## Novel Spoiler Design Reduces Fuel Consumption for Minivans, SUVs

##### 12 November 2008
 Cross-sectional view of the new spoiler attached to the back of a modeled minivan. Click to enlarge. Source: Inchul Kim

A team of researchers has used the principles of fluid dynamics and numerical simulation to design a new rear spoiler for bluff-backed vehicles (such as minivans and SUVs) that can reduce drag and lift significantly.

In a paper published in the International Journal of Vehicle Design, Inchul Kim of Metacomp Technologies, in Agoura Hills, California, working with Xin Geng and Hualei Chen of the University of Michigan-Dearborn report that the aerodynamic drag and lift on a mini-van moving at 108 kph (67 mph) are reduced by 5% and more than 100%, respectively, when the new spoiler is attached to it.

With as much as 65% of the power required for ground vehicles to travel on a highway at 70 miles per hour is being consumed due to aerodynamic drag, the reductions from the spoiler could increase fuel economy by up to several miles per gallon, the researchers say.

A traveling vehicle experiences two main aerodynamic forces: drag and lift. Drag (air resistance) is in the opposite direction to the movement. Lift is perpendicular to the drag and to the road. The greater the drag, the more energy is needed to propel the vehicle and so the more fuel that it uses to cover the same ground at a given speed. Lift reduces the amount of friction between the tires and the road and so lowers traction. This also reduces efficiency as well as deleteriously affecting handling.

Total aerodynamic drag acting on a moving body is the sum of friction drag (the drag force component on the body due to the shear stresses) and pressure drag (the drag force component on the body due to the pressure).

The total drag on a streamlined body such as an airfoil is contributed mainly by the friction drag and is very low at high Reynolds numbers(CD ≈ 0.01 at Re ≈ 106). In contrast, the drag on a body with a bluff back is contributed mainly by the pressure drag and is very high (CD ≈ 1.2 at Re ≈ 106). This, the researchers say, is because the boundary layer flow separates from the rear top of the body so that the pressure magnitude at the rear of the body is much smaller than that at the front.

Conventional spoilers resemble an inverted plane wing and generally work by increasing the downward force on the back of the vehicle as well as improving the flow of air across the bluff rear. The new rear spoiler resembles a wave in profile rather than a wing.

In developing the spoiler for bluff-backed vehicles, the researchers focused on three conditions:

• The rear-spoiler should act as a diffuser when it is attached to the roof end of a vehicle so that the pressure on the back of a vehicle with the spoiler should be higher than that on the back of a vehicle without the spoiler.

• Normally any additional attachment to a vehicle causes an additional drag due to the presence of it that is attached to a moving body. The rear-spoiler should be designed in such a way that the drag on the spoiler itself should be much smaller than the total drag or be negative (i.e., in the direction of the vehicle motion).

• The lift on the spoiler itself should be minimal if it is positive or be negative (i.e., in the direction to the ground).

The scientific principle and geometry of the new rear-spoiler are completely different from those of conventional spoilers that have been used so far. The new rear spoiler acts like a diffuser when it is attached to the back of a vehicle, and thus, the pressure on the back of a vehicle with the new spoiler is higher than that on the back of a vehicle without it.

The new rear spoiler can be applied to other minivans, vans, sports-utility-vehicles and buses. With the new spoiler attached, the vehicles having a bluff back would have not only a higher mileage but also better stability.

—Kim et al. (2008)

Resources

• Kim, K., Geng, X. and Chen, H. (2008) Development of a rear spoiler of a new type for mini-vans, Int. J. Vehicle Design, Vol. 48, Nos. 1/2, pp.114–131 doi: 10.1504/IJVD.2008.021155

Any good reasons why the many thousands engineers working for the Big-3 did not apply this type of spoiler 50+ years ago?

How about a mechanical spoiler that would be automatically raised at 50+ mph and automatically adjusted to minimize drag and optimize lift at any given speed to reduce fuel consumption.

"Any good reasons why the many thousands engineers working...."
Unless they are forced to by the Government, they don't give a rat's ass.

DS:

Would they change their mind if they were to be out of a job within a few months?

HarveyD:

I'll bet you a Starbucks coffee, the management at GM will be the same clowns after the \$25 Billion bale out as before.

They have been clowns for decades, beginning from the oil shock of the 70's. I would expect them, as the world's biggest auto manufacturers, to seize the initiative and be the FIRST to develop fuel sipping cars like hybrids and market to the people. You should expect to see the Volt in the showrooms 4-5 years ago.

I don't think the bailout will help GM (and the the other two).
Knowing their track record they'll just squander it.
I don't think they deserve it. Let them fail.
Let them go bankrupt.
Spend the bailout money on Teslas and Zaps and Project Better Places.
I bet this will generate twice as many jobs as the big 3 currently employ.
AND help the environment while freeing North America from oil dependency.

This spoiler is not all that different from what came standard on my dad's old 1978 Impala wagon, so it's not exactly a new concept. The general idea is to move air from a high pressure zone to a low pressure zone.

Gee, does it count that I had an airfoil on the back of my Chevy Camaro Z-28 in 1967 when Super Premium Sonoco 260 cost about 30 cents a gallon. I guess GM was just ahead of the times back then.

