I’m always for energy saving ideas when they payback the effort. Here’s one that would be an advantage for our long haul American Interstate trucking companies. This semi has both side wings and a boat tail to decrease wind drag.
It is pretty simple really:
‘Boat tail’ decreases fuel consumption for trucks by 7.5 percent
From a Delft Technical University press release
A boat tail, a tapering protrusion mounted on the rear of a truck, leads to fuel savings of 7.5 percent. This is due to dramatically-improved aerodynamics, as shown by road tests conducted by the PART (Platform for Aerodynamic Road Transport) public-private partnership platform.
Here are the other places wind resistance on a semi-truck can be addressed for fuel savings:
Public highways
A boat tail is a tapering protrusion about two metres in length mounted on the rear of a truck. The boat tail had already proved itself during wind tunnel experiments and computer simulations, both conducted at TU Delft, in theory and using small-scale models. Now an articulated lorry fitted with a boat tail has also undergone extensive testing on public highways.
Emissions
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. The improved aerodynamics, depending on the length of the boat tail, resulted in reduced fuel consumption (and emissions!) of up to 7.5 percent. The optimum boat tail length proved to be two metres.
PART
The tests were conducted by PART. This is a platform in which academics, road transport manufacturers, transport companies and shippers work together. The platform aims to reduce fuel consumption in the road transport industry by improving aerodynamics. PARTs ambition is to achieve a 20 percent reduction in fuel consumption and CO2 emissions in the road transport industry by 2020. TU Delft acts as secretary of PART. PART has previously conducted road tests on a new generation of aerodynamic sideskirts, which are to make their commercial debut later this year.
More information
More on PART: www.part20.eu
More about the side wings: www.ephicas.eu
This idea is around 40 years old. NASA did a study on trucks in the 1970s, and concluded the “boat tail” was the optimal design for wind drag. The study went no where though – until now.
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-100-DFRC.html
It sure seems to have taken these guys a long time to figure this out.
Who can forget the works Porsche 917 Long Tails beating the Gulf/Wyler (sp) more conventional 917s at Le Mans back in the late ’60s or early ’70s ?
Also I remember my friend’s ’62 VW Bus & backing right off the throttle 40′ behind semi trucks traveling up & down California on ‘Old 99’. Eventually, he over revved & blew the engine (36 HP !) doing that when behind a real cruiser of a truck driver doing 75 – 80 mph !
Fuel savings from trucks are nothing new. Just down the road from were I grew up, a very small (5 truck) company owner designed the most efficient truck ever. This was in 1971 and it looked like this.
http://www.paymastertruck.com/DNN47/Portals/1/FirstPMNoTrail.jpg
As Dean H, writes, it was 40% more efficient than others at the time. Later models still work well. He had a real problem getting it sold, as truckers didn’t like the looks. Went on to work with Ryder trucks and make more improvements.
http://www.paymastertruck.com/DNN47/Info/LaterModels/tabid/86/Default.aspx
Confirms that there is nothing new under the sun, and especially on TV.
Ron Dean (10:01:26) :
“This idea is around 40 years old. NASA did a study on trucks in the 1970s, and concluded the “boat tail” was the optimal design for wind drag. The study went no where though – until now.”
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-100-DFRC.html
Many drag reduction tricks have been adopted in newer trucks, but for some reason this boat tail is left in the dustbin. There are many articles, patents even, on the idea from over the years. I may be wrong, but I suspect it makes the rear end squirrelly under certain conditions. I can’t help but think that were this to save a lot of money and not kill people there’d been long ago all kinds of truckers and companies screaming to stick them on their trailers. It wouldn’t have taken long to figure out how to get it off and on, or design something else that worked the same.
Curious this is being looked at now, when the push is on to save the planet.
This will not just make money for the trucking companies, but another ten million for Vin Diesel.
Anybody actually own a boat that has one of those boat tails ? Just curious.
If the gizmo cuts the drag; it stands to reason that it would diminish the effect of drafting, which is dependent on driving in air that is moving forward.
The 3-M sharkskin tape that Dennis Connor used on Stars and Stripes in the 1987 Americas Cup match in Fremantle Autralia; only works in water; it wouldn’t work in air. You can now buy fly lines (from 3-M Scientific Anglers) that have that sharkskin finish. They shed water like a greased duck’s back.
There might be other surface finishes which reduce viscous drag in air. I notice that modern fighter aircraft have a dull matte finish on their pain jobs. Part of it is stealth (377 Ohm paint); but part of it is viscous drag; but maybe it is only effective at high airspeeds; so wouldn’t work on trucks.
