Contour-corrupted rooflines and lift
 

Since this subject has come up I wanted to share one tid-bit of data, actually quite rare in the popular press.
--------------------------------------------------------------------------------------
In 2014, CAR and DRIVER tested a 2014 Cadillac CTS VSPORT at the A2 Wind Tunnel.
When compared to the 'template,' the roof contour of the Caddy strays a bit, going hypo-contour for a smidgeon, then recovers at the decklid trailing edge.
Any flow instability due to the 'off the reservation' flow would be sequestered atop the backlight and boot, isolated to that region.
At 100- mph ( 161 km/h ) the VSPORT developed 30.6-pounds of rear lift, and 40.8-pounds front lift.
The curb weight is 3,998-pounds. EPA test weight would be 4298-pounds.
A gross, plan-view, 'wing area' is 98.02 square-feet. Gravitational wing loading = 43.1 pounds/ square-foot.
Aerodynamic loading is negative 0.72-pounds / square-foot at 100-mph.
At 100-mph, the VSPORT experiences 98.3% of it's static wheel loading.
As a 'wing', and with a plan-view Coefficient of Lift = 0.00007284227709, 'take-off' velocity for the car, at Le Mans, on the Mulsanne Straight, would be 776 - mph. Supersonic.
As someone who was born yesterday, and just fell off the turnip truck, I'm inclined not to concern myself with the 'lift' of production vehicles, as was the habit of Hucho when he published his second- edition.
I'm especially inclined not to concern myself with vehicles who's rooflines resemble the streamline profile.
Spirit was essentially zero-lift at DARKO. Hoerner has published pressure profile data for streamlined cars which clearly demonstrate positive loading at nose and tail, cancelling any lift in between.
I'm compiling a list of contour-corrupted fastback cars which would suffer separation- induced lift, some of which are in production today. I'll add that as a near-future addendum.
I anticipate push-back, from a certain gentleman in Australia, who, no doubt will completely discount the validity of the DARKO and A2 data. All I can offer is, an invitation for him to take every vehicle previously tested, to a moving-road wind tunnel and publish the contrasting data. There exists no other way to defend criticism of extant data.

A2 wind tunnel:

https://www.a2wt.com/images/DSC01356.JPG

Darko:

https://i.postimg.cc/j5dy11DZ/darko.png

Mercedes wind tunnel:

https://s1.cdn.autoevolution.com/ima...el-66459_1.jpg

I suggest people look up 'wind tunnel blockage factor' and then make your own judgement. Basically, car manufacturers, F1 teams (etc) don't build huge wind tunnels because they just like spending money.

I am afraid this is just gibberish.

What does 'hypo-contour' mean?

What is 'off the reservation flow'?

What does 'sequestered' mean?

And what is 'contour corrupted'? (title of thread)

To be honest, Aerohead has developed his own weird theory and then has to develop his own vocabulary to describe it. None of this stuff is in any current textbook on car aerodynamics.

And re the Cadillac. It's not a car I am familiar with, but I see a Cd listed of 0.29. From that, you can be pretty confident of attached flow right down to the trailing edge of the boot lid, and from that, you can be pretty confident of a fair amount of rear lift as the air travels around the curve from the roof to the rear window. (I'd be happy to see some smoke stream pics, if anyone can find them.)

If the car develops at 100mph 30.6-pounds of rear lift, and 40.8-pounds front lift, I'll let someone else find the frontal area and do the calculations for the coefficients of front and rear lift. My guess, and it is only that, is that the figures would be quite different in free air (and not a tiny wind tunnel), but even as they are, you can start getting a feel for how car shapes produce lift.

As to Aerohead's calculations, he is either deliberately muddying the water or is confused. No one is expecting the car to fly - yet another strawman argument of the type that Aerohead is so fond of adopting.

What kind of variations or errors will we see in a small wind tunnel that are not present at the large wind tunnel?

