Quote:
Originally Posted by kach22i
Say for instance we mount a 1/6 scale model of the car to the roof of the full sized car. The Cd of the model should be close to that of the full sized car without the roof attachment, right?
My hypothesis here is that when thinking about "scale", be it for a more aerodynamic mirror, roof luggage, trailer or an entire car body, we may have far for liberties at hand than normally accepted following the template at the standard scale.
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Yeah...No.
I thought the same thing once.
At the end of the day, we're not running scale models through the air, we're running full size cars. The Template is designed to be under the wheels and at the top of the highest point of the car, because that is what the gross volume of air is being affected by. Garnishments will obviously affect the overall shape and thus the Cd, but we cannot shrink the template onto small features and do elemental analysis on them to see if they'll optimize the entire shape.
I had a hard time with this myself a few years back and really thought as you do, and when I came to the realization that I was wrong, it sort of set a good fundamental understanding of aerodynamics for me which has not changed since. This whole conversation took place
HERE.
Of course it is entirely possible that I just misconstrued what you were trying to say, and if so I apologize. These are good talking points worthy of hashing out for sure if we are to come to a good understanding of how to optimize the shapes of our vehicles to reduce drag.
Oh, and the Reynolds Number, which I'll admit is a bit of a mystery to me in detail, but the basics of it state that: A 1/6th scale model may indeed have a very different Cd than the full sized version. That's my take away, maybe someday I'll edumacate muhself on the vagaries of it, but for now, I'll just understand it to know that scale definitely changes things.