# 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 v ^{ 2 } A (1) *

* where *

* F _{ L } = lifting force (N) *

* c _{ L } = lifting coefficient *

* ρ = density of fluid (kg/m ^{ 3 } ) *

* v = flow velocity (m/s) *

* A = body area (m ^{ 2 } ) *

### Drag Force

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

* F _{ D } = c _{ D } 1/2 ρ v ^{ 2 } A (2) *

* where *

* F _{ D } = drag force (N) *

* c _{ D } = drag coefficient *

* ρ = density of fluid (kg/m ^{ 3 } ) *

* 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 m ^{ 2 } * , 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/m ^{ 3 } ) (100 m/s) ^{ 2 } (20 m ^{ 2 } ) *

* = 84000 (N) *

* = 84 (kN) *

The drag force can be calculated

* F _{ D } = 0.06 1/2 ( 1.2 kg/m ^{ 3 } ) (100 m/s) ^{ 2 } (20 m ^{ 2 } ) *

* = 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.