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
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