5% improvement in drag? You can get much the same at lower cost by using vortex generators. You can buy them, they're call Airtabs (google it), or you can make them yourself, like the guy two doors down from me did. His old beater got a 3% improvement in mpg after an hour's work and \$5 in plastic-card stock. His juryrig doesn't look pretty but his van was ugly to begin with so he doesn't care.

Yes GM, Ford, and Chrysler could have made more efficient cars. There are ways to drive that use less gasoline. Neither the companies nor the drivers had much interest in reducing fuel use.

Would any young man in the US buy a car that had a fifteen horsepower rating and took twenty seconds to get to seventy miles per hour? What if it only had one piston? Constantinescu made a torque converter that would allow a car with low horsepower and only one piston climb any hill (slowly).

The expensive gasoline of the last year is only because of the failure of the US government to prevent speculation in the US government controlled oil supply.

Low drag is obviously not a feature that is an important selling point for a 300 hp sports car where style is master. Nor is it important for an SUV where size is important. All increases in efficiency have come secondary to pollution only by government regulation. ..HG..

Interesting idea: give Tesla and Aptera \$25 Billion with the contingency that they have to locate manufacturing operations in the proximity of the current Big 3 to prevent massive frictional losses in the labor market.

Let's face it, it's not the workers that suck, it's the management and group think philosophy (UAW is another story, IMO not a bad idea they just got greedy).

With \$25 billion, I'm quite confident that Tesla and Aptera could spark an automotive revolution and take us completely off foreign oil.

Just imagine the engineering and tooling you could buy with that kind of money in the present economic environment! When the companies are on their feet the company could be sold to the public markets at which point the taxpayer might actually make a profit! (seriously)

To give 12 billion to GM when the company is worth 2 billion on the stock market is a fraud. It will be better for everybody to let one company of the three fail and let the other survive if they can.
I agree that this momey will be better spent in ev tehnology. My guess is that for \$25 billion one can make a diference if invested in production facilities for large format batteries.

Minivans are EVIL!!! We must all start a hate minivans campain to go with out hate SUVs campaigns. We can sneer at minivan drivers and tell them, "you can get by with a fuel efficient car, you evil, evil, person." "You support terrorists." "You are KILLING mother Earth!!!"

Al Gore is the greatest!!! Go Obama!!!

A minivan is not bad if it is used to carry 6 or more passengers.
Minivans have lower drag coefficients than SUVs.
It would be clever if the manufacturers make minivans with
high torque, 4-cylinder diesel engines.
Like the new Mercedes-Benz engine:
2143 cc displacement,
power: 204 HP
torque: 369 lb-ft
this generous torque is good enough to move any minivan.

http://www.greencarcongress.com/2008/04/mercedes-benz-i.html#more

The Toyota Sienna weights about 500 kg less than a GM Suburban, and,
the Sienna can carry more weight than the Suburban.
(with the specs. of the vehicles sold in México)

The Saturn Vue Greenline SUV's have a spoiler similar to this.

Why wouldn't this also work on tractor trailers, station wagons, or even most hatchbacks?

It also seems that there is a large opportunity for the aftermarket to provide retrofits for popular cars, much as they do now, except that these would actually provide some amount of benefit instead of only being eye candy.

DS:

You may very well be 200% correct. Where do I send the two coffee?

What I find a little surprising is the fact, that many banks were helped around the world almost without questions asked.
Actually, a big Swiss bank just got a \$50 billion package by the Swiss National Bank and a week later that same bank announced that it's going to pay \$7 billion in bonuses. (It reminded me of the AIG guys going on some expensive Spa-trip after their bailout).

I find it odd, that banks losing money, despite not investing in expensive R&D, tooling and factories, can easily get a bailout and if a company is an expert in vehicle engineering, design and production they're supposed to be on their own.
Keep in mind, it's comparitively easy to pop up service companies from scratch, but nobody will pop up a large vehicle industry from scratch. If GM would go belly up, it's gone and probably won't be replaced by some new, innovative American start up.

I don't remember banks inventing electricity, vehicles, aircrafts, computers or freeing the world from the Nazis and I don't see why and how particular failure-banks may help us getting any further

Might try something like this on my pickup, since I don't have a shell or anything like that it might help my mileage on the freeway.

Aerodynamics is complex. At different speeds, airflow changes. Also at different speeds, air must be made to flow to accomplish different objectives. Those people declaring that old spoilers can do what this new spoiler can do are wrong.

If drivers don't have leadfeet, use of a simple older-style drag reducing spoiler might meet their objectives. But fast drivers have much more complex needs. To reduce drag & be able to cause downforce at high speeds, this new more complex airfoil spoiler will be needed.

I have a pickup with (dual) sliding back windows. I've found out that I can increase my mileage up to 2 MPG just by fully opening both back sliding windows, and rolling down both side windows a couple inches or so. This isn't very practical when it raining or the 6 months of C-O-L-D weather in Wisconsin. This principal is similar to the spoiler in that it replaces the drag (low air pressure) with air. This reduces the drag on my vehicle. My hard toneau cover on my bed dramatically reduces the drag of the bed as well. Now if I could only reduce the drag of my tailgate. The spoiler doesn't look it would be very durable on a working truck.

The idea about the new concept of this spoiler is not surprising. It seems not new but sounds innovative though. If this could be possible to reduce fuel consumption, I will really buy one. But for now I will just used my rebuilt engines.

Great to know how aerodynamics can be apply in different fields. This concept seems new to me and I agree with the ideas and research above. If created perfectly, this is very efficient.

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