What causes car drag?

[JulianEdgar]

Originally Posted by aerohead

Again, what in the world will measuring the pressure profile accomplish towards lowering the Cd 0.25, down to Cd 0.09? Possession of a pressure profile implies that we have something of comparative nature with which to guide us. Up, down, or sideways.
If we agree that the roofline on the Insight is 'streamlined', we ought to leave it alone, other than extending its length, while boat-tailing the sides and diffuser, to achieve even higher pressure regain, higher base pressure, lower pressure drag, and lower drag.
A BEV Insight would lose the grille opening almost completely. The belly could be perfect. Tesla mirrors would help. Front skirts. Boat-tail. ( Three-Wheeler made a fine one! ) 80-mpg is not uncommon on a good day, at real highway velocity.

Ah well, that shows one difference between us. You'd rather read very old books, make up theories - and guess.

I'd rather test and measure.

It's just a pity that your theories and guesses have been believed by so many people here over a long time.

Your view that attached flow does not cause drag is just one of the many incorrect ideas you have promulgated.

[aerohead]

Originally Posted by JulianEdgar

Ah well, that shows one difference between us. You'd rather read very old books, make up theories - and guess.

I'd rather test and measure.

It's just a pity that your theories and guesses have been believed by so many people here over a long time.

Your view that attached flow does not cause drag is just one of the many incorrect ideas you have promulgated.

Hucho told us both to read everything we could get our hands on.
None of your more current publications do any more than nibbling at the edges of drag. The grand gestures were done long ago.
Non-attached flow implies separation. With that you not only lose the battle, you lose the war. Snatch defeat from the jaws of victory.
Very strange ideas. Oliver Sacks would have loved the challenge.

[JulianEdgar]

Originally Posted by aerohead

Hucho told us both to read everything we could get our hands on.
None of your more current publications do any more than nibbling at the edges of drag. The grand gestures were done long ago.

So you haven't read any aero textbook published since 1987 and yet you know more modern books don't have anything new in them.

Seems to be a bit of a problem there...

[JulianEdgar]

Originally Posted by aerohead

Again, what in the world will measuring the pressure profile accomplish towards lowering the Cd 0.25, down to Cd 0.09? Possession of a pressure profile implies that we have something of comparative nature with which to guide us. Up, down, or sideways.)

I've just re-read this. It's honestly like Aerohead doesn't realise that 80-90 percent of drag is caused by high pressures pushing backwards on the front surfaces of the car, and low pressures pulling backwards on the rear surfaces of the car.

Decrease those pressures on the front, and/or increase those pressures on the back, and you have less drag.

We don't have to compare the pressures to other shapes; we simply work on changing the pressures on the car we have.

Maybe he needs to watch the video?

[aerohead]

Originally Posted by JulianEdgar

So you haven't read any aero textbook published since 1987 and yet you know more modern books don't have anything new in them.

Seems to be a bit of a problem there...

textbook data would be an edited compilation of data from many sources, yes?
In that regard, I have followed light and heavy evolution, World Solar Challenge aerodynamics, Shell and SAE mpg competition aerodynamics, International Human Powered Vehicle competition ( as a member ), land speed record evolution at Bonneville ( as a USFRA member , race participant, double land speed record holder, race team consultant, facilitator for laboratory testing), in addition to my own inventions ,research, and testing.
I've yet to see anything in contemporary literature which usurps the primacy of early research. Including your referenced SAE Papers, of which many appear to be authored by 22-year-old graduate student candidates, who've never been out in the real world yet.
None of your expert panel, to my knowledge, have, in their professional careers, done anything which pushed the envelope of road vehicle aerodynamics of knowledge of any magnitude, with the exception of Hucho.
If you ever make the mistake of incorporating the work of Hoerner and Koenig-Fachsenfeld into your reference library, you'll likely suffer incalculable and fatal damage to your aerodynamic world view.
Arguing from a position of knowledge has never been your strong suit. Pity!

[aerohead]

Originally Posted by JulianEdgar

I've just re-read this. It's honestly like Aerohead doesn't realise that 80-90 percent of drag is caused by high pressures pushing backwards on the front surfaces of the car, and low pressures pulling backwards on the rear surfaces of the car.

Decrease those pressures on the front, and/or increase those pressures on the back, and you have less drag.

