1. Forces of Flight
Flight and Space
© 2011 Project Lead The Way, Inc.

2. Scalar and Vector Quantities
A scalar quantity has only magnitude
A vector quantity has both magnitude and direction
Scalar Quantities
Length, area, volume, speed, mass, density, pressure, temperature, energy, entropy, work, power
Vector Quantities
Displacement, direction, velocity, acceleration, momentum, force, lift, drag, thrust, weight
To understand the forces that act on an airplane during flight, we first must understand a couple of basic terms which describe these forces.
Math and science were invented by humans to describe and understand the world around us. We live in a (at least) four-dimensional world governed by the passing of time and three space dimensions; up and down, left and right, and back and forth. We observe that there are some quantities and processes in our world that depend on the direction in which they occur, and there are some quantities that do not depend on direction. For example, the volume of an object, the three-dimensional space that an object occupies, does not depend on direction. If we have a 5 cubic foot block of iron and we move it up and down and then left and right, we still have a 5 cubic foot block of iron. On the other hand, the location, of an object does depend on direction. If we move the 5 cubic foot block 5 miles to the north, the resulting location is very different than if we moved it 5 miles to the east. Mathematicians and scientists call a quantity which depends on direction a vector quantity. A quantity which does not depend on direction is called a scalar quantity.

3. The Car: A Vector Example
A car drives on a straight road heading due east at mph...
The speed of the car is 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
East

4. A force may be thought of as a push or pull in a specific direction
A force may be thought of as a push or pull in a specific direction. A force is a vector quantity, so it has both a magnitude (size) and a direction. So when we describe these forces, we have to specify both the magnitude and the direction. This slide shows the forces that act on an airplane in flight, which include Lift, Weight, Drag, and Thrust. We’re going to look at each of these individually, but first, a little from the “Fathers of Flight”.

5. Weight is a force that is always directed toward the center of the earth. The magnitude of the weight depends on the mass of all the airplane parts, plus the amount of fuel, plus any payload on board (people, baggage, freight, etc.). The weight is distributed throughout the airplane. But we can often think of it as collected and acting through a single point called the center of gravity.
Flying encompasses two major problems; overcoming the weight of an object by some opposing force, and controlling the object in flight. Both of these problems are related to the object's weight and the location of the center of gravity. During a flight, an airplane's weight constantly changes as the aircraft consumes fuel. The distribution of the weight and the center of gravity also changes. So the pilot must constantly adjust the controls to keep the airplane balanced.

6. 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.)

7. 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.

8. To overcome the weight force, airplanes generate an opposing force called lift. Lift is generated by the motion of the airplane through the air and is an aerodynamic force. "Aero" stands for the air, and "dynamic" denotes motion. Lift is directed perpendicular to the flight direction. The magnitude (size) of the lift depends on several factors including the shape, size, and velocity of the aircraft. As with weight, each part of the aircraft contributes to the aircraft lift force. Most of the lift is generated by the wings.

9. Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
Lift
Lift: The force that directly opposes the weight of an airplane and holds the airplane in the air.
Simplified:
Lift: The upward force that works against the downward pull of gravity
Image From Nasa:
Project Lead The Way®
Copyright 2006

10. Lift A positive force Needed to overcome the weight force
Lift is directed perpendicular to the flight direction.

11. Lift Amount of lift depends on several factors including
Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
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
Density altitude is the density of the air at different altitudes. The higher the plane, the less dense the air.
Project Lead The Way®
Copyright 2006

12. Lift Most of the lift is generated by the wings
Air pressure below the wing is greater than air pressure above the wing

13. As the airplane moves through the air, there is another aerodynamic force present. The air resists the motion of the aircraft and the resistance force is called drag. Drag is directed along and opposed to the flight direction. Like lift, there are many factors that affect the magnitude of the drag force including the shape of the aircraft, the "stickiness“ of the air, and the velocity of the aircraft. Like lift, we collect all of the individual components' drags and combine them into a single aircraft drag magnitude.

14. Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
Drag
Drag: The force that resists any object trying to move through a fluid.
Simplified:
Drag: Resistance of the air (technically a fluid) against the forward movement of an airplane.
From Nasa:
Project Lead The Way®
Copyright 2006

15. Drag
As the airplane moves through the air, the air resists the motion of the aircraft.
Directed along and opposed to the flight direction.

16. Drag Factors that affect the amount of drag the shape of the aircraft
Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
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
Types of Material – cloth or wood would have more drag than metal
Painted metal has more drag than unpainted metal. (The Shamu plane gets less mpg than a regular plane.)
Project Lead The Way®
Copyright 2006

17. To overcome drag, airplanes use a propulsion system to generate a force called thrust. The direction of the thrust force depends on how the engines are attached to the aircraft. In the figure shown here, two turbine engines are located under the wings, parallel to the body, with thrust acting along the body centerline. On some aircraft, such as the Harrier, the thrust direction can be varied to help the airplane take off in a very short distance. The magnitude of the thrust depends on many factors associated with the propulsion system including the type of engine, the number of engines, and the throttle setting.
For jet engines, it is often confusing to remember that aircraft thrust is a reaction to the hot gas rushing out of the nozzle. The hot gas goes out the back, but the thrust pushes towards the front. Action <--> reaction is explained by Newton's Third Law of Motion.

18. Thrust Simplified: Thrust: The push that moves an airplane forward.
Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
Thrust
Thrust: The force which moves an aircraft through the air.
Simplified:
Thrust: The push that moves an airplane forward.
From Nasa:
Project Lead The Way®
Copyright 2006

19. Aerospace Vocabulary
Flight and Space Unit
Lesson 3 – Propulsion Systems
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
On some aircraft, such as the Harrier, the thrust direction can be varied to help the airplane take off in a very short distance.
Project Lead The Way®
Copyright 2006

20. 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.

21. 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.

22. Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Image Resources
National Aeronautics and Space Administration (NASA). (n.d.). Virtual skies: Aeronautics tutorial. Retrieved June 24, 2009, from