Boat tail on trailer vs. deflector in front: The beginnings of a clean slate project

[jime57]

Interesting project! I was just looking at your cab faring idea. I think you want it the way you have shown it, but I see no reason not to extend it all the way down to truck bed, and outward, as shown, to full width of trailer. Looking at what the long haul trucks have, it is pretty much that way. With the short setback from trailer front to hitch pin, and the rounded front of the trailer, you should not require a lot of clearance. The most likely interference will be at top, when the truck rear wheels hit a dip. That will close the clearance very quickly. You could use a "soft" edge to the faring to avoid damage, then if you see signs of contact, you could simply trim off a bit.

[skyking]

When I turn the rig hard over the side of the trailer can touch the back of the cab when it gets to 92 degrees or so. I'll need to hinge a panel on either side that can swing out of the way in a hard turn and then swing back and latch securely and be gust-proof. Bringing it all the way to the truck bed would be nice, but overcomplicated. I have really heavy duty stake pockets in my metalwork for a support bar, maybe I'll just make a short Lion's mane deflector for the side of the cab and mount it off that.

[jime57]

Originally Posted by skyking

When I turn the rig hard over the side of the trailer can touch the back of the cab when it gets to 92 degrees or so.

That is a lot more angle than I would have guessed you would be striving for, but of course, I don't know your driving/parking conditions. I'm a motorhome guy so don't always understand the 5th wheelers.

I think that if you can achieve a partial completion of the template with roof work and a reasonable length partial boat-tail, you are going to see some worthwhile improvement.

With fuel prices at these levels, there is some healthy interest among the RV set. I'm also looking at smoothing out the top of my Newmar, and potentially adding a boattail of about 2 meters. Hucho has some data which indicates a Cd reduction of about 7.5% for long haul trailers with such a boattail.

A big design issue is going to be staying legal with the lights. There may also be legal issues with the boat-tail itself. I'm from VA and we have annual safety inspections here.

[skyking]

It is very handy to back it around on a very tight circle to get into and out of places. I will have plenty of lights on the folding boat tail, it will end up with brake/tail lights at bumper level, on the end of the boat tail and up high at the roof line. As long as it is lighted properly it should be no problem with the DMV.

[slowmover]

Originally Posted by skyking

I spent a lot of time hanging out under the truck yesterday while I was mounting the Cumaru (Brazilian Teak) running boards. It would be very, very easy for me to do a full belly pan! That running board is the right height, about the same as the frame and cross members.
I could get at least back to the rear differential with one.
If I pan the truck, does that mean I can omit a front air dam, if I get it all brought together smoothly?

Hope you'll continue with these thoughts.

Sure do like that truck bed. The CM brand is popular here in South Texas among oilfield hotshot truck owners, and I've long admired the all-aluminum beds by Alum-Line. Don't often see aero work on this type, but some designs better than others.

Is there a link to a thread elsewhere about the truck rear suspension.

Is that trailer running AL-KO axles? If original they are possibly/likely past due for replacement. A friend recently spec'd heavier axles than stock on his 34' aero aluminum 1990 conventional AVION as the original configuration was no longer available and other brands may not be up to the task. I don't recall if he also went to taller tires/wheels, but he did indicate an slight increase in ride height (the thought of all this being that some other dimensions may change if axles/wheels changed).


DODGE & AVION: great combo.

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[skyking]

I think about it all the time. I am putting a kelderman-like rear single bag at the back spring mount today, Have that all fabbed up waiting for the air bags to come in.
http://www.keldermanairride.com/pdf/...uctions_2_.pdf
Something similar to that with some differences in how the swing arm is captured.
The air ride 5th wheel in the bed is something I dreamed up. It works pretty good so far. You hit a big bump, look in the mirror and watch the 5th wheel travel about 3" soaking that up. I accidentally made it home from the beach with a full glass of water on the counter!
I am constructing my own pin box with an elastomeric bearing in it, and thinking about an air slide feature that will let me bring the trailer in close to a fairing. I'd set a minimum distance that would accommodate the angle I can get driving forward with the wheel hard over. I could pull the pin with air, lock the trailer brakes just like a pup trailer and slide it back for maximum maneuvering.
I figure no more than a foot of travel but that could be huge in the aerodynamic department.

I don't know what brand of torsion axle, probably either al-ko or dexter. They do seem a bit "stiff", not moving much when I jacked the rig up to do a brake job. It does look good in the mirror going down the road, appears to ride nice.
I can weigh my rig for free at the State DOT scale on the way to and from our beach lot. They are very nice dual pad digital scales. I have checked the rig and adjusted the front ride height several times. I have the axles at 4200 and 4020, which is pretty close to a perfect balance.
I have backed onto them with only one side on and checked lateral balance as well.

[slowmover]

Forgot: I have heard fifteen years cited as a wear-by date (unofficially) on torsion axles (less if the trailer is rarely used). The Al KO and HENSCHEN sites list measurement procedures for determining correct ride height. DEXTER probably does too. There's room to play with starting angles to dial in what is wanted.

Thanks for the info on the air system. Am impressed (as always, by fabrication skills). And a commendation for what so few are willing to do: proper axle weights FF-RR and side-side.

I saw the same mpg with my truck [sig] as with a half-dozen other 2nd & 3rd Gen Dodge CTD owners pulling 31'-34' all-aluminum aero trailers: 13-16 mpg (speeds from 55 to "about" 65 mph; backroads and Interstate). Some were 4WD but mainly 2WD. My combo was loaded to .92 of capacity when fulltiming and the axle weights revealed a pretty even split of vehicles at around 7,500-lbs each; just over 15k gross. It'll be of interest to many the record of this 5'er for FE.

Have bookmarked and will be sending others to this thread!

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