Quote:
Originally Posted by duncan
Just a small comment
Frontal area x CD gives drag for a non "streamlined" shape,
There are two types of drag - form drag and skin friction
If you can properly streamline a shape such that the air follows the surface, does not detach and rejoins nicely
Which is nearly impossible in a ground vehicle
Then you eliminate "form drag" and you end up with skin friction which is proportional to the "wetted area" and NOT related to the frontal area
|
*Frontal projected area (A), X coefficient of aerodynamic drag (Cd), = drag factor (CdA), of any shaped vehicle.
*Surface friction drag + pressure drag = profile drag.
*There's also:
*cooling drag (where applicable)
*ventilation drag (where applicable)
*interference drag
*induced drag
*windage drag associated with the spinning wheels
------------------------------------------------------------------------
*When you eliminate pressure drag,your profile drag is reduced to surface friction drag which is associated with the wetted area.
With this graphic for streamline bodies,you can see that pressure drag is eliminated at around l/d= 3.5,then drag goes up as the length increases beyond the l/d 'sweet spot.,' due to the increasing wetted area.
