Accordion Kammback for big rigs ?
 

I see a LOT of big rigs that drive without a trailer. It seems to me that a simple spring loaded accordion structure could be placed behind the cab of the vehicle.
The structure would not only act as a Kammback for the rig when operated alone, but would also seal the gap when driven with a trailer. ( It would simply be compressed )
I know we discussed this sort of thing before, but I wanted to start a fresh post.

( This sort of spring loaded structure could also be added to the back of the trailer as a partial boattail , but as those of us that have worked around rigs know, the trailer that is picked up usually doesn't belong to the driver of the rig. Plus, there is the added complexity of having to open the doors which swing to the sides )
I see this Kammback idea as a small step towards making big rigs more fuel efficient, but without any hassle for the driver. )

So ... why would this NOT work ?
http://farm4.static.flickr.com/3177/...927efe28da.jpg

A very interesting idea. I could see it get some what complex designing it to pivot with the trailer. Plus don't forget you need a way to plug in the air brakes/Lights after hooking up the trailer.

The inside of the assembly would be hollow. All air lines and such could be easily hooked up and stored.
Since the assembly is designed like an accordion, it would easily flex when corners are taken.

Questions to ask...

1. What % of their operating life are they no hooked up to a trailer?
2. When hooked up to a trailer, what % of losses can be attributed to rig/trailer gap?
3. What is the penalty for ridges oriented orthogonally to flow?
4. Of course, Cost v. benefit :p

I've seen the accordion stuff on trains/subways... But I think that's more of a trade off for turning....

1. They would be mounted to the back of the cab. The assembly would make contact with the trailer as it was driven towards it. It would then compress like an accordion.

2. I would have to look into this.Others members here know more about this. I would think that anything helps though - especially when we are talking about a gap that is around three feet.

3. Good question - you're the one with the CFD program. :D It might be an interesting thing to research.

4. The assembly could be made out of canvas / tent material or rubber with a tension spring mounted within it. I would think canvas / tent material would be more durable ( wear and tear and the effects of sunlight on rubber vs. canvas / other materials. ) I would think the weight would be offset by the fuel savings - especially when driven without a trailer. ( It would be hollow and just fold out like a tent )

The ridges would become more rigid and closer to the ideal shape when flexed outward.

hehe, I'll put it on my list of things to model :p

With respect to #1 - I meant how often is the rig running without it's load... I would think the most benefits to be had would be when the rig is running by itself, no tractor....

Here is a link to a paper that Cummins came out with (I think in 2007). I have seen other figures than these for big rigs, and some have said up to 20% of the overall drag of the rig can be attributed to the trailer gap, but I can't find it right now. In the mean time, enjoy the whitepaper!

All the rigs I've seen have the connections dead center of the front of the trailer. So some how you would need to be able to get inside after docking the trailer to hook up the lines

From what I understand you can create the shape of a teardrop with separated panels with just a small loss compared to a smooth surface. I would think this would be the same sort of thing.

Another question is what about reefer and flat bed trailers? The cooling unit of a reefer would end up inside of the accordion.

FastPlastic - good points !!
I knew there had to be something that wouldn't work with a sytem like this.
I hadn't thought of these two problems.

It's an awesome idea, but here are a couple more hurdles to go over;

-Weight, these trucks have strick on road weight restrictions and every pound you add to the rig is one pound less cargo they can haul.

-Assuming your accordion has at least three sides, which includes a roof, where does the stack exhaust vent? If like your picture, the stacks are behind the farings, this could cause some trouble.

-Plus wont the accordion shape itself cause some sort of turbulence?

What if the assembly could be used without the tension of the spring to activate it.
The trucker could connect all the hoses and such and then pull the assembly back like a curtain once he was finished. If he/she was hauling a load that needed to have a cooling unit he/she would simply not pull it all the way back to meet the trailer.

I think the problem with this is that the most truckers would never use it. I see lots of trucks with flip up air deflectors that the truckers never bother to crank down once they are done disconnecting their load.
With the spring activated sytem, the trucker wouldn't have to actually do anything to make it work.

If truckers had to pay for their fuel out of pocket, then I can see the 'curtain' style sytem work.