Those boattails just aren’t going to work. Since a trailer is length, width and height limited, it’s volume limited. Adding volume to the trailer to save fuel is less cost effective in the long run than adding volume to carry freight. Freight pays the bills. It may work on short trailers where GCWR is maxed out, like beer trucks. Mmmm, beer…
Roger Carr (02:17:59) and LarryOldtimer (23:44:10), thanks for the reference on US fossil fuel reserves. It would be (and to some extent already is) the height of folly not to use our abundant resources for fear of CO2 and other eco-boogeymen.
George E. Smith (10:52:21)
The sharkskin does work in air, George. Airbus did some years a few years ago and got a 1to 2% drag reduction on a jet airliner. The biggest problem is determining the airflow direction to orient it properly. This works on powered aircraft in cruise as the aircraft flys over a narrow angle of attack range, not so well on gliders which need low drag over the whole speed range and the airflow can change direction significantly.
Other problem was pressurization air leaks causing bubbles in the applique.
I bought some of the 3M sharkskin in 1987. Never got around to installing it on anything and still got it.
As commenters here have pointed out, all this truck drag reduction stuff dates back 35 years(first oil shock).
Here we have universities and private industry paying to do the same stuff again. Is the human race losing its corporate memory?
Is this an example of research being corrupted by governments making excessive amounts of money available for it?
Do we have too many wannabe research scientists? Look at all the poor quality research being put out by the warmies.
That would make perfect sense, the experience of land speed racers with long tailed streamliners fits that expectation exactly.
It would move the center of pressure to the rear when the trailer was hit by a cross wind gust, that would make the trailer tend to “wag its tail” in cross winds, If the frequency of gusts happened to match the natural oscillation cycle at a harmonic frequency, you could easily get the trailer swinging wildly from side to side in some cross wind conditions. It would also increase the “sail area” of the trailer to side winds, so both the side force would go up in high cross winds, but you increase the likelihood of the trailer blowing over if struck by a strong cross wind. That happens often enough as it is, when semitrucks are driving at right angles to gusty high winds. Here in Colorado during high wind events, they frequently have to close some highways to “high profile” vehicles to prevent blow over. About 20 years ago I watched a blow over occur right in front of me on I25 near Colorado Springs, just south of Monument hill in cross winds of only about 60 mph. The truck driver, was getting blown sideways, and gradually drifted to the edge of the pavement. Once he dropped the wheels off the pavement it was all over, and the vehicle rolled in the median, totally destroying the trailer.
In a gusty cross wind quartering from the rear, it would likely rip the boat tail right off the trailer, as it pressurized that big cone, while creating a high pressure area on the up wind side, and a strong low pressure area on the down wind side.
As a driver sharing the road I would not want to be anywhere near that thing in the type of high winds we sometimes have here in Colorado an Wyoming. I’ve had conventional trucks be blown almost a half a lane into my lane by a strong cross wind gust on several occasions.
Larry
Truckers are already trying to put 53 ft trailers into places designed for 45 ft ± trailers. Especially on the congested coasts the limit has been reached. Reduce the trailer length to 48 ft and then you might be able to run boat tails on a large scale, but the swing on sharp turns will still be hazardous in congested areas. Rookies will tear a lot of stuff up!
As mentioned wind gusts will be catching these boat tails making the already high profile trailer less stable in crosswinds much easier to flop over anywhere or to skid loose on less than dry pavement. Having seen a person in a car crushed and killed, believe me, you do not wish to see it again. Very bad idea and fills me with dread.
“”” Mike Borgelt (12:00:09) :
George E. Smith (10:52:21)
The sharkskin does work in air, George. Airbus did some years a few years ago and got a 1to 2% drag reduction on a jet airliner. The biggest problem is determining the airflow direction to orient it properly. This works on powered aircraft in cruise as the aircraft flys over a narrow angle of attack range, not so well on gliders which need low drag over the whole speed range and the airflow can change direction significantly. “””
Well the original 3-M sharkskin tape that Dennis Connor used, has a preferred direction; the version they put on the fly lines does not; and it works as a result of the surface tension of water. In that sense it is less like true sharkskin. The flyline is even called sharkskin. It makes the surface hydophobicsince surface tension will not allow thw water to wet the surface at standard T&P, because of the short radius of the surface cavities.
When you pick up the SS floating flyline from the water, it literally rains underneath the line. also as a result of the bumpiness of the line, it shoots through the guides like crazy; and in the process it makes a hell of a lot of audible noise.
The 3-M tape is now illegal; at least for Americas Cup boats; but the sailors achieve similar results by sanding the surfaces with the right grit size sand papers.
