How To Line Up Template - Sports Car Design

[cfg83]

kach22i -

Originally Posted by kach22i

Just playing with one of my original car designs (for fun).

I'm using the green template BamZipPow posted here:
http://ecomodder.com/forum/showthrea...-c-9287-9.html

1. Is it alright that the green does not quite touch the ground plane?

2. Which overlay is lined up correctly, any of them?

Industrial Design pictures by kach22i - Photobucket

...

As what has been said, the first one, with the overlay scaled slightly up to line up with the bottom of the wheels.

What I like about this is that I *think* I see a CRX wheelbase mated to a Ferrari(?) inspired shape.

CarloSW2

[winkosmosis]

Originally Posted by kach22i

Thanks, I thought that was the closest.

Always line up with the "high point" of roof?

The first mark with the zero degrees, that is the center of the roof, or does it have to cut through the driver's head?

If your whole roof conforms to the template, then where is the center? Doesn't it shift back a couple of feet on my example?

It doesn't really matter because the template has no relevance to the aerodynamics of the vehicle, because a car isn't shaped like a half teardrop that touches the ground. The very fact that you're trying to figure out where to place it is proof.

The air doesn't care about templates, it cares about whether it can stay attached to your body lines and how big a hole you end up punching in the atmosphere once flow departs the rear end.

[aerohead]

Originally Posted by winkosmosis

It doesn't really matter because the template has no relevance to the aerodynamics of the vehicle, because a car isn't shaped like a half teardrop that touches the ground. The very fact that you're trying to figure out where to place it is proof.

The air doesn't care about templates, it cares about whether it can stay attached to your body lines and how big a hole you end up punching in the atmosphere once flow departs the rear end.

Did we miss the part about your advanced degree in mechanical engineering and 30-years of experience in a full-scale automotive wind tunnel?
Perhaps you can share some of your peer-reviewed professional papers from your vast library and archive.
No longer would you have to suffer the incoherent ramblings of the ignorant and uninitiated.

[winkosmosis]

Originally Posted by aerohead

Did we miss the part about your advanced degree in mechanical engineering and 30-years of experience in a full-scale automotive wind tunnel?
Perhaps you can share some of your peer-reviewed professional papers from your vast library and archive.
No longer would you have to suffer the incoherent ramblings of the ignorant and uninitiated.

You pulled the "template" out of your butt. You can't just overlay a half teardrop shape on a car arbitrarily and claim that following that shape on part of the body is the optimal way to improve aerodynamics. It's just a crutch to avoid critical thinking.

The OP's images demonstrate perfectly how arbitrary this baloney is.


What matters here is whether airflow can stay attached to the rear window and depart smoothly when the body ends. Like I said... The air doesn't care about your "template".

[winkosmosis]

Originally Posted by kach22i

For reference
Automobile drag coefficient - Wikipedia, the free encyclopedia


For a template comparable, the new 991
Automobile pictures by kach22i - Photobucket

According to the almighty template, the 911 sucks. And yet it's one of the most aerodynamic sports cars at 0.28 Cd. You know why? Because the roof and rear window are sloped shallow enough that airflow remains attached and doesn't detach until the rear spoiler. Those angles are what matter here. If you made the 911 look like the template, there would be no advantage for flow attachment, and the cross section of the rear end would be much bigger.

This is a perfect example of the arbitrary and nonsensical nature of the template.

Forget templates and just make sure the curves of the body allow attached airflow all the way back at the desired speed! BTW, you notice there aren't different versions of the template for different speeds?

[kach22i]

Originally Posted by cfg83

What I like about this is that I *think* I see a CRX wheelbase mated to a Ferrari(?) inspired shape.

The rear glass of the CRX and even the 1st gen Insight along with Porsche and many other influential cars were in the back of my mind as I sculpted clay five years ago. The clay car was set up with as a V6 rear engined car in mind.

The drawing and template are set up per the FFR contest held this spring (Subaru based-mid), I posted some of my other entries here:
700+ Designs: Please post your designs here for all to see - Page 4

Here is the main influence, if there is one; the Shalako by Dick Dean.
Shalako


I'm pretty sure I had a model as a kid, or knew someone who did.

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

Winkosmosis, I see your point which is why I did the overlay. The old air-cooled 911's had a 30 degree rear slope (tangent line), the water-cooled 911's have a 20 degree rear slope, which as I understand it is a minimum. I've read that air starts to leave the surface between 10-15 degrees, but 20 degrees is acceptable (unless you are an aircraft wing).

Also remember that the rear deck rises on later air-cooled Porsche's to grab (induct) some of the air which has already started to leave the 30 degree slope. This retro Singer does a nice twist on that concept.

http://www.carsinpedia.com/car_day_a...ils.php?id=399


The tear-drop overlay is an "idea shape", that does not mean it is useless in the real world or should be ignored. I think it means "keep it in mind - reference it", if you fail to match it, come as close as you can.

My degree is in architecture, but my other interest make me a student of many sciences including aerodynamics and acoustics. I'm here to learn, and not to lecture to experts.

[autogyro]

Here's an outline I did in Flow illustrator, which has an angle of 27 deg. Notice has the flow stabilizes with no seperation. This illustrates why CFD will yield different results from the panel method.

http://www.youtube.com/watch?v=lKHURePuSZo

Go for it!

BTW your outline very much resembles the Alfa tipo 33 Stradale, surely a heartbreaker, if there ever was one.

File:Alfa Romeo Tipo 33 Stradale Side.jpg - Wikipedia

[kach22i]

I have a second set of questions on another design on mine, it's a three fold question.

1. The high point of the roof below is the top of the windshield (with the targa top off), right?

Industrial Design pictures by kach22i - Photobucket


2. Does the template, or at what degree does the template work on open top targa style cars?

3. Targa roof on - see below......................is this any better than the first design on page one? What does that roll bar step do to the aerodynamics?

Industrial Design pictures by kach22i - Photobucket

[kach22i]

Originally Posted by autogyro

which has an angle of 27 deg.

I measured your angle by holding my adjustable triangle (old school drafting tool) up to my computer screen and measured the tangent angle at 15 degrees (approx.).

I think the "average angle" is the important part, call it the tangent line angle if you want.

The angle at which air flow starts to leave is important, and that is as claimed; 27 degrees. However, the mindset of a designer says this is a 15 degree fastback, not a 27 degree fastback.

I just want to clarify this issue, as tossing numbers around can be misleading at times.

[euromodder]

Originally Posted by winkosmosis

According to the almighty template, the 911 sucks. And yet it's one of the most aerodynamic sports cars at 0.28 Cd.

What makes you think 0.28 is good ?
Shorter cars like the Audi A2 have done better despite their poorer L/D ratio.

The 2012 Mercedes B-class is 0.24 (with eco package, 0.26 without) despite it being rather short as well.

The Schlörwagen - which is more or less the template in 3 dimensions - only has about half that Cd.