[All Darc]

Bye bye plan to contact their team to the creation creation a ideal wheel streamlined covers for Morelli's design...

Speed it's a factor for supersonic planes. In supersonic the aedynamics it's a bit different. I remamber this reading this forum somewhere. I didn't knew very low speed was also factor.

Originally Posted by aerohead

Motor vehicle aero drag is basically a function of pressure drag.
Pressure drag is a function of flow separation,or lack thereof.
Flow separation is closely associated with the health of the boundary layer.
The best attached flow for 'real' vehicles is with a fully turbulent boundary layer.
This will occur when the Reynolds number goes super-critical,which for 'real' cars, occurs at about 20-mph.
If you keep a car below 20-mph,you can keep it in a laminar boundary layer,which really reduces turbulence-induced surface friction.
Surface friction isn't a problem with 'real' cars and a laminar boundary layer would actually increase pressure drag (overall drag) in a 'real' car.
The Ecorunner,by being 'short' ,and driving 'slow' can claim a very low 'laminar' Cd,but this would never possible with a 'full-size car,moving at real highway velocity.
The Reynolds number is associated with length,kinematic viscosity,and velocity.Once you get to around Rn = 500,000,the boundary layer will transition,from laminar,to turbulent (TBL).Golf balls are artificially roughened to trigger the immediate transition to TBL,allowing flow to remain attached longer before separating,thereby reducing the low pressure wake (pressure drag),and extending the distance of the drive.
The Rn of cars is measured in millions.