Quote:
Originally Posted by JulianEdgar
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 aerodynamicists have detailed to me, the description here of relationship between induced drag and lift now well outdated.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. |
* Don't tell me what I was attempting.
* You brought up wings.
* I used what aeronautical engineers use.
* As to the template is 3-D, I'm only saying what Hummel page 57,59,61, Table 2.1, Hucho page 107, 117,119, 141, 160, 199, 200, 202, 203, 209, Daugherty and Franzini ( page- 295, figure 10.10, Page 297, page 315 ), and the others say, it's the 'OPTIMUM' shape for low drag.
* I don't see tufts in contemporary wind tunnel testing by manufacturers.
* I could care less about Formula-1.
* Hucho, a PhD mechanical engineer, who ran the VW climatic wind tunnel for a decade.
* Nowhere in Hucho's text ( Schenkel, Ohtani et al., Buchheim et al.,etc. ) did I find a rear spoiler application which was NOT being applied to a car without separation, except for like the C-11 III, which was a 250-mph record car, or full-blown race cars, which are nor germane to passenger cars. Even in the section on high-performance sports cars and race cars he published, on page 281, that in the absence of a elevated tail, ' it is also possible to use a spoiler, the decisive feature being the relative height of separation in relation to the rest of the body.' He's not installing a spoiler on a car with 'attached flow', but quite the contrary.
* When your Porsche 911 Carrera was sold in the USA, the national speed limit was 55-miles per hour. At that speed, your Porsche developed 19-pounds lift. This nay have something to do with Hucho's cool handling of the issue.
* You like to imply instability in the 'template.' Bring your bona-fides.
* ROAD & TRACK measured the rear lift of the Volkswagen 1600 Squareback at 70-pounds at 100-mph. The Karmann -Ghia was also 70-pounds. The Beetle had zero rear lift. The original Porsche 912 / 911 had 59.6-pounds rear lift, a little short of the Squareback.
I gave you a couple lift table references which indicate that lift is a function of separation, not attached flow. The trends are clearly delineated. And oddly enough, spoilers added to many high-end sports cars ascend to the contour of the template exactly. The Dodge Viper Coupe and Shelby Daytona Coupe are two which immediately come to mind. From their rear contours, neither car would be capable of attached flow in the proper sense of the definition.
* The caveat for lift associated with attached flow would be limited to 'track' cars, with which splitters, spoilers, or wings are added for downforce, with little added mass penalty to acceleration and braking. Again, that would not be germane to passenger cars and 'normal' driving.
* There's another issue with lift which has to do with premature flow separation. Like on the Porsche Macan, Cayenne, that whole genre of SUVs, Jaguar's I-Pace. By mutilating the roof with the 'raked-roof,' they're removing roof which could otherwise be providing gradual pressure rise, no lift, and lower drag. When Audi's E-Tron 'Sportback' comes out, see if it's rear lift isn't lower than its stablemate. Its got 20-counts less drag just from the shape.
I'm going to sign off here ,then look at your Amazon image.