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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 12-26-2009, 11:40 PM   #1 (permalink)
Master EcoModder
 
puddleglum's Avatar
 
Join Date: Oct 2009
Location: Red Deer, AB
Posts: 421

Rondo - '07 Kia Rondo EX
Last 3: 20.47 mpg (US)

Tinkertoy2 - '00 Toyota Echo base
Team Toyota
Last 3: 46.03 mpg (US)
Thanks: 39
Thanked 95 Times in 69 Posts
What is the effect of crosswinds?

I've been reading a lot on this site about determining Cd by coastdowns and the importance of "no wind" to be accurate. Also, there is lots of discussion on reducing frontal drag. I haven't been able to find much on how crosswinds effect drag and fuel economy. My experience is that crosswind seems to drop my mileage just as much as a headwind. I found one article relating to soapbox derby cars that said that a crosswind changes the effective frontal area as it moves the angle of the headwind around to the side of the car and changes the way the air flows over the body. (sorry if I'm not expaining this very well) If I understand the article correctly, a 25mph crosswind could double the effective frontal area of my car at 60mph. I would like to understand this better and would appreciate if some of you experts could explain this better or direct me to the info if this has been discussed already. The wind blows a lot here and I'm wondering if crosswind should be taken into account when thinking about reducing aero drag.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 12-27-2009, 12:05 AM   #2 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,761

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,585
Thanked 3,548 Times in 2,215 Posts
Aero in yaw seems to be my province for some reason.

http://ecomodder.com/forum/showthrea...rx-7115-3.html
__________________



Last edited by Frank Lee; 12-27-2009 at 01:52 AM..
  Reply With Quote
Old 12-27-2009, 09:30 AM   #3 (permalink)
Left Lane Ecodriver
 
RobertSmalls's Avatar
 
Join Date: Aug 2008
Location: Buffalo, NY, USA
Posts: 2,257

Prius C - '12 Toyota Prius C
Thanks: 79
Thanked 284 Times in 197 Posts
Stand in front of your car and look at how aerodynamic it is, and note the frontal area. Now step to the side so you're looking at it from a 20 angle, like a crosswind does. Its frontal area is much larger, and chances are the side of your roof is now a large part of the trailing end of your car.

Don't judge a car solely by its CdA with 0 yaw, look also at its crosswind sensitivity. Rounded sides are nice to have, as is a short overall length.

As an exercise, picture a tractor trailer, bus, or Club Cab longbed pickup in a crosswind. Longer vehicles suffer the worst in crosswinds.
  Reply With Quote
Old 12-27-2009, 01:32 PM   #4 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by RobertSmalls View Post
...Don't judge a car solely by its CdA with 0 yaw, look also at its crosswind sensitivity. Rounded sides are nice to have, as is a short overall length....
I'm not much of a sailor but...

Several friends that are avid sailors pointed out that, with the right shape, a good side-wind can actually make the car more slippery due to the sail effect.

A good airfoil shape also has this tendency up to the point of stall. So, in this case making the tail longer actually helps....

And again, the above only works for low angles of yaw. These designs are always a compromise.

If the wind is coming at you at 90, then you have more losses due to the larger surface area.

Jim.

Last edited by 3-Wheeler; 12-27-2009 at 05:50 PM..
  Reply With Quote
Old 12-27-2009, 04:48 PM   #5 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,696

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

Stealth RV - '91 Chevy Sprint Base
Thanks: 88
Thanked 407 Times in 285 Posts
Sail cars, like ice boats, really take off when hit with a good side gust. Getting the angles right takes you to what is in effect a negative frontal area, by sneaking the usual low-pressure zones up the side and over part of the nose. With cars, it is usually more a matter of minimizing negative effects, and maintaining stability. It is a big topic, one best kept in mind as a frequent complication while learning the other basics.
  Reply With Quote
Old 12-27-2009, 05:53 PM   #6 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by Bicycle Bob View Post
Sail cars, like ice boats, really take off when hit with a good side gust. Getting the angles right takes you to what is in effect a negative frontal area, by sneaking the usual low-pressure zones up the side and over part of the nose. With cars, it is usually more a matter of minimizing negative effects, and maintaining stability. It is a big topic, one best kept in mind as a frequent complication while learning the other basics.
Hi Bob,

So from the above, can a boat tail help or hurt in a car application, regarding the change in CdA and side winds?

Certainly, MetroMPG's big gains in efficiency is nothing to sneeze at after his boat tail was added. And I'm sure he tested on calm days.

Thanks, Jim.
  Reply With Quote
Old 12-27-2009, 06:24 PM   #7 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,696

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

Stealth RV - '91 Chevy Sprint Base
Thanks: 88
Thanked 407 Times in 285 Posts
Yes, a boat tail can help or hurt. YMMV.
Test Team Test! Go Coast Coast!
  Reply With Quote
Old 12-27-2009, 07:27 PM   #8 (permalink)
Master EcoModder
 
Join Date: Jan 2008
Location: Victoria , Australia.
Posts: 499
Thanks: 20
Thanked 46 Times in 33 Posts
A good question Puddelgum and one which I am sure is not considered much if at all by many discussing fuel economy and aerodynamics.

Cross winds have two effects in the main.
The first being to expose more of the vehicle surface area to the wind , and the second being to change the (ideally) smooth flowing air into a torrent of turbulence on the side opposite the side being attacked by the cross winds.
How much this second factor damages aero varies a huge amount and I am not sure there are any numbers out there to help even get into the ball park.

Pete.
  Reply With Quote
Old 12-27-2009, 11:03 PM   #9 (permalink)
Banned
 
Join Date: Dec 2009
Location: NY
Posts: 865
Thanks: 29
Thanked 111 Times in 83 Posts
Quote:
Originally Posted by Bicycle Bob View Post
Sail cars, like ice boats, really take off when hit with a good side gust. Getting the angles right takes you to what is in effect a negative frontal area, by sneaking the usual low-pressure zones up the side and over part of the nose. With cars, it is usually more a matter of minimizing negative effects, and maintaining stability. It is a big topic, one best kept in mind as a frequent complication while learning the other basics.
Anyone who has ever ridden a racing bike (or even done hiking) knows this: if the wind is at your back, it's a gift. If you are headed into the wind or blown sideways by it, it's a drag... literally.

Now, maybe if our cars had adjustable sails...
  Reply With Quote
Old 12-27-2009, 11:36 PM   #10 (permalink)
Master EcoModder
 
puddleglum's Avatar
 
Join Date: Oct 2009
Location: Red Deer, AB
Posts: 421

Rondo - '07 Kia Rondo EX
Last 3: 20.47 mpg (US)

Tinkertoy2 - '00 Toyota Echo base
Team Toyota
Last 3: 46.03 mpg (US)
Thanks: 39
Thanked 95 Times in 69 Posts
Thank you for all your replies. I'm guessing that mods like removing roof rails will be of much more benefit in a crosswind situation than in calm air. What about belly pans vs air dam and side skirts. I know they both are proven to work but would a belly pan be affected less by crosswind than sideskirts?

  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Testing: WAI's effect on engine warm up Daox EcoModding Central 24 01-13-2011 10:41 PM
SAE Paper 800087 The Effect of Inflation Pressure on Bias, Bias-Belted, and Radial CapriRacer Hypermiling / EcoDriver's Ed 18 07-06-2008 07:36 PM
Tips: corridor effect question joycebgood Hypermiling / EcoDriver's Ed 13 05-29-2008 04:15 PM
Smooth Road Effect newtonsfirstlaw General Efficiency Discussion 7 01-16-2008 06:37 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com