Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 06-24-2017, 04:06 PM   #661 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 9,056
Thanks: 1,962
Thanked 2,945 Times in 2,302 Posts


There it is! Bravo.

It reminds me of nothing so much as a faithful rendition of Thee Holy Template.



Maybe a little Dymaxion.

  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (06-24-2017)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-19-2017, 11:42 PM   #662 (permalink)
EcoModding Apprentice
 
Join Date: Dec 2011
Location: San Francisco, CA USA
Posts: 137
Thanks: 6
Thanked 50 Times in 29 Posts
I spent some time today in Rhino 3D trying to fit a smooth curve to the Aero Template. I started by using sections of ellipses to make it easy to have all of the curves with a zero angle at the starting/high point. Then I did an "extend line by arc" which starts with the arc tangent to a horizontal line at that maximum height point.

It looks to me like the angle numbers on the template have some problems. Perhaps I didn't find the most recent version of the template, I looked at the A, B and C threads. Maybe someone can spot where I've gone amiss. I've attached a screen capture from my spread sheet.

The small and medium ellipses have a common center (at the origin to match the template and height, the medium is longer in the horizontal axis. The large template is aligned with the origin but the center is dropped a fair bit because both horizontal and vertical dimensions are increased.

It seems to me that all the curves should start at zero and continually increase in angle in a smooth fashion. The template curve eventually stops increasing and goes to a straight, presumably tangent, line of 22 degree angle.

I didn't bother with the tangent line as that would probably start at different places on the different semi-elliptical curves and the anomaly was showing up in the early part of the curve.

On the template the 10%-increment station angles start at a 3.5 degree difference at 10% (3.5-0) go to a 2 degree delta at 20%, jump to a 6.5 degree delta at 30% and then back down to 3, 3.5, 2.5, 1 and 0 when the straight line kicks in.

The angles of the smaller ellipses become more vertical at about the 50-60% stations but the curve on the template is erratic well before that point.

The arc seems a pretty good fit to the template with the delta rising very slightly. It could be truncated at the 60% station where the value is 21.7612 degrees and go straight from that point.

I realize that most people are probably using the template tool and comparing it to photos, but if they are wanting to make something based on the angles shown they may have problem.

On the other hand, maybe if the shape was developed empirically it works better with a few spots where the curve gets rough.

ETA: the arc I used is roughly 162% of the total length of the template. I did it by eye so I'll go back later and make an arc that is an even 1.6x the length to see how that looks.

cheers,
Michael
Attached Thumbnails
Click image for larger version

Name:	AeroTemplateCalcs.jpg
Views:	44
Size:	34.8 KB
ID:	22215  
__________________
http://www.eurospares.com

Last edited by Michael Moore; 07-19-2017 at 11:53 PM..
  Reply With Quote
The Following User Says Thank You to Michael Moore For This Useful Post:
aerohead (07-22-2017)
Old 07-20-2017, 12:27 AM   #663 (permalink)
EcoModding Apprentice
 
Join Date: Sep 2012
Location: Motor City
Posts: 196
Thanks: 0
Thanked 138 Times in 87 Posts
I have my similar spreadsheet around somewhere. I posted some results, but images are stored in Photobucket.

I attached where I ended, and arc 5.56 times the height of the template. I think we agree, it's an arc.
Attached Thumbnails
Click image for larger version

Name:	Arc.JPG
Views:	17
Size:	23.5 KB
ID:	22216  
  Reply With Quote
Old 07-20-2017, 01:01 AM   #664 (permalink)
EcoModding Apprentice
 
Join Date: Dec 2011
Location: San Francisco, CA USA
Posts: 137
Thanks: 6
Thanked 50 Times in 29 Posts
The angle numbers for a 1.6X length radius arc:
0, 3.5833, 7.1808, 10.8069, 14.4775, 18.21, 22.0243, 25.9445, 30.001 so that could be an extended straight line at the 60% station.

