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-   -   Want low drag? Don't follow a template. (https://ecomodder.com/forum/showthread.php/want-low-drag-dont-follow-template-38791.html)

JulianEdgar 11-13-2020 04:24 PM
Want low drag? Don't follow a template.
 
I see Aerohead, completely undaunted, is back to spreading his misconceptions about his beloved template. Here's video I did on that subject a month or so ago.

(If you wish to comment, please watch the entire video, including the citing of five completely differently shaped low-drag templates.)

https://www.youtube.com/watch?v=hxmbQhcNWy8

Using Aerohead's template as the guide in aerodynamic car modification and assessment is, unfortunately, quite absurd.

If only it were that simple!

IRONICK 11-13-2020 04:32 PM
Not again!

kach22i 11-13-2020 04:57 PM
I enjoyed the video, thank you for posting it.

For reference a post of mine from 2017 questioning some of the same things.

You need to click the link to read the whole post including charts from a another forum reference.

https://ecomodder.com/forum/showthre...s-34840-4.html
Quote:
Originally Posted by kach22i (Post 533713)
I agree with what everyone else has been saying about reducing Cd and lift if you can. I'm offering this example for reference because it is so iconic and well tested.

Sourced base image below because I could not find the one out of a book Aerohead scanned into his forum gallery which shows a template overlay.

https://en.wheelsage.org/porsche/911...ctures/o3rqv5/

Then I overlaid the one of the forum's AeroTemplates from here (not sure which page):
http://ecomodder.com/forum/showthrea...ion-21952.html

The combination:
Aerodynamics by George Kachadoorian | Photobucket
http://i184.photobucket.com/albums/x...psfts5pm3z.jpg

This overlay was done to provide some context for the chart quoted below, which shows a lowering of Cd and lowering of lift with ducktail.

Spoilers: front and or rear - Page 2 - Pelican Parts Technical BBS


Going back to one of my first comments about getting the rear spoiler to fill out the template, it looks as the Porsche 911 RS kept it just below that line for some reason unknown to myself.

Maybe your testing can examine what happens when you fill that gap in your comparative Honda Civic project. At what point does the Cd stop being lowered and starts going back up.

If your 3D printer does not allow for curved or wavy top edge of rear spoiler, then try a square notched or comb filter pattern, something like a bread knife edge.

The point would be to see if there is less drag when the vortex coming off the Gurney flap is broken down to smaller elements and is less planar or a constant cylinder of rolling air mass.

836 Gurney flaps - Aerodynamics - Civil Engineering Handbook
http://www.civilengineeringhandbook....02_250_427.jpg


Concept of wavy spoiler: Distribution of energy verses concentration of energy, which may help control oscillations.

If one "feathers" the edges as found in nature (bird feathers, whale fin tubercles) just to see what happens, there might be a nice surprise - or not.

Be brave, take a chance. Have no regrets because each failure is just another step in learning, and learning is a life long path - or at least it should be.;)

EDIT: One more chart.
Spoilers: front and or rear - Pelican Parts Forums
http://forums.pelicanparts.com/uploa...1227215216.jpg

The 3.3 turbo tail is different than the spoiler type Ducktail, it extends out and is sometimes called a Teatray or Whaletail.

Similar to the below shown on a later model.
Spoilers: front and or rear - Pelican Parts Forums
http://forums.pelicanparts.com/uploa...1227215362.jpg

I should note that there is less drag and less lift with the type shown on the red car (tray/wing) verses the earlier green car (duck).

If you go to Bonneville you are more likely to see rear mounted horizontal extensions than near vertical ones for the same reasons. Each one attempts to fill out the Aero-template in it's own way.
With the Jaguar and Tesla shown in the video, is air attachment of tufts absolute proof of the lowest drag possible?

Perhaps the very slight imperfection of a physical medium that has mass/weight and surface area (the yarn tuft) has not been overwhelmed by the ever so slight pressure differences.

It is their own weight that is holding them down (gravity) and not air pressure or air flow?

In a 1930's NCAC video posted earlier this month the demonstrator using a small wind tunnel used a wand with what looked like long stringy bird feathers much lighter and delicate than a yarn tuft, and this allowed him to actually show vortex formation around a cube.

Are yarn tufts infallible and indisputable?

