Beware old and new aero data
 

Can I put forward an idea?

A preamble: I love historical context. There is nothing in any area of car aerodynamics of the past that I am not interested in. Show me old aero cars and data - and I am always interested. That's a major reason I went and saw the Tropfenwagen in two museums in Germany, and admire the Tatras, Citroens and Chrysler Airflow so much.

But you need to acknowledge that old car aero data comes with some very major shortcomings. Primarily, they are in the measuring and testing methodologies that were then used.

Take the wonderful Tatra T87. It had a drag coefficient, when recently measured full-size in the highly-respected Volkswagen wind tunnel, of 0.36. Nothing special, eh? However, models of the car were being measured at the time of the car’s development at CD = 0.24!

Or what about the ground-breaking pre-WWII research vehicles, created by the German FKFS institution under the leadership of Wunibald Kamm? The models were dubbed the K1, K2 and K3. One reference states that K1 had a CD of 0.23 (and a model measured 0.196), K2 apparently had a CD of 0.23 – but K3 had the much higher CD of 0.37! So what happened to K3? – after all, it looked much the same as the two earlier cars. Well, K3 was tested full-size in the Volkswagen wind tunnel in 1979… In fact, it’s very likely that K1 and K2 had drag coefficients that were similar to K3. Good at the time - but absolutely nothing to try to take lessons from today.

So old info - based on measurements of models, or done in wind tunnels without moving floors or moving wheels - is all highly suspect.

And what about NACA data, or that great old textbook, Theory of Wing Sections by Abbott and Doenhoff? It's a book I have (I think I have all the major aero textbooks) but it's one that has as little relevance to the shape of current cars as data on low drag wheel covers on a WWI aircraft has. It's all interesting - but tech papers on wheels on low drag cars with smooth undercovers are in a quite different world to a WWI aircraft! (Not to mention the different galaxy of aerofoil profiles measured in free air!)

I read somewhere 'what is the time cut-off for scholarship'? The answer to that question is very easy: when the current evidence suggests that our understanding has changed. Patterns of airflow don't change, but they way that they are measured, modeled and predicted has changed massively over time.

I've recently been reading a 1960s textbook. It's very well regarded - in fact an absolute classic on engine tuning. But the material on tuning air/fuel ratios and ignition timing is so simplistic as to be useless for any current engine. In fact, to be honest, it sounds like they're trying to tune a lawnmower. And yet the author worked on, and helped develop, F1 engines....

If you don't keep up with the current research evidence, you're doomed (I think anyway) to falling into the trap of "it's always been like this" - when, maybe, it isn't any more.

" Patterns of airflow don't change, but they way that they are measured, modeled and predicted has changed massively over time."

And that sums up best what will always be the one thing certain, I think.:)

old and new
 

Just read this thread.I'm away from my library and do not have access to my materials.
While I don't disagree that there is evidence that there are discrepancies between early data compared to more contemporary data obtained for the same vehicle/model,there do exist modern data which compares favorably with early reporting.
I don't believe that broad stroke generalities best serve this argument,but rather, maintain that any specific vehicle should be treated on a case-specific basis.
The Tatra was incapable of 'low drag' due to its aftbody.
Of thefive 'K-cars' built by Fachsenfeld at FKFS,only the Mercedes-Benz'experimental-chassied,diesel-powered,overdrived,1941-42 K-5,personal personal car of Kamm's was rated as low as Cd 0.23.It's the only 'drop-nosed' K-car.It's the only K-car with full wheel skirts.K-5 maybe the only K-car with Kamm's patented cooling system (which is what he is actually famous for,as the
'Kamm' -back is actually the property of Fachsenfeld,and the reason Hitler wanted Fachsenfeld at FKFS).K-5 had the longest aftbody of all the K-cars,the secret to its low drag.
Airfoil shapes would be relegated to sub-critical Reynolds number solar racers,and NACA (NASA) quanta would be valid.
The really 'low-drag' shapes which could be applied to passenger cars would be based upon Paul Jaray's,1922, streamline half-body,which modern wind tunnels and CFD re-verify,with each generation of university investigation.
In his second edition of Aerodynamics of Road Vehicles,Hucho wrote that any difference in drag,associated with wheel rotation during testing indicated such an insignificant difference in results that it wasn't pursued.General Motors Research Labs had come to the same conclusion from it's testing at Cal Tech in 1953.It would have been considered an absurd proposition in truck and trailer testing,due to wheel environment turbulence.Only open-wheel race cars were deemed worthy of the extra trouble/cost.
Today's F-1,Indycar,and NASCAR' billion-dollar racing programs mandate that 'ALL' areas of aerodynamics be investigated.
One curiosity always hiding in the room is that,given rolling-road wind tunnels,and million-dollar public relations budgets,and the ability to develop 'porous' low-drag wheelcovers,when tasked with setting land speed records,all auto manufacturers choose the totally sealed,convex disc,MOON wheel covers,the lineal descendant of WW-I era aviation; and can be seen on all extant Boeing 727s.

