Does skin friction scale up on small cars ?

[aerohead]

Originally Posted by ecomodded

With my hand against my car door while driving, i noticed no airflow pushing my hand, but only when my hand was against the door panel. Could be the air is passing over the back of my hand with little disturbance at 50 - 60 kmh, i 'll try higher speeds when i need to use the highway.

Once the form is good having a polished smooth surface would benefit the cd, no ?

Hoerner reported that when they painted the Luftwaffe fighter planes like the Me 109 and Fw-190 with flat camouflage paint,that the aircraft didn't suffer any appreciable loss in performance.These planes were already immersed in prop wash so all the surfaces were already in turbulent boundary layer with high skin friction losses.Our cars are in a similar situation.
The Me 262 was a different animal,as it's Junkers Jumo 004 turbojet engines were wing mounted outboard,leaving the fuselage and wing roots 'clean.'Consequently,the 262' fuselage came in at Cd 0.08,vs Cd 0.15 for the Me 109.
There are stories of 'waxed wing' performance differences for aircraft,but there again,these are under 'flight' conditions are are not germane to automotive technology.
You could probably brush paint an automobile and it wouldn't measurably affect the mpg.