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Old 11-21-2008, 12:19 AM   #1 (permalink)
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Question 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 ?

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Old 11-21-2008, 12:38 AM   #2 (permalink)
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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.
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Old 11-21-2008, 08:39 AM   #3 (permalink)
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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.
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Old 11-21-2008, 09:48 AM   #4 (permalink)
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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

I've seen the accordion stuff on trains/subways... But I think that's more of a trade off for turning....
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Old 11-21-2008, 11:24 AM   #5 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
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

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. 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.
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Old 11-21-2008, 11:29 AM   #6 (permalink)
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hehe, I'll put it on my list of things to model

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....
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Old 11-21-2008, 12:03 PM   #7 (permalink)
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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!
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Old 11-21-2008, 02:36 PM   #8 (permalink)
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Quote:
Originally Posted by Cd View Post
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.
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

Quote:
Originally Posted by trebuchet03 View Post
Questions to ask...

3. What is the penalty for ridges oriented orthogonally to flow?

I've seen the accordion stuff on trains/subways... But I think that's more of a trade off for turning....
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.
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Old 11-21-2008, 03:37 PM   #9 (permalink)
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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.
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Old 11-21-2008, 03:47 PM   #10 (permalink)
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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?

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