Wind Tunnel testing ????

I pull a fw and a couple of years ago I made a small air deflector to attach to my truck. Not a big wing like I have seen on some pu cabs. I also made deflectors on the sides. It has made a big difference (9-10%) on my gas mileage. Usually I take the deflector off after a camping trip, but I left it on this time. The other day I had to take some yard debris to the dump and like usual
there were some leaves still in the bed. As I drove home I noticed that I had somewhat of a tornado of leaves in the back. Normally the leaves would blow around and then go out. These leaves stayed with the truck for some time. After reading some of the posts and links here, I'm thinking there may be some kind of a low pressure created that I think would be a good thing at the front of a towed vehicle.

Wind tunnel testing is very expensive and putting the data derived into a redesigned body even more so.

So, does anyone believe that and industry that doesn't even put reliable tires on their product would make such an investment for the benefit of their customers?

Dakzuki,

You are correct...it is more then just a pretty face. Visited
the Carefree site... my version is called the Travel'R , and
that teardrop cover houses the motor head, tractioner, and
attaches to the roller bar assembly. Upon review of the technical
diagrams I will defer any repair work to the appropriate
personnel.

Charles

cdlaine wrote:
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

Isn't that a Carefree electric awning? If so, the electric motors are under those end caps.

double post.

Matt_Colie wrote:
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.

Almost true but not quite.

The Vixen in the mid 1980's was also designed using wind tunnel tests. It was smooth all over and underneath. The rear wheels had panels that covered the opening. My 21' gas unit got 20 mpg and would almost coast forever!

Aero is just a mess on trailers. They have things sticking out everywhere. Ladders, AC, vents, awnings, non flush windows, moldings; you name it; they are an absolute mess.

Then there is the flat back that tries to suck the trailer back from where it came from.

Just to give some an idea of how much of a mess these trailers really are:
I used to work on airplanes. One owner wanted a faster airplane. We took all the button head rivets off and installed flush mount rivets. About a 14 MPH gain just by installing flush mount rivets. :E

This is on a very aero clean airplane. Now go out and look at your trailer. See the problem here?

Airstream comes the closest but even they are miles away.

Like I said in another thread. We can design a very clean aero trailer but nobody would want to buy it or live in it.

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.

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

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.