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Lift and Drag

Lifting Force

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

F L = c L 1/2 ρ v2A                                        (1)

where

F L = lifting force (N)

c L = 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

F D = c D 1/2 ρ v2A                                     (2)

where

F D = drag force (N)

c D = drag coefficient

ρ = density of fluid (kg/m3 )

v = flow velocity (m/s)

A = body area (m 2 > )

Required Thrust Power to overcome Drag Force

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

P = F D v                                       (3)

where

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

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

= 84000 (N)

= 84 (kN)

The drag force can be calculated

F D = 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. Involving velocity, pressure, density and temperature as functions of space and time.

Related Documents

Hot Air Balloons - Calculate Lifting Weights

Calculate hot air ballons lifting forces.

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