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Old 05-13-2020, 11:09 AM   #29 (permalink)
aerohead
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irrelevant

Quote:
Originally Posted by JulianEdgar View Post
This is just a dump largely of misunderstandings, outdated references, and irrelevant citations.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.'
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