[ears perk up] So what was that like?
That's why I like Computation Fluid Dynamics. Software has changed massively over time. Having a moving floor is possible in meatspace, having an undulating/textured moving floor is possible in CFD.

It pairs well with Generative Adversarial AI.

Two Minute Papers: This AI Does Nothing In Games…And Still Wins!
hardware.slashdot.org: AI Drives Innovators To Build Entirely New Semiconductors

Increasingly powerful computers arguing with each other about the ultimate design for a use case. It should be fun to watch.

I did not say that all new data disagrees with old, I said that old data should be treated with suspicion when the current evidence suggests that our understanding has changed.

I am quoting data from Stromlinienautos in Deutschland (Kieselbach), P 84 for K1 - K4 and Aerodynamics of Road Vehicles (Hucho) (P 21) for K5.

As is typical with cars from the 1920s and 1930s, when tested in a modern wind tunnel, they all recorded much higher drag figures.

For example, you mention K5 as having a long afterbody as 'secret for its low drag'. It had a measured Cd in a modern wind tunnel of 0.37! So much for its secret. As I already mentioned, K3 was also measured in a modern wind tunnel at 0.37.

They were fascinating for the time, but to bring up these old cars as if they have anything to teach us today is just absurd.

Yes, I agree - so to use data relating to NACA aerofoils for shaping normal road cars is treading on very thin ice indeed. One obvious discrepancy is the thickness of the boundary layer on the rear parts of real road cars versus an aerofoil.

Yes Jaray was a very good aerodynamicist, and refined his craft working on the aero of Zeppelin airships. But his pure shapes are a long way from practical road cars.

These views are now completely outdated for road cars. Any aerodynamics textbook published over the last few decades covers the major increase in drag associated with testing vehicles with rotating wheels. It's why all car manufacturers now use 5-belt wind tunnels with rotating wheels.

What have Boeing 727s, Land Speed Records, F-1, NASCAR and Indycar got to do with road car wheel design for lowest drag? The most recent tech research shows that, for road cars, fully enclosed wheels are not always best for low drag. I've already cited those papers here in another thread. It's an excellent example of why not keeping up with the literature means falling into the trap of "it's always been like this" - when, maybe, it isn't any more.

old/new
 

*The suspicion issue has been reported on for decades.
*Since,as of Hucho's earlier writing,and specifically to good agreement of drag coefficients for specific cars tested in modern tunnels,compared to original literature,only a fair assessment would be derived from those very same shapes being tested with rotating wheels and the variability published.