Can these variations be corrected for and adjusted as with polling data?

I think every single factor that is measurable will likely be in error. 'Low Speed Wind Tunnel Testing (Barlow/Rae/Pope) is the book to look at ('low speed', as in sub-sonic). It has a large number of chapters devoted to corrections.

Here's a key passage from that book relating to wind tunnel test section size:

https://i.postimg.cc/mr16vsNV/IMG-0794.jpg

So yes you can see from this that correction factors exist, but the recommendation (AFAIK) still remains at a max of 5 per cent blockage.

As I said, you can be sure if smaller, cheaper wind tunnels were fine, car manufacturers, race teams, etc, wouldn't have all built huge (and massively expensive) wind tunnels.

blockage ratio
 

According to Hucho, reliable, zero-yaw numbers have been recorded in tunnels with blockage ratios as high as 30%.

gibberish
 

1) hypo is below contour.
2) off the reservation is off the profile
3) sequestered is, the flow instability (separation bubble ) is captured between the backlight and end of boot,with no chance of making it to the 'base' of the car and contaminating it with low pressure.
4) 'Corrupted' means that the ground rules of fluid mechanics are violated by the shape. The 'template' contour produces laminar flow. By straying off the template contour you jeopardize the boundary layer which is responsible for flow separation, which is responsible for pressure drag.
5) all streamlining has to do with minimizing, or eliminating flow separation.
6) The Cadillac poses only a small perturbation. It's virtual lack of rear lift is a testament to the pressure-producing capability of a streamlined shape.
If you'll revisit Figure 2.4, page 51 of Hucho, you can see how,over the last 14.5% of the body, local pressure rises all the way back to local barometric pressure. Depending on rear overhang, and low pressure under the body, due to a diffuser, rear lift can be zero, like the VSPORT's.
7) In Hoerner's Fig. 9.4 page 160, you can see the Jaray car Sawatzki tested in 1941, with atmospheric pressure acting on the nose, a large pulse of positive pressure acting against the cowl area, then the last 23% of the body under a positive pressure gradient, acting at a distance behind the rear axle, like a wing on an F1/Indycar, or your cantilever spoiler on the Insight.
Sure would be cool if you could get into Bernoulli's Equation and Mair's and Buchheim's work on boat-tailing. Only then will you understand the value of 'corrupting', or what Lanchester referred to as 'mutilating' the streamline body.
Nobody disputes your pressure measurements, but there's an issue with the quality of the body shape you're measuring, as related to boundary layer 'health' that must be addressed. This is where I'm coming from. And it's something your aeronautical engineer and aerodynamicists may have never had to contend with, as 'low drag' may never have been a priority with the legacy carmakers they worked for. Don't know.
The new head of design for Volvo's Polestar Division is having to overcome a lot of institutional inertia with parent Volvo, who's always relied on selling 'emotion', not technology.

You do realise that the diagram you nominate is for inviscid flow?

That is, it's for for an imaginary fluid having no viscosity?

You did read the description on the next page that states:

In the real, viscous flow there exists a drag force, but it cannot be explained by considering an ideal, inviscid fluid.

If you are using this diagram - and others with similar concepts - no wonder your theory is so divorced from the reality of car aerodynamics.

Addition:

In fact, for people interested in seeing how confusion (and weird theories) can develop, it's worth having a good read of pages 51 and 52 of Hucho, second edition. It explains really clearly how a simplified aerodynamic model (ie non-viscous fluid) cannot be used to explain what happens on real cars.

