This business of different CDs even for the "same" aeroplane is exactly why I was asking for the equivalent flat plate area.
It is a much simpler concept and beats trying to figure out whether everyone is using the same reference area.
Here is a good description from a name that seems to come up a lot:
8/26/94
Analytical Methods {NWNet}
The concept of "equivalent flate plate area" comes from noting
that while:
Drag Where: Drag = resistance force
CD = ------------------ rho = density
.5 rho Vel^2 Sref Vel = Velocity
Sref = Ref Area
is nondimensional, the Sref is awkward, as how the reference area is
chosen can differ. So if we instead define:
Drag
f = -------------
.5 rho Vel^2
the Sref no longer appears, but f has the units of length squared. If
English units are used, you get the equivalent flate plate area (f) in
units of square feet. Note, this does not mean that a flate plate of
the same area as f would have the same drag - a flate plate has a CD of
roughly 1.17 (in 3-D flow, according to Hoerner and 1.98 in 2-D flow),
not 1 as implied in the equation! We can see this from:
Drag = CD .5 rho Vel^2 Sref
where Sref is the frontal area of the plate. Hence, the equivalent
flate plate area is:
CD .5 rho Vel^2 Sref
f = ----------------------
.5 rho Vel^2
So you can see that the flate plate of area Sref has an equivalent flat
plate area 1.17 times its true area (in 3-D flow)!
-Dave Lednicer
Analytical Methods, Inc.
NACA Report L5A30 can be found here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf
By the way when saving a copy locally, don't do as I did a few years back and save it under its original name.
You will never find it again! Name it something appropriate.
- Ivan.