Scaling the Template

[Xist]

Freebeard, what did the moderator tell Billy Madison?

Sven7, before creating my Forester boattail thread, I created this picture:

and then posted this one:



Whether or not the template scales, I believe that we can start tapering in the bottom as soon as possible behind the rear wheels.

[Sven7]

Oh, sorry, I did that too on the Anal Probe. The point of my RV post was the scaled template on the roof of the RV.

[ChazInMT]

Originally Posted by Xist

Whether or not the template scales, I believe that we can start tapering in the bottom as soon as possible behind the rear wheels.

The bottom of the boat tail should not exceed 10° from what I've seen in ecomodder a bunch of times, so your template under the template thing isn't really a good idea.

[freebeard]

Xist -- "...and may God have mercy on my soul?"

Whether or not the template scales, I believe that we can start tapering in the bottom as soon as possible behind the rear wheels.

...as soon as possible behind the driver's feet.

[Xist]

Originally Posted by ChazInMT

The bottom of the boat tail should not exceed 10° from what I've seen in ecomodder a bunch of times, so your template under the template thing isn't really a good idea.

When I posted my pictures, Aerohead wrote:

Originally Posted by aerohead

I'd maintain the upper curvature as you have it,but for the lower,it will depend on where you begin your diffuser.So it's angle will be 2.5-degrees,or around 4-degrees depending,and you can ignore the red line since you have so much ground clearance to begin with.
You may want to do it in 'installments',to see how you like parking 'n such.If you think you can live with more length then go for it.

I did not try to figure out what that meant since I only shared the images for entertainment. I guess that I was the only one that thought that it was funny.

I usually am.

[kach22i]

Most of the time when we get a nice flowing canopy on a car such as the +2005 Mustangs or the F-Body Camaro's we in the forum can generally agree not to mess with it in an attempt to Kammback it, because close enough is good enough, right?

Is the below VW XL1 an example of this?

Automobile 2 - Odds And Ends Photos by kach22i | Photobucket


I suspect there is an algorithm or something which can be used when scaling down the template to conformity, in essence saying (by a measure of scale), that when you scale down the template you scale down your measure of success by "X" amount.

Either that or by measuring the volume or space not within the template 3D shell, one could calculate the percent or an actual number one will suffer losses as compared to the ideal template.




I don't need anyone to agree with me with what I see in these exercises, I know what I see. I will however eventually find the answer or the reasoning over time for what I see in these exercises.

So far the reasoning given by others or excused in absence leaving me to wonder, is not satisfying at all.

In my humble opinion, one cannot, and should not attempt to 2D fit a 3D template, and certainly one demanding more explanation than simply lining up with the highest point on the roof as this one.

NOTE: I used the two best images of the XL1 which I could find, one seems to have a slightly longer nose.

Will someone please post the Cd number the idealized 3D aerodynamic Template-C is supposed to give us?

[kach22i]

Originally Posted by ChazInMT

Here is a link to the new template outline alone in HiRes if you wanna grab it. Made it Just4U.

Thank you, I was using the version with the person standing next to it, but it was not "official" from what I was reading. In addition, there is now an even newer version with a more sloped windshield area, and that looks to be a work in progress as well.

Originally Posted by ChazInMT

Oh. And you still can scale the thing if you want, and you're right, you'll probably have attached flow when you do scale it, but it won't be an optimized shape.

The template is a guide to optimize the shape of an Entire Vehicle, because when you scale it to fit, the top line of the rear portion automatically becomes the ideal shape the air likes to see for the least overall resistance taking into account the form drag and the skin drag.

I cannot argue with a thing said, it's pretty much what I've been trying to convey as a matter of fact.

Originally Posted by ChazInMT

And most cars are flat on top for 4-6 feet across, making them something of a wide 2D shape, so you may wanna think about that before you muddy the waters with a 2D vs 3D thing. If you want to build a trike or bike, then you may not be able to make much use of the template because they are taller than they are wide.

The template overlay studies most people post are still in profile only, once in a while get posted in top view, but typically much later if at all. I'm sure that I'm guilty of the same thing here as I did not show the top view of the VW. It's an important issue, to remember in my opinion as real life is in 3D - and so are vortexes.

Originally Posted by ChazInMT

Finally, 0.13 is the ideal Cd for a vehicle following the template.

Found it here

Thank you ChazInMT, some of this information get buried very deep in the threads. I see that the most idealized number is only 0.08 without wheels and scraping the ground.

There seems to be room for improvement on the VW, 0.189 verses 0.08 of the ideal shape.

[aerohead]

Originally Posted by Sven7

According to that, this would be correct? Am I interpreting that right? Phil?

