Archive for the ‘Aerodynamics’ Category

Racers, Start Your Engines

January 29th, 2011 Comments off

Flying Lizard Porsche/Riley Daytona Prototype

The racing season officially starts today!  The Grand Am Rolex Sports Car Series is running its 49th annual 24-hour endurance race at Daytona as I type this.  And while the France family dumbed down the series back in 2003 with the introduction of the low-tech tube-framed Daytona Prototypes, the racing is exciting at least.  Endurance racing is supposed to be about patience and strategy, but this running is already off to a sprint-race-like start.  It’ll be interesting to see if the pace can be maintained while the little hand travels twice around the clock…

Audi R15 TDI Le Mans Prototype

The more relevant sports car series, the American Le Mans Series, has their winter test at Sebring early next month, with the racing commencing in mid-March.  Meanwhile, Formula 1 starts its season in Bahrain about the same time.  NASCAR also begins its long and boring season next month … but does anybody really care?  (Though it’s the most popular series in the U.S. – much like McDonalds is the most popular restaurant – it’s essentially a spec-series using outdated technology, and its huge fan-base has been in decline of late.)

Sebastian Vettel's 2010 Renault-powered Red Bull F1

But more importantly, Cub Scout Pack 350 held their Pinewood Derby this morning, and your author’s 7-year-old son took first place in his den!  Sure, the construction of the car was very much a father-son project (emphasis on the father).  After all, it’s unwise to hand over saws and power tools to a 1st-grader.  But the boy designed the profile, and repeatedly rationalized his design decisions based on the fact that we wanted to optimize the aerodynamics.

…And if that doesn’t solidify my credentials to bring you this blog, then I don’t know what does!

2011 Pinewood Derby "Blue Pirate"


March 8th, 2010 Comments off

There’s a big push to increase the fuel efficiency of our country’s – our WORLD’S – passenger cars.  All of the major automakers are working on more fuel-efficient engines, hybridization, electrification, lightweighting, idle-reduction, and other technology pathways in an effort to meet more stringent CAFE standards in America and compete in the new, greener automotive landscape.

But what about trucks? No, I don’t mean the pickup in your neighbor’s driveway.  I mean the big, 18-wheeled, freight-haulin’, diesel-drinkin’, noise-makin’ semis that move approximately two-thirds of our nation’s freight around, accounting for around 7 TRILLION dollars annually – a substantial portion of our economy.  These trucks get, on average, around 6 miles per gallon.  Horrible, right?  (Well, consider that these trucks, when fully loaded, weigh up to around 80,000 pounds – about the same as 20 passenger cars.  If you assume the cars get 25 mpg each, then the group as a whole gets the equivalent of 1.25 mpg.  In that respect, the semi ain’t so bad…)

…Which brings me to my point.  When talking about fuel efficiency in the trucking industry, FREIGHT efficiency is the proper metric.  (Units of freight-ton-miles-per-gallon are most often talked about.)  And despite the fact that not much effort has been put forth historically into improving the freight efficiency of long-haul trucks, that trend is certainly changing.  The US Department of Energy recently announced awardees under the SuperTruck program – funded in part by the American Recovery & Reinvestment Act of 2009 (i.e., the Stimulus Bill) – to improve the freight-fuel-efficiency of Class 8 trucks by 50%.

And how is this being accomplished?  Although the impacts of hybridization in long-haul trucks may be modest, electrification can have a LARGE impact in idle-reduction at truck-stops.  (Today, when truck drivers take their mandatory rests at truck-stops, they must let their engines idle to maintain the heating, cooling, and other ancillary functions within their cab.  Having an auxiliary power unit – whether battery or fuel cell – could eliminate this need.)  Aerodynamics plays a HUGE role as well.  Think about it – semi-trucks today are a bit like a brick – an extremely large brick – blasting down the freeway at 70 mph.  Aerodynamic improvements are the low-hanging fruit.  Even simple add-ons that address the gap between the cab and the trailer, the space between the trailer and the road, and the flow-field immediately behind the trailer can have significant impacts.

Beyond this, truck OEMs are working on improvements with more efficient engines through downsizing and downspeeding combined with improvements in the transmission and controls.  The use of waste heat recovery systems is being investigated to capture some of the heat energy that is released through the exhaust system, converting it to electricity to power accessories.  Even driver aids, such as eco-feedback to provide information about the fuel-economy impacts of driving habits, and intelligent route mapping that considers traffic and topography in plotting the most optimum course for shipment, are being considered.  Super-insulated cabs to reduce the heating/cooling load, and super-wide low-rolling-resistance tires are also being developed.  The list goes on and on!