Did these blimp derived shapes of the 1930's use yarn tufts at all to arrive at their shapes or to collect data?

Do present day automobile manufactures with wind tunnels use yarn tufts?

If yarn tufts are 90% accurate, that would leave 10% on the table, room for improvement.

How close to idea are yarn tufts?

EDIT-1

Looks like back in 2001 NASA was using polyester not wool, and glued not taped with very specific procedures and requirements such a syringes to keep the glue glob size down.

PDF Download:
https://www.google.com/url?sa=t&rct=...Ft9VnAkyPjVl77

.................................................. .....................................

EDIT-2

https://media.springernature.com/lw6..._Fig2_HTML.png

Getting an error on providing a link for the above image, found via Google image search with phrase "aerodynamic tuft accuracy".

I assume it's showing reaction sensitivity or response times of various tuft filaments.

Cd 11-13-2020 06:43 PM
Does anyone here have access to a Mercedes A class sedan ?
The car has an excellent .22 Cd, yet not only deviates from the template, but also has a short trunk / boot that you would think would keep flow from reattaching.
I seemed to recall it having quite a bit of tumblehome to the rear, and thought this maybe what helps the flow reattach, but after looking at one that my neighbpr has, I see that is not really such a big factor.

The reason I am asking is to see if someone would be willing to do a tuft test at the rear of the car to show what happens with the airflow. *

The .25 Cd LS-430 had an even steeper back window, but it has a longer trunk / boot that could help the air to reattach.

* or some CFD images of the rear of the car.

kach22i 11-13-2020 07:23 PM
Jul 27, 2018
Mercedes-Benz A-Class sedan has lowest drag-coefficient of any production car
https://www.firstpost.com/tech/auto-...r-4822801.html
Quote:
Mercedes-Benz has announced that its upcoming A-Class sedan will be the most aerodynamic car on sale. The company claims that the new A-Class sedan has a coefficient of drag (Cd) 0.22 and a front area of 2.19 square meters. Mercedes-Benz says the new A-Class sedan's class-leading aerodynamic properties can be attributed to the effort gone into refining the shape of the car. The designers spent countless hours in the wind tunnel while the use of virtual modelling techniques gave further insight into developing an optimal aerodynamic shape.
From the above they did a lot of work where you just don't see it.

https://www.mercedes-benz.com/en/veh...-class-saloon/
http://forums.pelicanparts.com/uploa...1605313273.jpg
http://forums.pelicanparts.com/uploa...1605313273.jpg
Quote:
The new A-Class Saloon takes advantage of the favourable conditions provided by its long rear end to undercut even the already exemplary A-Class with hatchback (Cd value from 0.25). With a benchmark of Cd = 0.22 the new saloon model even equals the original world record of the CLA Coupé. Thanks to the frontal area of 2,19 m², smaller than that of the CLA, the new A-Class Saloon has the lowest aerodynamic drag of all production vehicles worldwide.
Great numbers, but far from theoretical idea.

JulianEdgar 11-13-2020 09:02 PM
Quote:
Originally Posted by IRONICK (Post 636288)
Not again!
That is exactly what I thought when I saw Aerohead posting all the same old rubbish. Surely, I thought, you're still not trying to mislead people in this way?!

freebeard 11-13-2020 09:04 PM
People don't change.

It only took 10:29 to burn my dinner. :( I think I punched in 4000 on the microwave.

Anyway, I assert you have fallen into the same pitfall as others. Nobody looks at the front view with it's hemicircular profile. It's as hard and fast a rule as the profile. It makes it a proper windshield header for side-by-side seating difficult. VW Beetle has an optimal profile with a flat windshield for optical clarity (ignore the blind spots behind the A-pillars).

Anyways, I made an argument for a superelliptic profile here. I noticed that Blender's geodesic generator has superilleptic options. Maybe I should revisit that.

edit:
I found Ducted radiators for low drag more helpful.

So what do you think of the difference between a velocity driven radiator system vs a power-driven fan and air cooling? IIRC VWs boxer four had 1500cu ft/min displacement to work with.

aardvarcus 11-13-2020 09:42 PM
1 Attachment(s)
Am I the only one to notice that you aren't even using the current version of "the template" and that some of the pictures of cars in your video fit the AST-II?


