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New Boat Tail Design Could Improve Class 8 Truck Fuel Economy by 10%

9 November 2005

Boattail
The Clarkson boat tail during geometry optimization testing.

Vehicle drag is a costly problem for the long-distance heavy-duty trucks. A modern Class 8 tractor-trailer can weigh up to 80,000 pounds and have a wind-averaged drag coefficient around CD=0.60. As speed increases, so does the energy required to overcome aerodynamic drag. At 70 mph, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck.

A team at Clarkson University has developed a new implementation of an well-known concept to alleviate some of the drag: an unventilated, planar-sided cavity device attached to the rear of the trailer—also known as a boat tail.

The Clarkson implementation, which is designed to minimize interference with the vehicle and is now being patented, delivers more than a 0.6 mpg improvement in fuel economy in preliminary testing, according to Prof. Ken Visser, the research leader. That might sound like a low figure, but in the context of a vehicle that delivers 5 to 6 miles per gallon, that’s better than 10%.

The Clarkson researchers evaluated more than 100 different design geometries, where cavity length, boat tail angle, and inset from the trailer edge were varied at yaw angles up to 9 degrees. They found that the optimum geometry of a four-foot device with a boat tail angle of 10° and no inset could reduce the indicated drag coefficient up to CD=0.12.

Composite Factory of Plattsburgh, NY has teamed up with Clarkson University to develop a prototype of a viable commercial version of the open cavity design. The researchers are organizing a year-long fleet test of 50 vehicles to confirm the results under varied real-world operating conditions.

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November 9, 2005 in Diesel, Fleets, Fuel Efficiency | Permalink | Comments (16) | TrackBack (0)

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An exemption on length for boattailing should be on the agenda.

"At 70 mph, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck."
Should semi trucks be traveling at 70mph on our highways? In europe all heavy trucks are electronicly limited to 89 kph.

I have to check the EIA numbers and see how much fuel is used by commercial trucking.  The US uses about 4 million bbl/day of distillate, but not all of that goes for vehicles and not all diesel fuel goes for semi-trucks; still, even a large fraction of 400,000 bbl/day is a whopping load of fuel.

"even a large fraction of 400,000 bbl/day is a whopping load of fuel." I assume you mean to say 'a small fraction of 400,000 bbl/day but I agree completely. A .6 mpg increase may sound tiny but these trucks get very poor gas mileage (5-6 mpg) and drive a ton of miles so this incremental improvement equates to a significant quantity of saved gas.

On that note, I wonder what portion the savings from putting these on all semis in the US would be of the annual output of drilling in ANWR... (ANWR at its peak would produce an estimated 870,000 bbd) If we were serious about domestic energy security (and not simply about Exxon's profits) we would be looking for a number of simple energy efficiency measures like this. We could easily make much more significant gains towards energy security through efficiency than through drilling in ANWR.

"65% of total energy expenditure---" The losses to heat, noise and friction are undoubtedly over 65%. Can we be more precise with our discussion?

Damn. No more drafting.

Bet Ernie Rogers could have figured that one out too! He's the engineer that put a "tail" on his silver VW TDI New Beetle to get phenom mpg. If they can patent this truck tail, Ernie should patent his bug tail!

I'd be shocked if these devices don't start appearing soon. The trucking companies are getting hammered by the high cost of diesel. They'd be insane not to implement something like this. The thing would probably pay for itself in a very short time considering the miles driven and the mpg rating of these vehicles. Don't think government mandates are necessary here. No brainer economics oughta drive this one pretty quickly.

"The losses to heat, noise and friction are undoubtedly over 65%. Can we be more precise with our discussion?"

What is meant is that 65% of the energy output by the engine is used up overcoming aerodynamic drag, nothing to do with the efficiency of the engine itself.

I remember reading about something similar to this over ten years ago. Nothing became of it then. I believe it wasn't implemented because it is a safety hazard, if someone rear-ended a truck with one of these it would be driven through their windshield.

Not to mention when the truck pulls up to the warehouse, what's the driver going to do with that thing?

"Should semi trucks be traveling at 70mph on our highways? In europe all heavy trucks are electronicly limited to 89 kph."

I have been a professional truck driver for over 20 years, and I will say it one more time..... Whatever speed cars are traveling, trucks should be allowed to go the same speed, Why? It is very simple, two objects traveling at the same speed creat less FRICTION (Traffic accidents) than two objects traveling at different speeds. It is absurd to think it is safer to have trucks traveling at 55 mph and allowing cars to go 70 mph. If you look at the states that do have this idiotic rational you will see that their truck vs. car accident is rate is WELL OVER 50% higher than the states that allow the 2 vehicles to go the same speed. If you are on a 4 lane highway (2 lanes in each direction) there is a constant birrage of people passing the slower trucks, not safe. however if both are running the same speed, much less passing, much less accidents. IF PATT and CRASH had thier way trucks would have to travel on the shoulder running in first gear waving flags and flashing lights, the thinking behind this theory in absurd. All I am saying, I dont care what speed you want me to run, just make ALL vehicles run the same speed. Lawmakers wont do that though, because they all drive cars and dont want to go slower, the "split speedlimit" has no effect on anyone but the truckers......so they think. Ever see a car rearend a truck, I have, it isnt pretty. And one last note, I am not in Europe, I am in America :)

Everything starts somewhere. Remember when the kw t600 came out, everyone said ugly truck,no way were they ever going to drive one.Best fuel mileage and best selling truck in a very long time. It will take time but i belive it will catch on. I run from TX. to WA. every week and with the 62+ mph wind i just had in Wy. i sure could use one.Where do i sign up.I am a o/o with my own trailer,i bleive it would work out well. Company trailers ,i dont think so.Look at the way the company drivers tear up the equip., "beacuse its not mine".

Everything starts somewhere. Remember when the kw t600 came out, everyone said ugly truck,no way were they ever going to drive one.Best fuel mileage and best selling truck in a very long time. It will take time but i belive it will catch on. I run from TX. to WA. every week and with the 62+ mph wind i just had in Wy. i sure could use one.Where do i sign up.I am a o/o with my own trailer,i bleive it would work out well. Company trailers ,i dont think so.Look at the way the company drivers tear up the equip., "beacuse its not mine".

The problem with this 'news' is that the fuel economy improvements with this device are grossly overexaggerated. This concept has been around for 20 years and the potential fuels savings are only 2-3%

Also, this design results in frequent damage and operational problems. Drivers forget to open the doors and the unit will be damaged too often. Additionally, the space the boat tails require present problems in the truck yard and parking lots.

There are important changes that can be made to improve aerodynamics for trailers, but this one is more hype than anything else.

Quote from above:"these trucks get very poor gas mileage (5-6 mpg)"

Actually they are much more efficient than any car on the road. Reason 80,000 lb vehicle 6 mpg compared with normal SUV 5,000 lb vehicle 20ish mpg. If you do the math this makes tractor-trailers about 4.5 times more efficient lb for lb. I wonder regularly why we stuggle to create 90 or 100 mpg cars and trucks, as this would only be the same efficiency already available on semis and busses.

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