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Old 08-03-2012, 05:26 PM   #471 (permalink)
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Originally Posted by 3-Wheeler View Post

I thought that's exactly what I did in post #465.

The total length of the shape is drawn 5:1, at the ground plane level. And the trailing angle just touches 22 at the very end.

Not sure of anything I would change to match what you are describing.

From that information, it would appear that the Streamlining Template is slightly too short based on what you are describing above.

The 'Template' image in post#465 is different from the original Template-C.Perhaps I should never have posted it.
The purpose of the Template was to aid in aft-body streamlining and I 'lost' some of the original Template nose to honor the convex hemispherical nose pushed by all the Doctors of Philosophy.
If you will go back to the Template thread you'll find the original Template of which is plainly shown how it originated from the 2.5:1 streamline body of revolution in ground reflection,with L/H = 5.1 'virtual' body.
On page-1 at the 'Aerodynamic Streamlining Template Part-C,below the new image,in the second thumbnail is the original 2.5:1 Template.It is the 1.78X Diameter aft-body which is of interest to us.

Last edited by aerohead; 08-03-2012 at 05:45 PM.. Reason: add data
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Old 08-03-2012, 06:12 PM   #472 (permalink)
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So Phil, is this the better image?

Sincerely, Neil

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Old 08-03-2012, 06:24 PM   #473 (permalink)
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Originally Posted by NeilBlanchard View Post
So Phil, is this the better image?

Neil,I won't say it's better,but since we've been using the 'newer' image,it seems like folks have lost sight of the 'Template' origin which is only depicted in the original image.
As long as members realize where the 'newer' image comes from we're okay.Otherwise the science of it is lost and we spend precious time arguing form.
I appreciate you posting the 'original',hope it helps fill in some blanks.
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Old 08-05-2012, 02:55 PM   #474 (permalink)
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If any project here deserves front page recognition , surely this one does .
Anyone else in agreement ?
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Old 08-05-2012, 07:50 PM   #475 (permalink)
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Originally Posted by Cd View Post
If any project here deserves front page recognition , surely this one does .
Anyone else in agreement ?
good idea!

I put up a poll to this effect:
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Old 08-06-2012, 05:11 PM   #476 (permalink)
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Jim - could you confirm the accuracy of the figures in this short description for the home page?

What happens when you start with one of the most aerodynamic production cars ever sold and add a custom-crafted tail to make it even more efficient? Initial testing showed an improvement in fuel economy of 10.27% at 56 mph, or tentatively around a 18% reduction in aero drag.
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Old 08-07-2012, 07:20 AM   #477 (permalink)
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Thanks to whomever put this thread on the front page.

I don't think I've seen it before.

A very handsome project.
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Old 08-07-2012, 01:30 PM   #478 (permalink)
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Originally Posted by MetroMPG View Post
Jim - could you confirm the accuracy of the figures in this short description for the home page?
Yes, Metro, that sounds very accurate.

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Old 08-08-2012, 01:50 PM   #479 (permalink)
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The slew behavior under side wind load

When driving any car onto a section of glare ice with a side wind load, you will always see the front end slew in the direction of the wind. The reason is that the front tires lose their hold on the road first. That makes the rear tires the fulcrum of a lever. The rear wheels have next to zero friction resistance to rotating at different speeds. You would need a very long tail indeed, or a very large fin to compensate.

In heavier cars the car won't slew as much because the wind doesn't provide enough force to accelerate the mass of the car appreciably in such a short period of time.

Not so hard to figure this out. The Insight has flat enough sides that you can treat the whole side projection as a flat plate with roughly equal force throughout. Assign it some value per square inch, say 1. With a value of 1 per square inch, the force disappears and you just use the area times the distance. No need to use calculus. Just measure the height of the side at rough 6" intervals. (Or figure it as best you can using measurement points that make sense to you.) Then, for each foot, (or inch) distance (depending on how big a spreadsheet you want to make) multiply that area times the distance of the midpoint of the section from your lever fulcrum.

Depending on the scenario, the lever fulcrum will usually be the rear wheels or the front wheels. Only if the whole car is on glare ice will the fulcrum be the center of mass of the vehicle. You could estimate that by driving the car onto a teeter board (or metal plate) and finding the approximate spot where the car balances.
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Old 08-09-2012, 02:31 PM   #480 (permalink)
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Being an extremely lightweight FF car, the Insight probably balances closer to the front wheels. The tail extension, while it does give some weight to the back, gives a lot of mechanical advantage to the wind. The weight added is negligible compared to the amount of torque introduced by wind hitting the tail normal. The sidewall grip of the rear tires should be just enough to hold the car true, though.

While the tail does add surface area normal to side winds, the Insight's tires should be able to handle the force without any tragic outcomes. I would think that the rear tires would lose friction before the car's mass over the front wheels do.

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