Lift and Drag

Body - like an airfoil - in fluid flow

Lifting Force

The lifting force acting on a body in a fluid flow can be calculated

FL = 1/2 cL ρ v2 A                                        (1) 


FL = lifting force (N)

cL = lifting coefficient

ρ = density of fluid (kg/m3)

v = flow velocity (m/s)

A = body area (m2)

Drag Force

The drag force acting on a body in fluid flow can be calculated

FD = cD 1/2 ρ v2 A                                     (2) 


FD = drag force (N)

cD = drag coefficient

ρ = density of fluid (kg/m3)

v = flow velocity (m/s)

A = body area (m2)

Required Thrust Power to overcome Drag Force

The thrust power required to overcome the drag force can be calculated

P = FD v                                       (3)


P = power (W)

Example - Aeroplane and Airfoil Lift - Drag and required Thrust Power

For an aeroplane with velocity 100 m/s, wing area 20 m2, a drag coefficient 0.06 and a lift coefficient 0.7 - the lifting force acting on the airfoil can be calculated

FL = 0.7 1/2 (1.2 kg/m3) (100 m/s)2 (20 m2)

   = 84000 (N)

   = 84 (kN)

The drag force can be calculated

FD = 0.06  1/2 (1.2 kg/m3) (100 m/s)2 (20 m2)

   = 7200 (N)

   = 7.2 (kN)

Required thrust power to overcome the drag force:

P = (7200 N) (100 m/s)

  = 720000 (W)

  = 720 (kW)

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time

Related Documents

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