*Kieselbach may have it wrong.It may have been
Ludvigsen who reported on the confusion of K-car nomenclature.
*The Landsberg (sp?) Castle car tested by VW is not the K-5.It's Cd 0.37,in light of its mutilated belly pan,would not be germane to the K-5.
*The Schl'o'rwagen,at full-scale,if I remember correctly,returned a Cd very close to that of early reporting at Gottingen,compared to the VW tunnel,with static wheel testing.
* Hucho has corroborated Hoerner's numbers.
* Horner has corroborated NASA's (NACA) numbers.
*Which all support Jaray's Zeppelin numbers.
*Jaray's small car returned lower drag in more modern testing than originally reported by Klemperer.
*Modern testing of 'typical cars' of old is not germane to modern testing of 'specials'.We need specificity.
*As to the K-5's 'secret,' the entire premise of much of the FKFS research dealt with body length vs drag.'Verhungungsverhaltnisse'.They corroborated Walter Lay's research,who's research corroborated Jaray's,along with Elliott Reid at Stanford,and others.
*I would want to tread very lightly when implying that the older research has nothing to offer us.I smell confirmation-bias,and that has no place in science.
*Aircraft,by design,are separation free at 'flight' conditions,and are all ruled by surface friction drag,of shock-wave drag depending on Mach#.It's really not germane to road vehicles,of which drag is fundamentally a function of flow separation.
*'Practical' is not a scientific metric.It cannot be quantified.It's very subjective and only an arbitrary invention of the human mind.
*If truly low drag is the topic,then body length is the arbiter.It's not negotiable.Physics as it is.
*And again,FKFS gave us the template for active aerodynamics in the mid-1930s which would address the 'practical' length argument.
*If outdated,can you explain why contemporary record vehicles continue to borrow from near-century old technology?
*I have your book.Your sources haven't proven anything,nor made a case against full-coverage,convex wheelcovers as an all-emcompassing universal absolute.What your messengers have published is highly contextual and dismisses an environment in which even lower drag can be attained if automakers weren't enslaved to the Paris dressmaker.
*Ignoring brake cooling,if porous wheels have superior low drag characteristics compared to full-coverage,convex discs,why don't we see them when land speed records,or fuel economy records are set?

Sorry, but I honestly can't make any sense of a lot of what you have written. So I'll take up just the one point.

If you wish, you can dismiss technical papers that don't agree with your premise that full wheel covers are always best for drag. You can even drag in odd statements about Paris dressmakers. I, however, like going on the evidence of peer-reviewed technical papers.

The current technical literature unambiguously shows that full wheel covers are not always best for low drag in road cars.

I don't like seeing people being given incorrect advice. It wastes their time, energy and enthusiasm.

point
 

The conclusions drawn in the peer-reviewed technical papers are contextual.I believe you touch on that in your book.I don't advocate driving with MOON covers,in light of brake cooling issues.I've done that and devolved to a porous cover which accommodates cooling air to the calipers and drums.
And on a case-specific-basis I'm okay with a messenger reporting on research of a specific vehicle, in light of all that vehicles design particulars.But that's as far as I'll go.
Automakers are beholden to the stylist.Aerodynamicists may be given a little latitude to best optimize a wheel cover as long as it's in keeping with the spirit of the stylists vision.It's true of any feature on a car.Some committee may accept the data from the wind tunnel,and then base a new car design solely on aesthetics.Volkwagen has a chance to sell a Cd 0.31 Golf/Rabbit in 1975,but couldn't because of contract constraints with Georgetto Giugiaro.We had to wait decades before we could get a Cd 0.31 VW,and thousands died in battle in the meantime,over the difference in oil to power those high-drag VWs. There's more at stake in aerodynamics than academic arguments.
I didn't give any advice that I know of without caveats.

Well, of course. But 'contextual' is the whole issue here: the context is that in some cases, full wheel covers increase drag. Isn't that the point?

I am sorry, but I have seen lots of advice here - including from you - that is stated without any caveats whatsoever. Here's an example that was being used in a signature:

"At 55 mph, a 10% drag reduction translates to a 5% increase in fuel economy. At 70mph,a 10% drag reduction translates into a 6% increase -Phil Knox (Aerohead), Aerodynamics Seminar #2"

No caveats there.

(Nothing on what proportion of total drag is made up by CD vs rolling resistance - which is car-dependent? Nothing on the change in engine efficiency - BSFC if you like - as the rpm changes? For a discussion of this sort of thing, see Barnard, Road Vehicle Aerodynamics Pages 54-55, and Stone, Motor Vehicle Fuel Economy, Page 136.)

[time for some popcorn. It's gonna be epic]

Honestly, there is a lot of misinformation discussed here (and of course some excellent information as well). I sometimes think that people don't even stop to think for a moment before accepting advice / statements that have been made. Then they apparently become gospel - weird.

