144.17

On September 17^th Canadian engineer Todd Reichert squeezed into the cockpit while his crew installed the aerodynamic shell around him.  A rather tight fit, it does allow for the centimeter or two height variation a human body can experience during the day.  He switched on the GPS, pedal ergs and other instrumentation,  twin video screens and the radio.  A crewman gave a push to get Eta rolling... 

 

Engineering - the best engineering - is an elegant set of compromises to accomplish some task as best you can manage.  There is a certain beauty when the task is aimed at a limit.   Human powered vehicles offer delicious challenges.  I was fortunate enough to have had a modest involvement in early human powered flight, but the land speed record is special as bicycles are the most efficient means to move a human on a hard, mostly smooth surface.  

 

An adult in good physical shape can easily ride a bike at twenty kilometers per hour at an equivalent fuel economy of about a thousand miles per gallon.¹ A Tour de France class bicycle can level speed of about 60 km/h with the strongest riders.  At such speeds an athlete, and an elite bicycle rider has the highest power to weight ratio of any athlete for periods over a few minutes, is delivering about six hundred watts to the pedals.  The problem is wind resistance - about ninety percent of his effort goes into moving and swirling air.  To go faster you need to attack air resistance.  The same for moving an average person on a bike faster for the same amount of power.  Aerodynamics dominate.

 

If you look at the kinetic energy involved in moving air a simple model  shows power required is linear with the frontal area of the vehicle and air density, but increases as the cube of velocity.   If you want use as little power as possible, speed is your enemy, but if you want to go fast or be efficient at speed, beating air resistance is where you focus.  Going a bit more deeply the area confronting the air flow is an effective area... namely the area you physically measure times the coefficient of drag or C_d for the vehicle.  You can think of the C_d as a number that describes the aerodynamic slipperiness of the vehicle.  A falling piano or brick has a large C_d while a car typically has one that is much lower.  A falling human before opening her parachute has a C_d of about 0.8 to 1.2 depending on how she holds her body.  A person sitting upright on a bike is about 1.0, a TdF racer in full crouch about 0.7.  A Ford Model T is about 0.95 while many of the best cars are about 0.24 to 0.26.²  The VW One Liter was about 0.18 .. probably close to the limit for a street legal multi-passenger four wheeled automobile.   

 

Todd's Eta has a C_d of about 0.03. 

 

Todd is an outstanding, but not,  elite athlete.  The Eta needs about 265 watts to go 100 km/h on level ground.  Your car's air conditioner needs about 2,000 to 4,000 watts on a warm humid day.  The numbers quoted for the Eta vary a bit depending on the development of the product, but figure over 9,000 mpg equivalent at a legal highway speed in the US.³

 

So a few weeks ago he opened it up and went an honest 144.17 km/h ... just under 90 mph.  Just his muscles using the just plain food for fuel.  

 

Take a look at their video from a year ago:

 

I suspect they can push further even without going to an elite athlete.  I wouldn't be surprised to see 100 mph some day - that would be like breaking the two hour marathon .. everything has to come together, but it is theoretically possible.

 

This has implications for velomobiles - the rare streamlined bikes you see mostly in Holland and Germany.  It would be easy to install a three hundred watt electric motor with a very small battery - one or two kilowatt-hours would give great range and cost almost nothing - and have a vehicle capable of highway speeds. Of course you'd need safer highways..  On the other hand thirty or forty km/h speed limits with streamlined human-electric hybrids may be practical in some areas.  

 

You probably don't want to get me started on the merits of active transportation though...  The transportation we have is based on legacy standards that go back over two hundred years.  We're left with cars of a certain width, footprint and now even speed.  There has been a large improvement in nearly everything about the car, but I wonder what it would be like if we had standardized on 500 or 1,000 kg vehicles and 50 km/h rather than 110 - 130?  On the other hand we could have standardized on 4,000 kg tanks - the shape of cites and suburbs would be a different animal indeed.

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¹ This is the food energy burned and makes the assumption that a gallon of gas has about 36.6 kWh of energy.  Since the human body is only 20 to 25 percent efficient riding a bike, the power delivered to the pedals is much less and replacing the person's legs with an electric motor would improve the equivalent fuel economy by a factor of three or four.

² The reason why oil changes aren't easy is cars now have aerodynamic pans and farings under their body to clean up the airflow.

³ This is power delivered to the crank.  Factoring in human efficiency reduces this to somewhat under 3,000 mpg - how sad.  Of course you get get exercise riding any bike, so it isn't necessarily a bad thing.

 

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Recipe Corner

Nothing for now..  I'm playing with my new immersion cooker (improperly called sous vide cooking).  I had a homemade unit a few years ago, but it was too frustrating to use.  It interests me as 99% of the cooking done in them centers around meat - cooking produce is a poorly explored area, so I'm playing and making mistakes.  

Something real next time