44 replies to this topic

[Brewskier]

This is from Kodachromes thread, this is his rig.




That flap that runs from the top of the camper to the front of the windshield... is that to lower wind resistance? I was thinking about this the other day, how the wind will get caught in that gap between the camper and the truck. This seems like a good fix. Can these be bought somewhere and attached, or is it a custom job?

[brp]

He made it. There are some people who have fit non-custom fairings in a custom way. Yakima makes a fairing, but it is not very large. Also, some people do something like this

http://www.rv.net/fo.../print/true.cfm

Whatever you do, you want to accomodate any flex so that the parts don't hit each other when flexed on uneven terrain.

[MarkBC]

I'm interested in something like this, too.

I wonder how much difference it makes in fuel-mileage? Must be lot's of opinion/info out there on camper-farings, as brp's link suggests.

[ski3pin]

Here's a thread that covered some of the wind deflector ideas.

Deflectors

[brp]

I am in the process of making one. I am only going to spend about $50. With gas prices what they are and going on multiple thousand mile trips, should pay for itself with even a small MPG increase. It also keeps the ride quieter. Some people have the problem of moisture getting under the front edge pop-top when driving hwy speed in the rain, I imagine it would cure that, although I have never had that problem.

I'll post up when it is made. I am using mostly schedule 80 PVC conduit for the frame, I don't have the actual fairing yet.

[chnlisle]

I'm interested in something like this, too.

I wonder how much difference it makes in fuel-mileage? Must be lot's of opinion/info out there on camper-farings, as brp's link suggests.

I don't remember anyone giving a definitive answer on fuel savings with the fairing. I too would be interested in a real comparison.

[ski3pin]

I don't remember anyone giving a definitive answer on fuel savings with the fairing. I too would be interested in a real comparison.

A challenge for our scientists? Lets see some numbers. We want to know.

Last month we did a road trip up to Oregon. Drove Interstate 5. Noticed new skirts under the trailers on the big rigs. It looked like it was for wind deflection to increase aerodynamics and increase mileage. We hadn't seen these before.

[Overland Hadley]

Noticed new skirts under the trailers on the big rigs. It looked like it was for wind deflection to increase aerodynamics and increase mileage. We hadn't seen these before.

The rigs with the ''skirts'' have a lot less dirty air behind them. I have first hand knowledge of this because I bike on a road that has semis on it. At one point I read the fuel savings that theses rigs get, it was significant but I have forgot the exact number.

[MarkBC]

When I put my camper on my truck the mileage dropped from 14 to 12mpg. Without any real facts or knowledge my gut feel was that this drop was due to increased air drag rather than the increased weight.
This seems like such a basic/obvious question that it must have been answered before, if not on this site then on some truck or other camper site.

I bet one or more of the more truck-y guys on WTW already know...or have a definite opinion, at least.

[highz]

OK, Ski, here's a bit of underlying theory, which you may remember from physics class. I defer to our engineers and truck-y types for the practical application. Also, this is simplistic - Turbulence caused by the gap between camper and cab must play some role which the following doesn't address.

Aerodynamic drag is a force opposing the direction of motion, but we are really more interested in the power it takes to overcome this force. That power (force times velocity) is
(Thanks to Wikipedia for providing a cut-and paste formula )

rho is the fluid (air) density, A is roughly the cross section of truck and camper impacting the air, v is the speed of the truck relative to the air (not the ground, unless the air is still), and C_d is the drag coefficient. Turbulence probably means C_d becomes a function of speed for your particular rig, but considering that is beyond my pay grade. Turbulence is a hairy problem.

What's important here is not so much the values of the different constants, but the fact that the power needed to overcome this drag goes up as the speed cubed. The biggest effect you can make on fuel consumption is to slow down.

Even so, an air dam makes the ride quieter at high speed, and no doubt cuts down on turbulence, so even if it doesn't have a big effect on gas mileage, it may still be worth the cost of adding one. If the semi skirts improve fuel mileage by reducing turbulence, that's a good sign it could help.