FORCES IN FLIGHT

1. FORCES IN FLIGHT Weight (Gravity) Lift Drag Thrust

2. Weight • A force that is caused by the gravitational attraction of the Earth • Depends upon all of the parts of the airplane, plus fuel, plus payload on board (freight, people, baggage, etc.) • Distributed throughout the plane • The airplane moves around a single point known as center of gravity

3. Why is weight so important? • Flying encompasses 2 major problems: • Overcoming the weight of the plane • Controlling the object in flight • Weight changes constantly as fuel is consumed • Pilot must constantly adjust controls and fuel distribution or keep it “trimmed”

4. Lift • In order to overcome weight force, planes must generate opposing force of lift • Created by the motion of the plane through the air • Perpendicular to the flight motion • Magnitude of lift is dependent on shape size and velocity of the aircraft

5. How is most lift generated? • Most lift is produced from the wings • Distribution of lift around aircraft is vital to solving problem of control • Acts through a center of pressure (avg location of pressure on the wing) • Roll, pitch and yaw are used in combination with the aerodynamic surfaces to control plane

6. Drag • Considered a resistance force • Due to air resisting the motion of the aircraft • Directed along and opposed to the direction of flight • Shape of aircraft, “stickiness” of the air and velocity affect drag

7. Thrust • Mechanical force created by the engines to move the aircraft through the air • In order to overcome drag, propulsion systems are used to generate thrust • Magnitude is dependent on type of engine, number of engines and the throttle setting

8. How does thrust work? • It can be confusing to remember that thrust is a reaction to hot gas rushing out the nozzle of the engine • The hot gas goes out the back, but the thrust pushes toward the front • This action – reaction is explained through Newton’s 3rdlaw of motion • Examples http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/third_law_motion.html

9. Newton’s 1st Law of Motion • An object at rest will tend to stay at rest unless acted upon by unbalanced force • An object in motion will stay in motion with the same speed and direction unless acted upon by an unbalanced force • That resistance to change is known as inertia. • Known as the law of inertia

10. Practice with 1st Law • Answer the following: External force or no external force • An F-9 is flying at 250mph at 30000 ft • The F-9 turns southwest at 250mph • The F-9 increases its speed to 275mph • The F-9 drops to 25000ft at same speed & direction

11. Answers: • An F-9 is flying at 250mph at 30000 ft No external force • The F-9 turns southwest at 250mph External force (direction/velocity change) • The F-9 increases its speed to 275mph External force (speed/velocity change) • The F-9 drops to 25000ft at same speed & direction External force (gravity)

12. Newton’s 2nd Law of Motion • Acceleration of an object is dependent upon two variables: net force acting on the object and the mass of the object • Formula: f = m x a • This can be used when determining excess thrust of an airplane

13. Determining Excess Thrust • Excess thrust = Thrust – Drag • Fex= T – D • Fex = m * a (Newton’s 2nd law) • a = Fex/ m • So, a = T-D/ m Fex = Excess thrust a = accelleration m = mass T = thrust D = drag

14. 2nd Law Practice Problem #1 • An airplane has a mass of 150,000 kg and it is moving at a rate of 400 mi/min2. • What is the excess thrust currently? • Remember Fex = m * a

15. Answer Problem #1 • An airplane has a mass of 150,000 kg and it is moving at a rate of 400 mi/min2. • F= m * a • F = 150,000kg * 400 mi/min2 • F = 6,000,000 kg*mi/min2

16. Practice Problem # 2 • An small airplane has an excess thrust of 4,250,000 kg*m/s2 and has a mass of 8500 kg. • What is the acceleration of the plane? • Remember a = Fex/m

17. Answer Problem #2 • An small airplane has an excess thrust of 4,250,000 kg*m/s2 and has a mass of 8500 kg. • a = F/m • a = 4,250,000kg*m/s2/ 8500 kg • a = 500 m/s2