Do you really believe what you stated in the video that aerodynamics works off the ratio of photographed dust in a wake balanced against a perpendicular vector of the rear angle?

JulianEdgar 11-13-2020 11:29 PM
Quote:
Originally Posted by aardvarcus (Post 636322)
Do you really believe what you stated in the video that aerodynamics works off the ratio of photographed dust in a wake balanced against a perpendicular vector of the rear angle?
I don't even know what "aerodynamics works off" means....

If it means "aerodynamic drag" then yes, a reduction in wake size (usually giving less drag) is one of the things that needs to be balanced in the rear extension design against the created lift-induced drag component (that gives more drag).

In the case of the photographed Roomster, too steep an extension angle (note: still with attached flow) gave higher measured drag, despite the smaller wake.

Incidentally, that Roomster example is in my aero book, and was specifically cited by three of the professional aerodynamicists who reviewed the book as a good example. In fact Dr Hucho liked the Roomster wake pics so much that he asked me for high res versions.

JulianEdgar 11-13-2020 11:37 PM
Quote:
Originally Posted by freebeard (Post 636318)
People don't change.


edit:
I found Ducted radiators for low drag more helpful.

So what do you think of the difference between a velocity driven radiator system vs a power-driven fan and air cooling? IIRC VWs boxer four had 1500cu ft/min displacement to work with.
[Groan]

Freebeard, I never just guess stuff. I measure things, and I read formal references.

I know it's become de rigueur on this sub-group to knowledgeably pontificate in a context completely absent of any actual evidence, but I am not part of that.

Answer to your question: I have no idea.

aardvarcus 11-14-2020 12:46 AM
Quote:
Originally Posted by JulianEdgar (Post 636325)
I don't even know what "aerodynamics works off" means....

If it means "aerodynamic drag" then yes, a reduction in wake size (usually giving less drag) is one of the things that needs to be balanced in the rear extension design against the created lift-induced drag component (that gives more drag).

In the case of the photographed Roomster, too steep an extension angle (note: still with attached flow) gave higher measured drag, despite the smaller wake.

Incidentally, that Roomster example is in my aero book, and was specifically cited by three of the professional aerodynamicists who reviewed the book as a good example. In fact Dr Hucho liked the Roomster wake pics so much that he asked me for high res versions.
I see you are ignoring the part of my post about not using the AST-II template, which fits several of your example cars in your video per my overlay.

Apologies I did not precisely define all terms in my question.

I do not understand your correlation of a photographed wake size to drag, as a photograph can not lend insight into how the airflows that become the wake are exerting pressure on the vehicle.

I realize that your post acknowledges the effects of the steep extension not aligning with this expected result of smaller wake equals lower drag.

I am aware of what is in your aero book, seeing as how I own a copy. Care to comment on why there are so many examples of modifications made to match "the template" in the DIY section?

JulianEdgar 11-14-2020 01:11 AM
Quote:
Originally Posted by aardvarcus (Post 636332)
I see you are ignoring the part of my post about not using the AST-II template, which fits several of your example cars in your video per my overlay.
Why pick that one? Why not pick one of the five differently shaped ones shown in the video? No doubt we could find lots of cars that match those five too. So what does all that mean? Absolutely nothing. Using a template - any template - is just absurd. If only it were as simple as following a template....

Quote:
I do not understand your correlation of a photographed wake size to drag, as a photograph can not lend insight into how the airflows that become the wake are exerting pressure on the vehicle.
The angled extension reduces the wake size, as evidence by the dust. Typically, a reduced wake size = reduced drag. As you say that is not definitive, but it's a guide that is right most of the time. But by all means do some pressure testing x area and let us know the results - I don't have a monopoly on testing.

Quote:
I am aware of what is in your aero book, seeing as how I own a copy. Care to comment on why there are so many examples of modifications made to match "the template" in the DIY section?
I am not sure what you mean? None of my modifications in the book were done following a template (any template) and no template is mentioned (let alone lauded) in my description of any modifications in the book. That reflects the professional literature, where 'pure shapes' are given typically only a few pages in a full book - they're simply not that important in the real world. Reading only professional literature and doing my own testing, I'd never even heard of a template when I wrote the book. Had I done so, I would have spent some pages debunking the approach.

