified:

Lift: The upward force thatworks against the downward pull of gravity

Lift

• A positive force• Needed to overcome the

weight force• Lift is directed perpendicular

to the flight direction.

Lift

• Amount of lift depends on several factors including– Shape of the aircraft– Size of the aircraft– Velocity or speed of the aircraft– Shape of the wing– Density altitude

Lift

• Most of the lift is generated by the wings

• Air pressure below the wing is greater than air pressure above the wing

Drag

Simplified:

Drag: Resistance of the air (technically a fluid) against the forward movement of an airplane.

Drag: The force that resists any object trying to move through a fluid.

Drag

• As the airplane moves through the air, the air resists the motion of the aircraft.

• Directed along and opposed to the flight direction.

Drag

• Factors that affect the amount of drag– the shape of the aircraft– the "stickiness“ of the air– the speed of the aircraft– The type of material used on the

aircraft

Thrust

Thrust: The force which moves an aircraft through the air.

Simplified:

Thrust: The push that moves an airplane forward.

Thrust

• Overcomes drag• Airplanes use a propulsion

system to generate the thrust• The amount of thrust depends

on many factors associated with the propulsion system– type of engine– the number of engines– and the throttle setting

Thrust

• The direction of the thrust force depends on how the engines are attached to the aircraft.

• When engines are located under the wings, parallel to the body, thrust acts along the body centerline.

Forces Summary

• The motion of the airplane through the air depends on the relative strength and direction of the forces you’ve been shown.

• If the forces are balanced, the aircraft cruises at constant velocity.

• If the forces are unbalanced, the aircraft accelerates in the direction of the largest force.

Image Resources

• National Aeronautics and Space Administration (NASA). (n.d.). Virtual skies: Aeronautics tutorial. Retrieved June 24, 2009, from http://virtualskies.arc.nasa.gov/main/maeronautics.html