Some independent truckers do pay for their own gas. So there would be some market for them. I agree it would probably work better if there was a way to move it. A motor or hydraulic setup would be optimal. But would also add to the weight and price.

Depending on the kingpin position on the trailer it can have quite a bit of headswing. In a full turn the entirity of the accordian would be suspended on the corner of the trailer, and only at the top of the accordian. It would need to be designed in such a way that the lower part was never extended past the bar that runs along the top. This would produce gaps and reduce effectiveness. Further reduction would be caused by the compressed folds when a trailer is hooked up (I'm not even sure if it would be more aerodynamic than having open space while compressed). Lastly, those air lines (and power cord) usually connect to the middle of the front of the trailer which wouldn't be so bad to work around with the accordian thing, but in some cases the connection point is near one of the corners (I know a very bad design as it causes the most possible stretch during full turns). In those trailers especially, and to a lesser degree in the trailers with the connection in the center, during and after a turn the lines must have unimpeded travel. This is quickly complicated when you take into account that turns do not always happen on level ground, if a truck is turning and cresting a hill for example, the air lines will be stretching across a much different area of the accordion occupied space than on level ground. The only way I think you could be assured of safety would be to cut fairly large sections of the bottom rear accordion out (and since there is going to be a gap there anyway it likely won't have too much of a detrimental effect).

It's a good idea, and would work great for trucks while bobtailing, but in this day and age a bobtailing truck is losing money for everyone involved so I doesn't happen all that much. The 20 miles to go pick up a trailer is a dop in the bucket compared to the 1000+ miles the truck spends to deliver the load after pickup.

To be effective I think we need a smooth, rigid surface that doesn't interfere with the air lines. I have proposed an idea to a manufacturer, but haven't received a bid yet for a prototype yet:

first is a top piece that spans the distance between the back of the sleeper and the front of the trailer. It connects via a hing on the sleeper and rests upon some sort of low friction, low vibration connection in the center of the trailer (that would accommodate x and y axis motion, the small amount of z axis motion should be handled by the hinge), the center mount is a pivot point and with the small amount of motion accommodation mentioned previously this top piece will remain stable during turns of all sorts. While bobtailing it can be set to an optimal downward angle off the back of the sleeper, and could even be built with a slight curve to help in that capacity.

next is a pair of side pieces which are connected to the existing side fairings and extend back past the front of the trailer. They ride on small wheels, or balls, or a low friction material. When a trailer is in a turn they continue to follow the sides of the trailer either with springs holding them in or a natural curve in their material.

Problems: during the resolution of a full turn the trailing edge of one side wing will be riding along the front of the trailer and be forced to negotiate the curve of the trailers corner. This will require some sort of guide materials on that edge of the wing and will create a lot of stress there, this in turn will create a gap and possibly some unaerodynamic shapes. I expect that this will still result in a net gain (or loss in terms of drag rating) in aerodynamics. Alternatively we are thinking of mounting the guide materials onto the corners of the trailer instead, it isn't something we have been able to think our way around, we need to get some models going and see effects.

We would have a very similar problem as the accordion in terms of air lines, but the trailers I plan to use these on have center mount airlines and I was intending to put a block on the trailer front to force the wing to bend outwards to and never interact with air lines.

The biggest drawback to all this: It must be somewhat custom built for the application. I do not think a one-size fits all solution can be made, and the system on the truck and trailer have to be matched up. This works for my use as these trucks have dedicated trailers and mostly they are all identical anyway. In cases where non-matched units have to work together they can take the wings off the truck and fold the top piece down against the back of the sleeper.

I apologize for how long winded this is, I hadn't intended it.

By the way, This isn't merely a thought experiment. I own a small fleet of trucks and trailers. Fuel is our biggest expenditure. Any amount saved means more profit. If this system could net 5% less fuel consumption it would mean aprox. $120 per week per truck in savings. So even if it ends up costing $3,000 per unit, it has paid for itself within half a year, and I expect we can get it down to less than that, and with more than 5% savings eventually. Although I expect a kamback style air dam on the rear of the trailer will have a larger impact and cost less. That is a different project.

