Category Archives: Transportation

Transportation Resistance

From Galileo to Elon

Over 400 years ago as the story goes, circa 1590, Galileo performed a scientific experiment which has been reproduced in schools across the planet to this day. Galileo went to the iconic leaning tower of Piza and dropped two balls, one larger and heavy than the other. As everyone knows, they hit the ground about the same time. This disproved Aristotle’s hypothesis that heavier objects fall faster.

What both Galileo and Aristotle were not considering was an aspect of fluid dynamics – air resistance. Basically air is a fluid and it gets in the way of movement. Anyone who rides a bike or paddles a canoe knows it’s a lot harder with the wind at your face; that is, greater air (or wind) resistance. Even if the air is standing still, it still gets in the way and slows things down. The faster you go, the more important the wind resistance becomes.

A bicyclist can make about 15 to 20 mph without too much difficulty but more than that is a problem due to drag. Get rid of the drag and the sky is the limit. Cyclists have attained well over 100 mph riding behind vehicles outfitted with a fairing to shield the cyclist from wind resistance.

In years past when fuel costs were low, the extra energy expended to overcome wind resistance was not important in motorized vehicles. It is today and will continue to become more important as fuel costs rise. Nowhere is wind resistance, that is aerodynamic drag, more important than in the trucking industry.

The first effort in the industry was the addition of fairings over the cabs of 18-wheelers which resulted in a 15% increase in fuel efficiency. A more recent innovation is the addition of side skirts on each side and between the wheels of big rigs, which have been shown to improve fuel efficiency by 5 to 15 percent depending on design. Finally “trailer tails” are being added to extend the saving another 5%. All together this add up to over 30% fuel savings, with payback times of a about a year for fleet vehicles.

Small steps to save fuel or increase speed result from reducing drag, but what if you could completely eliminate drag by eliminating the air itself? Listen up. Elon Musk is the billionaire savant who produces the wildly successful Tesla electric car. He also pioneered private industry space flight with his SpaceX company, which is regularly delivering supplies to the International Space Station orbiting above earth.

Mr. Musk has proposed building giant evacuated tubes into which transportation vehicles could attain speeds in excess of a thousand mph. These tubes would work just like the little canisters that deliver your checks and cash back and forth from the bank window to the remote drive-up station. The only difference is that people or bulk goods would go in the canisters, and travel thousands of miles at thousands of miles per hour. He has suggested that eventually an underground transportation network could transport people from New York to Los Angles in 45 minutes! That requires a speed of about 4,000 mph.