Cadillac
 

1) the published drag coefficient is Cd 0.32.
2) the published frontal area is Af 24.5-sq-ft ( 85.078% of gross area )
3) a scaled comparison to the template suggests perfectly attached flow at the decklid spoiler.
4) at 100-mph, the car generates 30.6-pounds of rear lift, retaining 98.3 % of it's static wheel loading.
5) EPA test weight of the car is 4298-pounds.
6) 48 % of weight is borne by the rear axles ( 2063-pounds )
7) at 172-mph, rear lift is 90.52-pounds, compared to 207-pounds for a 1969 Volkswagen 1600 Squareback.
8) Hucho stated, in his 2nd-Edition, that if the car's aft-body trailing edge was simply raised to the elevation of the production spoiler, both lift and drag characteristics would be improved. One can infer what they wish.
9) the fastest posted speed limit in the United States is 85-mph.
10) rear lift on the Cadillac at this velocity is statistically meaningless.
11) it would be less with the template. By default.

inviscid
 

1) Free flow, outside the boundary layer IS considered inviscid flow.
I stated that we're looking at 2-D flow. Which is basically what your looking at when you do your centerline pressure profiles.
2) And of course, we don't live in a d' Alembert's Paradox world of non-viscosity.
3) The value of the schematic, was the example of a body experiencing positive pressure downstream of 'lift', which is germane to streamlined bodies.
4) You like wings, Hucho goes on elsewhere to show the same thing for a RAF 101 symmetrical airfoil, at 4-degrees angle-of-attack, and zero lift. This is a real foil in a real laboratory, and real air, at supercritical Reynolds number.
5) And as I shared with you many months ago, Abbott and Von Doenhoff's book demonstrates zero-lift conditions for every extant airfoil known at the time of their publication. Your aeronautical engineer friend will have that. My aeronautical engineer friend Larry Mauro does.
' The drag and lift of a body depend strongly upon the angle of attack.' Hucho, page 202, Re: Stollery & Burns Ref. 4.83.

Blockage Ratios
 

Is this something we want to explore? I posted to you on this many months ago. You act as if you didn't get the memo.:o

Aerohead, can you post some visuals on this?

I did find the below, and it is different than the boundary layer I had imagined you were describing.

I imagine that the first layer of boundary air can cause all sorts of drag, lift and vortex formation so we better not ignore it, right?

https://www.google.com/amp/s/www.res...1_30496832/amp

image
 

1) You're looking at a 'laminar' wing section in 2-D flow.
2) The 'center-most' structure, all in white is the actual wing.
3) The black region around it is both the thin laminar boundary layer ( LBL ), then, where the wing is thickest, the air the fastest, and pressure the lowest, you see the immediate jump to thicker turbulent boundary layer ( TBL), which continues to thicken with distance, caused by the higher skin friction of a TBL.
4) For a wing, the TBL aggravates drag due to the higher surface friction.
5) The outer inviscid flow travels over the boundary layer as laminar flow.
-------------------------------------------------------------------------------------
A) In a road vehicle, Earth's boundary layer turbulence almost completely prevents the existence of a laminar boundary layer. One paper published for a full-scale RAM pickup determined that the truck had 30mm of LBL, right at the leading edges.
B) A TBL can withstand a higher positive pressure gradient in the direction of flow, so it's actually an advantage for a motor vehicle.
C) Since road vehicle drag is dominated by pressure drag, and pressure drag is a function of separation, the whole point of streamlining is to minimize, or totally eliminate separation.
D) Lift is solely a function of pressure.
E) Pressure is solely a function of local velocity.
F) Vorticity is a function of intersecting flows of varying velocity ( pressure). You might witness a fast moving storm-swollen stream enter into a slow-moving river, and where the two meet you'll see swirls, eddies, gyres, and turbulence, which can actually eat away at the riverbank. This is happening in the Antarctic ice sheets right now. And Clear Creek, along our property.
G) Streamlined shapes don't have pressure increases ( especially spikes) of sufficient magnitude to overcome the TBL's ability to adhere to the surface it's flowing over at any point.
H) Kamm and Fachsenfeld took a full-length streamliner and then just started chopping away the tail and recording the changes.
-------------------------------------------------------------------------------------
I'll have to figure out something about images. I lost over $770 worth of pictures when photobucket decided extortion was going to be their new business model.