- Streamlined bodies don't develop lift? What, then, is an aircraft wing?

- Airflow over the curved upper surfaces of a car doesn't develop lift? Really, when you can see in any pressure measurement diagram of a car all that top surface lift?

- Percentage drag reductions can be precisely quantified as fuel economy gains? And that's apparently irrespective of the car?

- Kamm tails (as opposed to the use of simple separation edges) are somehow great for drag? Really? What's an example, and don't give me those K cars from the 1930s that now measure at 0.37!

- There is a perfect streamline template shape? And this is irrespective of the thickness of the boundary layer (which will be car-dependent)?

- Box cavities are a panacea? And that despite almost no mention in the technical literature?

- Coast down tests are accurate? And that's when even the experts hate them (unless they're using very sophisticated equipment).

- Full wheel covers are always best for low drag? There are specific, recent tech papers than contradict that.

It's a bit frustrating when you see so many people putting in work and enthusiasm to modify the aero of their cars when there is so much poor advice being given out.

Note that I am not throwing the baby out with the bath water - there is some excellent information here, and some very good testing (especially mileage over long periods). And that's great. But it's so frustrating reading older threads where suggestions are made, I think to myself 'that won't work' (or - often - 'the difference will be so small, forget it'), and then after a lot of time and effort, the OP says 'that didn't make any difference'.

You may want to avoid The Lounge. :)

There've be a few times that other posters confirm my suspicions. One was when HHOTDI moved the folding tent from the top of his New Beetle to a hitch mount and the drag was lower than no tent at all. https://ecomodder.com/forum/showthre...tml#post390588
tinypic.com ate the pictures. Another one was when someone CFD'd this and got some improvement over a flat transom.

https://ecomodder.com/forum/member-f...14-1-42-00.png
It uses longitudinal rolling vortexes just like the Cybertruck.

caveats
 

*The 5%,10% etc. rule of thumb is from PhD, Gino Sovran,General Motors Research Laboratory, contributor to SAE publications,and personal friend and mentor of Wolf Heinrich Hucho.These relationships have been shared by GM,Ford,Chrysler,and Hucho,extending into recent times.
*The relationship is predicated solely upon drag reduction,and I've addressed the implications of BSFC degradation for not gear-matching in the seminars,as per Gino Sovrans admonition in the SAE literature.Hucho repeats this cautionary tale in his textbooks. I'm quite familiar with the relationship. Once upon a time, I had a personal relationship with Glen Scharf,of GMs Aerodynamic Laboratory.I could simply call on the phone,share data,and he was gracious enough to help me navigate the drag implications of delta-drag,based upon delta-mpg.Glen is the individual who stated that my modified CRX had Cd 0.235,based upon my Bonneville speed record, coastdown data from the Chrysler Proving Grounds,and tank mileage.

