Drag Coefficient

you have that book, ok I can work with that
have a look at page 35
whats going on here is he's extrapolating the drag of a larger aircraft from another design. And he says:

"The drag coefficient is D/(qxS) so that the drag coefficient for the Lancair IV is 0.0212. Assuming that the Stallion has the same drag coefficient, the flat plate drag area of the Stallion is 0,0212 x 140=3.0 sq ft.

Some of you may ask, "well how accurate is this very simple calculation?" When I determined the flat plate drag area of the Lancair IV, I used the actual, flight test, flat plate area of the Lancair 200, which is 1.6 sq ft. The Lancair 200 has a wing area of 76 sq ft. The drag coefficient , CDo is then 1.6/76 = 0.021. The Lancair IV falt plate drag area was then calculated as 100 x 0.021 = 2.1 sq ft. This is amazingly close to the actual flat plate area drag of 2.12 sq ft."

now I want you to note, he isnt using a 2D area of the front profile of the aircraft, and that he adjusts the figure to the actual drag. And just look at the Lancair IV he discusses, does it really appear to have a front profile of 2.12 sq ft ?

back to pp 35

"The flat plate drag area is the area in square feet of a flat plate that is turned 90 degrees to the airstream. This plate has the same profile drag as the entire aircraft. This assumes that 90% of a flat plate area has a CD = 1.0"

by that, a sq ft is 1.11

 

What you are quoting is a rule of thumb crutch to compare aircraft drag because of the way they often use wing plan area instead of frontal area to calculate drag coefficient. Would you care to tell us what this has to do with published Cd figures for cars?

This might help you understand the ways aircraft Cd is determined.
The Drag Coefficient

Automotive Cd ratings are simpler, they are function of projected frontal area and actual aerodynamic drag. None of the aircraft consideration of plan (top) view wing area.

 

look you asked me questions which led to resources, I used your resource to demonstrate something so you could follow it. Now your asking me what that has to do with cars and Im supposed to jump through that hoop too

I already understand that quite well
at one time I had a strong interest in ground effect vehicles and could work all that out for myself

he gives you the FPD
so does the toytown resource you used before
Shape Effects on Drag
so does this
http://www.madabout-kitcars.com/kitcar/kb.php?aid=327now I get the feeling non of this will make you happy, but then, Im not here for your happiness..