Reflections on the potential of human power for transportation

Tuesday, December 27, 2011

Back to the Future: Before Edison2's Very-Light Car

"Those who cannot remember the past are condemned to repeat it." George Santayana, 1905
In September of 2010, the Progressive Automotive X-Prize concluded with the announcement that the Very Light Car from Edison2 had won 5 million dollars for best performance in its mainstream vehicle class. The class was a four passenger car with four wheels arranged in the traditional rectangular layout. It was the only vehicle in the class to achieve over 100 MPGe. What is interesting about the VLC was it was powered by a 40hp. 250cc I.C. engine and weighed only 830lb. The efficiency was attributed to the light weight and very low aerodynamic drag, (a CD of 0.160 in a later version.
Now cyclists, probably more than any other group of commuters, know the significance of both aerodynamic draw and vehicle weight on efficiency.  The efficiency of chemical to mechanical work in muscle is about 25% and mechanical power generated by the human body is fixed at about ½ Hp or less for periods of about an hour. So it is not unreasonable to use top speed as an indicator of vehicle efficiency.
Since the vehicle weight is usually a small component of the system weight (vehicle & rider), and then is only noticeable in acceleration/deceleration and hill climbing, its influence on vehicle velocity is significantly less than air drag. (Yes, weight will affect rolling resistance as well)
George Georgiev and his Varna team have probably achieved about the lowest aerodynamic drag of a human powered vehicle. In 2009 his Varna Tempest, with Sam Wittingham as the motor, covered a flying 200m. averaging 82.8mph. That same vehicle covered 56.3 miles in an hour on a GM test track. From an aerodynamic standpoint, it takes 3.2X the power to go 82.8mph than it does to go 56.2mph, but oddly enough the later record was harder to break. Exercising in an enclosed space for an hour requires adequate rider cooling and supplying fresh air to breathe without compromising the aerodynamics.
Now the Tempest could not have competed for the X Prize.  There were two alternative vehicle categories. One consisted of a two-side-by-side- passenger layout and the other two-passenger-tandem layout.   There was a motorcycle with outriggers in the tandem category as well as a side-by-side pedal-assisted electric tricycle in the side-by-side category. But there was no single occupant category, which is unfortunate, since so many short trips are made by vehicles with only one occupant.
The idea of a single-occupant, all-weather, high-efficiency commuter vehicle is by no means new. Pedal-powered velomobiles such as four-wheel Velocars and three-wheel Fantoms were used in Europe during WW2, when conventional cars were not available. Several design surfaced during the bike-boom in the USA during the early seventies. The human-powered-vehicle movement which began in the mid seventies has spawned numerous novel designs. And of course, there is the Sinclair C5 pedal-assisted electric tricycle from the early eighties.
My favorite is Bob Bundschuh’s marvelous Pedicar from 1973. While its use of four wheels and its linear-pedal motion may not have been optimal, it definitely captures the potential utility of such a vehicle. I believe the Pedicar is the template for a future commuter vehicle.
As of yet, these vehicles have not caught on as a serious transportation alternative. The designs may not have been adequate and energy concerns weren’t as important as they are now.
But maybe now the world is finally ready for them.
Hephaestus