gospel
 

*Look to THEORY OF FLIGHT,by Richard Von Mises, DOVER Publications, for an introduction to the concept of the streamline body, conceived in 1907,by Frederick W. Lanchester, who was one of only two people on Earth with a true command of aerodynamics, Ludvig Prandtl being the other.
*Airfoils have nothing to do with streamline bodies.
*And again, if you will re-visit 'THEORY OF WING SECTIONS Including a Summary of Airfoil Data, Appendix-IV, by Abbott and Von Doenhoff, you'll be re-acquainted with 118-families of airfoils, all of which are zero-lift, depending on angle of attack, also addressed in Von Mises work.
*Wait until you see the pressure profile over a streamline body and it's zero-lift before you condemn them.
*Yes, if properly gear-matched, a 10% drag reduction will approximately relate to a 5% improvement in constant velocity,55-mph, highway driving (not to be confused with any EPA Highway testing protocol);for any vehicle which has undergone only a shape change.
*As to 'Kamm' tails, technically, it would be 'Koenig' tail, as Reinhard Koenig-von Fachsenfeld holds the patent for the 'K' truncated tail. Kamm is given the credit, but he's really known for his low-drag cooling system. And yes, in the context of the model studies conducted at FKFS, the K-tail might as well be considered ideal.FKFS starts with the entire streamline body, then begins lopping off sections, documenting the drag change as a function of the degree of truncation.'Verjungunsverahaltnisses'. Hucho states that this is the only path to low drag, and the premise of aerodynamic streamlining.
* The Langenburg Castle K-car is not Kamm's K-5,Cd 0.23 car, it is the K-3.It was Jerry Sloniger of ROAD & TRACK,August,1982,page 66, who tracked down the proper nomenclature of these cars. Kaselbach is incorrect in his data presentation. Kamm's car was Cd 0.23,diesel-powered,overdriven,85-hp,and top speed of 113-mph.HOT ROD Magazine featured photos of the K-5 in 1963,depicting tuft-testing.The flow is virtually ideal up until it reaches the rear radii of the tail, something not depicted in in the FKFS drag tables.
*There is a perfect streamline template shape. Hucho gave us all the critical elements for its construction in his 2nd Edition of 1987.At 1/3rd-scale,it returned Cd 0.1201 at DARKO,with compromised wheel fairings. It's a sure thing. You don't have to worry about boundary layer or anything else.It's pre-tested, at any scale you choose, up to 250-mph.
*Would you like to show me where I've ever implied that box-cavities are a panacea?
* I have only recommended that people approach CAR and DRIVER, and see if they'll conduct the coastdowns at Chrysler Proving Grounds, E.Chelsea, Michigan.They know the SAE protocols,have scientific-grade weather system,and optical fifth-wheel, as well as access to Chrysler's all-wheel scales, a dedicated test-track, where they conduct the rapid, back-to-back coastdowns, plus custom software for the data reduction.Top speed is conducted on the 8-mile oval, with only stop-watch,and no aerodynamic excrescences of any kind. They tested my CRX in 1991,afer the speed record at Bonneville. Call for current pricing and availability.
*As to the wheelcovers, your messengers have yet to re-test previously-measured static structures on a rolling-road wind tunnel, and publish the discrepancy between the two readings. I've yet t see any bona fides,prima facie evidence for the superiority of aspirated covers,except in specific cases.And curiously, when GM,Ford,or Volkswagen set out to establish land speed records, their choice of wheelcover is the MOON disc, even though they have access to virtually any 'secret-weapon' design. And to the rotating wheel supremacy issue, Dennis Semanaitis,of ROAD & TRACK,August,1982.p.35,reported:'[Rotating wheel] Tests have shown that wheels and tires of an ordinary passenger car generate added drag of 0.005 or less....The idea of a moving belt has been explored,though most believe its complication outweigh any potential improvement in realism.'
Hucho, in 1987, states,'The rotation of the wheels isusually not taken into consideration in wind tunnel testing; testing is carried out with the wheels stationary.When the wheels are integrated into the body the roration of the wheels appears to have negligible influence upon the forces and moments acting upon the vehicle (Second Edition, page 419).

As at Permalink #4, I solicit documentation. My favored search engine only points to the Meredith Effect.

The major effect of a rolling wheel appears at the leading edge of the contact patch[es]. Shouldn't have much effect on the body itself.

documentation
 

Automobile Magazine (I think) published two, hardbound books which included brief histories of both Jaray and Kamm. I believe that this is the source of the information. Both books will be easy to locate,I'll look. Since Germany lost WW-I because it ran out of oil and rubber, Hitler was very concerned that his up-coming war might be jeopardized the same way (which turned out to be case).In exchange for all Fachsenfeld' aerodynamic patents,he was to be given free rein at the FKFS laboratory/ wind tunnel in Stuttgart (it's right next door to Daimler-Benz (Mercedes-Benz). Kamm's low drag cooling system would also help the war effort.Kamm would commute back and forth to Berlin in his K-5,while Porsche commuted there and back in his 60K10 Berlin-Rome racer.

Thnx.

This is just a dump largely of misunderstandings, outdated references, and irrelevant citations.

To save time, I'll pick out just five completely wrong statements.

Well then, you must have a unique definition of what comprises a streamline body. Earlier you defined a streamlined body as one with attached flow. (Which is correct.) And aerofoils have attached flow. Hmmm.