1) OK, so now you can work out the front and rear coefficients of lift for us - based on frontal area and not the deceptive plan view as you did before.

2) and 3) Seriously, you're still applying the template to guess where airflow goes? Even when I have run multiple tuft pics showing the airflow not following the template at all?! That's just very odd.

4), 5) and 6) Yes, what is your point? We're not expecting the car to fly. Maybe read pages 180 and 181 of my book that reference the SAE papers showing how small a lift force needs to occur before it impacts car stability?

7) Yes, lift coefficients have dropped considerably since 1969. What is your point?

8) Page reference please for that specific statement? I am not aware of any such statement in the book.

9) and 10) See above.

11) Lift would in fact be more with the template - repeatedly saying something doesn't make it true.

Normal mix of Aerohead irrelevancies and the justifiable of the unjustifiable.

Fact 1: Aerohead cited the diagram and said of it:

The Cadillac poses only a small perturbation. It's virtual lack of rear lift is a testament to the pressure-producing capability of a streamlined shape.
If you'll revisit Figure 2.4, page 51 of Hucho, you can see how,over the last 14.5% of the body, local pressure rises all the way back to local barometric pressure. Depending on rear overhang, and low pressure under the body, due to a diffuser, rear lift can be zero, like the VSPORT's

Fact 2: The diagram is for an imaginary, viscous-free (inviscid) fluid. The accompanying body text says of the diagram:

On the rear part of the vehicle's upper surface a steep pressure rise occurs, and it is in this region where considerable differences exist between the real flow of a viscous fluid and the inviscid flow shown here.

Fact 3: Aerohead's description of what the diagram shows is completely contradicted by the text, which makes the clear point that the diagram does not apply to real cars, especially in terms of pressures on the rear half (exactly the area Aerohead references).

1. I've already quoted the best reference that I am aware of on subsonic wind tunnel testing, and what it says about blockage factors.

'Low Speed Wind Tunnel Testing' (Barlow/Rae/Pope):

https://i.postimg.cc/mr16vsNV/IMG-0794.jpg

2. To suggest that car manufacturers, F1 teams (etc) build huge wind tunnels when there is no need to do so is simply not credible.

All cars operate in boundary layer flow ie flow where the viscosity of air is important. So as soon as you see a description of inviscid flow, you know it's purely theoretical (and of course any pressures that are derived from an inviscid flow model are going to be wrong on real cars).

To give you an idea, consider the following diagram of flow around a cylinder:

http://galileo.phys.virginia.edu/cla...11/cylflow.gif

With non-viscous (ie purely theoretical) flow, the drag is zero! To put this as my father did to me when I was a little kid, to move the cylinder upstream or downstream would take equal force! Clearly, ignoring fluid viscosity isn't a good idea when trying to make aero changes in the real world...

OK
 

1) I'm not interested.If you are, do your own work.You talk of wings. For wings, the plan-view area of chord and span is used.
2-3) The template was created to serve as a Go NoGo. It's derived from technology developed in the 1920s by NACA ( NASA). Its contour is incapable of producing flow separation ( that's why you'd want to use it). If you go ahead and revolve the contour you get a half-body of revolution. The VSPORT is close to the contour. Its profile is a bit mutilated, but flow perturbation would be limited to a very small area. Your tuft study does not have scientific rigor. It's fraught with shortcomings. Automakers don't use it.
4-5-6) Sometimes you appear to be obsessed with lift issues. Given the lift values reported for the Cadillac, Hucho's non-concern with lift was only reinforced. If you're a Princess and can feel a pea under a stack of mattresses, that's your problem. Lift is not associated with attached flow.
* revisit your polar diagrams for wing sections.( A. Silverstein, NACA Report 502, p. 15, 1934 will be a revelation ).
* Hucho, p. 122 ( aspect ratio )
* Hucho, p. 151, Fig. 4.54 (attached flow= lower lift)
* Hucho, p. 217, Fig. 5.4, RAE 101 aerofoil @ 4-degrees offset flow pressure distribution, both sides.
* Hucho, p. 282, Fig. 7.34 ( attached flow = lower lift )
7) what is your point?
8) I can't exit this post to see what I posted in order to reply.
9-10 ) ditto
11) you have measured a half-body in a wind tunnel? If a wing produces zero lift, what would make a half-body produce lift? Hucho presented data for only full bodies of revolution being tested, which is not germane to half-bodies. The virtual aspect ratio for a half-body isn't even 0.3, due to transverse curvature. It would be best characterized as two wingtips joined together. Wing circulation strength is function of shape, velocity, and 'orientation' ( angle-of-attack ). You are speculating about the template's ability to generate lift. An extremely contextual subject.

