Aerodynamic Streamlining Template: Part-C

[ChazInMT]

CLICK ME FOR ANOTHER RENDERING OF AST-II

I took the time to make this, it would be simple now to modify. It is made with a 1.7 aspect aft end which matches exactly what Aerohead drew as his AST-II.

Let me know if this helps, hurts, upsets, needs adjusting, needs to be deleted, needs anything.

[freebeard]

Thank, nicely done. When I Saved I prepended a '-->' so that sort it sorts to the top of the directory 'Aero Technical'.

[aerohead]

Originally Posted by ChazInMT

I have analyzed Phils Gen II template and there are some niggling issues I think are worth mentioning in case they need to be corrected.

I'm afraid what may have happened is that in the course of scanning the new images in, they got their aspect ratios messed up, and what we're left with is a fatter/shorter version of the previous template.

With the new Car Template Dwg, It seems to have an aft body ratio of 1.7 d when before Phil was indicating 1.78d for this same ratio. If you look at this drawing I made using essentially the same shape as Phils teardrop, but shifting forward the breakover point to make the aft body 1.78, there is a bit of a difference.









Big Version Here to look at.



What the new template does in essence is shift the alignment point on top of the template back 5% from where it was before with respect to the 1.78 aft body ratio.

Here are the 2 different teardrops, one with 1.71, the other 1.78. The difference in this picture is not discernible.



In the Bigger version Here you can sort of see a difference.

And here You can see it when zoomed in.



If this is the intention to go with a 1.71 aft body ratio then who the heck am I, as a plebian compared to Phil, but to say anything other than "Let's Roll".

If this is not the intention, than I think I can easily generate a new very precise drawing to fill in where Phil is using a drawing board and pencil.

Here's the New (My longer version) template on the old "Car" to see the change.



Bigger Version of Same

Here is my analysis of the teardrop GenII drawing.



I hope this makes sense what I'm trying to point out, the difference seems to be right on the edge of significant since the new template as drawn deviates from the old by 5%. From all that Phil has said to this point, it seemed he wanted to simply tweak the shape making faster in the first 30% and flatter in the aft 70%.

*Wind tunnel flow photos and tuft testing suggested that the 'Template' architecture was too conservative.This troubled me as much as any of the members.
*Some vehicles 'fit' while others seemed too 'fast' as Hucho warns us about.
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*This 'other' teardrop was still within the realm of the 2.5:1 free-air fineness ratio,would have Cd 0.04,but had a bit more 'aggressive' contour,more like Prius and 1st-gen Insight,and respects W.A.Mair's 22-degree limit to protect the boundary layer.
*It's 'slower' downstream.It doesn't hit 22-degrees until down in the area chopped away for ground clearance.
*This newer contour would allow a bit better rear visibility through the backlight.
*It really needs to be thought of based on its own original architecture,independent of the original drop.
================================================== =======
*I've done comparisons with both and it appears that one will work better than the other depending on vehicle.
*So I wanted to present both.
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*There are some other contours that we could consider for 'Templates' which I'll present in the future,but none of them can provide the drag reduction of the two I've posted and still allow for outward visibility or ground clearance.
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Thanks for all the imaging magic! No way do I have the facility to enhance the visuals as you have done.We're miles and kilometers ahead of my chicken scratching.

[ChazInMT]

Originally Posted by aerohead

*This 'other' teardrop was still within the realm of the 2.5:1 free-air fineness ratio,would have Cd 0.04,but had a bit more 'aggressive' contour,more like Prius and 1st-gen Insight,and respects W.A.Mair's 22-degree limit to protect the boundary layer.
*It really needs to be thought of based on its own original architecture,independent of the original drop.

Thanks for all the imaging magic! No way do I have the facility to enhance the visuals as you have done.We're miles and kilometers ahead of my chicken scratching.

First off, Thank You Phil for staying with us here in this Forum. Your insights are truly appreciated by me and everyone else I'm sure.