I've seen lots. One example is a wing, and they allow aircraft to fly.

It doesn't even need any reference citations to prove this is absurd. (But as a bonus I previously gave two references that show this not to be the case.) Just think about it for a minute. Given that rolling resistance (the other determiner of fuel consumption) changes little with cars of different CD, how can this rule of thumb validly apply to cars that might vary in CD from 0.5 to 0.25? To put it simply, the proportional change might be to something making up half the total vehicle resistance, or one-quarter! And yet the outcome is the same?

No test of any of these K cars in a modern wind tunnel has given what we would now call low drag values. Hardly surprising. And yet you still quote these drag figures as if they are valid. More spreading of misconceptions.

Seriously, this is flat earth stuff.

Pick up any current textbook on car aero.

Talk to any current professional aerodynamicist.

Think for a moment why every major car manufacturer in the world has spent millions (billions?) upgrading their wind tunnels, or building new ones, that incorporate the facility to have turning wheels on their test cars.

And they're all wrong - because of something you read in Road and Track in 1982?

You're beginning to understand the aerohead we all know and love. :) Asterisks for paragraphs but never a space between sentences.
https://en.wikipedia.org/wiki/Senten...al_typesetting

Sure you could have vehicles with the same rolling resistance and wildly different CD, but when I think of specific examples they seem to have a positive correlation. You say .5 CD I’m thinking hummer H2 has some serious rolling resistance, You say .25, I’m thinking insight. I always thought the 5/10 was more just a rule of thumb

The nearest parallel I can think to all of this is the old argument about engines 'needing back-pressure'.

I used to have this argument all the time, especially with older modifiers, about 20 years ago. They, too, would quote outdated magazine articles, outdated books, etc. Then they'd tell me the results of their tests - how power went down with free-flow exhausts. They had all sorts of theories as to why back-pressure was needed, and what terrible things would happen without enough back-pressure.

And, unfortunately, some people modifying their cars listened and were terrified of putting on large exhausts and freeflow mufflers.

I very much doubt 'engines needing back-pressure' was ever a valid concept, and with the advent of engine management and the ability to tune an engine so much more finely than with points and carbies, it is of course now just rubbish. But to this day, some people believe it.

That's why I hate seeing BS being spread in car modification - unless it is challenged, it gets a life of its own. And I really like seeing people succeed, not following bad advice and so going on to achieve substandard outcomes.

Yes, you are right - I was exaggerating so people could more clearly see the point. But what about 0.28 vers 0.35, or 0.25 versus 0.30 (etc?). You can see that rolling resistance will often be little different, so the same illogicality applies.


Rules of thumb expressed in precise numerical relationships is, I think, really dumb. There is typically very little evidence that supports them, but their simplicity is seductive. A dangerous combination!

I cover the topic here - Deceptive Rules of Thumb in Car Aerodynamics:

https://www.youtube.com/watch?v=v_Btd0PUtjY

aerohead has achieved performant outcomes. You can find them in his albums: https://ecomodder.com/forum/member-aerohead-albums.html
https://ecomodder.com/forum/member-a...april-2005.jpg
You really haven't lived until you hear about surfing at Da Nang with a smoke flare or see him go off his meds in The Lounge.

edit:
Maybe you could look at this thread: ecomodder.com/.../index-phil-knox-aerodynamics-seminars-mod-data-lists-7118.html from 2009.

Anything that can't be falsified should still be valid. No?

Happy on that criteria not to have lived.

I think spreading misinformation to people wanting guidance is really poor, especially when the sources of correct information are readily available.

It's simply wasting the money, effort and enthusiasm of others.

I started to, but there was so much that was wrong / outdated / irrelevant I gave up.

It's a nice idea, but no, it's not valid.

Specific example: Aerohead's understanding of how car shape influences drag works for the BMW 2002 (and notchback cars of a similar age), but is completely wrong for current cars. This in turn leads him to give quite incorrect advice as to how apparently low drag shapes create lift - or don't, as the case may be.

And there are many other examples.