Basically, people here have been sucked-in over a long period of time by a completely fallacious approach, vehemently argued by someone who hasn't even read a professional aero textbook more recent than 1987.

As I said in the video, you need do only the most rudimentary testing on a variety of cars to see that much of what is said here about the template is just rubbish. It's no coincidence that those people here who have actually done that testing are also those that most question the validity of the template approach.

freebeard 11-14-2020 01:20 AM
Fair enough. I'm down to one Beetle anyway. It's still a pile of parts, I'll have to come up with my own d*mn plan.

If I had your resources I could test a Coanda nozzle and vent the exhaust into the wake of the rear tires. Just to see what happens.

I wondered about the yellow arrow as well. It appears to be a normal, but I suspect you intended a resultant vector.

Are you assuming Ecomodder is always and only about templates? Maybe you should get out more.

JulianEdgar 11-14-2020 01:43 AM
Quote:
Originally Posted by freebeard (Post 636336)
Fair enough. I'm down to one Beetle anyway. It's still a pile of parts, I'll have to come up with my own d*mn plan.

If I had your resources I could test a Coanda nozzle and vent the exhaust into the wake of the rear tires. Just to see what happens.
My aerodynamic test resources cost very little.

But to be fair, my aerodynamics reference materials cost more (spread over 25 years) and my home workshop cost a lot (spread over 35 years).

But what you are describing shouldn't cost much.

All car modification has costs, so I figure if you're broke it's not a good hobby to want to pursue! These days, I spend $1000 a year on modifying my Insight. Bought the new lower ratios gearbox about a year ago, and just last week bought the clutch and gearbox rebuild kits. So that's the thousand for this year.

Quote:
I wondered about the yellow arrow as well. It appears to be a normal, but I suspect you intended a resultant vector.
Not sure what you are describing.

Quote:

Are you assuming Ecomodder is always and only about templates? Maybe you should get out more.
My comments relate only to the aero sub forum. I don't read anything else on the site.

aardvarcus 11-14-2020 08:09 AM
Quote:
Originally Posted by JulianEdgar (Post 636335)
Why pick that one? Why not pick one of the five differently shaped ones shown in the video? No doubt we could find lots of cars that match those five too. So what does all that mean? Absolutely nothing. Using a template - any template - is just absurd. If only it were as simple as following a template....



The angled extension reduces the wake size, as evidence by the dust. Typically, a reduced wake size = reduced drag. As you say that is not definitive, but it's a guide that is right most of the time. But by all means do some pressure testing x area and let us know the results - I don't have a monopoly on testing.



I am not sure what you mean? None of my modifications in the book were done following a template (any template) and no template is mentioned (let alone lauded) in my description of any modifications in the book. That reflects the professional literature, where 'pure shapes' are given typically only a few pages in a full book - they're simply not that important in the real world. Reading only professional literature and doing my own testing, I'd never even heard of a template when I wrote the book. Had I done so, I would have spent some pages debunking the approach.

Basically, people here have been sucked-in over a long period of time by a completely fallacious approach, vehemently argued by someone who hasn't even read a professional aero textbook more recent than 1987.

As I said in the video, you need do only the most rudimentary testing on a variety of cars to see that much of what is said here about the template is just rubbish. It's no coincidence that those people here who have actually done that testing are also those that most question the validity of the template approach.
I would pick "that one" because it is the one most people on here use. Also based on your comments on what you believe it is supposed to represent it would be the more accurate one to use. (Not that I believe the claims asserted of what "the template" means.) I realize the main basis of your video is that "the template" doesn't fit the cars you posted, thus it would be counterproductive should the template start fitting several of them closely.

I have built and tested several "angled extensions" on several vehicles, the results are already documented on this site. Results logged over many thousands of miles. Does this qualify as the most rudimentary testing?

I have several "basic shapes" saved that I use in my planning. Tools in a toolbox for design. I do not have the time or computing/testing resources to develop original aero designs from scratch. I am not hung up on proving any of them right or wrong. I have repeatedly used the AST-II and/or the AST top view and the resulting projects hit my projections for drag change reasonably closely and made the handling changes I desired. Thus I will continue using them.

