Want low drag? Don't follow a template.

[freebeard]

His example of the latter was: Clouds bumping into each other make thunder.

Did he ever map the electrical potentials distribution on the converging clouds? Hmmm? Down, up and sideways?

Everyone integrates received wisdom into their perceptual framework. (The eye cannot see what the mind does not know) It's important that that framework be robust.

I only know of one person that didn't accept anything he couldn't reason out on his own. He went silent for two years while he thought it over and then began to speak in compoundwordings. His opus is Synergetics.

[JulianEdgar]

Originally Posted by freebeard

Did he ever map the electrical potentials distribution on the converging clouds? Hmmm? Down, up and sideways?

Everyone integrates received wisdom into their perceptual framework. (The eye cannot see what the mind does not know) It's important that that framework be robust.

I only know of one person that didn't accept anything he couldn't reason out on his own. He went silent for two years while he thought it over and then began to speak in compoundwordings. His opus is Synergetics.

Yes, I have a biography of Buckminster Fuller. Pretty strange guy.

[freebeard]

The best way to insure you will be remembered by people is to have an elemental form of carbon [C-60] named after you.

[aardvarcus]

Originally Posted by AeroMcAeroFace

Attachment 29641

I must have done this wrong then. I have tried quite a few times though. I think template wisdom would suggest reaching up to the template to get lower drag.

They must have separated flow all the way down the back.

"Aerohead, I think you mentioned something about the tumblehome playing a large part in keeping flow attached once the rear glass goes out of the curve of the template." Flow is 3d, there are C-pillar vortices that can cause the flow to attach. However it is not always the result of C-pillar vortices, the EV1 had a lot of attached flow from the side of the car going over the back window. I would think that the XL1 is the same.

Try fitting the AST-II.

[Vekke]

Even I have used the wrong template as the ecomodder tool uses the wrong old template :/.

I remeber that I wondered that template fitting to XL1 long time ago. And found that post That was 7 years ago:
https://ecomodder.com/forum/showthre...tml#post354218

[AeroMcAeroFace]

Originally Posted by aardvarcus

Try fitting the AST-II.

So there are different templates, and the AST-II is the one to use? Why have people been encouraged to use a different one for the past 10 years?

Does this solve the PRIUS debate? Does that fit the different template? If it does then maybe the template is usable, but on the centreline where flow is front to back, not necessarily elsewhere.

[freebeard]

The default template has a frontal aspect that is hemi-circular. How many exercises in curve fitting do you see that respect it?

[aardvarcus]

Originally Posted by AeroMcAeroFace

So there are different templates, and the AST-II is the one to use? Why have people been encouraged to use a different one for the past 10 years?

Does this solve the PRIUS debate? Does that fit the different template? If it does then maybe the template is usable, but on the centreline where flow is front to back, not necessarily elsewhere.

Yes there are different "templates" (diagrams) from different sources. Side views, top views, front views.

I can not tell you that the AST-II is the one for you to use, or whether you should be using a diagram at all. But if you want to know which diagram you might find that is an exact match for the rear curvature of the Honda Insight, VW XL1, Several Generations of Toyota Prius, 7th gen Celica, etcetera then I would suggest you use the AST-II. Or if you hate "diagrams" just use a side view photo of any one of those (or many other) cars that share the exact same rear curvature as a function of height.

I am not sure who on this site over the past decade has been encouraging the use of the AST-I over the AST-II. I have been on this site about that long, and have not seen any pressure to use the older version. The OP of this thread is just about the only one I know doing overlays using the old version.

What generation of Prius is in question? I have fit the AST-II diagram to several generations of the Toyota Prius, some of them are exact matches.

Usable for what? If you are choosing to attempt to copy one or more 2d diagrams into a 3d shaped part, obviously there are some details to be worked out. As freebeard has mentioned, most of us are not in hemisphere shaped vehicles. Most users of this site that have used the tools to actually build things seem to have figured those sorts of things out.

[JulianEdgar]

Originally Posted by aardvarcus

I am not sure who on this site over the past decade has been encouraging the use of the AST-I over the AST-II. I have been on this site about that long, and have not seen any pressure to use the older version. The OP of this thread is just about the only one I know doing overlays using the old version.

Huh? I am using the template nominated in the tools section of the site, the one I have seen used numerous times when purporting to do each of the following (absurd) uses:

- 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)

If you want to pick a different template - fine, but it's an equally absurd approach.

I don't know how often it has to be stated, but 'low drag shapes' (let alone any sort of template) are given basically zero coverage in any current textbook on car aero. And it's not because they've forgotten to include it.

So you can either decide that this site has come up with an extraordinary breakthrough in car aerodynamics.... or this site is on the wrong track. I am afraid in any car engineering debates, I always back the professionals over amateurs - and professionals certainly don't use any type of aerodynamic template.

[aardvarcus]

Julian,

Did I comment on your diagram use incorrectly? You are using the AST-I for all your overlays, are you not? In your videos and posts and such?

I really don't see that many users using that diagram (AST-I not II) on this site for those purposes.

Using a diagram at all may be absurd, but in terms of relative absurdity I would consider using a diagram that exactly matches the XL1, Prius, Insight, etcetera to be less absurd than applying a diagram intended for a use on a vehicle that is in cross section a hemisphere. Once again, I don't have any hemispheres parked outside.

If the notion of someone who does not have development resources mimicking the rear curvature as a function of height of some of the most respected low drag vehicles is absurd, then yes please count me among the absurd. I saw a really good quote on this the other day, it said "This is one occasion when copying one of the generic low-drag shapes will probably get you 90 per cent there."

The professionals may not use a diagram, but it is funny how so many of their "low drag" designs end up with almost exactly the same rear curvature as a function of height.

I don't think it is a groundbreaking revelation to make a higher drag vehicle (e.g. Toyota Tacoma) to have a rear curvature as a function of height that matches a respected lower drag design (e.g. Toyota Prius). But I also don't think that measured long term tank to tank 10% better MPG is the "wrong track." Perhaps it is a "non-ideal track", and there is perhaps a percent or so left on the table. If I was a professional, with all the professional modeling resources at my fingertips I could know for sure about that percent.