Spoiler Alert: Minivans and SUVs Could Become More Fuel Efficient
by Brian Merchant, Brooklyn, New York 
on 11.16.08
Image courtesy of Motoring File
A specially designed rear spoiler could increase the fuel efficiency of minivans and SUVs, according to a new study detailed in Green Car Congress. The study reveals that such a spoiler could both reduce drag and nearly eliminate aerodynamic lift—effectively saving several miles per gallon worth of gas consumption.
The researchers used principles of fluid dynamics and ran numerical simulations in order to craft an ideal design for a spoiler specifically designed for bluff-backed vehicles. The study was published in the International Journal of Vehicle Design, and it found "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."
And those numbers, especially the inconsequential-seeming 5 percent of drag relief, can add up to major fuel savings:
"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."
It should be emphasized how different this spoiler is from those we're accustomed to seeing on performance cars, and the small ones already installed on some SUVs and minivans—these spoilers may appear a little strange by comparison:
"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."
So there you have it: minivans with wave-like spoilers that'll get you extra miles to the gallon—pair that with hybrid technology and it sounds like a better way to take the kids to soccer practice to me.
More on SUVs and Minivans:
Beijing Auto Show: Escalade SUV is GM's Star, Huge Cars are in ...
GM Closing 4 Trucks and SUV Plants, Betting More on Smaller Cars ...
Help Bring Toyota’s Hybrid Minivan to the U.S. : TreeHugger
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Er...67mph?
How about driving say, 60mpg, thereby saving 7mpg while skipping the thousand dollars that car makers would charge for the new spoiler?
You could install an aftermarket one way cheaper than the factory can do it for.
$1000 for an OEM spoiler? John, you must work for the Air Force where you are used to paying $600 for toilet seats and such.
In the real world, this would add maybe an extra $200 to the sticker. But hey, I'll sell you one for $1000 if you want. :P
Partial concession to Willy Bio.
I just checked and a "conventional" aftermarket roof-back spoiler for luxury SUV goes for $350 to $420. For the cheaper versions its' more like $250-$320.
That is just the cost of goods. The labor cost for painting to match the body and fix it to the top will be, say, at least $200: so look for a total cost of aftermarket spoiler to be around $600 plus tax. Could be higher if its a new design or painting charges are more.
"How about driving say, 60mpg, thereby saving 7mpg while skipping the thousand dollars that car makers would charge for the new spoiler?"
If it saves gas at 67mph, it saves gas at 60mph, so not a bad idea. 108kph and 67mph is an odd speed to do a study at IMO. There are many states with speed limits in excess of 70 mph, so many people probably drive faster than that (and some are stuck in bumper to bumper stop and go traffic and would love to move that fast!)
You can tell how bad the aerodynamics of an SUV or van are in part by how much dirt and road grime ends up on the rear window, and you rarely see this on the more rounded back of the newer crossover vehicles. More than one way to skin a cat.
108 km/h works out to 30 m/s, which are the units most used in aerodynamics. Well, I don't know about the USA which may use furlongs per firkin for all I know.
I installed vortex generators on the back of my van (using 2 cut - up yogurt containers) which gave me about a 5% decrease in fuel consumption so this seems realistic.
Then I put pretty commercial ones on and since they are so expensive I have not been taking them on & off for testing.
The rate of flow of air over a spoiler (or anything else) is characterized by aerospace engineers by something called a Reynolds number, not by usual velocities like kph and mph. The Reynolds number has its roots in the fact that if you scale down a model of car by 50% you also need to test it in the wind tunnel at lower air speeds to get test results that are representative of the real thing at full size. The proper air speed, though, is not necessary 50% of the full-scale air speed -- in large part because you cannot scale down the air molecules to suit the model. Even though this result was obtained by numerical simulation, the theory on which the simulation is based relies on Reynolds numbers to characterize velocity accurately.
All of which is to say that the researchers most likely used a convenient Reynolds number that is representative of travel at highway speeds. The exact speed in kph or mph that it corresponds to would depend on the size of the vehicle being studied, so in the end you sometimes have some oddball numbers like that.
"How about driving say, 60mpg, thereby saving 7mpg while skipping the thousand dollars that car makers would charge for the new spoiler?"
I have a full size truck with a cap on it so pretty much the same as a full size suv. Dropping from 65 to 60mph gains less than 1mpg. dropping to 55mpg I gain 1mpg on long trips. So drpping frm 67 to 69 osn't going to save 7mpg.
John,
The point of this new spoiler is for automakers to integrate them into the design, hence my referral to "OEM".
An OEM version would cost them maybe $20-$50 in materials and add a few seconds of robot assembly time. So give it a nice markup, and you have about $200 added to the sticker.
Sure, aftermarket, who knows?
"Er...67mph?
How about driving say, 60mpg, thereby saving 7mpg while skipping the thousand dollars that car makers would charge for the new spoiler?"
Units John, Units. one mph less does not equal one mpg more. Behaivor is important but better tech magnifies good behaivor.
Years ago, I added a factory optional rear window spoiler to a '79 Malibu station wagon. It helped keep the rear window clean and improved my 60 mph fuel economy by ~ 2 mpg. Not bad for a $20 spoiler from the salvage yard and a can of touch up paint.