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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 07-15-2017, 03:55 PM   #1 (permalink)
Master EcoModder
 
Join Date: Sep 2012
Location: Motor City
Posts: 272
Thanks: 0
Thanked 212 Times in 131 Posts
RV / Square box leading edge interesting stuff...

Stumbled on two interesting tidbits relative to leading edges on square boxes, particularly RVs and box trucks.

First is the first attached image. Just wrapped up a 2 week RV trip. Saw a few late model Jayco Class C motorhomes on our trip. Didn't take picture myself (should have) but googled a random image and attached it. Google says a Jayco Redhawk or Greyhawk has the feature. It's the leading edge/face treatment of the box near the cab doors. The rounded bubble is only part of the face piece. There's a"normal" square edge beneath it. I can't say that it is an aerodynamic device, but it obvious to me it would help. Maybe it was done to improve the wind noise or something.

Second is a document I found searching for some information on frontal area tow ratings from the manufacturers (yes, some do spec frontal area in addition to weight for tow ratings). It's Ford service bulletin about the frontal area and weight ratings for the 2017 Ford cutaway van.

https://www.fleet.ford.com/truckbbas...ml/Q-246R5.pdf

Note that it specs a 2.4" leading edge radius for box type trucks over a certain frontal area. We know 4% of the width is a minimum, that'd be slightly more than 2.4", but very interesting to see something like this directly from a manufacturer. I suspect there's no engineering behind the number (too bad). I'd guess 2.4" is probably what someone like U-Haul uses on their boxes, and Ford grabbed that as a working minimum. U-Haul does claim aerodynamic leading edges on the advertising of some of their trucks, so the story seems to fit.

There's also some ridiculous 1700mm spec for the stripped chassis. But this too appears to be a number grabbed from a manufacturer. The only RV built on the stripped chassis right now is the Thor Axis/Vegas. It's been around a couple years now. Note its shape below...

So maybe the Jayco devices help them meet the new Ford restrictions? I've only seen it on a Jayco, so far.

Attached Thumbnails
Click image for larger version

Name:	2017-Jayco-29XK-Redhawk-Class-C-motorhome-10431P-10053[1].jpg
Views:	337
Size:	97.5 KB
ID:	22191   Click image for larger version

Name:	2016_ThorMotorCoach_Axis[1].jpg
Views:	667
Size:	67.8 KB
ID:	22192  

Last edited by ennored; 07-15-2017 at 09:41 PM..
  Reply With Quote
The Following 4 Users Say Thank You to ennored For This Useful Post:
aerohead (07-22-2017), BamZipPow (07-23-2017), gone-ot (07-15-2017), KamperBob (07-16-2017)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-16-2017, 06:29 AM   #2 (permalink)
Banned
 
Join Date: Oct 2009
Location: Fort Worth, Texas
Posts: 2,442

2004 CTD - '04 DODGE RAM 2500 SLT
Team Cummins
90 day: 19.36 mpg (US)
Thanks: 1,422
Thanked 737 Times in 557 Posts
Frontal area as context for towing recommendations is older than I remember, and that's fifty years ago.

Degree of radius of vehicle edges is 1920s, IIRC

Entry aero is nice. But means little without trailing.

Sidewall edge radius is what distinguishes an aero RV from one non-aero.
  Reply With Quote
The Following 2 Users Say Thank You to slowmover For This Useful Post:
aerohead (07-22-2017), BamZipPow (07-23-2017)
Old 07-16-2017, 07:57 AM   #3 (permalink)
Recreation Engineer
 
KamperBob's Avatar
 
Join Date: Dec 2009
Location: Somewhere USA
Posts: 525

Black Stallion - '02 Toyota Tundra 4WD xCab

Half Pint - '06 Yamaha XT225
Thanks: 333
Thanked 138 Times in 103 Posts
I vaguely recall some Ford vehicles specified frontal area in the tow rating. Ironic as it was on a forum for molded fiberglass "egg" campers and a Ford lover dinged the spec for not appling to a Scamp with such generous edge radii. Cd missing, yes, and CdA would be better but depending on the tug, which sets up the flow field that trailers follow, it still falls short of the whole picture. My point is complexity of aero. Many (most?) lay folks probably don't understand or care so maybe "why bother" is the conclusion auto manufacturers came to long ago. (shrug)

As for the Axis, it's side profile may help keep bugs off the windscreen and rooftop A/C unit. My GF has a class A (older, boxier) and solar gain while traveling can be a problem. That Axis better have one heckuva dash A/C system and/or excellent glass treatment to reflect the heat rays.

