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Old 10-03-2013, 04:56 PM   #602 (permalink)
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never been there

Originally Posted by Tesla View Post
Thanks for that, I still need to play with this equation a bit more.
I've been reading a variety of things from Semi-Truck aero through to Belbouth design for engine air intakes, but one thing that struck a chord was rocket nozzle theory.
A perfect rocket nozzle will have maximum efficiency when gass departing is at the same pressure as the surrounding atmosphere, if it is higher it is wasted energy, when it is lower pressure it creates drag.
From this, in an abstract way I started to look at template theory as an inverted rocket nozzle, the ultimate goal is to leave the air behind the vehicle completely stationary, as if the vehicle had never been there.
That's it in a nutshell.
If you string-line the streamline half body you'll notice that the pathway length of the tail is twice that of the forebody.
Which suggests that the deceleration ramp necessary for attached flow must provide an aerodynamic residence time over the aft-body which is twice the dwell time as that over the nose.
It's the premise for the area rule/sectional density.
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