Here I made a "Digital Copy" of your AST-II and maintained the 1.7 aft portion per your guidance in the last post. It is within a pixel or 2 of what you have drawn, I did leave out some details and took the liberty of "Arching" the angle measurements.

I must say the degree of precision in your drawing becomes apparent as I was tracing it, it is difficult to explain why I say that, but it is very noticeable as I used my drawing tools as to how close you come to some very ideal curves. My hat is off to you once again.

Please tell me if this offends you somehow and I'll delete it from here immediately.

This is a small version.



Click HERE for a big (1600 x 800) full resolution detailed JPG version

[Frank Lee]

^Looks more like the classic teardrop than any of them.

[freebeard]

It's coming in to focus.

[Frank Lee]

I was thinking of the old Clark Y from 1922:



What does the 20% Clark look like overlayed?

[aerohead]

Originally Posted by ChazInMT

First off, Thank You Phil for staying with us here in this Forum. Your insights are truly appreciated by me and everyone else I'm sure.

Here I made a "Digital Copy" of your AST-II and maintained the 1.7 aft portion per your guidance in the last post. It is within a pixel or 2 of what you have drawn, I did leave out some details and took the liberty of "Arching" the angle measurements.

I must say the degree of precision in your drawing becomes apparent as I was tracing it, it is difficult to explain why I say that, but it is very noticeable as I used my drawing tools as to how close you come to some very ideal curves. My hat is off to you once again.

Please tell me if this offends you somehow and I'll delete it from here immediately.

This is a small version.



Click HERE for a big (1786 x 887) full resolution detailed JPG version

It's great! These images I post are done on 11X17-inch stock with mechanical pencil and french curves.And they can't approach the accuracy of a CAD -type work with the curve-fitting tools available.
If members attempt to scale -up the images for bulkhead measurements,my bumpy drawings would require the 'curve-fitting' that the CAD accomplishes.
When I fabricate,I must use a 20-length of Schedule-40,1-inch PVC pipe to bend over the bulkhead stations to dial in a smooth curve.
With the computer images members can go right to an accurate measure.
Way better! And muchas gracias for all the computer magic!

[aerohead]

Originally Posted by Frank Lee

I was thinking of the old Clark Y from 1922:



What does the 20% Clark look like overlayed?

Frank,Al printed your image for me and then I enlarged it,along with an image -reverse.
Joining them up in mirror-image they create the contour of a streamline body of revolution of L/D= about 2.617 which would be separation-free as a half-body near the ground.It would have Cd 0.08,allowing for ground proximity,and sides tapered and rolled like a Spitfire wingtip.
I like it.And it doesn't have my 'bumpy' lines!
Hucho might say it's a smidge long,but if one were to to use this contour it would hardly make for any regrets.
PS I meant 20%,not 29%.The edit feature does not allow for correcting it.Sorry for confusion.

[kach22i]

Originally Posted by aerohead

Frank,Al printed your image for me and then I enlarged it,along with an image -reverse......It would have Cd 0.08,allowing for ground proximity,and sides tapered and rolled like a Spitfire wingtip.
I like it. And it doesn't have my 'bumpy' lines!

If it looks like a wing, then what sort of lifting forces are we talking about?

..........from page 50

Originally Posted by aerohead

This Generation-II 'Template' was 'built' from a different L/D= 2.5 streamline body of revolution.I've identified it's source within the image.
*As a 'free-air' body,it would have Cd 0.04
*As a half-body in mirror-image ground proximity it would have Cd 0.08.
*Adding wheels would bump it up to around Cd 0.13
*Adding wheel fairings would lower the Cd.

Aerodynamic forces acting upon a car body


Are there any posts showing the center of internal volume, lift (center of pressure) or mass based (if based on a FWD car) for the 3D aero-template?

Aerodynamic forces acting upon a car body

........center of pressure point CP where NCP = 0