The French Civil Aviation University 081 Principles of Flight Aerodynamic Forces 1 The French Civil Aviation University Content: 1) Forces acting on an airplane 2) Lift 3) Drag 2 The French Civil Aviation University How does an airplane fly ? 3 The French Civil Aviation University 1- Forces acting on an airplane 4 The French Civil Aviation University In straight and level flight at constant speed with no turning moments the aircraft is said to be in equilibrium, it means: THRUST = DRAG WEIGHT = LIFT 5 The French Civil Aviation University 2 -THE LIFT The purpose of the wing is to produce enough upward force to raise the aircraft mass. 6 The French Civil Aviation University Chord Line : The chord line is the straight line intersecting the leading and trailing edges of the airfoil • Relative airflow: The direction of the airflow with respect to an airfoil • Angle of Attack (AoA): The angle measured between the relative wind and the chord line of the airfoil 7 The French Civil Aviation University The physics principles used for the creation of Lift Newton's Third Laws To every action, there is an equal and opposite reaction. 8 The French Civil Aviation University The physic principles used for the creation of lift Bernoulli’s Principle As the velocity of a fluid ( in this case the air) increases , its pressure decreases P+V=C 9 The French Civil Aviation University As air flows over the top surface of an airfoil it is accelerated, therefore pressure is reduced. The pressure difference between the low pressure on the top of the wing and relatively higher pressure on the bottom of the wing creates an aerodynamic force that we call Lift. 10 The French Civil Aviation University Some videos: Bernouilli`s principle: https://www.youtube.com/watch?v=gGpdUQh_DCM Newton’s law : https://www.youtube.com/watch?v=mn34mnnDnKU 11 The French Civil Aviation University 3- LIFT FORMULA L= ½ . ρ . V2 . S . CL Where: L = lift Cl = lift coefficient ( AoA, camber, surface condition ) (rho) = air density V = air speed S = wing surface area 12 The French Civil Aviation University 2 ways to control the LIFT ! L= ½ . ρ . V2 . S . CL Air speed or Angle of Attack (AoA) The faster the airspeed, the more lift produced As AoA increases lift increases, 13 The French Civil Aviation University However there is a Limit ! 14 The French Civil Aviation University 3 - THE DRAG Drag is the aerodynamic force that opposes an aircraft's motion through the air. Drag is generated by every part of the airplane. The aircraft are submitted to two types of drag: 1- Induced drag: Drag caused by the lift 2- Parasite drag: a) Form drag b) Interference drag c) Friction drag 15 The French Civil Aviation University Form drag is created when the airflow has actually separated from the airfoil 16 The French Civil Aviation University Interference drag is created where two different objects meet and disturb the free stream airflow Examples of this include where: • The wing meets the fuselage • The elevator meets the fuselage 17 The French Civil Aviation University Skin friction drag is the force between the free stream air and any object passing through it KEEP THE AIRPLANE SURFACE CLEAN !!! 18 The French Civil Aviation University As the airspeed of an airplane increases parasite drag continues to increase exponentially 19 The French Civil Aviation University Induced Drag • Created by parts of the plane that create lift • Greater the lift, greater the induced drag • Induced drag is proportional to lift Lift create wingtip vortices and induced drag 20 The French Civil Aviation University Factors which affect induced drag are: - wing shape - aspect ratio - lift and weight - speed 21 The French Civil Aviation University Total Drag Total drag = Parasite drag + Induced drag Note: • At low airspeeds induced drag is high and parasite drag in low • At minimum drag speed both induced and parasite drag are at a minimum • At maximum speed induced drag is low and parasite drag to high • Minimum drag occurs where the induced drag = parasite drag Minimum Drag Speed = Best Glide Speed 22 The French Civil Aviation University DRAG FORMULA D= ½ . ρ . V2 . S . CD Where: CD - Co-efficient of drag – shape and angle of attack ρ (Rho) – Free stream air density V – airspeed (TAS) S –wing surface area 23 The French Civil Aviation University Summary 24 The French Civil Aviation University REFERENCES : https://www.boldmethod.com https://www.nasa.gov 25 The French Civil Aviation University THANK YOU FOR YOUR ATTENTION Any Question ? Mail : [email protected]