Since you apparently don't know, FYI there are photographs of "template based" projects in your book. You may want to edit them out in the second edition.

freebeard 11-14-2020 12:25 PM
Quote:
My aerodynamic test resources cost very little.
My $1K for this year is to own and operate a 1990 XFi. The most recent model year I've owned to date. The Arcimoto FUV will bust my budget, [insert deity] willing.

Quote:
But what you are describing shouldn't cost much.
The closest I've gotten. It was measured and destructed, I never took it on the road, obviously.
https://ecomodder.com/forum/member-f...9-100-0629.jpg
Quote:
My comments relate only to the aero sub forum. I don't read anything else on the site.
ecomodder.com/forum/instrumentation.html

JulianEdgar 11-14-2020 03:47 PM
Quote:
Originally Posted by aardvarcus (Post 636344)
I would pick "that one" because it is the one most people on here use. Also based on your comments on what you believe it is supposed to represent it would be the more accurate one to use. (Not that I believe the claims asserted of what "the template" means.) I realize the main basis of your video is that "the template" doesn't fit the cars you posted, thus it would be counterproductive should the template start fitting several of them closely.
I am not sure how you reached that conclusion. The 'main basis' of the video is that the template is used here in the following ways (the text is straight from the slide in the video):

It is claimed to allow you to:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

All these purported uses are simply rubbish!

Quote:

I have built and tested several "angled extensions" on several vehicles, the results are already documented on this site. Results logged over many thousands of miles. Does this qualify as the most rudimentary testing?
Yes, sure.

Quote:
I have several "basic shapes" saved that I use in my planning. Tools in a toolbox for design. I do not have the time or computing/testing resources to develop original aero designs from scratch. I am not hung up on proving any of them right or wrong. I have repeatedly used the AST-II and/or the AST top view and the resulting projects hit my projections for drag change reasonably closely and made the handling changes I desired. Thus I will continue using them.
Sure - but that is completely different from pretending that the template shape can be used for any of the purposes listed above. What you have said is more along the lines of "I fitted 150lb springs front and back and I am happy with the results". Great - but that doesn't mean they gave you the best results, or that other people fitting the same spring rates to their cars will get good results.

freebeard 11-14-2020 05:06 PM
Agreed about your four claims. I think what value the default template has is for canopies, blisters, aerocaps, external hinges & etc. With a higher fineness ratio.

This is as close as I could find a fit for the 'default' template:

https://i.imgur.com/Ah5JdCu.jpg
https://i.imgur.com/x1hiJcm.jpg

A sectioned Type II could be center steer, between the front wheelwells. It fits the hemicircular front profile.

My "Template":

https://i.imgur.com/5jTnVud.png

Three-quarters the wheelwell drag, but it needs to be truncated to a box cavity.

ME_Andy 11-14-2020 07:06 PM
Julian, please take a deep breath and DO NOT reply to my post.

We are lucky to have a template from (as I understand it) a retired professor. It's been useful in many cases. I'm sure it's not perfect for all cases but it's the best tool contributed so far.

I would welcome some input from somebody else about evidence or scientific basis behind the template.

Edit: here's the background for the template. https://ecomodder.com/forum/showthre...rt-c-9287.html

Now that disagreement has been expressed I hope we can move on.

ME_Andy 11-14-2020 08:01 PM
Quote:
I placed Sunraycer under the template,it was a perfect match.Bill Watson's airship "White-Dwarf" of 1984 is about 2.57:1 ratio. Watson worked with Burt Hibbs,aerodynamacist for Sunraycer. Both of AeroVironment. This shape seems to end up on some of the most efficient vehicles known in the world,I believe it to be a shoe -in for aero-modding.Those with more advanced aerodynamic toolbags will will no doubt venture out into some of the more exotic shapes,but for amateurs,I believe this form can serve us well.

JulianEdgar 11-14-2020 08:29 PM
Quote:
Originally Posted by ME_Andy (Post 636375)
Julian, please take a deep breath and DO NOT reply to my post.

We are lucky to have a template from (as I understand it) a retired professor. It's been useful in many cases. I'm sure it's not perfect for all cases but it's the best tool contributed so far.

I would welcome some input from somebody else about evidence or scientific basis behind the template.

