Aerodynamic Streamlining Template: Part-C

[freebeard]

Thanks. I stayed up all night one night making that. It was done for a thread about retractable boattails. The scalloped edge is deprecated, it was to be a self-inflating feature.

The cooling (intake on the sides, exhaust on the bottom) is uncompromised. There's no consideration of engine access in the model.

I was showing it for the connection between the Gothic arch and The Template. Here's a similar example, a double-walled inflatable on a variable-wheelbase tricycle:

[aerohead]

Originally Posted by freebeard

What about the rounded tail of the Schlorwagen/Volkhart-Saggita/Dymaxion compared to the sharp pointy object that it The Template? Better to truncate it like the Cobra Dayton coupe?

The Template sorta predicts the separation off the back of the Schl'o'rwagen

In the wind tunnel we see that the flow doesn't necessarily adhere to the back of the roofline

In the closeup we see how the flow is lost down the roofline.

Kamm would have us loft the roofline up to at least the Buchheim et al. contour and then chop it off if we wanted the same length.
For the Volkshart Saggita it's the same story

The flow separates just like the Beetle's,above the backlight.
The Dymaxion Car has a more correct roofline,but the nose is all wrong.Bucky let too much air have access to the underbody and nothing is done to shield the wheels

With the Cobra Daytona Coupe,they've angled the truncation which allows a torque moment to be produced from the low base pressure riding under and forward of the rear spoiler location,enhancing downforce at the sake of drag.
http://www.conceptcarz.com/images/Sh...-12-AI-a09.jpg

[aerohead]

Originally Posted by skyking

Before I start the big trailer project, I want to prove out materials and methods on a trailer for the new beetle. Since it is foam and glass and a bit large, my concern is how it will do in winds. It will be very light when empty, and about 4' tall by 11' long by 5 1/2' wide.
I hope to follow the template accurately in profile, and have some of the body of revolution aspects of it, but the plan taper will be somewhat limited for practical purposes.
This is still by far the best shape to combat side winds and stay put behind the tractor, right? A light trailer plus side winds plus lift is a bad day.

The upper edge radii will be your friend in crosswinds and gusts.Make 'em as large as you can tolerate,like Airstream,Argosy,Casita,Scamp,etc..Without them,the trailer width would have to be 1.6X body height just to have flow attachment over the top in a violent side gust.This is the reason for many rollovers.

[freebeard]

Figure 8.44 is very instructive.

The tricycle drawing started as an ellipsoid, but with a 'chin' added, like the B-17G. The drawing was done about 1972.

[aerohead]

Here is an effective fineness ratio drag table published by Hucho.It is correct for both streamline bodies of revolution and elliptical bodies.
Hucho's example was a 1966 VW Beetle 1600.
You see that the lowest drag available (Cd 0.04) occurs at the higher Reynolds number,at the intersection of L/D= 2.5.

If the body is shorter it experiences separation-induced pressure drag.
If the body is longer it experiences increased surface friction drag.
Either one increases profile drag.

She's right in the 'sweet spot.'

[freebeard]

I like that he uses the VW Beetle as a benchmark. It's relevant to my interest.

1.75/2.5=0.7. Assuming a 12' length, increasing the Beetle's fineness ratio to 2.5 would require a 5.14ft boattail. What is the included angle at the tip of the optimal body? I used 45°, as close enough to 2*22° in my experiment with redwood lath, and got a boattail length of 3ft.

[CFECO]

Turn the body, 180 degree's, and use the back as the front. The later the year, the better the Flow.

[sendler]

There is some contradictory information between some of these charts. How is the round shape shown as the same cd as the airfoil at .09. You have posted other charts with the cd of a round rod much higher.

[freebeard]

Turn the body, 180 degree's, and use the back as the front. The later the year, the better the Flow.

How's the X-Car project coming along?

[CFECO]

Since I don't have access to a shop, the X-Car will stay in the model stage for now. Since mama said we "might" need a UTV to tool around in when we go camping, I'm working on a design for an Electric Buggy, with the possibility of adding a small gas generator, to charge while traveling, for extended range. It's story is here in the Hybrid section, under... Off Road Hybrid Buggy. I have friends with a motorcycle shop, looking for a project and a "perceived budget" of $5,000 or so, the cost of a used Yamaha Rhino UTV.