Morgan (07:00:44) :
Hard to believe no one has brought up the recent Mythbusters episode in which golf ball-like dimples reduced a car’s fuel consumption by about 10%.
http://access.aasd.k12.wi.us/wp/baslerdale/2009/10/24/mythbusters-golf-ball-car-better-gas-mileage
I wish they had had that episode a couple weeks earlier. I could have gone to a junkyard and got a set of body panels for my Saturn (they come off real easily) and put dimples in them and then put them on on my way back from Oklahoma yesterday. That would have been a good 500 mile test. 500 down normal, 500 back dimpled.
The nature of aerodynamics like this has been known for a long time, as many posters have pointed out. So why is this suddenly in the news now?
In the UK with trucks of all sizes limited to 56mph in line with EU policy once they get onto the main roads (at least the ones that are not congested and are relatively free moving) they are often so close to each other they must pretty much be using the each other as Aero aids anyway. Sometimes in parallel rows, one truck taking miles to pass another.
A few years back just after the law changed to allow bigger trailers but also the introduction of speed restrictors a trucker told me that at long last he was in a truck that was fuel efficient and had plenty of reserve power – until he came to a slope. At that point he would normally have built a little speed before the slope so that he could keep the engine at its optimum power output for most of the run up the hill. But being speed restricted he now had to go down through the gearbox. He reckoned it cost about 30% fuel economy in those situations – and there are many of those situations for UK truckers.
Quite frankly there are greater benefits with no other issues against them to be had from looking at fuel efficiency in engines (which is of course happening) and improving the infrastructure (which if course for roads, in the UK and most of the EU is not).
Meanwhile our local sub-government (under the EU) in London talks of spending untold billions to add another high speed (i.e. Passenger) rail link to connect the UK’s largest cities (London, Birmingham, Manchester and Glasgow/Edinburgh) apparently to encourage fewer people to fly between those places. It seems to me that with rail ticket priced the way they are they majority of people using the service are probably politicians, academics (on funded trips to other places of learning) and perhaps ‘entertainers/celebrities’. Ok there are a number of business people as well but on those very rare occasions when I use the train to go to London (no point in driving there) the perpetual conversations suggest that most of the business people, unless commuting to work as a daily ritual, maybe don’t really need to be making the trip.
So if they stuff all the money for the next 20 years into a single rail link on a route that is already available today the chances that the rest of the infrastructure will fall apart are that much greater. Perhaps that is part of the plan. After all once the carbon taxes have made all forms of travel affordable only by the richest members of society who would need the infrastructure?
It seems that that is where the money will go – a white elephant development that has little or no meaning for the lives of everyday people whose more direct infrastructure requirements will be ignored – at best. There is no benefit whatsoever adding aero aids to a truck that spend most of its time stuck at low speed in broken infrastructure.
My understanding is that the US already moves a far greater proportion of it’s freight by railroad than does Europe.
There has been lots of research into aerodynamics of cargo trucks. Basic issue: if you must reduce the cargo capacity to reduce the fuel economy, make sure that you reduce the latter more than the former, otherwise there is no net gain. And the resulting vehicle must be practical as well.
My suspicion is that a lot of what is interpreted as “aggressive” or “fast” driving by trucks on US interstate highways is really an effort by the driver to keep as much momentum as possible in order to save energy and speed. I drove a 1000-mile trip in a 26′ truck, and drivers of cars thought nothing of dashing in front of me, slowing greatly, and then speeding up again. Meanwhile I’m trying to accelerate on an uphill grade and know that I won’t get above 45 MPH for another mile and a half because I’ve lost all of that energy.
Yes this one of many designs produced over the years. The intention is to increase the the aerodynamic pressure at the rear of the vehicle and thus reduce the difference between the pressure at the front and rear. It can be very effective but is fraught with problems.
This because of the danger of side [cross] wind buffet on the increased lateral area towards the rear which tends to cause the rear of vehicle to yaw or crab sideways at the rear.
In a vehicle with a short rigid wheelbase this is quite desirable since by yawing the whole vehicle slightly into the direction of the side or cross wind it automatically counteracts any tendency to sideways drift.
I believe the first car maker to successfully exploit this idea was Maserati in the 1970’s.
But on an articulated, effectively hinged, wheelbase it is likely to cause serious difficulties in heavy side [cross] winds because although the tail moves laterally the front of the vehicle does not and this can only counteracted by the driver yawing the tractor unit with not necessarily predictable effects: depending on skill, loading, speed and force of the side [cross] wind etc.