Edit: here's the background for the template. https://ecomodder.com/forum/showthre...rt-c-9287.html

Now that disagreement has been expressed I hope we can move on.
Um, you didn’t address even one of my specific criticisms of how the template is used here!

ME_Andy 11-14-2020 08:32 PM
I would like you to realize that your opinion has been expressed. The personal attacks should stop. Find something else to talk about. Is that unreasonable?

JulianEdgar 11-14-2020 08:33 PM
Quote:
Originally Posted by ME_Andy (Post 636376)
Quote:
I placed Sunraycer under the template,it was a perfect match.Bill Watson's airship "White-Dwarf" of 1984 is about 2.57:1 ratio. Watson worked with Burt Hibbs,aerodynamacist for Sunraycer. Both of AeroVironment. This shape seems to end up on some of the most efficient vehicles known in the world,I believe it to be a shoe -in for aero-modding.Those with more advanced aerodynamic toolbags will will no doubt venture out into some of the more exotic shapes,but for amateurs,I believe this form can serve us well.
Sure. Now apply it to a range of other solar cars and see that there’s no match whatsoever!

The debate has never been whether the template is a low drag shape. It’s one of at least five in the literature - all with quite different shapes.

JulianEdgar 11-14-2020 08:38 PM
Quote:
Originally Posted by ME_Andy (Post 636379)
I would like you to realize that your opinion has been expressed. The personal attacks should stop. Find something else to talk about. Is that unreasonable?
What personal attacks?

I am criticising the spreading of misinformation that is leading people astray. Or would you seriously rather that misinformation keeps being spread without being challenged?

Why don’t you address the specific criticisms I have of the template approach? I listed them above.

ME_Andy 11-14-2020 08:43 PM
Quote:
Originally Posted by JulianEdgar (Post 636381)
What personal attacks?
This is a personal attack:

Quote:
I see Aerohead, completely undaunted, is back to spreading his misconceptions about his beloved template
Please move on.

JulianEdgar 11-14-2020 09:55 PM
Quote:
Originally Posted by ME_Andy (Post 636382)
This is a personal attack:


Please move on.
It’s the literal truth!

So just confirm for me, you really would rather that misinformation from an individual goes unchallenged? Really?

If you think the template, as used here, is great, why not address my specific criticisms of it?

ME_Andy 11-14-2020 10:24 PM
OK, I'll watch the video.

0:23s : "apparently ideal shape" -- I've never seen anybody here claim that. The original description doesn't claim that.

2:10 : you're right, the template doesn't predict where the flow detaches to a high degree of accuracy. It's maybe 20cm off or so. Big whoop. Nobody claimed the template was perfect, it's an approximation. The original description even says, it should be useful for amateurs.

2:53 : "there's a small separation bubble at the rear of the window". Big whoop. Probably caused by the antenna.

4:41 "testing beats following every template" : yep, agree. If you have time to do so

7:54 The Sagitta and the Taycan look really close to the template to me. Not perfect.

In summary, the template isn't perfect. OK, great. What are we fighting about here?

JulianEdgar 11-14-2020 10:29 PM
Quote:
Originally Posted by ME_Andy (Post 636389)
OK, I'll watch the video.

0:23s : "apparently ideal shape" -- I've never seen anybody here claim that. The original description doesn't claim that.

2:10 : you're right, the template doesn't predict where the flow detaches to a high degree of accuracy. It's maybe 20cm off or so. Big whoop. Nobody claimed the template was perfect, it's an approximation. The original description even says, it should be useful for amateurs.

2:53 : "there's a small separation bubble at the rear of the window". Big whoop. Probably caused by the antenna.

4:41 "testing beats following every template" : yep, agree. If you have time to do so

7:54 The Sagitta and the Taycan look really close to the template to me. Not perfect.

In summary, the template isn't perfect. OK, great. What are we fighting about here?
Here are my criticisms of how the template is used here:

It is claimed to allow you to:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

All these purported uses are simply rubbish!

freebeard 11-14-2020 10:30 PM
I agreed with you at permalink #18.




[crickets]

I think your aggrieved 'come at me bro' attitude is tiring. But.... The forum is pretty much dead except for this 'controversy' and The Lounge, so....

ME_Andy 11-14-2020 10:37 PM
I guess we have very different opinions on the meaning of "rubbish" and "approximation".