I have no idea of Aerohead's circumstances, but in an area like car aero, if you stop reading any material after Hucho second edition, you're likely (to a greater or lesser degree) to be wrong in multiple areas in any advice you give.

I agree with what I have read from Aerohead on coastdown testing, and testing of models in wind tunnels without taking into account Reynold's numbers inconsistencies.

But so much of other material that he states - usually with no qualifications at all - is simply garbage.

And garbage that I think is dressed up in high falutin' language that gives it false credibility. (But as a teacher of writing, that might be just my unwarranted bias.)

In the (now locked) Climate Change thread we learned that aerohead refuses to consider the papers referenced daily on Suspicious 0bservers*.

*Universe is a Dipole, a Scalable Torus/Jet

document
 

The book is 'AUTOMOTIVE QUARTERLY,Vol 21,No.2,with the article: 'AERODYNAMICS AND THE ATTAINABLE AUTOMOBILE-WUNNIBALD KAMM',by Jerry Sloniger,pp. 178-191
The article has a photo of the K2 ,K-car,the only K-car with Kamm's cooling system.
-------------------------------------------------------------------------------------
The data on the cooling system is actually from Rich Taylor's 'SEARCHING FOR THE PERFECT .10',Popular Mechanics,September,1981,p.158.
'He positioned the radiator air intake at the very nose,in the area of highest pressure,then ducted the cooling air out again at the base of the windshield.Just at the point where the airflow was starting to slow down and enter a low-pressure area,Kamm's design ejected a shot of relatively high pressure air. This helped preserve the boundary layer up and over the roof.'

This kind of attack is really not useful. Not everything aerohead says is right, or wrong. The exact same reality applies to you. This is a group that cross-examines everything. Your claims too. As for aerohead, in certain spheres he has earned significant credibility. That truck freebeard posted about has done top speed tests at Bonneville and been in atleast one professional wind tunnel. And it has thousands and thousands of miles of real world MPG data. Before that verhicle, there was a highly modded Civic CRX that was at least top speed tested at Bonneville. He has done his own fabricating and has shared what he learned for fun and for free here and elsewhere. All of that deserves more respect than you are granting.

irrelevant
 

*Streamline body refers to the streamline body of revolution,from which is derived the streamline half-body, the 'basic' body Hucho refers to as the source for the lowest drag possible automobile. If you don't know what this is,you're never going to make it in aerodynamics.
*Automotive aerodynamics diverged from aeronautical engineering a long time ago.Any discussion of airfoils as associated with automobiles is not germane.You should know that.
*At a fixed BSFC,mechanical driveline efficiency, accessory losses,and power absorption coefficient for the tires, the only variable in the 'approximation' is the aerodynamic portion of 'ROAD LOAD HORSEPOWER.'
If aerodynamic horsepower constituted 80% of the Road HP total,at fixed highway velocity,which was Hucho's claim,the scientific observation at the time was,that any 10% reduction in aerodynamic drag would relate to a 5% improvement in fuel economy for a gasoline-powered automobile,a bit more for diesel powered.Automotive engineers representing their corporation used this metric well into the 2000s ,reporting at car shows and special events.It's just a simple rule-of-thumb.Nobody ever claimed it as a universal engineering absolute.If you don't like it,take it up with Gino Sovran.I'm just the messenger.
*The only extant example of the K-cars to survive is the K3,Langenburg Castle car,which has been reported as having the 'worst' drag of all the series.And its belly pan had been adulterated,with parts missing,deformed,and bent down into the airstream during testing at VW. If you can find a June,1962 edition of HOT ROD Magazine,you'll find a photo of the enigmatic Cd 0.23 K5,on page 38,only spoken of by Kamm in 1965 shortly before his death.The K5 is a permutation of the K2,which embodies a drop-nose,'ideal' nose (using Volkswagen's terminology).This may be the only photograph of this car. If a Tesla Model 3 qualifies as 'low drag',then the same distinction might be paid the FKFS.
*And again,your modern,contemporary 'aerodynamicists' as you refer to them,only have credibility if they take surviving examples of previously tested vehicles,with static wheels,and re-test them on a rolling road and publish the difference.Otherwise,they and you yourself have no bona fides,no empirical evidence,and no credibility.No science.
*Perhaps Australia offers remedial classes in reading for comprehension and critical thinking.Some of you're comments suggest a complete lack of perspicacity,and a complete failure of Richard Feyman's admonition,to never open your mouth unless you've exhausted all avenues of exploration as to the possibility that you're incorrect in your premises.I do give you high marks in 'insult.'