If the vehicle is taller than it is wide,I would consider treating it as a 'section' rather than a 'half-body.'
For the 'section' the plan-view taper would determine the streamlining.
In plan-view you would mimic the contour of the lowest drag 'section',then pattern your roof contour to mimic what you arrived at for the sides.Somewhere (maybe in the 'Full-boat-tail 'trailer thread is the drag table for 'sections.'
--------------------------------------------------------------------------
If the vehicle is wider than it is tall,then use the 'Template'.
--------------------------------------------------------------------------
If you're interested only in limited length,with absolutely no intention of future additional drag reductions,then consider the Wolfgang Klemperer streamlined 'minivan' of 1922.NASA's Dryden Research Center Econoline boat tail has this profile.It's what I did on the VW Transporter in college without knowing it.
Klemperer measured Cd 0.16 for the wind tunnel model.It looks like Hucho or Rolf Buchheim re-tested the same model for the VW 2000 project and measured Cd 0.15.
The hitch is that the vehicle must look exactly as Klemperer designed it and it is very doubtful that you'd be able to see out of the car.
Hucho ran into this problem and VW had to morph Klemperer's shape so much that they ended up with only Cd 0.25.
This is why I stay away from it.

[aerohead]

*The 1/6-scale model would not have the same Cd as the full-scale car until 120- mph due to the Reynolds number effect with the boundary layer.
*The 'Template' can only be applied as is shown.It is absolutely contextual.The alignments must be at identical scale and position.
---------------------------------------------------------------------------
*For canopies,blisters,tanks,radomes,nacelles,etc.,you should consult 'AERODYNAMIC DRAG',by Sighard Hoerner.It is the book(s) which is most listed as a reference for such specific information,including Hucho.
*When 'combination',or,'composite' body structures are pieced together,the interaction of each component can create 'super-velocity' effects upon adjoining components and their aerodynamic characteristics are altered by the interactions.
The 'Template' would in no way be appropriate for designing such structures.
--------------------------------------------------------------------------
If you're interested in only limited 'low drag',then there are many options.
The NASA Dryden van would be one.This design would be patterned after DOT vehicle length and other restrictions.It does not reflect an 'ideal' solution,just an arbitrarily optimized one.

[kach22i]

Originally Posted by aerohead

..........the Wolfgang Klemperer streamlined 'minivan' of 1922.

In my search to find images of this vehicle I found an intersting website.

Concept Cars and Aerodynamics, 1917-1940
by PETE on MAY 2, 2013
Concept Cars and Aerodynamics, 1917-1940


Still no signs of the Klemperer in question.

EDIT-1:

Originally Posted by aerohead

*The 1/6-scale model would not have the same Cd as the full-scale car until 120- mph due to the Reynolds number effect with the boundary layer.
*The 'Template' can only be applied as is shown.It is absolutely contextual.The alignments must be at identical scale and position.
---------------------------------------------------------------------------
*For canopies,blisters,tanks,radomes,nacelles,etc.,you should consult 'AERODYNAMIC DRAG',by Sighard Hoerner.It is the book(s) which is most listed as a reference for such specific information,including Hucho.
*When 'combination',or,'composite' body structures are pieced together,the interaction of each component can create 'super-velocity' effects upon adjoining components and their aerodynamic characteristics are altered by the interactions.
The 'Template' would in no way be appropriate for designing such structures.
--------------------------------------------------------------------------
If you're interested in only limited 'low drag',then there are many options.
The NASA Dryden van would be one.This design would be patterned after DOT vehicle length and other restrictions.It does not reflect an 'ideal' solution,just an arbitrarily optimized one.

Seems to me like there are very limited opportunities to apply the template to existing and typically flat sided (and rectangular wheel layout) automobiles.

I don't think that I'll even bother considering these limitations, as it will never be perfect. Anyone who does a template overlay must be a misguided fool and totally ignorant to boot, right?:

http://ecomodder.com/forum/showthrea...c-9287-13.html

Originally Posted by aerohead

Here's something to consider.
*The lowest Cd for a streamline body of revolution in free-air is 0.04.
* The Template,in free-air,has Cd 0.04.
* When the Template is 'split' in ground-reflection it is Cd 0.07
* When the 'ground-clearance' is cut away from the 'half-body' the Cd is 0.08.
* When skinny wheels are added to it the Cd jumps to 0.12.
* When wheel fairings are arranged around the wheels/tires,the Cd drops to 0.089.

http://ecomodder.com/forum/showthrea...c-9287-47.html

Originally Posted by freebeard

If you're up for it, try the Squircle. That's the one in the middle here:

Is this the official Part-C aero-Template Cross Section?

http://en.wikipedia.org/wiki/Squircle


I've always assumed the Part-C aero-template would look like this (see image below) in front view, but I'm still looking for it.

http://www.thetruthaboutcars.com/201...n-three-parts/