Guessing
 

In another thread I wrote: "To be honest, I think the huge underlying issue - that I am afraid you, Freebeard are a strong part of - is that speculation has become largely the culture of this group. To be blunt, posters just guessing."(And I wasn't picking on Freebeard, but as a prolific poster he's a person who does a lot of guessing.)

What I meant by that is this.

Car aerodynamics is a very complex area. This is particularly so because changing one area of the car is likely to impact airflow behaviour in completely different areas. It is not like altering (say) suspension, where a change in suspension spring rates won't affect the engine's air/fuel ratio.

While I mention this idea in my Veloce book, after reading it, both Dr Thomas Wolf of Porsche and Rob Palin (ex Tesla) suggested to me that this point needs to be far more greatly emphasized. That is, the 'element reductionism' approach, where different aerodynamic elements of car can be viewed separately, is not a good idea. For example, Rob suggested to me that altering the rear separation height may impact the height of the front stagnation zone!

So any modification that makes a major change in airflow at one location (and if it isn't a major change, it is unlikely to do anything measurable) is likely to cause changes elsewhere.

Furthermore, the impact of a specific modification is very hard to assess based only on its description.

So - a simple example - a front air dam may increase or reduce drag. It depends on the existing undercar aero and the height of the air dam.

A rear spoiler may increase or reduce drag - on a car with attached flow, it depends on the increase in pressures of angled rear panels versus the increase in the size of the wake.

Boat-tail extensions may increase or reduce drag - it depends on the force vectors (direction and magnitude of the forces) as the airflow wraps around the curved panels versus the reduction in wake size versus the disruption in trailing vortices.

Obviously in that context, numerical / shape rules of thumb are, to put it mildly, highly problematic.

That's why the literature has no agreement on the best angle for rear diffusers, no agreement on the best angle for boat-tailing, no agreement on best ride height for low drag, no agreement on the ultimate low drag shape for a road car, no agreement on the best design for low drag wheels - and so on. (Those who pretend there is agreement simply haven't read widely and recently.)

Now does that mean that no advice can ever be offered?

No it does not.

For example, I think you can be pretty confident in saying that, on a car with a rough underside, a full undertray will reduce drag and lift. If you are building a car from scratch, any of the five(!) differently-shaped low drag templates in Hucho (2nd ed) would be good starting points. Wheels with flat faces are very likely to have lower drag than those with many exposed spokes.

But - and here's the key point - no-one can say with certainty what an outcome is until the modification has been tested. Without trialling modifications and testing them, you are - to a much greater degree than in other car modification - blundering around in the dark. But instead of saying that, on this group it's far more likely that someone will ask about a modification, and people will simply leap in with guesses - guesses that apparently are treated as quite credible.

But my observation is that those guesses are often based on rules of thumb, misquoted or selective use of references (eg quoted angles), irrelevant historic parallels (that aren't) and so on.

And let's look at that point about misusing examples from the past. When I have pointed out that an old reference may be useless as a guide to today's modification, it's been demanded of me: "Well, what in fluid dynamics has changed since that book was written?" The answer is: "Nothing."

But it's the wrong question.

Our engine designs don't look like those of the 1930s and 1940s because our understanding of combustion chamber design, tuned length intake systems, variable camshaft systems (etc, etc) has changed. As have our requirements of engines. We don't take the combustion chamber design of a Merlin and say that all modern engines should have their combustion chamber designs based on it - and if current engines aren't doing that, they're wrong. The combustion behaviour of fuels hasn't changed since the Merlin, but our understandings and requirements have.

On my YouTube channel people write in all the time asking for advice. So for example I run a video testing rear wing and spoiler combinations on the back of a Subaru Impreza for lift/downforce. Someone writes: "Is it the same with the DC5 Integra?". How would I know? How would anyone know who hasn't done testing (or seen manufacturer's testing)? How could such a question even be asked - or expect to be answered?

So the next time someone here asks for advice on a car aero modification, stand by - unfortunately - for the contribution of a lot of guesses.

I'll respond to the bolded parts since they are presumably salient.

Like fixing the Beetle too-fast back can impede engine cooling. Like that?