Delta's smoothly rise from 3.5833 to 3.8143 at 60%.

It looks like I'm getting 5.66X the height for the arc radius so that's pretty close agreement.
__________________
http://www.eurospares.com
  Reply With Quote
Old 07-20-2017, 01:08 AM   #665 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,345

Appliance White - '93 Geo Metro 4-Dr. Auto
Last 3: 42.35 mpg (US)

Stealth RV - '91 Chevy Sprint Base
Thanks: 50
Thanked 213 Times in 152 Posts
It is a decade since I ran Rhino, but I seem to recall it being able to fit a smooth curve to a set of X-Y coordinates. Only the laminar flow shapes need a pure mathematical progression.
  Reply With Quote
The Following User Says Thank You to Bicycle Bob For This Useful Post:
aerohead (07-22-2017)
Old 07-20-2017, 02:19 AM   #666 (permalink)
EcoModding Apprentice
 
Join Date: Dec 2011
Location: San Francisco, CA USA
Posts: 137
Thanks: 6
Thanked 50 Times in 29 Posts
Bob, I tried that with points I extracted from the template but once I turned on the curve analysis tools they proved to not be very smooth. I think the points have to be located properly to help the smoothness. Running the "fair curve" command several times helped, but the curve moved away from the template. The curves generated by the arc or ellipse commands are pretty much dead smooth, as I'd expect since they are mathematical constructs and not "let me guess that the point should go about here on this not very clear bitmap in the background."
__________________
http://www.eurospares.com
  Reply With Quote
Old 07-20-2017, 07:00 AM   #667 (permalink)
Master EcoModder
 
sendler's Avatar
 
Join Date: May 2011
Location: Syracuse, NY USA
Posts: 1,976

Honda CBR250R FI Single - '11 Honda CBR250R
90 day: 103.51 mpg (US)

Ninja 250R SE Green - '09 Kawasaki Ninja 250R SE
90 day: 65.9 mpg (US)

2001 Honda Insight stick - '01 Honda Insight manual
90 day: 60.68 mpg (US)

2009 Honda Fit auto - '09 Honda Fit Auto
90 day: 38.51 mpg (US)

Kawi Ninja650 - '07 Kawasaki Ninja650
90 day: 54.85 mpg (US)

PCX153 - '13 Honda PCX150
90 day: 103.38 mpg (US)

2015 Yamaha R3 - '15 Yamaha R3
90 day: 81.28 mpg (US)
Thanks: 259
Thanked 473 Times in 358 Posts
The best airfoil generator I've found is at Wind and Wet.
.
Online airfoil plotter
.
  Reply With Quote
The Following 4 Users Say Thank You to sendler For This Useful Post:
aerohead (07-22-2017), ChazInMT (07-20-2017), KamperBob (07-21-2017), Old Tele man (08-30-2017)
Old 07-22-2017, 02:16 PM   #668 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 8,378
Thanks: 10,314
Thanked 4,406 Times in 2,447 Posts
curves

Quote:
Originally Posted by Michael Moore View Post
I spent some time today in Rhino 3D trying to fit a smooth curve to the Aero Template. I started by using sections of ellipses to make it easy to have all of the curves with a zero angle at the starting/high point. Then I did an "extend line by arc" which starts with the arc tangent to a horizontal line at that maximum height point.

It looks to me like the angle numbers on the template have some problems. Perhaps I didn't find the most recent version of the template, I looked at the A, B and C threads. Maybe someone can spot where I've gone amiss. I've attached a screen capture from my spread sheet.

The small and medium ellipses have a common center (at the origin to match the template and height, the medium is longer in the horizontal axis. The large template is aligned with the origin but the center is dropped a fair bit because both horizontal and vertical dimensions are increased.

It seems to me that all the curves should start at zero and continually increase in angle in a smooth fashion. The template curve eventually stops increasing and goes to a straight, presumably tangent, line of 22 degree angle.

