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Old 09-09-2020, 07:20 PM   #25 (permalink)
aerohead
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fastback / squareback

Quote:
Originally Posted by JulianEdgar View Post
Cars use frontal area in the calculation of coefficients of drag and lift. You were attempting to muddy the water by using plan area not frontal area.



Typical Aerohead non sequitur. I agree that the template (in 3D) is unlikely to have flow separation. That does not automatically lead to it being the best shaped body to use. A dog has four legs. Not all animals with four legs are dogs.



Are you serious? Carmakers have used tuft testing for getting on for a century. Every single professional aerodynamicist who reviewed my book complimented me on the quality of the tuft testing I show. One said it was the clearest he'd ever seen. Another Formula 1 aerodynamicist told me that only people who don't know anything about car aero deride tuft testing. Here's an example of a carmaker not using it:





I am not obsessed with lift. It's just that it doesn't make good sense to utterly ignore it, as you do.

Lift is not associated with attached flow? You really believe that? Honestly, if you do, that is about a fundamental misunderstanding of aerodynamics as it's possible to get. Words fail me.



The report has only 13 pages.



Aspect ratio is not relevant here. On the basis of what two professional car aerodynamicists have detailed to me, the description here of the relationship between induced drag and lift is now well outdated. (But from what I understand, this is an area of some disagreement between aerodynamicists.)



Fig 4.54 does not mention lift. Fig 4.55 does though. It shows exactly what I have stated many times. Lift is higher with a fastback shape than a squareback shape. In fact, it's such a clear diagram of what really happens, here it is:



As this diagram so clearly shows, I am afraid your understanding is completely backwards.



Um, Fig 5.4 is showing aerodynamic side forces, not lift/downforce. Did you read the text?



This diagram shows the presence of a spoiler that causes earlier separation, not better flow attachment. That's exactly what I wrote in my book, and when reviewing this part, Dr Thomas Wolf (the current head of Porsche aerodynamics) agreed with my analysis. But hey, what would he know?

So what I am finding, and as someone else here identified a while ago, is that when I spend the time to look up each of the references you cite, you are very often misquoting and/or misunderstanding them.
Look at the angles represented in the table. They're all in separated flow.
Drag minimum for the fastback occurs at 15-degrees and you'll see it's lower lift on the other table I believe ( I didn't bring the book with me).Lift minimum is at zero-degrees and full-attachment on the roof.
The lift over the slope is a function of low pressure due to premature separation,closer to the roof location of lowest pressure ( just ahead of the windshield header ), and the vortex train.
* On the NACA Report, I wanted you to see the polar diagram for the Clark-Y aerofoil, and it's zero-lift at negative 5.6-degrees angle-of-attack, negative lift at negative 8,2 degrees angle-of-attack, and maximum lift at positive 15.6 -degrees angle-of-attack. Daugherty and Franzini published that it's 'essential' that this relationship be understood.
* On aspect ratio, one needs to understand that on a car we're looking at 0.3, and on say, a Piper Cherokee, it's 6.0. It is relevant.
* I couldn't link to you Amazon reference. I'm not much with computers.
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