Getting inside would be pretty easy, just bungee it to the back of the sleeper while you want access to the front of the trailer.

You definitely don't want this to be covering a reefer unit that is running. The exhuast would be trapped, the air would get excessively hot. It would ruin both the accordion and the reefer.

You could probably design something that works with reefers, but the top half of the front of the trailer would be exposed and the savings would be much less. It is probably a waste of time.

Many flatbeds carry oversized loads that use the space between the trailer and sleeper for product overhang. (I run 3 trucks that regularly load 60 foot rebar, and 8 feet of it rests between the cab and the front edge of the trailer). For flatbeds that are dedicated to a lumber run or something that doesn't extend beyond the front of the trailer I think a modified accordion is a great idea. You have to modify it so that the trailer (and/or product) pushes the accordion out of the way in a turn but doesn't damage it (or the product), and doesn't interfere with the air lines..

Weight is an issue, but I can't imagine this thing weighing very much. Diesel weighs ~8 pounds/gallon.. I can see many owner/operator and fleet manager sacrificing the range of 15-20 gallons for the fuel savings, and thus increased range on the other 175 gallons in the tanks. If you could get 10% fuel savings out of it (though I doubt it would be that high), it would be the same weight even running 17 gallons less.

Most of those air deflectors are bolted in place. For most drivers it isn't their responsibility to save the company money by getting up there in the rain and unbolting it. Most companies wouldn't want the liability of having a driver get up there in the rain and risking falling. Don't blame the truckers for the companies failure to buy the right equipment for the truck. Those fairings belong on trucks pulling vans or reefers. Flatbeds would probably be best without anything up there, or a device that can be remotely lowered. Those things are really just a band aid for the crap design or the setup.

A lot of trucks (maybe even the majority) have the exhaust stacks sitting right behind the door, so they wouldn't interfere with the accordion. As an example most of my trucks have the exhaust coming out right in front of the first set of rear tires under the truck. This is probably hell on underbody aerodynamics, but it also doesn't interfere.

Demian : You have some clever ideas !
Thanks for the critique.
As far as the weight issue is concerned, I keep thinking of how lightweight that this thing could be if it were made of ( nylon ? )tent fabric with an aluminum support.

It would be cheap to make and waterproof too.

Here is something I thought of on the way to work this morning ...

You are trying to solve an issue when these rigs are running without a trailer.

Well nearly 100% of them have the roof fairing that pushes air over and around the trailer portion. What if that was designed in a way that when empty it could be flipped back, reducing the frontal area and in its flipped back position act as a partial boat tail. This way we add negligible weight and have no storage issues.

As part of this invention the now exposed roof can have a shape to help steer the air into the boat tail. When not in use it become the functional fairing it was before.

big rigs
 

Cd,Hucho has a chapter of his book dedicated to big-rigs with all the numbers 'n stuff.Also,The Dallas Public Library,downtown,has a technical library on one of the floors.They have "Automotive Engineering" periodicals which,from late 1970s,to 1980s,have myriad research paper reports on big-rigs,again with a lot of predictions for mpg.---------------------- You're on a good path,but you may find that many ideas have been fully fleshed-out over the last three decades.----------------- The big challenge is to commercialize the stuff.I think even Kamm said that coming up with ideas was the easy part.It was selling the idea which posed the greatest challenge.----------- You may have to do like bondo(Brett Herndon) and just go for it.

Trik That Truck!
 

I think you could do this with a bar that the cap could pivot around and slide up/down on. Probably could be motorized and you would just have to have some manual clips to remove it or secure it in each position, like a convertible top or a Jeep Wrangler hood.
I added the red vertical bar to show where it would pivot around; it probably could also drop down with the cap when stored like this:
http://img377.imageshack.us/img377/4...attrucktw3.jpg

Even easier than a crazy pivot/slide mechanism.... Fair the inside of that thing and add one hinge at the rear end.... So when working as a wind deflector for the trailer, the "bottom" of it is tapered plastic/fiberglass that's not doing anything... When working without a trailer, flip the entire thing over and the old "bottom" becomes the tapered top :thumbup:

