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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 05-18-2011, 07:19 PM   #161 (permalink)
EcoModding Apprentice
 
Join Date: Jul 2010
Location: Tucson, AZ
Posts: 245
Thanks: 111
Thanked 163 Times in 63 Posts
Thanks for info aerohead. My RV, and especially Randy's RV, I think will benefit from aerodynamic studies on semis, since the 'taller than wider' shapes are similar. My RV is also 8 feet wide, so the ideal length for a boat tail 'template' design would be about 14.5 feet long, according to the width X 1.8 equation. Looking at the curve of the template, I'm surprised it's not longer than that. I think for practicality's sake, though, this one will have to be 6 to 8 feet long.

The info from the link to the NASA/Dryden project that wyatt posted in his email above, notes that leaving off the last four feet or so of the pointed tail in their van project only resulted in a net gain of 0.004 drag, so I'm hoping the shorter length won't be too detrimental.

Doing a full belly pan on my RV is going to be a pain in the neck, but if the truncated boat tail yields sufficient gains I'm game.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 05-20-2011, 04:33 PM   #162 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
Nasa

Quote:
Originally Posted by orbywan View Post
Thanks for info aerohead. My RV, and especially Randy's RV, I think will benefit from aerodynamic studies on semis, since the 'taller than wider' shapes are similar. My RV is also 8 feet wide, so the ideal length for a boat tail 'template' design would be about 14.5 feet long, according to the width X 1.8 equation. Looking at the curve of the template, I'm surprised it's not longer than that. I think for practicality's sake, though, this one will have to be 6 to 8 feet long.

The info from the link to the NASA/Dryden project that wyatt posted in his email above, notes that leaving off the last four feet or so of the pointed tail in their van project only resulted in a net gain of 0.004 drag, so I'm hoping the shorter length won't be too detrimental.

Doing a full belly pan on my RV is going to be a pain in the neck, but if the truncated boat tail yields sufficient gains I'm game.
orbywan,that's correct.The last bit of boat-tail creates a virtual tail( phantom tail )when chopped off.Air skipping over the small wake as if it were a solid cone.
For the 'Template',when doing a car:
* @ 100% = Cd 0.13 ( with no wheel fairings )
* @ 90% = Cd 0.13
* @ 80% = Cd 0.133
* @ 70% = Cd 0.14
So you can see that,and as others have published,there is little benefit doing the entire tail.
I chose 75 % for the Prius tadpole.
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
orbywan (05-20-2011)
Old 05-20-2011, 05:15 PM   #163 (permalink)
EcoModding Apprentice
 
Join Date: Jul 2010
Location: Tucson, AZ
Posts: 245
Thanks: 111
Thanked 163 Times in 63 Posts
Thumbs up

Thanks for the info. A phantom tail, that's a good way to put it. So I guess the curved surfaces at the rear help the air 'make the corner(s)' at the rear and meet up, theoretically, at the point where the four planes would converge if the tail were complete?

If this works I may try the belly pan if I can find the right materials. Do you have any idea how to 'treat' the dually rear wheels? There's got to be some crazy things going on there as the air goes over, around and through the tires.
Should there be some kind of diverter in front of the tire sets to help direct the airflow? How about behind the tire sets?

What kind of improvements did you realize with the Prius 'tadpole' tail?
  Reply With Quote
Old 05-20-2011, 06:50 PM   #164 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
corners/duals/Prius

Quote:
Originally Posted by orbywan View Post
Thanks for the info. A phantom tail, that's a good way to put it. So I guess the curved surfaces at the rear help the air 'make the corner(s)' at the rear and meet up, theoretically, at the point where the four planes would converge if the tail were complete?

If this works I may try the belly pan if I can find the right materials. Do you have any idea how to 'treat' the dually rear wheels? There's got to be some crazy things going on there as the air goes over, around and through the tires.
Should there be some kind of diverter in front of the tire sets to help direct the airflow? How about behind the tire sets?