In particular I find the trivial treatment of all shapes generating lift to be simplistic in the extreme. Airfoils perform predictably in clear undisturbed flow, but once a ground plane is introduced all that goes out the window.

back pressure
 

Back issues of HOT ROD Magazine are your friend.They have published for decades on this topic and have the controlled,laboratory,engine test-cell, dynamometer data to back up all the dialogue.

This the one?
https://lh3.googleusercontent.com/-Y...mm-WagenK1.jpg

https://www.allcarindex.com/producti.../fkfs-k-wagen/

https://www.fkfs.de/fileadmin/media/...kfs_D_kamm.jpg
https://www.fkfs.de/aktuelles/pressebilder
It must have had an OP fan.

this one ?
 

That's K2. And you can see Kamm's extractor vent at the base of the windscreen.K2 and K5 are the only K-cars with Kamm's cooling system.For K5,you'd take K2 and put Volkswagen's 'ideal',low nose from 1976 onto it.In the orthogonal view photograph of K5 undergoing tuft testing in HOT ROD,shot from behind and above the car,you can't even see the nose,it's so low.

A Rabbit nose on that would look weird. Volkhart-Sagitta?
I confuse easily. More like Morelli?

Trying [in vain] to find the Hot Rod picture I went down a rabbit hole about the XP-39

rabbit nose
 

It would be the very organic,fully radius'd,low stagnation point nose Hucho depicted in his text.If I hadn't lost everything to photobucket I could have shared the image.:(

Unlike what you write, the material in my book (which basically I am quoting from for nearly everything I write here) was checked before publication by four expert car aerodynamacists.

They included:

• the head of aerodynamics at a major car company
• an F1 aerodynamicist
• a professor of aerospace (and author of two major books on car aero)

...and of course my official technical consultant and reviewer for every page in the book, Dick Barnard. Dick's CV:

Richard Barnard is a world-renowned aerodynamicist. He started his career as an undergraduate aeronautical engineering apprentice at Handley Page Ltd, and later became Principal Lecturer and Postgraduate Research Tutor at the University of Hertfordshire, and is currently a Visiting Research Fellow. He is also a founder member of the UK Wind Engineering Society, and a Fellow of the Royal Aeronautical Society (FRAeS). He has been a consultant for numerous companies, including Jaguar and Rolls-Royce Bentley. Richard is the author of Road Vehicle Aerodynamics and has written many technical papers.

That is why I am very confident in the material.

So when I read what you write, which is very often completely or in part wrong, I am cross that you are leading people astray. It becomes even worse when you persist in saying the same thing, despite the errors in what you are saying being pointed out.

Misconceptions are fine - no one is perfect - but to continue to give people poor advice, is in my opinion, unforgivable.

I have this really odd moral belief that people modifying their cars should actually be given the best advice available. That way, they spend less of their money, time, effort and enthusiasm being wasted by pursuing courses of action that result in outcomes that often don't achieve what was promised.

This debate reminds me of the medical advice we're being given by various experts in the field about the coronavirus.

EG, should we wear a mask or should we not?

What seems simple turns out to be not so much. :-)

Reminds me of:
https://imgs.xkcd.com/comics/duty_calls.png
https://imgs.xkcd.com/comics/duty_calls.png

Love that one.

How about this? The door has been opened, in lawyer-speak, to comparing airplanes and 1930s aerodynamics to today. 'How about a little of this?'[Dennis Hopper]

https://radiocms-images.us1.eldarion...IRUS-DRONE.JPG
kfgo.com: Delivery drone flies medical supplies to Britain’s Isle of Wight

https://upload.wikimedia.org/wikiped...ndial_1936.jpg
https://en.m.wikipedia.org/wiki/Burnelli_UB-14