Quote:
Originally Posted by aerohead
I've been chugging back through Aerodynamiks des Kraftfahrzeugs by Koenig-Fachsenfeld and looking at material he worked on under Kamm at the FKFS which is germane to the 'organic' vs 'cubist' teardrops.
It looks like they tested both images (left) and (right) as passenger car bodies,with wheels,at 'standard' ground clearance.
The (left) body produced Cd 0.12,the (right) body Cd 0.21.
I've contacted a local German tutor to help with translation,but from the tabulated data I think this is what they found.
FIAT,in a 1986 SAE paper investigated fastback bodies and demonstrated how the Cd is corrupted without both tumblehome and edge rounding,something which is a feature of the body of revolution.
Jaray cheated the form with his pumpkin seed of 1922 so we've got 'options.'
I'll try and have something for Saturday at the latest.
|
--------------------------------------------------------------------------
I'm still working through the German-English translation and I haven't heard yet from the tutor but have roughed-in some text and believe that the following is an accurate portrayal of what K-F and Kamm did at FKFS:
*Using a slice of airfoil twice as wide as the section height,with a thickness ratio of 15.38%,with a ground clearance equivalent to standards circa 1938 (around 9.25-inches (235mm)) they got Cd 0.19.
-------------------------------------------------------------------------
*Adding wheels gave Cd 0.24.
-------------------------------------------------------------------------
*Adding plan-view camber to the body produced Cd 0.1938.
-------------------------------------------------------------------------
*Adding rounding to all the upper edges produced Cd 0.161
-------------------------------------------------------------------------
*By restoring the plan-view radius to the nose produced Cd 0.12.
-------------------------------------------------------------------------
*K-F/Kamm did 'remeasuremnts' (Nachmessungen) to a reproduction of Walter Lay's 1933 aerodynamic research model from the University of Michigan.They recorded an identical Cd 0.12.
*Lay's model# 10 with 'JEEP Wrangler' windshield couldn't better Cd 0.24,as with the FKFS compromised nose.
--------------------------------------------------------------------------
FIAT's aeronautical laboratory,in their SAE Paper# 860212 reported that a 'fastback' car (Template) suffered a 32.6% drag increase with compromised forebody leading edges, which reinforces the conclusions of Lay,K-F,and Kamm.
*Fiat's research also showed that of fastback (Template),notchback,and squareback body styles,that the fastback was most sensitive to upper body rounding and suffered the greatest drag increase without it.
-------------------------------------------------------------------------
*Jaray and Kamm were both airship 'Luftschiff' people.
*Jaray was designing Zeppelins at the same time Kamm was serving in military with observation balloons.
*Kamm's doctoral dissertation was on streamlined teardrop-shaped balloons of which he patented circa 1919 as the K-Balloon.
*All Allied barrage-balloons of WW-II were lineal descendants of the K-Balloon.
-------------------------------------------------------------------------
*At FKFS,the half-airship 'halbeluftschiff',Half-streamline body of revolution 'halbestomlinienrotationsk'o'rper',was always the 'Alpha' form from which all the attempts to 'cheat' were done.
--------------------------------------------------------------------------
*The half-body has a good enough forebody for subsonic flow.
*Most importantly,it has the sectional density in the aft-body necessary for the gradual pressure rise which will prevent the reverse-flow that triggers separation and the attendant pressure drag aerodynamicists demand that we avoid if we're to achieve really low drag.
--------------------------------------------------------------------------
*We can push the shapes around in frontal elevation.Jaray did it.Lay did it.Kamm did it.Which means that production automobiles are game.It is a condition of boundary layer 'legislation.'
-------------------------------------------------------------------------
*We can't mess around with it much in side elevation or plan-view.If anything,you'd go hyper-template,but never steeper.
-------------------------------------------------------------------------
*With 'zero' streamlining you're looking at Cd 0.86.
*With ' complete' streamlining Hucho says we can approach the drag of the body sans wheels (0.07-0.09).
*Hucho also says that these lower values will be achieved only through airfoil and half-body forms.
* You can consider the 'practicality' of a 'wing-car.'
*And we've demonstrated above what happens when you 'template' a 'wing-car'.
You can fool most of the people most of the time.You can fool the atmosphere non of the time.