You guys are kind of doing the pie-in-the-sky thing. You aren't going to convince truck manufacturers to make massive design changes that won't work universally with all applications. Drivers/Owners won't buy them (I mean, I might, but 90% won't). Trucks are a very conservative beast, even the newer aerodynamic designs like:

Freightliner Century class:
http://www.freightlinertrucks.com/me...y-class-st.jpg

and

Peterbuilt 387:
http://www.larsongroup.net/images/he...ot%20Final.jpg

are not universally accepted. You see alot of the freightliners on the road because they are cheap, but I see more of trucks like:

http://www.sftrucksales.com/inventor...=2019540&img=1

If people won't accept the frontside of the truck being aerodynamic they certainly aren't going to accept any weirdness to the rear end. I hope they change soon though. Trucking in this country could save a ton of money with good design changes, but until then I think discussions about how we can change existing designs is more useful. (along the lines of the mod discussions about production cars).

PS. the Cummins white paper is dead on regarding fuel consumption. I really appreciate that link, I had read most of the information elsewhere, but it quantified the loss due to tractor/trailer gap nicely. Every 10 inches beyond the first 30 inches results in ~2% increase in drag which is ~1%decrease in fuel economy (although when we enter the realm of extreme reduction in drag that 2 to 1 ratio will not hold). So, when not hauling extremely long product I could gain ~8% in fuel economy by adding an accordion style kamback.. It would probably even be more because of the nice curving slope on the back end. I very much worry about the effects of either the ruffles of the accordion or the flappiness of some sort of canvas, can anyone comment on this? 8% fuel savings represents about $300 a week.

I fully agree Demian. I was just presenting an idea.
I have no intention of even trying to ask anyone to produce this thing.

However, if this thing could be made of nylon tent material it would be really light and
it wouldn't absorb water and mildew / get heavy like canvas /would be lighter and more durable than rubber )

(Just think of how lightweight that a nylon tent is. I'd bet I could lift even a large tent easily with one arm.)

The nylon fabric could be bought at any large cloth store. To make things less complex, it could be designed like a curtain that simply pulls back to meet the trailer.

( Minding the hot exaust stacks and any other such things of course.)

One more thing that I thought of : The middle section of the top portion of the Kammback could be pulled downward and secured when there is a cooling unit on the trailer. This would actually direct air right into the unit and it might even operate better than within the open section of a conventional setup.

I'll have to do some illustrations when I get back home.

When I spoke of discussing existing designs, I was really commenting on the picture posted by gascort (no offense intended!). It is basically a redesign that would have to be done by a manufacturer, not a "mod" that we could apply to current designs.

I know I was critical at first, but I have come to see some good use for an accordion style kammbak for flatbeds. It would be much easier to use with a flatbed than my design (which is intended for vans). To load overlength rebar on this design all you have to do is collapse the accordion down so that the rebar's overhang clears the accordion. To do the same with my design would require removing at least the side panels, which is certain to be a chore for the driver (and would require the liability of them using a ladder in the rain), and likely the top piece as I am uncertain that it would be very useful without the sides in place.

Nylon is certainly light, but will it fray when it flaps in the wind (while the accordion is in the contracted position?)

Hopefully it would last long enough to 'defray' the costs.

I would like to try something like this, but I don't bobtail enough to matter. The "closing the gap part would need alot of work. because of when the trailer is at 90 degrees in relation to the truck when in a hard turn. Maybe there could be a work up of snaps up and down each side of the rear of the truck, and on the front of the trailer, then stretch an elastic/spandex material between the two so it flexes with flex and moderate turning. It still doesn't deal with hard turning.

A simple test boattail could be a large conduit rod starting at one side of the bottom of the cab, following the curvature of the sleeper up and over and back down the other side. Make serveral just like it, except taper them in each one. on the truck frame, make some type of flag pole holder to set them in while bobtailing. Just a driver's simpleminded perspective.

Thanks for posting SmallFry. I thought this thread was long dead.
I sort of gave up on it when I saw what NASA did decades ago.
They did some aero studies on big rigs and simply used this ingenious ( but common sense ) idea : hinged gap fillers.

http://www.dfrc.nasa.gov/Gallery/Pho...l/ECN-4724.jpg

I do wonder how that this sort of setup would work in a jacknife type turn though.
Would it flex enough ?