We don't have to compare the pressures to other shapes; we simply work on changing the pressures on the car we have.

Maybe he needs to watch the video?

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Maybe I need to ignore comparative analysis of your measured pressure profiles.
1) according to your own measurements, and all normalized to 70-mph ( 112.654-km/h ):
* the Jaguar XE has the lowest drag ( delta 379.6-pounds )
* the M-B 230 has the next-lowest drag ( delta 392-pounds )
* the M-B 211 has the third-lowest drag ( delta 397.4-pounds )
* and the 1st-gen Insight has the highest drag ( delta 660.2-pounds )
* In light of the fact that M-B 230 has the highest published drag, while the Insight has the lowest!
I find this very interesting and worthy of explanation.

[Vman455]

How did you calculate those figures without a complete pressure map of the cars in question? You know as well as anyone here that drag force on a three-dimensional body cannot be calculated from a few centerline pressures, and Julian has never claimed such.

[aerohead]

Originally Posted by Vman455

How did you calculate those figures without a complete pressure map of the cars in question? You know as well as anyone here that drag force on a three-dimensional body cannot be calculated from a few centerline pressures, and Julian has never claimed such.

If I have to explain it to YOU, there's no reason for us to ever communicate directly again.
I can't believe you're even asking such a question after all you've written!

[AeroMcAeroFace]

Originally Posted by aerohead

Including your referenced SAE Papers, of which many appear to be authored by 22-year-old graduate student candidates, who've never been out in the real world yet.

Arguing from a position of knowledge has never been your strong suit. Pity!

As if not being out in the real would, or being a 22 year old graduate student means your research is not valid, SAE papers are often written by manufacturers, research papers are peer reviewed. It doesn't matter what age or who wrote the paper.

"How did you calculate those figures without a complete pressure map of the cars in question? You know as well as anyone here that drag force on a three-dimensional body cannot be calculated from a few centerline pressures, and Julian has never claimed such."

aerohead here is doing what is known as argument from authority, believing he is the authority here and gets upset if anyone challenges it. I think Vman455, that because it comes from aerohead that is evidence enough of its truth, but maybe only in one persons mind.

[aerohead]

Originally Posted by AeroMcAeroFace

As if not being out in the real would, or being a 22 year old graduate student means your research is not valid, SAE papers are often written by manufacturers, research papers are peer reviewed. It doesn't matter what age or who wrote the paper.

"How did you calculate those figures without a complete pressure map of the cars in question? You know as well as anyone here that drag force on a three-dimensional body cannot be calculated from a few centerline pressures, and Julian has never claimed such."

aerohead here is doing what is known as argument from authority, believing he is the authority here and gets upset if anyone challenges it. I think Vman455, that because it comes from aerohead that is evidence enough of its truth, but maybe only in one persons mind.

Belief is not in the equation.
There's a vast body of empirical science which precedes the existence of some of these authors.
I have no idea what constitutes their educational background.
I can tell you that references used to attack my posts belie an ignorance on the part of their authors which cuts into their credibility as any authority.
If you tell me that a cube is now, due to current observation, a spheroid, you can expect to get some pushback.
At least some of the SAE Papers, in their preambles, preface that their research is fraught with uncertainties, as well as completely contra-factual evidence to any general assertions. Especially rotating wheel drag measurements.
Nomenclature is sometimes incorrect.
No qualifications are made as to the degree of confidence of CFD results, as compared to any extant, corroborating evidence. Full-scale wind tunnel validation exercises. Lots of unknowns.
The premise for my comment about graduate students.
One CAN obtain a Masters Degree, and be 100%, scientifically incorrect regarding your thesis, as long as you satisfactorily navigate the protocols of the reviewing jury.
This is true for a PhD as well. You can ask Dr. James Hansen about this one.
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If any individual attempts to discount all previous research, under some, random, blanket, umbrella logic of temporal aspect of publication as a qualifier, the only proper defense for the position is, to retest exact replicas, in current laboratories, and present results, side-by-side, for direct comparison. Otherwise its complete intellectual dishonesty and disrespect to even broach the subject.
We got to the Moon and back because of a mathematician who died in 1783.
It's utter folly to summarily dismiss past contributions.
'Check your premises' (Rand )