Lift and Drag
Lift and drag forces acting on a body like an air foil in a fluid flow.
Lifting Force
The lifting force acting on a body in a fluid flow can be calculated
FL = cL 1/2 ρ v2 A (1)
where
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)
where
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)
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
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)