There exists received folk wisdom. Using, again, the Beetle as an example. 145s on the front, a rake, de-burblized (No side trim, fender-top turn signals, running boards). Collectively, Cal-Look. It was hashed out 1/4 mile at a time. Pro-street gave us the doghouse boat tail.

Isn't that testing? The very point I am making?

If trolling aerohead is getting tired, I'm not available as the next in line.

If someone has done testing on a particular car and can demonstrate the positive results, fantastic!

But if we were to take the advice of what worked on the Beetle and apply it to a Prius - and you see stuff like that here all the time, just not with those models - then it is not much better than guessing.

That is my point!

Fair enough. I gave it my best shot here:

https://ecomodder.com/forum/member-f...7-12-29-57.png

Stock Prius with Moons and spats, and FWD aircooled VW internal air flow. Well... a Porsche fan, Golf front axles....

I'd expect a 36hp DSS class engine to have economy equal to the stock Prius with maybe less acceleration (less weight).

36hp Challenge Classes and Rules

As long as I'm in the albums, here's me mocking the Template™

https://ecomodder.com/forum/member-f...-aero-bug2.png

Actually, a centered drivers seat and you could lose the top and rear fenders. Hmmm...

Very good!

What gets measured gets improved. I was well paid as a test /QA technician. That is why I do coast down tests and record the data. My hill drops 30 feet in 0.1 mile so I can compare different bikes.

Yes, it's a major reason why I am looking forward to your results.

If you don't guess at all, you won't know which test to perform.

Yes that’s quite true. But it’s very different suggesting some different approaches to test, compared with guessing that something will or will not work - and then giving that guess as advice to follow.

contribution
 

' the vehicle aerodynamicist must refer to a large amount of detail resulting from earlier development work. His success depends on his ability to transfer these results to his own problem and to combine results originating from many earlier developments to a consistent solution.
It is the intention of the present book to introduce the vehicle engineer to this approach.' Wolf- Heinrich Hucho, page one of Preface, 2nd-Edition.

fantastic!
 

Excepting of course, if Aerohead demonstrates it.:)

You very often take the example of what works on one car and imply / state that it is applicable to a completely different car shape.

You're probably the worst person here for doing the 'it worked on a Beetle so let's try it on a Prius' type of advice.

imply / state
 

* It goes back to the fluid mechanics ground rules Hucho wrote about :
' the essential experimental results, presented as ground rules of fluid mechanics and brought to general validity wherever possible;'
Hucho, page one of he Preface
* fundamentals are fundamentals.
* it's the whole point of his book!
* and I promise to continue whenever something dovetails into what's already established in the public domain.:)

Now he's got you doing it!

Yep, I think you lost that battle... Freebeard!

Proper names are proper names.

People call an octothorpe a hash, doesn't make them right. aerohead hasn't changed his handle yet, has he?

You haven't used my proper name yet. Please don't if you can find it, that's considered Doxing on Internet. And that's bad.

Thought.co seems reputable enough in their domain. On Internet, I'd follow the W3C Internationalization Working Group:
I couldn't find the classic article on designing input fields for names. They can start with apostrophes and High-ASCII characters.

The handle that a properly named individual is asked for when they sign up to EcoModder doesn't have to be capitalized. That is the nature of a handle or avatar, as it should be. Two of the three legs Internet stands on are anonymity and authentication (the third is cryptocurrency).

You had to provide identifying information to Google to sign up here. You didn't have to use your proper name and you shouldn't disparage people who choose not to.

Anyways, nobody is going to stop you being a b*tthole about it.

If I wanted to disparage people because of their handles I'd call Aerohead "Airhead" (as someone keeps suggesting I should do) and I'd probably call you "Firebeard"!

Capitalising a name is not disparagement, except in your world.

Knock yourself out, but namecalling does not show respect. At least you're calling it a handle instead of a Proper Name.

Oh to be a fly on the wall when you come across a Marxist-feminist who demands that you use their pronouns. Compelled speech.

[Shrug]

It's a fallacious, superficial argument premised - as so many of yours unfortunately are - on a rather literal and/or simplistic understanding of what is being discussed.

The rules of thermodynamics haven't changed in 100+ years - but today we don't design engines like those of the 1930s, or even 1960s or 1980s.

