Aerodynamic Drag of an Aircraft
Aerodynamic Drag of an Aircraft
Drag is the resistance an aircraft must overcome with thrust; it sets cruise fuel burn and top speed.
The drag is D = ½·ρ·v²·S·C_d. where ρ is air density, v the speed, S the reference area and C_d the drag coefficient.
Inputs
rho := 0.4 kg/m^3=0.4 kg/m^3
v := 250 m/s=250 m/s
S := 120 m^2=120 m^2
C_d := 0.03=0.03
Apply the drag equation.
D := 0.5·rho·v^2·S·C_d=45000 N
Results
In steady cruise thrust equals drag. The thin air at altitude reduces drag, which is why airliners cruise high despite needing higher true airspeeds.
Assumptions & limitations
- Subsonic, steady cruise.
- Constant drag coefficient.
- Altitude air density.