Figure 2.4
 

I posted a new thread dedicated to Hummel's Figure 2.4. Please check it out.
I agree with everything you've posted, however there's a context associated with everything I've posted. I'm glad you've brought this to the attention of the forum.

5% blockage ratio
 

Many readings of Hucho's chapter on wind tunnels helped me to understand the issue.
* On page 403 Hucho writes that the value of 5% is the limit for ' aircraft aerodynamics', not automobiles.
* On page 404, Hucho writes that ' condiderably higher blockage ratio is permissible for automotive aerodynamics.'
* On page 405, Hucho write that ' with streamlined walls the same result could be obtained with blockage of 20% as in test section with parallel walls with blockage of only 5%.'
* On page 407, Hucho writes that ' with 'adaptive-wall' tunnels with up to 30% blockage is fine.
* Later he writes that all these conditions are predicated upon the ability for yaw-testing, which is a different way to say that,with only zero-yaw measurements, even higher than 30% is okay.
* With a universal calibration model, Pininfarina, one of the smallest tunnels, returned values well within the standard deviation for a dozen or so tunnels tested worldwide.
* Adaptive-wall tunnels develop perfectly acceptable quanta, with blockage ratios of 30%. And this includes yaw testing.
* Curved-wall tunnels, as A2 and DARKO can provide perfectly fine numbers with even higher blockage ratios than 30%, due to the fact that everything is measured at zero yaw. There is no implication that results reflect anything but zero-yaw conditions.
* All this is predicated upon blockage correction factors developed from calibration testing in larger tunnels.
An example I gave you was the Toyota Prius.
1) We have a Cd for it from Toyota's wind tunnel
2) We have a Cd for it from A2. ( it was in the CAR and DRIVER 'Drag Queens' work which Don Sherman honcho'd ).
3) And we have a Cd for it from DARKO.
The Prius values, as a calibration model, allow us to 'adjust' measured coefficients between tunnels. An excepted practice within the industry.
4) Another wrench in the works is the fact that 'streamlined' cars upset the wind tunnel flow less than any other type during testing. They have a default safety margin designed in, as far as tunnel flow perturbation is concerned.
5) The other thing is that, the absolute values aren't as important as the trends in measurements, when limiting testing to a single tunnel as we did with Spirit. I could have done it all at A2. If I lived in Japan, I could have done all the work with the Toyota facility.
6) When you take all the conditions as a whole, a different picture emerges than one demanding a 5% blockage ratio. It's just not a universal absolute.
-------------------------------------------------------------------------------------
F1 is a multi-billion Euro / Dollar entertainment enterprise. It's a culture unto itself. Every trick in the book will be used to cheat within the rule book, to pull off a win. They're not going to leave any hypotheses untested. However that doesn't necessarily mean that there'll be any trickle-down technology useful in a passenger car. The tax code allows all expenses to be written off. And with millions in sponsor funding, it's skies the limit!

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:

https://m.media-amazon.com/images/S/...X300_V1___.jpg

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:

https://i.postimg.cc/9XdNGvQJ/IMG-0835.jpg

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.

attempting
 

* 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.

