1 / 23

Major aerodynamic forces on aircraft: Lift = L Drag = D Pitching Moment = M Thrust = T Weight = W

Figure 1. Aerodynamics: The science of the air flow around as well as the forces and moments acting on a structure in a moving airstream. Major aerodynamic forces on aircraft: Lift = L Drag = D Pitching Moment = M Thrust = T Weight = W. Steady level flight: Lift = Weight

nguyet
Download Presentation

Major aerodynamic forces on aircraft: Lift = L Drag = D Pitching Moment = M Thrust = T Weight = W

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Figure 1. Aerodynamics: The science of the air flow around as well as the forces and moments acting on a structure in a moving airstream Major aerodynamic forces on aircraft: • Lift = L • Drag = D • Pitching Moment = M • Thrust = T • Weight = W Steady level flight: Lift = Weight Thrust = Drag M = 0

  2. Airfoil Geometry • b = span • c = chord • S = planform area • Aspect Ratio = b2/S = A

  3. Sail Geometry Camber = t/c Aspect Ratio: A = b2/SA SA = Sail Area

  4. Forces on Wing & Sail Wing L = Lift D = Drag R = Resultant V = Relative Wind Sail

  5. Forces on a Sailboat A 6-Metre yacht Equilibrium of forces in the close-hauled sailing condition, Vt = 12 knots LWL = 23.5 ft Beam = 6.5 ft Draft = 5.4 ft Displacement = 94 lb Sail Area = 600 sq ft Lateral Area (hull) = 70 sq ft Angle of heel = 20°

  6. Basic properties of the atmosphere required • for sailing or winged flight • Density (function of p & T) • Viscosity • If air had density but no viscosity • Balloon flight is possible • No sailing or winged fight is possible • Early inviscid theory predicts no lift • Consequences of viscosity • Skin friction drag (unavoidable) • Boundary layer creation → lift

  7. Boundary LayerVelocity Gradient in Viscosity of Surface of an Airfoil Laminar Flow: Relatively low skin friction drag B.L. separates at relatively low α Laminar separation → large pressure drag Turbulent Flow: Relatively large skin friction drag B.L. remains attached to higher α

  8. Transition Laminar to Turbulence Determined by Reynolds number Re Re = VAl/ν = velocity x distance ÷ viscosity value v = called kinematic viscosity. It is basic property of air

  9. Boundary Layer → Circulation ← Circulation: air velocity higher on top surface than bottom By Bernoulli’s theory, pressure on top surface > pressure on bottom surface Typical airfoil pressure distribution

  10. Simplest (Quantitative) Theory of Lift & Drag(Based Upon Concept of Dynamic Pressure – q) Dynamic pressure = air density x airspeed2 q =ρv2/2 Sea level standard day ρ = .0024 slugs/ft3 = air density equivalent to .0768 lb/ft3 v must be in ft/sec v(ft/sec) = 1.47 x V(mph) Example: at 100 mph (SLSD) q = 26 lb/ft2

  11. Actual Lift Produced by a Wing Depends Upon: • Dynamic pressure – q • Wing area – S • Angle of attack – α • L = qSCL • CL = lift coefficient • CLvaries with α

  12. Drag Drag – retarding force D = q S CD CD = drag coefficient 3 Physical sources of drag Skin friction Pressure drage (due to separation) Induced drag (varies with lift)

  13. Drag Coefficient • CD = CDo + CDi • CDo due to skin friction and pressure drag • CDi induced drag coefficient • CDo is nearly constant C (for a given aircraft) • CDi = C2L/πeA

  14. Physical Origin of Induced Drag – Wing Tip Trailing Vortices Lifting line or bound vortex

  15. Downwash at Wind Due to Trailing Vortices Tips Local Velocity Vector Down Downwash

  16. Induced Velocities (Downwash) Due to the Tip Vortex Action

  17. Induced drag is a function of lift alone and has nothing to do with the angle of incidence except to modify it through the introduction of an induced angle

  18. Illustration of Downwash

  19. Telltale Action vs AOA

  20. Influence of Foresail on Airflow

  21. Influence of Camber on Force Components

  22. Force Components Sailing With the Wind

  23. Vortex Shedding

More Related