I don't mean to be a dick online. Have a good night (/day in Australia).

JulianEdgar 11-14-2020 10:51 PM
Quote:
Originally Posted by ME_Andy (Post 636392)
I guess we have very different opinions on the meaning of "rubbish" and "approximation".
Yet again you didn’t address my specific criticisms of how the template is used here.

JulianEdgar 11-14-2020 11:00 PM
Quote:
Originally Posted by freebeard (Post 636391)
I agreed with you at permalink #18.
Yes I noticed you agreed, but on the basis of your past posts, I don’t expect that you will make that clear at the time the misinformation actually is being disseminated.

Quote:
I think your aggrieved 'come at me bro' attitude is tiring. But.... The forum is pretty much dead except for this 'controversy' and The Lounge, so....
[shrug]

People who have the equivalent (non) argument of “I don’t like you so please be quiet” is one reason misinformation has flourished here.

ME_Andy 11-15-2020 12:05 AM
I've already acknowledged that the template isn't a perfect tool. That holds for all four of your bullet points.

Clearly it is a useful tool that provides a good approximation.

JulianEdgar 11-15-2020 12:34 AM
Quote:
Originally Posted by ME_Andy (Post 636395)
I've already acknowledged that the template isn't a perfect tool. That holds for all four of your bullet points.

Clearly it is a useful tool that provides a good approximation.
I know you're trying to be conciliatory, but unfortunately the template doesn't even hold for that.

Viz:

It is claimed to allow you to:

- Show where there is separated and attached flow on existing cars

This is very much yes/no - is the flow attached or separated? The template definitely does not show this on cars.

- Guide the shape of rear extensions

Absolutely not. The best shape rear extension will depend on a whole lot of factors, and following a preset template is no guide at all to gaining the best outcome.

- Show how rear spoilers on sedans should be positioned and shaped

Completely wrong. This confusion shown by Aerohead when describing how rear spoilers work is based on his belief in the template (and how rear spoilers worked on old cars), and following that advice will give terrible outcomes on any modern sedan.

- Allow the assessment of the ‘aerodynamic purity’ of cars

The idea that, if only car makers followed the template they would get so much better results, is complete rubbish. Therefore, overlaying a car and 'measuring it' against the template (to purportedly see how good the car is) is equal baloney. After all, why not pick one of the other five low drag shapes with which to do the comparison?

The template is just one of a bunch of different, low drag, theoretical shapes. If it were presented as that, then that would be quite correct, and I'd have no issues.

I don't know, maybe it started off like that - but it's certainly gone into crazy land since!

freebeard 11-15-2020 01:11 AM
Quote:
Yes I noticed you agreed, but on the basis of your past posts, I don’t expect that you will make that clear at the time the misinformation actually is being disseminated.
Not my battle. I gave up on criticizing the default template long ago. I've even slacked off on protesting passive-aggressive capitalizations.

Quote:
People who have the equivalent (non) argument of “I don’t like you so please be quiet” is one reason misinformation has flourished here.
Well, a pox on those people. I like your cranky self and I say Rave On. I think I prefer your work on Youtube.

JulianEdgar 11-15-2020 01:40 AM
Quote:
Originally Posted by freebeard (Post 636397)
Not my battle. I gave up on criticizing the default template long ago.
But don't you then feel guilty when you see people clearly going in the wrong direction when they follow the crap advice? People genuinely confused when their measurements / observations / thoughts don't at all match the template - and all the guff that has been extrapolated from it. (The latter is the important part.)

I worked 8 years as a school teacher, another 8 as an adult trainer, and been modifying cars (and writing about it) for 35+ years. And I hate people being given the wrong information.

But that doesn't mean that there is not room for disagreement. For example, Vman455 and I disagree on the purpose/presence of vestigial front spoilers on modern cars - but I think it's a literally debatable point.

On this sub-forum people are talking information that is so often wrong it's gobsmacking. I can even read individual participant's posts and immediately recognise where their aero misapprehensions have come from - because those misapprehensions are here and nowhere else. (In other words, this sub forum has developed a whole bunch of uniquely wrong 'understandings' of car aero.)