What kind of improvements did you realize with the Prius 'tadpole' tail?
orbywan,with respect to the tail,the air will separate right at the chop,but the turbulent wake will take the form of the continuation of the 'Template' outline.Air will follow over that turbulence and meet.
--------------------------------------------------------------------------
With respect to the duals,the only 'solution' for 18-wheelers with open under-carriage is an invention by the fella at Nosecone Corp.
He created a fairing which forces all the underside air out,along a semicircular path to the edge of the duals,preventing any air to collide with them and attempt to flow through.
The recent skirts you see today on 18-wheelers will do the same.Skirting the duals themselves cut drag about 6% more.
-------------------------------------------------------------------------- As far as the Prius goes,it remains an unknown quantity until tested.
The aerodynamic science surrounding its design is very mature and I have an exceedingly high confidence in its potential.
-------------------------------------------------------------------------- At 1,100 pounds 'overweight' my T-100 returned 5-1/2 mpg better than stock,pulling the un-finished Viking boat-tail trailer in December 2009,in arctic air,and 15-mph crosswinds.
-------------------------------------------------------------------------- My first 2-wheel trailer,with no belly,and no gap-fillers caused only a 2-mpg penalty for my CRX at 1,175 pounds over curb weight on a round trip from Denton to Los Angeles.
-------------------------------------------------------------------------- My first 1-wheel trailer returned 48 mpg ave. behind the CRX,over 4-states,over mountain passes as high as 10,600-feet,and speeds as high as 80 mph,all with 2 vacuum lines completely burned through on the carburetor.A condition I was unaware of until returning home.
--------------------------------------------------------------------------
I feel pretty certain that the Prius is going to pick up 7.5 mpg.
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
orbywan (05-20-2011)
Old 05-20-2011, 07:53 PM   #165 (permalink)
EcoModding Apprentice
 
Join Date: Jul 2010
Location: Tucson, AZ
Posts: 245
Thanks: 111
Thanked 163 Times in 63 Posts
More good information, thanks aerohead. I kept looking at the side deflectors on the semi's on the road and wondering exactly what the goal was there. Duh.
The undercarriage of my RV is obviously different that a semi's trailer, but do you think I should try the same approach, long diverter pushing the air to the outside of the each wheel set? That would be assuming no belly pan.

With a belly pan, would the general design be the same do you think?
  Reply With Quote
Old 05-21-2011, 01:12 PM   #166 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
sides/belly

Quote:
Originally Posted by orbywan View Post
More good information, thanks aerohead. I kept looking at the side deflectors on the semi's on the road and wondering exactly what the goal was there. Duh.
The undercarriage of my RV is obviously different that a semi's trailer, but do you think I should try the same approach, long diverter pushing the air to the outside of the each wheel set? That would be assuming no belly pan.

With a belly pan, would the general design be the same do you think?
There are two schools with respect to sides:
(1) make the flanks of the vehicle flush with the outside of the wheels and put a smooth wheel cover on.Allow some ventilation of the cover to help brake cooling on mountain downgrades.
(2) inset the wheels a bit,allowing a full skirt to be added.Provide shark gill exits to blend brake cooling air along the sides of the rig.
------------------------------------------------------------------------
The belly would be done as any.Renault demonstrated a 17% drag reduction with a full pan on VIRAGE.
Fachsenfeld got an OMNIBUS inter-city bus into the low Cd 2s with a pan.Under Cd 0.2 with inflated tail.
------------------------------------------------------------------------- On low drag vehicles the wheel drag can be half the drag.It's worth going after.
See what you've got and maybe take the easiest path.
--------------------------------------------------------------------------
PS,I looked up the Omnibus in Hucho's book.This is actually the first K-Tail,the K coming from Koenig in Fachsenfelds name.He beat Kamm to the patent office.Although Carl Breer had done a 'chopped tail' in 1934 with Airflow.
The bus,with inflated boat-tail had Cd 0.158.

