Beware old and new aero data

[JulianEdgar]

Originally Posted by freebeard

You're beginning to understand the aerohead we all know and love. Asterisks for paragraphs but never a space between sentences.

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 They, too, would quote outdated magazine articles, outdated books, etc.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.

[JulianEdgar]

Originally Posted by 2000mc

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.

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.

Originally Posted by 2000mc

I always thought the 5/10 was more just a rule of thumb

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

[freebeard]

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.

aerohead has achieved performant outcomes. You can find them in his albums: https://ecomodder.com/forum/member-aerohead-albums.html

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?

[JulianEdgar]

Originally Posted by freebeard

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.

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.

[JulianEdgar]

Originally Posted by freebeard

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

I started to, but there was so much that was wrong / outdated / irrelevant I gave up.

Originally Posted by freebeard

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

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.)

[freebeard]

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.

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

[aerohead]

Originally Posted by freebeard

Thnx.

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.'

[California98Civic]

Originally Posted by JulianEdgar

... 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.)

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.

[aerohead]

Originally Posted by JulianEdgar

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?

*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.'

[skyking]

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.