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Sure, a six-foot protrusion sticking off the rear end of any vehicle is kinda funny looking. Unless we're talking about a Porsche 917/30 or a Plymouth Superbird. Those cars have some very fine rear extensions. Okay, fine – a six-foot protrusion looks a little bit weird when growing out of a semi-truck's rear. Happy?
But a boat-tailed tractor trailer might be just what we need. Why? Because when fitted with such a piece of aerodynamic kit, total fuel-consumption reportedly drops by 7.5%. The tests in question were conducted by the Dutch PART (Platform for Aerodynamic Road Transport) public-private partnership platform on public roads. One truck without any aero-aid was driven around for a year, as was another truck with the boat-tail.

Not only did the boat-tailed machine get a 7.5% fuel economy bump, but at the same time, emissions were slashed by about the same margin. Even though these numbers are indeed promising, PART wants to figure out a way to reduce semi truck fuel consumption and emissions by 20%.

[Source: Science Daily]

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    • 1 Second Ago
      • 5 Years Ago
      I like the idea of the diffuser better. In order for it to work the maximum length of the trailer would need to be extended and only for a piece like the cone.

      The cone looks like its about 6 feet long. More than 10% of the length of a 53 ft trailer. If it nets an additional 7.5% improvement in fuel economy and you have to give up 10% of your load capacity then I think you have a negative result. If you allow the trailer to be 10% longer and only allow that additional length to be used for the areo addition and net a 7.5% in improved fuel economy then you are still further ahead if you just make the trailer 6 feet longer and allow for more cargo.

      I think a better result can be achieved with tires/wheels, diffusers, nose cones, skirts and light weight construction.

      My two cents worth.
        • 5 Years Ago
        Who said you have to give up 10% of your load capacity? Just put regulations in place that these can only be deployed on the Interstate (they won't be any good in urban traffic, anyway).

        All your other enhancements are totally sound ideas, but this isn't mutually exclusive, either. Add this to skirts, diffusers, etc, and you probably get that 20% improvement. Any fleet manager would kill for that kind of cost savings.
      • 5 Years Ago
      I wonder how it affects the draft or aerodynamics of the cars behind them.

      I think we need NASCAR to fire up their Draft Track and fill us in...
      • 5 Years Ago
      I wonder how many cars will get taken out when that tail swings around at intersections?
        • 5 Years Ago
        The end of that tail is WAY behind the rear axle, when the driver takes a turn it will swing out quite a bit. This isn't really a problem on a highway where the turns a gradual but in a congested area I would imagine that they could take out cars and light poles when the rear ends swings out. Granted I am not an expert, just fuzzy logic
        • 5 Years Ago
        Addendum: In the event that a multi-lane junction is too small for a driver with a boat-tail to execute a turn without scraping a car to it's right (a theoretical possibility) that can easily be solved by a turning rear axle. If the junction is too small even for that, then trucks should not use that junction.
        • 5 Years Ago
        I could easily imagine regulations around such devices as this that they can only be deployed on the highway.

        Yes, the driver would have to pull over and deploy them. Seeing that there are numerous reasons why a driver might pull over briefly anyway, I don't see a problem.

        (and, yes, I'm a former long-haul trucker...)
        • 5 Years Ago
        Have you been to MA or the Bay Area lately?
        • 5 Years Ago
        Or trailer length at that junction could be limited or require that the tail can be folded away. Why can't we edit our messages?
        • 5 Years Ago
        Only people that run red lights or can't drive.
        • 5 Years Ago
        No. But if people run into the back of a trailer, regardless of where that may be, that's their problem. Trucks are large, give them space.
        • 5 Years Ago
        Which means new trailers would need to be designed unless it's to be used (nearly) exclusively on the highway where I would imagine it would make the biggest difference anyway. Don't get me wrong I am all for new ideas and I am sure some brilliant people will make this work, just stating my thoughts (not that they're important anyway!)
      • 5 Years Ago
      2 different trucks? These guys clearly aren't scientists then.
        • 5 Years Ago
        Addendum: Swede apparently read the Science Daily text in its entirety, I only briefly scanned it. So basically it's already clear that the truck hasn't gone through the same elements - however we do not know if it had more than one pilot to add further validity to the test. Regardless, anyone with a minimum of knowledge of aerodynamics these days can attest to this concept's validity, it's basically a repetition of the teardrop design for cars applied to the semi - it reduces drag.
        • 5 Years Ago
        Where did you get that from?

        "An articulated lorry was driven for a period of one year with a boat tail (of varying length) and one year without a boat tail. "
        • 5 Years Ago
        We have done these sort of test at Argonne National Lab's. They is a company in the US that makes a inflatable housing that goes on the back of the semi that we did simulation work with and verified with wind tunnel experiments.

        “Commercial CFD Code Validation for Heavy-Vehicle External Aerodynamics Simulation,” W. D. Pointer, T. Sofu, D. P. Weber, in The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, pp473-483, R. McCallen, F. Browand, J. Ross editors, Springer (2004).
      • 5 Years Ago
      If it's available commercially, the next question is if it's legal and is it worth it. The length of most trailers are near or at the legal limit for length. I could see this on European-style trailers in the US though. Length limits for trailers in Europe are shorter than in North America. So equipping a boat-tail on a Euro-legal trailer in North America would not put the trailer over the legally allowed trailer length... But in Euro-style in Europe or typical-US-style trailers in North America, unless you shorten the trailer, is it worth it? Companies will have to give up cargo capacity to save 7.5% in fuel.