I like your idea, but can't really visualize it. Can you do a quick sketch ?

( And P.S. - nice sleek looking rig you drive )

SmallFry, demian, and everyone, I'm wondering what type of truckers DO end up driving the most bobtail miles?

Congratulations on your over 10 MPG's there, SF, btw. do much bragging? j/k

Cd, If you picture some rectangle outlines made of narrow white plastic pipe, and each rectangle is a little smaller than the last, and they nest together flat when pushed together...maybe that describes SmallFry's concept. The biggest recatangle is just behind the cab and the smallest is the tail of the Kamm-back.

just blue-sky-ing it >>> what about venetian blind-like material?... keep the nesting rectangles that provide the strong, collapsible frame, but put venetian blinds plastic in-between instead of fabric?...it's more of a telescoping idea. I have no idea how the "blinds" attach or how much they haff to rotate for turning corners.

Or maybe just line camping tent nylon fabric with something friction resistant where it touches the frame elements.

[edit: the venetian-blind material would probably just end up being a new kind of road-side debris, come to think of it. I'll just leave it in this post there in case someone can take maybe the "telescoping" idea to a good place]

I would say that the most bobtailing is probably done by Mobile Home trucks. After delivering they are almost always bobtailing back. The second most I see is Lowboy trucks. Not often, but sometimes they deliver their tractors and dozers on the trailer and just drop the trailer rather than pulling it back. I don't see a ton of van or flatbeds bobtailing, and especially not long distances. Keep in mind I see a very narrow spectrum of the entire industry.

I wonder if something like this would work for a bobtailing truck?

http://img225.imageshack.us/img225/8...640x480bp0.jpg
http://img225.imageshack.us/img225/0...jpg/1/w640.png

While searching for Truck aero stuffs, I found this: freightwing.com.

They also have products for "bridging the gap" between the cab and trailer. Freight Wing Incorporated - AeroFlex Fairing product info page

Why not make it simple. Have two vertical rollers with a sheet that attaches to the trailer and has a tension coil to keep it taut. A similar roller could be mounted on the top

Blue bombers idea is brilliant! roll curtains?

You should only choose a fabric which flex little so you wouldnt tear the curtain in pieces when you ride in rough terrain.

I have thougth of that thing and truck aeromodding for one month of time, because I have plans to start aeromodding firm for trucks here in finland. So all ideas are welcome to this post ;).

Another answer to the same questions.
Applicable to answer (could be modified to solve, tractor/trailer gaps) trailer boattail aerodynamics, this relatively inexpensive & easily deploy-able idea may work for most aero-improvement situations. Could be retro fitted to many older model designs & actuated by operators' air systems.
FuelSaver by ATS™

Besides offering tractor boattail form when not pulling cargo, I could imagine the side bags at full pressure to seal tractor/trailer gap. There is corresponding electronic valving controls releasing pressure on the inside bag when taking tight turning maneuvers, re-inflating when in a straight line configuration.

http://fuelsaverbyats.com/fuelsaver_black.jpg

Looks like the type of thing that should be mounted a little lower. That way the car behind it just bounces off when it gets too close. :D

Yeah, that would make a lot of fellow hyper-milers, here @ ecomodder.com for their best-ever mileage numbers. Drafting made a little safer...

There are some information about truck fuel economy:

http://www.everytime.cummins.com/ass...Whitepaper.pdf

Enjoy ;)

Post for a trucker.

Love the ideas.

My thoughts are an inflatable accorridan, with vinyl flap scales on the outside. Make it look cool (?reflective material, lights?) truckers will buy it.

Peterbuilt made a model based on the NASA picture displayed in this thread and it did get 10 mpg before computer controlled injectors, but fuel was a buck .xxx and no one bought the truck, and after a number of years the model was dropped.

Sitting ontop of a hot and loud diesel engine with cramped space and the prospect of an exploding turbocharger coming into the cabin made the NASA cabover unpopular. But if all those issues were addressed & the space saved by not having a hood was put to good use, such as a greatly expanded sleeper cab, this NASA configured cab-over would be popular.

I have a design for this, but can not get the money to market it.