I know some people who have posted here know far better, but either they can't be bothered posting corrections (especially when they'll be met with a wall of pseudo-tech BS from someone who apparently believes they're always right) or the peer pressure 'to be nice' keeps them quiet. (Obviously that's not me!)

Unfortunately I cannot see any change unless people start to do some decent on-road testing (throttle-stop, tufting, pressure measurement), read current aero textbooks or step out of the 'cult' (as someone described Ecomodder to me) frame of reference.

None of these actions takes much money, but they all require an effort.

freebeard 11-15-2020 12:19 PM
Quote:
But don't you then feel guilty when you see people clearly going in the wrong direction when they follow the crap advice? People genuinely confused when their measurements / observations / thoughts don't at all match the template - and all the guff that has been extrapolated from it. (The latter is the important part.)

..... And I hate people being given the wrong information.
No I don't feel guilty for others misapprehensions. I have more concern for the legacy media in my country trying to steer it's politics into the ditch.

I see Template Worship as one [misguided?] theme, alongside A-B-A testing, hypermiling and a number of others. Frankly, since I don't drive much anymore, I'm in it for the friendly persuasion in The Lounge.

Vman455 11-15-2020 01:23 PM
Quote:
Originally Posted by ME_Andy (Post 636389)
2:10 : you're right, the template doesn't predict where the flow detaches to a high degree of accuracy. It's maybe 20cm off or so. Big whoop. Nobody claimed the template was perfect, it's an approximation. The original description even says, it should be useful for amateurs.
The "template" has been used here for more than decade now to predict flow separation. Take a look at this thread about the 2010 Prius; in it, a bunch of posters theorize about flow detachment on the roof and rear window based on comparison to the "template". And not a one bothered to go out, tape some tufts to the car, drive it and look at them. Instead, they predicted flow separation (where, incidentally, none exists--which I know because I went out, taped some tufts to my Prius, drove it, and looked at them).

For a more recent example, look at the Honda CR-Z build thread. In that one, a poster writes about his efforts to obtain a high-resolution profile photo so he can "analyze" the car aerodynamically--presumably by comparison to the "template" (as if it is possible to "analyze" a car aerodynamically simply by looking at a picture of it).

***
I don't understand the pushback here. Whenever Julian has recommended a book, I've bought and read it. I bought the (inexpensive) testing equipment he has posted about. I've started measuring things myself; I don't have to take his word or any author's word for it. I've learned a great deal in the process, but most of all it has opened up a whole world of what I don't know.

What are you all afraid of? Are you afraid your previous beliefs about aerodynamics will have to be rethought? Do you think you'll "regret" learning something new, as someone threatened in another thread (under different circumstances, but the sentiment is what I'm getting at)? Or is it just that the idea that the field of vehicle aerodynamics is actually simple (an idea which appears to be so far from the truth as to be laughable), which has been promulgated on this site for more than a decade, is now so entrenched that you all truly believe it and no contrary evidence will be tolerated let alone investigated? What is it?

CigaR007 11-15-2020 03:01 PM
Quote:
Originally Posted by Vman455 (Post 636413)

For a more recent example, look at the Honda CR-Z build thread. In that one, a poster writes about his efforts to obtain a high-resolution profile photo so he can "analyze" the car aerodynamically--presumably by comparison to the "template" (as if it is possible to "analyze" a car aerodynamically simply by looking at a picture of it).
...and what is wrong with that ? He is doing the analysis on his own time, based on actual tuft-testing and body shape observations. If a relation can be established between the template and the observed air flow, I would consider that as added value. if it does not, then so be it. We move on. No drama.

Ironically, aerohead is one of the few people who actually took the time, his time, to provide some feedback in my build thread; yet people have the audacity to criticize him ? Where are the other viewpoints ? oh wait... they are too busy denigrating.

aerohead is not selling anything. Mr Edgar is. Keep that in mind.

freebeard 11-15-2020 03:53 PM
Quote:
Ironically, aerohead is one of the few people who actually took the time, his time, to provide some feedback in my build thread; yet people have the audacity to criticize him ? Where are the other viewpoints ? oh wait... they are too busy denigrating.
Further to the point, he [over]built the Baby Template and hauled it interstate to the best wind tunnel available at the time.

Quote:
aerohead is not selling anything. Mr Edgar is. Keep that in mind.
Yikes! :)


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