This one was based on simple frontal exposed area. Airplanes, missiles
etc use wetted area and then the cd to get the equivalent flat plate area.
Missiles and airplanes are quite a bit more elaborate to derive the efp.
Different shaped nose cones have different cd's then you have skin
effects from tube bodies, after body and wake effects plus anything
that sticks out like fins. And of course this all changes when the
motor is off. Unlike missiles which some people tend to frown upon
being live tested, you can easily find the drag of any vehicle by
doing coast down tests to verify the numbers.

Dave

> 
> > Nice formula!
> 
> You have to be careful with this (typical) formula that you measure
> the relevant "area" the same way that the people who determined the
> the drag coefficient did.  The rocketry folk usually doom themselves
> into having to specify drag coefficients of close to 1 to get the
> predictions of simulations to match measured reality, and that's
> with pointy, streamlined, rocket-shaped things.  They shake their
> heads at the drag coefficients quote for cars (0.4!), concluding
> that the car people must be measuring things differently than they
> are.  Perhaps the area used is the total surface area of the car,
> rather than just the frontal area.  I don't know that the question
> has ever been settled for sure.
> 
> BillW
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