My 2c
__________________
Recreation Engineer
  Reply With Quote
The Following 2 Users Say Thank You to KamperBob For This Useful Post:
aerohead (07-22-2017), BamZipPow (07-23-2017)
Old 07-16-2017, 11:45 AM   #4 (permalink)
Master EcoModder
 
Join Date: Feb 2014
Location: Missoula, MT
Posts: 2,652

Dark Egg - '12 VW Touraeg
Thanks: 300
Thanked 1,176 Times in 806 Posts
http://ecomodder.com/forum/member-he...117-154543.jpg
It makes me feel better about trying this on my Hi-Lo. That edge really stuck out into the wind being an 8' wide box. It only cost about $20 to add as well and has held up now 3 years although the tape could use a few new pieces.
  Reply With Quote
The Following 4 Users Say Thank You to Hersbird For This Useful Post:
aerohead (07-22-2017), BamZipPow (07-23-2017), freebeard (07-17-2017), skyking (07-16-2017)
Old 07-17-2017, 02:59 PM   #5 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,561
Thanks: 7,736
Thanked 8,554 Times in 7,041 Posts
Quote:
Originally Posted by slowmover
Sidewall edge radius is what distinguishes an aero RV from one non-aero.
Also one that will not rot out since the edge won't leak.

  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (07-22-2017)
Old 07-22-2017, 12:10 PM   #6 (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
leading edge

Quote:
Originally Posted by ennored View Post
Stumbled on two interesting tidbits relative to leading edges on square boxes, particularly RVs and box trucks.

First is the first attached image. Just wrapped up a 2 week RV trip. Saw a few late model Jayco Class C motorhomes on our trip. Didn't take picture myself (should have) but googled a random image and attached it. Google says a Jayco Redhawk or Greyhawk has the feature. It's the leading edge/face treatment of the box near the cab doors. The rounded bubble is only part of the face piece. There's a"normal" square edge beneath it. I can't say that it is an aerodynamic device, but it obvious to me it would help. Maybe it was done to improve the wind noise or something.

Second is a document I found searching for some information on frontal area tow ratings from the manufacturers (yes, some do spec frontal area in addition to weight for tow ratings). It's Ford service bulletin about the frontal area and weight ratings for the 2017 Ford cutaway van.

https://www.fleet.ford.com/truckbbas...ml/Q-246R5.pdf

Note that it specs a 2.4" leading edge radius for box type trucks over a certain frontal area. We know 4% of the width is a minimum, that'd be slightly more than 2.4", but very interesting to see something like this directly from a manufacturer. I suspect there's no engineering behind the number (too bad). I'd guess 2.4" is probably what someone like U-Haul uses on their boxes, and Ford grabbed that as a working minimum. U-Haul does claim aerodynamic leading edges on the advertising of some of their trucks, so the story seems to fit.

There's also some ridiculous 1700mm spec for the stripped chassis. But this too appears to be a number grabbed from a manufacturer. The only RV built on the stripped chassis right now is the Thor Axis/Vegas. It's been around a couple years now. Note its shape below...

So maybe the Jayco devices help them meet the new Ford restrictions? I've only seen it on a Jayco, so far.
That technology was patented by Dr. Paul MacCready of Aerovironment.
Access for the door swing may have limited the useful radius.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 07-22-2017, 05:05 PM   #7 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,561
Thanks: 7,736
Thanked 8,554 Times in 7,041 Posts
Were it I, the inner face would have a radius defined by the door-swing +1/2". Basically a quarter-round and a reverse curve.

Has anyone added blisters to the door skins yet?
  Reply With Quote
Old 07-23-2017, 11:20 AM   #8 (permalink)
Master EcoModder
 
Join Date: Feb 2014
Location: Missoula, MT
Posts: 2,652

Dark Egg - '12 VW Touraeg
Thanks: 300
Thanked 1,176 Times in 806 Posts
I think just making the box better is the answer.
  Reply With Quote
Old 07-25-2017, 10:57 AM   #9 (permalink)
EcoModding Lurker
 
grins2go_brett's Avatar
 
Join Date: Jul 2011
Location: Tempe, AZ
Posts: 26
Thanks: 2
Thanked 9 Times in 6 Posts
Quote:
Originally Posted by Hersbird View Post
It makes me feel better about trying this on my Hi-Lo. That edge really stuck out into the wind being an 8' wide box. It only cost about $20 to add as well and has held up now 3 years although the tape could use a few new pieces.
I'm curious...did you notice any difference in fuel mileage? I know it might be hard to tell unless you took the same road on different trips with the trailer.
  Reply With Quote
Old 07-26-2017, 06:11 AM   #10 (permalink)
Banned
 
Join Date: Oct 2009
Location: Fort Worth, Texas
Posts: 2,442

2004 CTD - '04 DODGE RAM 2500 SLT
Team Cummins
90 day: 19.36 mpg (US)
Thanks: 1,422
Thanked 737 Times in 557 Posts
Quote:
Originally Posted by Hersbird View Post
I think just making the box better is the answer.
With Orbywans boat tail, you'd be right.

Except it's still a Moho. A distinctly space and weight inefficient RV. Fuel burn will still be higher than an aero trailer with more living space and well chosen tow vehicle.

Having to tow another vehicle behind it is the "answer" to its shortcoming for local touring or grocery runs.

"Efficiency" with an RV starts with the premise that re-supply (of every kind; and water, electric & sewer are included) is the denominator: How many nights in one location for how many people? That's where to start.

Thus, fresh water supply is king.

A Moho gives this up in favor of having been designed as a commercial vehicle with a service life X10 what the owner of the RV will utilize. A penalty that can't be overcome.

All this is before price comparison.
.

  Reply With Quote
Reply  Post New Thread


Thread Tools




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