Theoritical doubt in aeronautical engg

[apst]

Homework Statement

is the drag on an airplane dependent on its weight?

Homework Equations

The Attempt at a Solution

it was told that the drag depends on lift and the lift,on weight,in turn.but i am unable to comprehend it physically.

 

[rock.freak667]

Friction due to aerodynamic drag is given by

F_d=½ρAC_dv²

C_d is the coefficient of drag depending on the shape of the wing. Thus aerodynamic drag is not really influenced by weight.

 

[apst]

thank you very much rock.freak667.it is very clear using the formula.but can you explain it physically?i mean by taking a practical example like a cylinder or airfoil?

 

[rock.freak667]

thank you very much rock.freak667.it is very clear using the formula.but can you explain it physically?i mean by taking a practical example like a cylinder or airfoil?

Well if you see here,http://en.wikipedia.org/wiki/Drag_(physics)" , the picture at the top right shows the flow around some of the shapes, the more streamlined the flow is, the lower the value of C_d. All the other quantities are the standard density of the air, area of the shape and velocity.

The aerofoil would be more "streamlined" than the cylinder meaning that air flowing past it will be able to pass over it more easily, so it would have a lower C_d value.

Designers try to minimize the friction due to drag as most of the energy consumed by the airplane or car or whatever is usually in overcoming aerodynamic drag.