Go to Ultimatecarpage.com

Go Back   Ultimatecarpage.com forums > Automotive forums > Technical forums


Reply
 
Thread Tools Display Modes
  #1  
Old 12-23-2011, 12:21 PM
Big time Big time is offline
Rookie
 
Join Date: Feb 2011
Posts: 134
What is more aerodynamic: Wide flared fenders or a wider body?

Let's suppose you are designing a supercar with a narrow cabin and a wide track.

What would be more aerodynamic?
A. To have a narrow body with the wheels being covered by wide fender flares. Maybe somewhat streamlined fender flares.
B. To have a wider body covering the wheels.
Reply With Quote
  #2  
Old 12-23-2011, 01:17 PM
NSXType-R's Avatar
NSXType-R NSXType-R is offline
Furniture
 
Join Date: Jun 2005
Posts: 11,608
East Coast of the United States
Just to let you know, instead of starting multiple threads, there is a thread where you can ask all these questions.

The Technical Questions Thread - Page 81 - Ultimatecarpage.com forums
Reply With Quote
  #3  
Old 12-24-2011, 09:00 AM
Cyco's Avatar
Cyco Cyco is offline
Enthusiast
 
Join Date: Sep 2004
Posts: 3,560
Perth, Australia
Send a message via MSN to Cyco
Quote:
Originally Posted by Eggnog
A string is exactly 9 long
A very well designed set of flares has the potential to be more aero (less change in cross sectional area at the cabin), but most are not well designed.
__________________
Chief of Secret Police and CFO - Brotherhood of Jelly
No Mr. Craig, I expect you to die! On the inside. Of heartbreak. You emo bitch
Reply With Quote
  #4  
Old 12-24-2011, 10:16 AM
Badsight Badsight is offline
Rookie
 
Join Date: Jul 2005
Posts: 436
N.Z.
check out the box fish, you dont need a tear drop shape to have low drag

http://en.wikipedia.org/wiki/Mercedes-Benz_Bionic

a good modern example of shape optimization is the 2012 Nissan GTR. basically looks exactly the same as the 2011 model
Reply With Quote
  #5  
Old 12-24-2011, 01:03 PM
coolieman1220's Avatar
coolieman1220 coolieman1220 is offline
Enthusiast
 
Join Date: Aug 2005
Posts: 2,057
New York City
coefficient of drag = cross sectional area
__________________
Gone:
09 Ducati Monster 696
09 Audi Q5 3.2
03 Infiniti G35 Sedan
07 Honda Civic Coupe LX 5spd

Current:
10 BMW 335d
12 Audi Q5 2.0t
10 VW Jetta TDI
11 Ducati Monster 796
Reply With Quote
  #6  
Old 12-26-2011, 10:51 AM
Big time Big time is offline
Rookie
 
Join Date: Feb 2011
Posts: 134
Quote:
Originally Posted by Cyco View Post
A very well designed set of flares has the potential to be more aero (less change in cross sectional area at the cabin), but most are not well designed.
Please elaborate.

I don't understand how flares can provide LESS change in cross section area. If you get a narrow body and wide flares the difference in area would be larger than a wide body which has more or less a constant area.
Reply With Quote
  #7  
Old 12-26-2011, 09:36 PM
csl177's Avatar
csl177 csl177 is offline
Enthusiast
 
Join Date: Feb 2006
Posts: 2,709
Way Down South
Quote:
Originally Posted by Big time View Post
Please elaborate.

I don't understand how flares can provide LESS change in cross section area. If you get a narrow body and wide flares the difference in area would be larger than a wide body which has more or less a constant area.
You asked which is more aerodynamic; simply put, the lowest CD should be most efficient... but isn't determined by frontal area alone.
It may be achieved both fendered or by complete coverage of the wheels (flares or not) but there are many other calculations required.

To wit:

CD = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape

CL = Coefficient of Lift

CS = Coefficient of Side Force

q = Dynamic Pressure in the Test Section

r = Mass Density of Air

A = Frontal Area of Vehicle

V = Velocity

Which brings us to an example of the required energy to propel an object to designed terminal velocity:

HP = (DV)/550 = (CDqAV)/550 = (CDA 1/2 r V2)V / 550 = (CDA 1/2 rV3)/ 550

Wherein

D = Drag Force

CD = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape

V = Velocity

q = Dynamic Pressure in the Test Section

A = Frontal Area of Vehicle

r = Mass Density of Air


Aerodynamic Drag:

CD: Coefficient of Drag

Invariant with velocity unless there is Reynolds Number sensitivity. The lower the CD the more efficient the shape is to the air.
With a reference frontal area of 21 ft2, a production car will have a CD around the 0.340 range


CDA: Coefficient of Drag Area

Coefficient of Drag x Area: CD x A

Reynolds Number: the ratio of inertial forces (vsρ) to viscous forces (μ/L) and consequently it quantifies the relative importance of these two types of forces for given flow conditions.

Dynamic Pressure: (PSF) A2 measures the test section speed in q which is the dynamic pressure.

q = r V2

Flow Rate: (ft3/minute)

CFM = Area (ft2) x Speed (ft/min)

Source: APPENDIX
__________________
'62 356S Notchback Hotrod
'64 VW Microbus 21 Deluxe
'67 911S Das Geburtstagsgeschenk
'68 911T Targa Sporto
'68 Mercedes 280 SL
'62 BMW 700 Sport
'63 BMW 700 Cabriolet
'72 BMW 3.0CSL
'72 BMW 3.0CSA
'70 914/6 GT

Last edited by csl177; 12-26-2011 at 09:40 PM. Reason: added source
Reply With Quote
  #8  
Old 12-27-2011, 02:02 AM
Cyco's Avatar
Cyco Cyco is offline
Enthusiast
 
Join Date: Sep 2004
Posts: 3,560
Perth, Australia
Send a message via MSN to Cyco
Quote:
Originally Posted by Big time View Post
Please elaborate.

I don't understand how flares can provide LESS change in cross section area. If you get a narrow body and wide flares the difference in area would be larger than a wide body which has more or less a constant area.
For a closed cockpit, i.e. Sedan/Coupe type car if the flares taper in at the front as the windscreen slopes up, and taper out at the back as the rear window tapers down then the cross section or the car has the potential to remain constant.

If, however, you have an open cockpit car eg Lotus 7, Sprite, etc running no windscreen, or only a tiny air deflector then the cockpit has no additional cross sectional area and you would be generally better off going for the wider body.

General rules of thumb only, you must measure to make sure! That is why I quoted Eggnog.
__________________
Chief of Secret Police and CFO - Brotherhood of Jelly
No Mr. Craig, I expect you to die! On the inside. Of heartbreak. You emo bitch
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Honda CR-V (RE) 2006-2011 dracu777 Matt's Hi-Res Hide-Out 30 01-28-2010 08:13 AM



All times are GMT -7. The time now is 12:15 PM.

 

1998 - 2019 Ultimatecarpage.com