Yet another Air Dam/Spoiler/Airfoil thingy

This is how it looks with the valence mounted. Note the little wave in the middle, this is the distortion in the molding:





* Adjusted image size using width=640

It was meant to be close to the cab and that's how it came out. When you have something that close you really appreciate how much the camper moves around relative the the cab. But it does not hit. The position was a guess, based on bug patterns, rain streams on the windshield, gut feelings:







* Adjusted image size using width=640

It looks pretty good, I do have to raise the camper another couple of inches higher to put it on or the valence will scrape the roof.

Now does it work? I just drove 900 miles from Napa to Anacortes, Wa. All the way up the Sacramento Valley on I5, about 25 knots of north (head) wind. Calmer weather in Oregon and Washington. The wind noise seems to be reduced, in that I can hear the tire noise and engine noise more distinctly. It isn't silent still, but improved. I've made this same trip several times recently, and the fuel mileage was about the same, at least within the range of variation. I've gotten as much as 14.5 for this round trip and as little as 12, this time one way 12.6 which combined with the headwind for the first 200 miles probably about the same.

The aerodynamics are certainly different, opening the window produces a slight breeze from the rear, opening the back window produces almost no wind, just lets in more road noise. If I stick my hand out there is accelerated air coming around the edge of the dam, and very little wind on top of the cab. It produces a faint wind whistle between about 35 and 45 mph, but goes away above that speed.

Now the problems. When I stopped for fuel in Oregon (it isn't any cheaper in Oregon right now than California - what's up with that!!??), I noticed that the slight distortion had become a large cave in. It hadn't hit anything but air and the occasional bug. With the middle caved in, there was a bug spatter pattern emanating in a V from there across the cab roof going aft. I still have a bug pattern underneath the overhang about matching the one I'd marked out prior to the dam, though fewer of them I think. I also had bugs across the camper bulkhead near the top, again like before the dam but not as many. How much of that is due to the failure of the valence to hold it's shape is a good question.



* Adjusted image size using width=640

Driving around locally here the valence is slowly returning to its former shape. I think my next step will be to stiffen the lower edge with something, strip of aluminum or perhaps laid up carbon fiber. I liked the idea of it being plastic to be resiliant from damage and also no damage the truck in a failure, but it clearly is not up to the task as is. Perhaps a Ford branded one would be better.

I'll be doing this trip again in early May and will see if the stiffened edge makes any difference.

I think if doing it again (and I may) I'd try moving it back just behind the cab clearance lights, using the 2WD version. Based on where the bugs hit the overhang this might catch most of the wind which is driving up from the windshield.

This should be cautionary tale for anyone considering such a project. The end result is that it "seems" there might be some decrease in wind noise. I suspect the design and construction of such a device could actually increase the noise. Any sharp edges could result in a whistle sound.

Before undertaking any project like this, consider the physics involved. The air trapped between the camper and roof of the truck forms a dead zone that effectively blocks the flow of air. This is easy to see. Drive through a rainstorm. The nose of the camper and the overhang area will be wet. A few inches behind the roof of the truck to the bed area will be dry. The same can be seen driving through an insect hatch. There will be no bugs in that area.

It looks good. I can see why you would want it behind the marker lights but the gap you need to account for movement of the camper may end up in the same amount of flow as you are having right now between the valence and windshield.

Have you considered combining your new valence with some foam between the camper and rear cab to disturb the flow of air?

JimK-NY wrote:
The air trapped between the camper and roof of the truck forms a dead zone that effectively blocks the flow of air. This is easy to see. Drive through a rainstorm. The nose of the camper and the overhang area will be wet. A few inches behind the roof of the truck to the bed area will be dry. The same can be seen driving through an insect hatch. There will be no bugs in that area.

Maybe on your camper, but provably not true on mine. Bottom of the overhang will be wet and is spattered with bugs. There is a line of bugs on the camper bulkhead and it will be wet in the rain. Opening the rear window resulted in a large wind through the cab. Air flow in the area is much different after installing the dam.

Any universal statements like that have to be treated with skepticism. Campers and trucks come in a wide variety, the spacing between the cab and overhang will differ, the overhang may end in front or behind the windshield depending on crew cab vs short cab, EW vs. NS bed, etc. Not quite an infinite variety but approaching that. Which also makes the design and installation of one problematic, others experience's may not be duplicable on your rig. I'm not suggesting what I did would work for others, but I am contributing to the knowledge pool.

BigfootBill wrote:
It looks good. I can see why you would want it behind the marker lights but the gap you need to account for movement of the camper may end up in the same amount of flow as you are having right now between the valence and windshield.

Have you considered combining your new valence with some foam between the camper and rear cab to disturb the flow of air?

From rain and bug patterns there seems to be a flow bubble at the clearance lights and just behind. I think the windshield deflects flow up, then it bounces off the overhang. So a shorter dam back a bit further might do some good, even though clearance would have to be maintained. I liked the position I have as it allows it to overlap the cab vertically, without hitting - but it leaves a gap. I didn't think that gap would be a problem judging from the stagnation of rain droplets towards the top of the windshield, but clearly there is lots of pressure there, enough to distort the valence.

Another thought is to add a rubber chin on the valence that actually contacts the windshield, closing the gap. It would rub, but that might be OK. I might try that at least as an experiment.

I wonder how a bug deflector on the front of the hood would change the airflow. May be something else worth considering.

HMS Beagle wrote:


Bottom of the overhang will be wet and is spattered with bugs. There is a line of bugs on the camper bulkhead and it will be wet in the rain. Opening the rear window resulted in a large wind through the cab. Air flow in the area is much different after installing the dam.
....

I have always had a boot sealing the space between the rear cab window and the pass through in the front of the camper. Perhaps driving without a boot and leaving one or more of these windows open might break the dead air pocket and allow water and a splatter of bugs to hit the bulkhead of the camper.