Published on September 15th, 2008 | by Nick Chambers
Do Cars Really Need to Look Like UFOs to Save Gas?
With the world focused on fuel economy, advanced car design seems to be converging around one point in space. And I do mean, literally, a point in space — a point sometimes seen flying over Roswell, or crashing in the Bermuda triangle.
Regardless of what you think about this type of design, it begs the question: do cars need to look like alien spacecraft to get decent fuel economy?
Recently, when I posted about the newly announced Honda Insight’s uncanny resemblance to the Toyota Prius, I sparked a rather *spirited* debate with fellow blogger and former Gas 2.0 writer, Ben Jones (ecomodder) regarding aerodynamics and why all high mileage cars are starting to look the same.
His point was that if we want good fuel economy, we shouldn’t be upset when all cars start to take on the same shape. Basically, we shouldn’t whine about cars looking more and more like flying saucers if we want to save gas.
But I wasn’t convinced that in order to get good fuel economy all cars will have to look like the Prius. I remembered reading about a Mercedes concept car based on the shape of a Box Fish that looked nothing like the Prius and had an unexpectedly better aerodynamic profile. Also, the Aptera Typ-1, which looks more like a mutant sperm than the Prius, has much better aerodynamics too.
So, you’re probably saying, “Yes, both the Typ-1 and the Mercedes Box Fish Concept have better aerodynamics than the Prius, but they’re so strange looking that they’ll only appeal to a very small portion of the population.”
And you’d be right. Which brings us back to the question of the Prius shape, but now framed in a different manner. Perhaps the answer is that the Prius shape is the most aerodynamic design you can have and still appeal to a large enough market to make a profit (and an environmental difference).
But is the Prius design really a good compromise? Does it do itself justice by trying to accomplish so much in one vehicle?
To get to the root of this, I decided to seek out an expert opinion and contacted MIT professor, Mark Drela. Dr. Drela is a professor of fluid dynamics in MIT’s Department of Aeronautics and Astronautics and has been an adviser to MIT’s Vehicle Design Summit regarding vehicle aerodynamics. In a response via email, Dr. Drela had this to say:
“All common cars, including the Prius, are aerodynamic bricks. The lowest drag shape that you can wrap around a passenger cabin resembles the front half of a sailplane fuselage. The Aptera comes pretty close, assuming they designed it properly.”
What he’s saying is that the Aptera Typ-1 probably represents the ultimate achievable aerodynamic shape for an enclosed vehicle with tires. He goes on to say:
“We know how to make extremely low drag vehicles (e.g. the Aptera), but the main problem is making them acceptable to consumers and making them ‘safe,’ however that is defined. I see it mainly as a marketing and lawyering problem, not an R&D problem.”
So there you go. The Prius is not the most aerodynamic shape, it’s the most aerodynamic shape that’s also visually acceptable and safe enough to meet standards. But does aerodynamics even matter that much? I mean, some cars today are getting excellent mileage and don’t look like the Prius or the Aptera.
The issue comes down to the fact that achieving good fuel economy on the highway is an entirely different beast than achieving it in the city. Trying to make one vehicle that excels at both creates a vehicle that doesn’t do well at either. As Dr. Drela says:
“At steady highway speeds, low air drag is most important. If you’re braking frequently, then low mass is most important. A hybrid squeezes the two very different missions into one vehicle, and you sort of get the worst of both worlds. It doesn’t do either mission as well as a targeted vehicle, and is more complex to boot.”
Instead Drela suggests that a better solution would be to have two targeted-mission cars:
- An extremely light plug-in electric car for city driving
- An extremely low drag internal combustion car for highway driving
He points out that, obviously, owning two cars is more expensive up front, but that the lifetime economics and energy use of this arrangement might prove that it is the best solution.
Purchasing two vehicles up front might be out of reach for most people, but, if Dr. Drela is right, perhaps we should be looking at ways to make this easier for everybody to do? Government incentives?
Certainly the car companies would be happy to sell you two cars at once — perhaps they could work up a discount on the second car purchased if purchased at the same time? Does this seem like a fantasy world that sounds great on paper but would never fly in reality? What do you think?
Posts Related to Fuel Economy and Plug-Ins:
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