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Open Roads Forum  >  General RVing Issues

 > Wind Tunnel testing ????

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Posted: 09/28/13 04:38pm Link  |  Quote  |  Print  |  Notify Moderator

Chris Bryant wrote:

The trouble with a Motorhome and aerodynamics is only partially due to being a big box- the classic Airstream, GMC, and Revcom designs were capable of being very aerodynamic, and had plenty of room, but as soon as you stick an awning on the side, an air conditioner on the roof, a couple of Maxxair covers, an OTA and satellite antennas, all bets are off.


So true...so true...





mileshuff

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Posted: 09/28/13 04:41pm Link  |  Quote  |  Print  |  Notify Moderator

Highway 4x4 wrote:

If you want better MPG, just keep it light and slow down. Or, buy an Airstream.


Wind drag has far more effect on mpg than weight. My new rounded front 5'er weighs 4000lbs more than my old flat front TT. I'm averaging better mpg towing the 5'er.


2014 Winnebago 26FWRKS 5th Wheel
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cdlaine

Desert Southwest

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Posted: 09/28/13 04:52pm Link  |  Quote  |  Print  |  Notify Moderator

Chris,

My add-on appendage manufacturer's have made some attempt
at aerodynamics... 5ver builder could do better on the rear.

Charles



* This post was edited 09/28/13 06:22pm by an administrator/moderator *


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deleted-2

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Posted: 09/28/13 05:00pm Link  |  Quote  |  Print  |  Notify Moderator

Charles,
Whats that teardrop looking deal on the awning there?
(nice looking fiver by the way)

cdlaine

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Posted: 09/28/13 05:07pm Link  |  Quote  |  Print  |  Notify Moderator

Jim,

Not sure..but think it is a cosmetic end cap cover for the
awning roll-up bar. Pretty sure it articulates at the final
close - up.

Thanks on the 5ver...they build a nice upper mid-level
rig... the usual minor issues, Shorter (34) so even though
heavier (for it's category) allowed us to pull with the
3/4 ton in my sig.

Charles

pasusan

PA

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Posted: 09/28/13 05:16pm Link  |  Quote  |  Print  |  Notify Moderator

cdlaine wrote:

Does anybody know if any in the RV industry are
using wind tunnel test results in manufacturing
build specifications ?Charles


The builders of my RV did.

"Aerodynamics
As one of Europe's most popular travel trailers, Award came to this continent with a proven shape which provides ease of towing with their aerodynamics proven in England in wind tunnel tests. Since its introduction our product has gone through many refinements which to this day make it one of the most towable travel trailers in North America."




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rhagfo

Portland, OR

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Posted: 09/28/13 05:50pm Link  |  Quote  |  Print  |  Notify Moderator

cdlaine wrote:

Does anybody know if any in the RV industry are
using wind tunnel test results in manufacturing
build specifications ?

I was watching MotorWeek and they showed /
demonstrated the effect of rear end drag
created by a what was a "boxed" rear end.
(the "smoke" broke up immediately after
passing the rear of the vehicle ). Apparently,
the smoother the transition post vehicle the
less drag...modifications included "smoothing"
under the vehicle. I don't understand all the
engineering/aerodynamics but does seem plausible
to apply testing to the RV industry. My review
of the European RV market seems to indicate
they are paying attention.

So, why is this important ? Average cost of gal.
of gas between $3.20 - $3.60 (diesel more)... and,
the experts "predicting" only going higher. Might be
time to give a little more then lip service to
RV aerodynamics.

What say the congregation ?

Interestingly, the wind tunnel effects have been applied
to just about any type watercraft, or aircraft...just haven't
seen the RV in the discussion.

Charles


Well the Europeans worry a little more about the cost of fuel, daughter lives in Ireland, currently gas is about euro 1.59 and diesel 1.49 a Liter. That is euro 6.16 for a gallon of gas, and euro 5.77 a gallon for diesel.
Carry that just a bit further, the gas is $8.33 a gallon US, and diesel is $7.80 f0r Diesel.


Russ & Paula
The Beagles Hedwig and Precious.
Portland, OR.
2001 Dodge 2500 4X4, 5.9 Cummins 5 speed, 3.55 gears, Pacbrake PRXB, DS Power Puck,Bilstien 5100's, 270,000 miles.
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tatest

Oklahoma Green Country

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Posted: 09/28/13 08:42pm Link  |  Quote  |  Print  |  Notify Moderator

Wind tunnel testing is cost effective for fine tuning the CD, especially where CAFE penalties are at stake and MPG on the sticker helps make sales. RVs are exempt, there are not even any test standards.

As happened with cars and trucks, the first big gains can come from reducing frontal area (get rid of basements, high ceilings, roof-top add-ons) and you don't need expensive wind tunnel time to measure results, the answers can come from coast-down tests and towing with a Tapely drag meter. A few manufacturers do measure drag vs speed with full scale RVs, both towables and motorhomes.

Wind tunnel comes in when you have the big stuff like size and shape sorted out, and you need a close look at air flow to take care of things like blending in mirrors, door handles, window to body transitios, hiding wiper blades from air flow, etc.

Basic shapes can be developed using small scale models rather than taking full size vehicles to the wind tunnel, lift and drag on bare models scale pretty well.

We've had a few rounds of trying to market sleeker RVs, and some of the B manufacturers have done pretty well with aerodynamics, making smoother transitions on basic shapes, blending in some of the high drag add-ons we insist on having. I think they are more successful in the market with the space compromises because B buyers have already decided where they want to be on size vs space.

C's could get better on the new front-drive, low-floor platforms becoming available, although we'll probably see Anmerican size motorhomes on the platform, the lower and narrower Euro-size will have to carefully test the market.

We've also always had a fewer lower profile, more smoothly shaped TT lines, but buyer preference remains with the cheaper to build square boxes that maximize usable space inside, and 8-wide, full height TT still sell better than the few 7-wide low profile models available. People want more headroom, more ground clearance, more space.


Tom Test
Itasca Spirit 29B
2001 Ranger Edge


Matt_Colie

Southeast Michigan

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Posted: 09/29/13 09:12am Link  |  Quote  |  Print  |  Notify Moderator

Wind tunnel testing (I have done some) is extremely expensive and time consuming. The last RV designed in a wind tunnel in the USA was done in 1972 for the GMC motor homes produced from 1973 to '78. Even those have been compromised by the later additions of bumpers, A/C, Pods and ladders. The testing models are at the RV Hall of Fame in Elkhart.

I can't believe that that any other manufacturer would expend the cost and time for such a program.

Matt


Matt & Mary Colie
A sailor, his bride and their black dog going to see some dry places that have Geocaches in a coach made the year we married.


Popsie

Livingston, TX, USA

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Posted: 09/29/13 11:13am Link  |  Quote  |  Print  |  Notify Moderator

Computational Fluid Dynamics is coming into its own as a substitute for wind tunnel testing.

Someday soon we may see improvements in RV drag reduction and fuel efficiency.

One aspect of studying drag for RVs are the differences between new-from-the-factory and add-ons and towed-behinds which can vary too much to be modeled cost effectively.

IMHO, adding a full belly pan and reducing riding hight are the easiest ways to reduce RV aerodynamic drag.

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