I didn't bother with the tangent line as that would probably start at different places on the different semi-elliptical curves and the anomaly was showing up in the early part of the curve.

On the template the 10%-increment station angles start at a 3.5 degree difference at 10% (3.5-0) go to a 2 degree delta at 20%, jump to a 6.5 degree delta at 30% and then back down to 3, 3.5, 2.5, 1 and 0 when the straight line kicks in.

The angles of the smaller ellipses become more vertical at about the 50-60% stations but the curve on the template is erratic well before that point.

The arc seems a pretty good fit to the template with the delta rising very slightly. It could be truncated at the 60% station where the value is 21.7612 degrees and go straight from that point.

I realize that most people are probably using the template tool and comparing it to photos, but if they are wanting to make something based on the angles shown they may have problem.

On the other hand, maybe if the shape was developed empirically it works better with a few spots where the curve gets rough.

ETA: the arc I used is roughly 162% of the total length of the template. I did it by eye so I'll go back later and make an arc that is an even 1.6x the length to see how that looks.

cheers,
Michael
The template is derived from two different sources of artwork published for Cd 0.04,2.5:1 streamline bodies of revolution,provided by Franzini et al., and Wolf Heinrich Hucho.
One is 'slow' and one is 'faster'.
Some production car greenhouses lend them selves to one,but not the other so I published two,which hopefully satisfies any given production architecture.
It's not a 'perfect' solution but has a high degree of confidence for users as far as eliminating aft-body flow separation,critical for profile drag reduction.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
freebeard (07-22-2017)
Old 08-30-2017, 06:06 AM   #669 (permalink)
s_t
EcoModding Lurker
 
Join Date: Aug 2017
Location: Brisbane, Australia
Posts: 18
Thanks: 0
Thanked 6 Times in 6 Posts
I've been looking at roof profiles, in relation to a potential motorhome as discussed in this thread: Aero Efficiency of Motorhome/RV vs Car & Caravan

In the below image are two roof profiles. The primary difference is how rounded they are just after the windscreen. Intuition tells me that the more rounded top would be the lower drag.



However, when I apply the template this thread is about, it tells me that the pointy one is better. Primarily because the downward taper starts significantly closer to the front of the vehicle (by roughly 10-12% of total vehicle length).

Pointy option - could even drop off steeper at the back for small tail cross section:



Rounded one - dropping off too quickly - needs larger tail cross section:


Post #604 in this thread has some modelling showing high pressure at the sharp point above the windscreen, which I think indicates rounding is better? (sure, I realise the front profile is quite different, but same general pattern probably applies)

Is the bluntness /sharpness of the front of the vehicle, and transition to the downward taper, really that insignificant relative to the position of the high point? Any comments/thoughts as to which is better?
  Reply With Quote
Old 08-30-2017, 07:53 PM   #670 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 9,056
Thanks: 1,962
Thanked 2,945 Times in 2,302 Posts
I wouldn't worry about it too much. The Template presumes taper in plan to equal the taper in elevation, and a half-circular cross section. The racer's aphorism is "It isn't how you punch the hole in the air, it's how you close the hole in the air." IOW the rear is more important than the front.

That said the bluff forebody of the Template insures the flow is uniform enough that it can support the taper without shedding vortexes. Any disruption such as the windshield header you mention can spoil airflow 'downstream'.

Why not go with the curved header and then a Tropfenwagen style rear with a flat top and tapered sides? It would have more interior space.


  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Aerodynamic Streamlining Template Part-B aerohead Aerodynamics 8 05-31-2013 01:23 PM
LED Headlight captainslug DIY / How-to 82 11-15-2011 02:32 AM
Maximum angle for boat tail? abcdpeterson Aerodynamics 72 10-25-2009 05:37 PM
Aerodynamic Streamlining Template: Part-A aerohead Aerodynamics 0 07-18-2009 03:37 PM
All items I scanned in the new product showcase dremd The Lounge 0 11-08-2008 05:14 PM



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com