Why is this important? By some estimations, the emissions (of pollutants AND greenhouse gases) from passenger vehicles in the U.S. could flatten out as our vehicles become more efficient, combined with the (slight) potential for mass-transit as our population increases.  (In developing countries however, that might not be the case, unless you’re an eternal optimist and believe that China/India/Brazil will seize the opportunity and grow more smartly than we did.)  Freight, on the other hand, will continue to grow with our population, magnified by the globalization of trade. Basically, if we don’t do something now, the problem could be huge.

Plus, freight companies are businesses.  Businesses make money (or fail).  Rising and uncertain fuel costs wreak havoc with their operating expenses.  More freight-efficient transport translates into more stable profits for freight companies, and more stable prices for the consumer.

Of course, we haven’t even begun to discuss rail-freight yet.  But that’s a topic for another day…

Single File, Please

December 6th, 2009 Comments off

Volkswagen L1 Concept

Back in September, at the 2009 Frankfurt Auto Show, Volkswagen displayed its L1 Concept vehicle, claiming an astounding fuel economy of 170 mpg.  How did they do it?  Well, they start off with an ultra-efficient hybrid powertrain comprised of a 0.8-liter turbodiesel (TDI, which I discussed here) and a 10kW electric motor.  (No plug needed here!)  They use an ultra-light-weight body of carbon-fiber and plastic.  And they designed it with an incredible drag coefficient (Cd) of 0.195.  Improving on the aero efficiency (a topic I discussed here), is a small frontal area, accomplished by arranging the two occupants of the L1 in tandem.  (Remember, the amount of power needed to overcome the air resistance when moving a vehicle is directly proportional to the frontal area, just as it is to the Cd.)

Nissan Land Glider Concept

Nissan Land Glider Concept

At the Tokyo Motor Show a little over a month ago, Nissan unveiled its Land Glider concept.  Unlike VW’s L1, the Land Glider is a pure electric vehicle, with two motors powering the rear wheels.  (No word on the energy efficiency of the vehicle.)  It also has novel technology, such as the handling-improving capability of leaning in the corners, and crash-avoidance sensors to maneuver the vehicle around objects with which it would otherwise collide.  The Land Glider also (presumably) is aerodynamically efficient – at least it looks that way.  And like the L1, this is achieved partly through the use of tandem seating.

Could this be the shape of things to come? Two-passenger vehicles have existed for a while, from sporty roadsters (like the Miata) to econo-boxes (like the Smart).  So, why not cut the frontal area down, and place the passengers fore and aft?  Is this just too impractical – or too unusual – for the average consumer to handle?  With many pushing for purpose-driven vehicles (rather than cars that can do everything, like what most of us drive today), we may eventually see a lot more variety in the types cars on the market.  It’s not so far-fetched that we may see a derivative of the L1 or Land Glider for sale in a few years.  And although tandem seating doesn’t really lend itself to a romantic time at the drive-in, it certainly can play a part at improving the fuel-economy once the wheels are in motion.


September 8th, 2009 Comments off

I’ve said (as have many others) that the Toyota Prius, (new) Honda Insight, and Chevy Volt all look similiar, at least insofar as the overall shape of the vehicles.  (My personal opinion is that that Volt is much better looking than the other two, with the new Prius coming in second, but this isn’t really related to shape.)  The reason for this is that they are all efficient vehicles, so one of their design goals was a low drag coefficient.  An article in this month’s Automotive Engineering International (Aerodynamics Soar) speaks to this, mentioning “complaints that cars like the Honda Insight and Chevrolet Volt, which balance similar missions of efficiency and cabin space, are derivative of Toyota’s Prius, when actually they are all recognitions of the fact that similar goals will produce similar designs.”

A recent video on the Chevy Voltage website talks a bit about the work that went into optimizing the aerodynamics of the Chevy Volt.  One remarkable data-point is that aerodynamic work on the Volt increased the all-electric range by 7 MILES from the original prototype!  Aerodynamic efficiency makes the Volt a PHEV-40, rather than a PHEV-33! To my knowledge, GM still has not announced what the Cd for the Volt is, except to say it’s the lowest of any GM vehicle since the EV1 (which had a Cd of 0.195).  For comparison, the Prius has a Cd of 0.25, and the new Ford Taurus (a modern vehicle for which aero is important, though not as high a priority as it is for hybrids) scores a 0.32.

The drag coefficient (Cd) is directly proportional to the amount of power needed to overcome the force of the air pushing against a vehicle in order to maintain a steady speed.  This power is also directly proportional to the frontal area of the vehicle, the density of the air, as well as the cube of the vehicle’s velocity.  So, fuel economy can be increased by improving the aerodynamics, reducing the size of the vehicle, driving in less-dense air … or, to an even greater degree, slowing down.  The third option seems difficult, and the fourth a bit boring…

If you still think that aerodynamics don’t matter, check out the extreme, where Cd is optimized at the expense of downforce, causing this Mercedes at Le Mans, and this Porsche at Road Atlanta, to become airborn!

Mercedes CLR at Le Mans, 1999

Mercedes CLR at Le Mans, 1999