AeroDynamics: Forces on an Airplane

What is Aerodynamics?

• Deals with the motion and forces acting on a body moving in air
• Concerned with the study of the interaction between air and solid objects

How Do Airplanes Fly?

• 4 aerodynamic forces act on an airplane in flight: thrust, drag, lift, and weight
• Conditions for flight: thrust > drag, lift > weight
• In straight and level flight, lift and weight are balanced
• During descent, gravity exceeds lift, and drag must overcome thrust

Forces Acting on a Plane

• Weight: weight of the airplane acts downwards due to gravity, should be minimized
• Thrust: mechanical force generated by the engine to move the aircraft forward
• Lift: mechanical force generated by a solid object moving through a fluid, acts perpendicular to the direction of fluid flow
• Drag: resisting force to the motion of the aircraft due to its relative motion with air flow

Formulas

• Lift formula: L = 1/2 ρ A V²C_L
• Drag formula: D = ρV²C_D/2
• Bernoulli's equation: (P/ ρg) + (V²/2g) + Z = const

Motion of an Airplane

• Pitch motion: up and down movement of the nose
• Rolling motion: rotation around the longitudinal axis
• Yaw motion: rotation around the vertical axis

Basic Parts of an Airplane

• Fuselage: main body of the airplane, houses the flight crew, passengers, and cargo
• Wings: generate lift due to the difference in curvature of the upper and lower parts
• Tail: provides stability and control to the vertical up-down movement of the nose
• Stabilizers: keep the aircraft in straight-and-level flight
• Elevators: control the climb or descent of the aircraft
• Rudder: defines horizontal flight and provides directional control
• Ailerons: control the rolling (or banking) motion of the aircraft
• Flaps: increase lift during takeoff and landing
• Propeller: provides thrust to the aircraft
• Airfoil: shape that conforms to the streamlines of the flow and prevents wake formation

Wing Generation of Lift

• Lift is generated by the difference in pressure above and below the wing
• Airfoil shape produces better lift than any other form of the wing
• Camber line: line joining the leading and trailing edges of an airfoil equidistant from the upper and lower surfaces
• Camber: asymmetry between the top and the bottom curves of an aerofoil in cross-section
• Angle of incidence: angle between the fuselage axis and the wing chord length
• Angle of attack: angle the wind makes with the wing (relative wind)
• Dihedral angle: angle between one of the wings and the horizontal plane in which the fuselage axis is situated