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Old 03-23-2013, 04:40 PM   #515 (permalink)
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Drag of geometric bodies

I'm starting a thread-within-a-thread as the images to follow are all germane to the 'Template.'
It will take some time to get them all completed and posted,so please bear with me.
I'm starting with what I feel is the most significant,the streamline bodies of revolution which in ground proximity,as 'half-bodies,show the highest potential as low drag forms.
They are all 'teardrops',and as you see from the table,their drag varies as a function of fineness-ratio,with highest drag matched,top and bottom;where the top is overwhelmed with surface skin friction,and bottom is overwhelmed by pressure drag.
The data was originally presented as a drag curve plot of frontal area Cd vs L/D.
The images are actually borrowed from 'section' profiles presented by C.J.Marchaj (of which he credits Sighard Hoerner for the quanta) and are not to be taken as 'templates',but only to illustrate the relationship of L/D to overall drag.
From the research of Jaray,Prandtl,and Rumpler,any of these bodies would see 'double' the drag in close ground proximity,and in mirror-image ground reflection.
The lowest Cd is associated with L/D= 2.1,although as a half-body in mirror-image,this body would violate boat tail tangent angles found to support attached boundary layer flow of 'bluff bodies' without artificial,power-induced stimulation.
Attached flow is absolutely essential to low drag.
An L/D=2.5 appears to be the minimum architecture which satisfies the requirement for complete attached flow and is the model for the Aerodynamic Streamlining Template.A 'teardrop' near the L/D= 2.5 appears fourth from the bottom of the table.
All the 'templates' to be presented will have a 'sweet spot',just as with wing sections and struts,where the curves for surface skin friction and pressure drag cross to create the drag minimum.These 'minimums' are what we're most interested in.

Here are some ellipsoids of differing drag and also some assorted geometric bodies which were tested at the same ground clearance.The latter are presented at the fineness ratio of minimum drag,or,'sweet spots,'according to the research of R.Barth.
Photobucket album:

Last edited by aerohead; 04-13-2013 at 04:42 PM.. Reason: add ellipsoids and assorted geometric bodies in ground proximity
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