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):

https://i.postimg.cc/9XdNGvQJ/IMG-0835.jpg

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.

fastback / squareback
 

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.

[Groan]

No they're not...

I don't quite believe that I am having to do this but here's the rest of the diagram.

https://i.postimg.cc/Vkgry9Wj/IMG-0837.jpg

1. Note how the wake is shown behind the two shapes.

2. Note how the wake is larger on 'A', indicated in the graph by the solid dots.

3. Note how the waker is smaller on 'B', indicated in the graph by the hollow dots.

4. Note therefore that there is attached flow in 'B'.

Honestly, this is becoming quite ridiculous.

You keep talking about wing profiles having the ability to develop zero lift at certain angles of attack. That's fine - there's plenty of data that shows that. Trouble is, it's another of your argument red herrings.

For example, let's give The Template a negative 5.6 degree angle of attack (as you nominate for the Clark Y) and then let's add a suitable underfloor profile (red).

https://i.postimg.cc/h4dZgs3W/template.png

I'd be pretty confident that lift would now be waaaay down. Trouble is, it's also now a completely different shape...

nothing to do
 

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.
--------------------------------------------------------------------------------------
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 ).
-------------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------------
The table also provides the asymptotes for each car's maximum crosswind CL.

wake is smaller on 'B'
 

--------------------------------------------------------------------------------------
1) Again, you completely miss the context of the 'small' wake.
2) This wake is not an artifact of slow, gradual, pressure rise,high base pressure, free of separation - induced,high-drag, three-dimensional, attached longitudinal vortex trains.
3) You've fallen into exactly the same fallacy as with the Porsche 911.
4) It is separation-induced, high-drag vortices which create the downwash which holds the flow down the slope. It violates everything Hucho advocates with respect to streamlining, and why he reasons that streamlined half-bodies are the direction for low drag. ( page-15,16,39,109,117,118,142,144,155,169,175,200,201, and 210.

'there's plenty of data that shows that.'
 

--------------------------------------------------------------------------------------
* Finally, after a year or so, you publicly announce that all wings are capable of zero-lift. This is real progress. Thank you!
* I've provided the underbody profile. It's basically flat until the long, 2.8-degree diffuser completes the belly. The rest of what you see is the wheel fairing package. SAE 'approach', breakover', and 'departure' angle limits for a passenger vehicles are respected.
* As to a car-width 'wing section' for an automobile, this was tested by Kamm at FKFS and returned Cd 0.21 as a lange-heck.
* Adding tumblehome reduced the drag to Cd 0.1764.
* Adding body camber and boat-tailing produced Cd0.1481.
* And the long diffuser takes it to Cd 0.1231 ( Template car measured Cd 0.1201 with crappy wheel fairings ).
* In front elevation, the 'template' car approximates a semicircle in cross-section. There isn't a flat surface on the car anywhere. It's all compound surfaces.
* A couple of 'wingtips' joined together would be a more accurate characterization of the form. It's a streamline half-body.
* The sides mirror the top contour.
* Pressures alongside are very close to up above.
* There is no vorticity.
* Boat-tailing creates continuous cross-sectional contraction and surface area reduction, all the way to essentially zero, over the latter 2/3rds of body length. That doesn't make for a very good 'wing.'
* Passive pressure acting over the aft-body would be at the highest positive values observable.
* Active suspension and reduced ground clearance offers opportunities.
* Active suspension offers body inclination opportunities.
* The tail can be 'deployable' as with Hucho's Figure 8.63.
* Static wheel loading due to travel weight may make the whole 'lift' issue a non-starter.
-------------------------------------------------------------------------------------
As a piece of crap, Spirit is quite stable at 108- mph. In crosswind, exposed ,on an elevated interstate highway. With wind tunnel tuning I would venture that it could perform any 'normal' driving functions without drama.

