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Old 09-11-2020, 11:45 AM   #28 (permalink)
aerohead
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nothing to do

Quote:
Originally Posted by JulianEdgar View Post
Fact 1: Aerohead said:



Fact 2: Here is the diagram to which I assume Aerohead refers (Fig 4.54 has nothing to do with lift, but 4.55 does):



Fact 3: This diagram shows exactly the opposite of what Aerohead constantly argues! As you'd expect, it shows that a fastback has far more lift than a square back. The transition to lower lift occurs when the flow separates. What a surprise (not).

Fact 4: Aerohead has not bothered to address this massive misunderstanding that he constantly displays.

I strongly suggest that rather than accepting the references Aerohead nominates, people actually check them. When I spend the time to look up each of the references Aerohead cites, he is - more often than not - misquoting and/or misunderstanding them.
In Figure 4.54, at the bottom of the table you can see the separation-induced vortex-drag increasing with the down-slope angle, up until 'burst' occurs. This is very important with respect to cars like the 911/ 912.
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In Figure 4.55, all the data presented is for separated flow and high vortex-drag. The drag minimum, and lower lift occurred at 15-degrees. You can clearly see the trend line down towards the 15-degree point on the table. And above, in Figure 4.54, you can actually see what the vortex-drag component is @ 15-degrees. The lowest lift occurred at the original roof contour ( actually on the 'template', but at high truncation ).
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With respect to fastback rear lift exceeding notchback rear lift, some counterfactual evidence is presented in Hucho's Figure 5.9, on page 221.
* A close examination of the lift table reveals a CL 0.4500 for the fastback, while the notchback version of the same car is CL 0.5085.
* The lift relationship for the two cars remains until 29-degrees of yaw, where they're identical rear lift values, then the fastback overtakes the notchback as the table ends, at 30-degrees yaw.
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The squareback shown, registered CL 0.2390, however this car is a Type 36, not a Type 31, as with the upper two cars. It, technically would not be an apples-to-apples comparison.
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The table also provides the asymptotes for each car's maximum crosswind CL.
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