Moreover the rearward yaw or crab of the trailer unit alters the lateral air pressures on it, depending on the design, and this can aggravate the problem, if designed to be self compensating it can cause the tail to oscillate, swinging to and fro, and the action and subsequent degree of yaw can build up with surprising rapidity unless the driver counteracts it promptly.
If it is not self compensating there is the risk that despite the driver trying to compensate it will steadily amplify the existing lateral drift until it becomes uncontrollable.
Moreoever because of the problems of the position of the centre of gravity of the trailer, and thus loading, and its wheel placement, it is not possible to predict with any certainty how it might behave for any given set of conditions: only the driver’s experience and skill can cope with this.
The only effective cures for this are automated dynamic ones which sense untoward lateral motion and correct for it. Aerodynamic attempts to do this have largely proved unsuccessful, whereas limited automatic rear wheel steering works very well. But although this was extensively researched and tested in the 1970’s/80’s I doubt it will ever be used on commercial articulated lorries.
I suspect the simple answer is to unfold your wind cheating device in fine weather and fold it up when the wind blows. Bit like a friend of mine, a noted yachtsman, who keeps his spinnaker in the bottom of a chest of drawers and has no intention of ever getting it out even on fine sunny days.
Kindest Regards
Back in 1934 Ferdinand Porsche made a car with a special tail resembling a water drop cut 3/4 near the thin end. Many cars began using that design in the 70s, especially de 1976 Alfa Romeo Giulietta 1.8, with a high and short tail that later inspired almost all other European cars.
See: http://imcdb.org/images/000/217.jpg
The CX coefficient (drag) was extremely low, even much better than the Alfa GTV 2.0 coupé, that had the same concept of truncated drop of water “à la Prosche”.
The secret seems to be in the turbulence created by the flat rear surface that replaces with advantage the missing part of the water drop.
Gareth (05:09:58) : “Rather than the tacked on boat tail, couldn’t you just have the rear doors shaped like \/ rather than — ?”
For aerodynamic efficiency, the taper angle has to be only a few degrees or so, as shown in the post. Using doors long enough to have a measurable effect on mileage would have all of the problems mentioned above: excessive length, added weight, added cost, and wind instability.
Regarding weight: I recall a land speed record car crash of the late 50’s or early 60’s. The car had a lightweight tapered tail held on by what appeared to be 1″ by 1/8″ steel straps–more than adequate under straight-ahead full throttle loads. But the car began to spin out due to mechanical failure of another component. At the resulting angle, the wind force on the tail easily broke two of the straps. The open tail caught the air like a great big scoop and turned the spin-out into a horrific end-over-end fatal crash. [may have been the Athol Graham car; I’m not sure] You have to design any such tail for loads during a tail-wag. The required strength means a lot more weight, which would also accentuate a tail-wag by adding mass at the very end of the trailer.
Ripper (22:48:53) :
Here in Australia we have the worlds most efficient road transport.
http://www.volvoadventures.com/164AusRoadTrain.jpg
To get the endorsement to drive those wiggle wagons, you have to have a glass of water on your hood for a whole month and not spill!
I don’t care how many baffles you put in there, I doubt you can come to a complete stop in that rig.
@ur momisugly D Johnson
If you’re completely free to play with the tail shape of the trailer (like, say, a NACA 0012 airfoil) then you don’t have to have the flow detach and cause drag. You could get a perfectly laminar flow around the trailer with the two side flows merging at the end of the tail. Of course this only applies perfectly to airflow along the long axis of the trailer. Air coming from the sides, i.e. at a higher angle of attack, would cause sideways “lift” and in most causes detach from the “wing” of the trailer at some point. Just being pedantic. 🙂
p.s. I don’t remember how to calculate the point of detachment either but I can still see the flow around a cylinder diagrams…
All aircraft have the sme device (a pointy tail) – it is not rocket science.
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BTW. Have you noticed that all those top-boxes people put on the roofs of their cars, are the wrong way around? Seriously, the pointy bit should be at the back, for maximum aerodynamic efficiency, not the front.
Don’t believe me? Take a look at any airfraft wing. The leading edge (front) is quite blunt, but the trailing edge (back) is as sharp as possible. Why? Drag is caused by eddied at the rear of a body, rather than a blunt front – as this truck demonstrates.
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>> John Wright (00:04:53) :
>>>This is killing a fly with a machine gun. Take a look
>>here: http://www.meridian-int-res.com/Aeronautics/Coanda.htm
I have seen a number of these already on European roads.
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I haven’t seen an explanation for this:
How do you get ther truck into a dock.
How much time and fuel does that take? Redeploying it?
Is that included in the length limits?
How many additional trucks does that require?
Oh, yeah. And how much does it weigh?
What do we do to replace the adjustable tandems?