Last edited by aerohead; 08-13-2011 at 04:49 PM.. Reason: added data
  Reply With Quote
Old 08-13-2011, 04:27 PM   #167 (permalink)
Aero Deshi
 
ChazInMT's Avatar
 
Join Date: Jan 2010
Location: Vero Beach, FL
Posts: 1,065

MagMetalCivic - '04 Honda Civic Sedan EX
Last 3: 34.25 mpg (US)
Thanks: 430
Thanked 668 Times in 357 Posts
This is probably one of the most useful and best tools on ecomodder, as long as it remains Un Sticky..I'm gonna bump it when it falls off the top page of aero threads.

Any one think this is a Bad idea, Let me know. I'm sure 99% of you think it's a good one, no reply needed.
  Reply With Quote
Old 08-13-2011, 05:31 PM   #168 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,803

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

Stealth RV - '91 Chevy Sprint Base
Thanks: 91
Thanked 459 Times in 327 Posts
A little knowledge is a dangerous thing, and this template is the least amount of information that can make people feel wise about airflow when they are not. I suspect that this thread does more harm than good.
  Reply With Quote
Old 08-15-2011, 11:25 AM   #169 (permalink)
Master EcoModder
 
Join Date: Feb 2010
Location: Elmira, NY
Posts: 1,781
Thanks: 319
Thanked 355 Times in 297 Posts
No substitute for during your homework starting with fluid mechanics basics then proceeding to aircraft design and automotive applications. Check local college libraries and book venders such as Amazon. The Society of Automotive Engineers list reference books and articles for a price. "Race Car Aerodynamics: Design for Speed" by Joseph Katz covers basics for DIY mechanics and has many references at the end of each chapter. Just remember modern race cars are more concerned about downforce than drag.
  Reply With Quote
Old 08-15-2011, 12:25 PM   #170 (permalink)
T-100 Road Warrior
 
BamZipPow's Avatar
 
Join Date: Apr 2008
Location: The Woodlands, TX
Posts: 1,920

BZP T-100 (2010) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 24 mpg (US)

BZP T-100 (2011) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 23.66 mpg (US)

BZP T-100 (2009) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 19.01 mpg (US)

BZP T-100 (2012) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 25.45 mpg (US)

BZP T-100 (2013) - '98 Toyota T-100 SR5
Last 3: 25.79 mpg (US)

BZP T-100 (2014) - '98 Toyota T-100 SR5
Last 3: 23.18 mpg (US)

BZP T-100 (2015) - '98 Toyota T-100 SR5
Last 3: 23.85 mpg (US)

BZP T-100 (2016) - '98 Toyota T-100 SR5
Last 3: 17.62 mpg (US)

BZP T-100 (2017) - '98 Toyota T-100 SR5
90 day: 20.78 mpg (US)

BZP T-100 (2018) - '98 Toyota T-100 SR5
90 day: 20.19 mpg (US)

BZP T-100 (2019) - '98 Toyota T-100 SR5

BZP T-100 (2020) - '98 Toyota T-100 SR5

2012 Scion iQ - '12 Scion iQ Base
Thanks: 3,479
Thanked 1,395 Times in 968 Posts
Send a message via ICQ to BamZipPow
Wink

Quote:
Originally Posted by Bicycle Bob View Post
A little knowledge is a dangerous thing, and this template is the least amount of information that can make people feel wise about airflow when they are not. I suspect that this thread does more harm than good.
I figure it's a start to git people going in the right direction...and that is a good thing!

__________________
Dark Aero-The world's first aerodynamic single wheel boat tail!

  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Maximum angle for boat tail? abcdpeterson Aerodynamics 80 11-03-2021 12:55 PM
Aerodynamic Streamlining Template Part-B aerohead Aerodynamics 8 05-31-2013 12:23 PM
LED Headlight captainslug DIY / How-to 82 11-15-2011 01:32 AM
Aerodynamic Streamlining Template: Part-A aerohead Aerodynamics 0 07-18-2009 02:37 PM
All items I scanned in the new product showcase dremd The Lounge 0 11-08-2008 04:14 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com