The rules of resonant mechanical systems haven't changed in 100+ years - but today we don't design suspension systems like those of the 1930s, or even 1960s or 1980s.

But I for one, will always keep reading historic documents on engine and suspension design - and aerodynamics - because I think the historic context informs current thinking.

But it's a completely different thing to think that it should dictate current thinking.

If you presented historic examples in the context of 'hey, look at this - isn't it interesting?' I'd be applauding what you do. But you don't - you pretend (or even believe?) that this history should be directing what we do now - and that is just ridiculous.

Your approach has unfortunately led you to have lots of mistaken beliefs about what is happening with airflow on current cars and then to - unforgivably* - advise people based on those erroneous beliefs. And you have been very successful - I can see time and time again people on this group parroting the falsehoods you have disseminated.

(*I don't care what you believe - lots of people believe all sorts of weird stuff. But I do care when you are leading others astray based on your incorrect beliefs.)

I was thinking about this as I mowed the grass today.

My degree level major is in sociology (and I have another in geography) and so I have studied with, and worked with, women with plenty of marxist-feminist philosophies.

And I have no issues. Why would I?

Your nominating this group tells us more about you than them!

Demonising others based on their beliefs - rather than arguing with those beliefs - seems to me to be an intellectual short-cut.

I'd let it go long ago. I have a degree also. I've learned a lot since.

How many philosophies in total? Do they compel your speech? It's the law in Canada.

I think your projecting.

And calling people names, like Airhead, is worst.

beliefs
 

You don't have enough education to be able to discern one way or another. What you believe means nothing to me. It's belief. Belief and science are not bedfellows. You're not arguing factually. You can no longer give it the time. Although you have endless time for non-constructive criticism. You can't even get the nomenclature correct. You lack fundamentals. Fundamentals don't change.
Some of the things you say are correct within a certain context, however you try to pass it off as a universal absolute. Even Ayn Rand would argue against your brand of 'logic.'
You're wrong about wind tunnels.
You're wrong about rotating wheels.
You're wrong about the 'template.'
Evidence doesn't appear to mean anything to you.
You're measurements are typically contextual.
You cherry-pick Hucho.
When I present Hucho's counterfactual evidence to one of your claims all I get is crickets.
If you want to discuss intellectual dishonesty, well , you wrote the book.
Book sales ahead of all else! Hucksterism reigns supreme. Buy my books! Buy my books! By my Books!
Your a real piece of work!
Man see's what he wants to see.

:eek:

You didn't address even one of my points, as usual. So maybe let's try again?

You wrote:


It's a fallacious, superficial argument premised - as so many of yours unfortunately are - on a rather literal and/or simplistic understanding of what is being discussed.

The rules of thermodynamics haven't changed in 100+ years - but today we don't design engines like those of the 1930s, or even 1960s or 1980s.

The rules of resonant mechanical systems haven't changed in 100+ years - but today we don't design suspension systems like those of the 1930s, or even 1960s or 1980s.

But I for one, will always keep reading historic documents on engine and suspension design - and aerodynamics - because I think the historic context informs current thinking.

But it's a completely different thing to think that it should dictate current thinking.

If you presented historic examples in the context of 'hey, look at this - isn't it interesting?' I'd be applauding what you do. But you don't - you pretend (or even believe?) that this history should be directing what we do now - and that is just ridiculous.

Your approach has unfortunately led you to have lots of mistaken beliefs about what is happening with airflow on current cars and then to - unforgivably* - advise people based on those erroneous beliefs. And you have been very successful - I can see time and time again people on this group parroting the falsehoods you have disseminated.

(*I don't care what you believe - lots of people believe all sorts of weird stuff. But I do care when you are leading others astray based on your incorrect beliefs.)

My motto for the day :
I'm watching anime. Appare-Ranman!:
https://www.anime-planet.com/images/...an-14110-6.jpg
https://www.anime-planet.com/images/...an-14110-6.jpg

https://i1.wp.com/nyc3.digitaloceans...80%2C720&ssl=1
https://i1.wp.com/nyc3.digitaloceans...80%2C720&ssl=1

'mistaken beliefs'
 

Curiously, after a close examination of ' Modifying the AERODYNAMICS of Your Road Car, I discovered the same mistaken beliefs being propagated within the book.
Isn't it interesting?