Table of Contents

Human Power and Propulsion




Because the human body is not 100% efficient, the heat generated during activity must be dissipated if sustained effort is to be maintained. Much of the work of propelling a human powered vehicle at speed goes into overcoming air resistance. This implies that in an open vehicle there is an adequate air flow over the operator to provide the heat exchange required to remove waste heat. In designing a vehicle with aerodynamic shrouding, however, provision must be made for heat dissipation from the rider. Air intakes and exhaust ducts may be required to achieve this.

The diagram shows the level of heat output of a cyclist and compares this with heat losses. A body surface temperature of 35 C, an air temperature of 15 C with a relative humidity 80%, and an effective body surface area of the cyclist of 1.8 m2 is assumed. The heat flux plotted on the vertical axis includes both convective and the evaporative components of heat transfer to the air. This heat transfer is compared to that achieved with a flat plate or cylinder at the same air velocity. Evaporation of sweet is seen to be an important contribution to heat loss. Body temperature will rise to dangerous levels if this cannot occur. Water replacement is required for sustained activity.

From: Abbott & Wilson,
"Human-Powered Vehicles," Human Kinetics (1995)