' BEST'
 

* The nose is 'best' according to Daugherty and Franzini, page 297.
* The tail satisfies Daugherty and Franzini's ' attention in streamlining must be given to the rear end, or downstream part, of a body as well as to the front.' page 297.
* ' for streamlining against subsonic flow a rounded nose and a long, tapered afterbody generally result in minimum drag.' D & F, page 315
* ' The drag of bodies with finite thickness mainly consists of friction drag, which is small in all cases in which no flow separation occurs. This can be achieved by slender shapes on the rear part of the body which produce only a weak pressure rise in the flow direction. Shapes of this kind are aerofoils and 'streamlined' bodies.' Professor Dietrich Hummel, page 57, Hucho, 2nd-Ed.
* ' [T]he shape of the body should be designed so that the flow remains attached and the pressure rise is as large as possible.' Hummel, page 59.
* ' The main contributions to the drag force originate from the rear part of the body.' Hummel, page 61.
* ' [I]t is very important to design a rear body surface which brings the divided streamlines smoothly together.' Hummel, page 61.
* ' Optimum shapes are 'streamlined' bodies having a very slender rear part.'
* Page 61, Table 2.1, 3rd from bottom: ' Streamlined body L/D = 2.5, Cd 0.04. ( the template)
* ditto, bottom of table, 'Streamlined half-body @ zero ground clearance = Cd 0.09. ( the template)
* ' Vortex type flow separations, related to inclined shapes of the base of a vehicle, may cause considerable contributions to the overall lift.' Hummel, page 64 ( Porsche 912 / 911 ).
* ' [W]ith refinements in aerodynamics progress is towards the body of revolution.' Hucho, page 107. ( just skip to the body of revolution and have all the progress in a single stroke )
* ' Separation-induced vortex trains : Fastback : induces downwash , leading to low separation line, short wake ( prismatic model ), drag. page 112.
* ' At points where the flow is opposed by a high pressure increase, it tends to separate from the contour.' ( Porsche 911 ) Hucho, page 117.
* ' drag induced by any vortices.' Hucho, page 118.
* ' Aspect ratio is very small for vehicles ( 0.3 ).' Hucho, page 122.
* ' there is not a simple relationship between the overall lift and drag for this profile drag / vortex-induced relationship.' Hucho, page 123-4.
* ' Three-dimensional longitudinal vortex pair' page 140.
* ' base pressure also depends upon the angle at which the flow separates from the contour.' page 141
* ' Mair's boat tail and 22-degrees, page 141.
* ' The highest drag.... results from vortex drag.' page 149.
* Figure 4.59, Ahmed body, attached flow = lower lift, page 151.
* ' [C]onvex surfaces must be matched to prevent high pressure variation along the flow path.' ( template ) page 160
* ' risk to sales.' page 188
* page 199 ( template )
* page 200 ( template )
* page 202 ( template )
* page 203 ( template )
* ' [T]he drag of the ( Cd 0.09 ) basic body is achievable. To what extent this can be approached in the development of a production vehicle is therefore more of a question of the balance of the requirements of the specification than of technical feasibility.' Hucho, page 209.

Normal mix of errors (eg comment re Fig 4.55) and irrelevancies (eg bringing in old-shaped notchbacks with separated flow).

I'll let people look at the diagram and make up their own minds as to what it shows with regard to:

• separated flow, attached flows and resulting wakes.
  
• lift of fastbacks versus squarebacks

https://i.postimg.cc/Vkgry9Wj/IMG-0837.jpg

You would honestly think the diagram is clear enough for anyone to understand...

This is why the Template has virtually no application to a passenger vehicle. And heaven forfend driving it sideways. That's where the fun is.

errors and irrelevancies
 

* ' [T]he vehicle aerodynamicist must refer to a huge amount of detail resulting from earlier development work.' Hucho , Preface
* The new Ford Bronco, upcoming Rivian pickup, HUMMER, and others will fall under these dimensional considerations.

no application
 

Would you like to argue your thesis scientifically?