      Another headache I just realized that the trailer door can be docked right at the dock.... the tail is in the way... how many facilities are going to deal with accommodating these kind of things? How would they load/unload? I would assume it would require the removal of the boat-tail and the "bumper" add-on. That wastes time and lowers efficiency, many trucks get to a facility load/unload and are gone almost as fast as they got there.

      I don't see this being widely adopted. Getting extra efficiency is awesome, but I doubt people would want to put up with the annoyances.
        • 5 Years Ago
        European combinations are limited to between 18,75 to 25,25 meters depending on where you find yourself within the EEC.

        Obviously you cannot load or unload with the tail in place, according to the resarch material the tail retracts into the body. The researchers have also tested inflatable versions, they retract within 30 seconds.
        • 5 Years Ago
        The tail appears to fold out of the way.
        • 5 Years Ago
        You know, I would put money on diffusers lining the back edge of the trailer being somewhat effective and less likely to cause problems. They could be purchased as a "spike" strip and affixed to the rear in any number of ways (magnetic probably the number one), so the driver could move them to each trailer they haul.

        Anyone know of any research on trailers with diffusers?
        • 5 Years Ago
        Rules are meant to be broken, laws are meant to be challenged.
      • 5 Years Ago
      I was thinking about something like this, except mine would cut into cargo capacity. I would also add dimples as well.

      The other day I was driving behind a milk truck, and I notice the rear end was dropping when it was sitting at the red light. After the truck turned at the intersection I saw that the driver raised the rear wheels to clear the corner.

      When looking at this concept, I was thinking maybe you can make this telescope when you get on the highway. However I haven't figure out how to handle the bottom part.
      • 5 Years Ago
      Here are some test numbers with the 7.5% and 20% figures.

      Truck A gets 5 MPG
      Truck B gets 5.375MPG (7.5% increase in economy)
      Truck C gets 6MPG (20% increase in economy)

      Doesn't look like much until you look at yearly numbers.

      If the trucks both drive 120,000 miles per year or 10,000 miles per month.

      Truck A will use 24,000 gallons of diesel per year or 2,000 gallons per month
      Truck B will use 22,325 gallons of diesel per year or 1,860 gallons per month
      Truck C will use 20,000 gallons of diesel per year or 1,667 gallons per month

      Truck B has a yearly savings of 1,675 gallons or 140 gallons per month
      Truck C has a yearly savings of 4,000 gallons or 333 gallons per month

      If that diesel costs $3.00 per gallon
      Truck B saves $5, 025 per year or $420 per month
      Truck C saves $12, 000 yearly or $1000 per month

      If the company has a fleet of 100 trucks this is a fleet savings of
      $502, 500 per year with B trucks
      $1,200,000 per year for C trucks

      The little changes can add up.
      • 5 Years Ago
      "Longer and more fuel efficient trucks are the future. "

      While trying to avoid the extrapolation-into-irrelevance trap, but doesn't that idea eventually just result in ...

      • 5 Years Ago
      Why not simply try to attempt to make the actual trucks more aerodynamic? It always puzzled me even as a kid how these large bricks of machinery are able to haul anything. That and why not attempt to create some form of guides under the trailer itself? Have it divert the air around the tires as to create less drag or in some case's have it create downforce?
      • 5 Years Ago
      Digging up old things here but:

      Rex: you are absolutely right, most of the fleets in the trucking industry have between 20 and 3,000 trailers which get 40,000-100,000 miles per year. When you run trucks that get 5.5 to 6.2mpg 7% starts to become very real amounts of fuel and money.

      @ Clavius: It would be ideal to stop hauling huge rectangles down the road but the trucking industry is quite resistant to change.

      All that said: there is an American company producing Trailer Tails and Side Skirts that return 5 - 7% efficiency gain each; 10-11% in tandem. The Tail collapses so cargo access is no problem. http://www.atdynamics.com/
      • 5 Years Ago
      That is pretty cool. I'm sure it also helps reduce their wind tail. Sometimes, thinking outside the box is all it takes.
        • 5 Years Ago
        Simple fluid dynamics tell you that this works physically.

        As for economically, the peices could be made by the same cheap material the trailer is made from. And when its time to dock, the walls around the unloading area would push this twards the body of the trailer. Then all that would be needed is a simple one way actuator that could push one of the panels (interlocking with the others) back out when the truck leaves the loading/unloading bay.
        • 5 Years Ago
        I am not saying it won't work, but I'm saying there's a lot of obstacles. If these things came to my warehouse I can see the tail being able to fold back, like doors, but the bottom part has to be removed, I can see the bumper tucking underneath through some mechanism so it can dock. But with reduced capacity, what took 5 trailers will take 6 or even 7 trailers... the 7.5% savings is partially mitigated.
        So this is not something I can see used universally, but I can see it's value in situations where it can work.
        The government could relax the limits on trailer length, then these trailers will have a harder time making turns at some intersections, to outright not being able to turn at certain places anymore because of the extra length. There are a lot of considerations to be made.

        I'm all for fuel savings. I think the side skirts on the trailer seen in the picture is the first thing everyone should adopt.
      • 5 Years Ago
      nice try...but no. These guy's profit is based on time, and having to fold this contraption out of the way at every stop if not something they would go for. They want to drop their trailer off and go, of get it unloaded and go.

      Maybe think of some way so they dont have to idle a huge diesel engine all night long while they sleep...that would probably save more fuel that this thing.
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