Principles of Flight

Four Forces Acting on an Airplane

• Lift: Upward force created by wings, keeps airplane in the air.
• Weight: Downward force due to gravity, opposite of lift.
• Thrust: Forward force from propellers or engines, moves airplane through the air.
• Drag: Opposite of thrust, limits airplane's performance.
  • Straight and Level Unaccelerated Flight: Lift equals weight, thrust equals drag.

Lift

• Airfoil: Wing is a type of airfoil, generates aerodynamic force.
  • Wings, propellers, and fuselage are airfoils.
  • Chord Line: Imaginary line connecting leading edge to trailing edge of wing.
• Flight Path & Relative Wind:
  • Flight path is the plane's travel path.
  • Relative wind is airflow opposite to flight path.
• Angle of Attack: Angle between chord line and relative wind, affects lift.

Theories of Lift

• Newton's Laws: Third law - action and reaction. Hand out of car window analogy.
• Bernoulli's Principle: Increased velocity of air decreases pressure.
  • Wing acts as a venturi; pressure difference lifts the wing.

Factors Affecting Lift

• Lift Equation: Lift = 1/2 x air density x wing area x velocity² x coefficient of lift.
  • Coefficient of Lift: Related to airfoil shape and angle of attack.
• Pilot's Control: Airspeed and angle of attack.
  • Limit to angle of attack - "stall".
• Wing Design Factors:
  • Planform: Shape of wing viewed from above.
  • Camber: Curvature, affects stall speed.
  • Aspect Ratio: Ratio of wing length to width.
  • Wing Area: Total surface area, affects lift.

High-Lift Devices

• Flaps: Increase lift and drag at low speeds, important for landing.
  • Steps in flap extension affect lift and drag differently.

Weight

• Gravity's Force: Always points downward from center of gravity.
• Variable Weight: Changes with equipment, passengers, cargo, and fuel.

Thrust

• Forward Force: Opposes drag, propels airplane.
  • Generated by propeller or turbine engines.
  • Propeller as an airfoil.

Drag

• Parasite Drag:
  • Direct result of air resistance.
  • Types: Form drag, interference drag, skin friction.
  • Increases with speed.
• Induced Drag:
  • Related to lift, caused by wingtip vortices.
  • Higher at slow speeds, decreases with increased speed.
  • Ground Effect: Reduces induced drag by altering downwash near ground.

Total Drag Curve

• L/D Max: Speed where lift is maximized and drag minimized - best glide speed.
  • Important for emergency landings.

Backside of the Power Curve

• Slower flight increases drag, requires more thrust.
  • Controls become less responsive.

Conclusion

• Understanding flight principles is crucial for pilots to control aircraft efficiently.
• Knowledge enhances piloting beyond mere navigation from point A to B.