A body moving in air, water, or other fluid medium is subject to a retarding force from the fluid, which retarding force is referred to as "the drag force", or merely as "drag". Drag is a function of (a) the velocity at which the body is moving; (b) the body's shape; (c) the quality of the body surface; (d) turbulence in the flow around the body; and (e) the viscosity of the fluid medium in which the body is moving. Since energy, frequently substantial energy, must be expended to overcome this drag force in order to keep the body moving at a desired velocity, it is desirable that this drag force be minimized. Heretofore, efforts to reduce drag have concentrated on streamlining the shape of the body and on smoothing or otherwise changing the quality of the external surface of the body. For example, modest reductions in drag (5% or less) can be achieved by such changes in the body surface as the use of parallel shallow longitudinal grooves in the after body of a streamlined body. However, even when these passive steps are taken, significant turbulence still exists in the medium at various places along the body, and the resulting drag on the body still makes a significant contribution to the energy required in order to maintain desired movement of the body.
A critical parameter for purposes of drag is the Reynolds number, R.sub.e, which is directly proportional to the velocity U of the body in the direction D in which the body is moving and to the length L of the body and is inversely proportional to the kinematic viscosity .nu. of the medium (i.e., R.sub.e =UL/.nu.). When R.sub.e exceeds a value which is normally in the range of roughly 400,000-500,000, but may be somewhat above or below that range depending on the parameters of the body and of the medium, flow around the body will become turbulent (i.e., instead of flowing smoothly around the body, the flow will contain random disturbances which cause drag to increase many-fold). Unfortunately, the value of R.sub.e at which turbulence occurs is exceeded in almost all cases of practical interest. For example, a car moving at as little as 3 miles per hour has already exceeded the R.sub.e value required for turbulence to occur and a ship or plane will exceed this value for any measurable speed.
As a result, significant efforts have been expended to smooth out turbulence and make the flow around a body laminar. This is important since, if it were possible to eliminate turbulence completely, it could in many instances result in a reduction of approximately 90% in drag on the body, reducing energy requirements for moving the body tremendously. Reduced drag can also permit smaller, lighter and less expensive engines or other drive mechanisms to be utilized, further reducing costs, and can be particularly critical for human powered craft, permitting the human operator to conserve energy and therefore to be able to travel longer and further. In addition, drag in general, and turbulence in particular, cause noise which is undesirable, particularly for submersible crafts used for marine research or for war.
While some efforts have been made to reduce turbulence induced drag, particularly in marine situations, such efforts have had at best limited success and there has been virtually no work to date in reducing such drag on a human powered vehicle. Parent application Ser. No. 08/652,673 (hereinafter "the parent application") teaches a technique for reducing such drag on a body moving through a fluid by reducing turbulence at the surface of the body in much the same way that this objective is accomplished by a swimming fish, namely by active control of lateral body flexing, and in particular by causing the body to be flexed at at least two points along the length of the body, with the parameters of flexure falling within predetermined ranges and there being a predetermined phase relationship between flexure at various points along the body. By using these techniques, reduction in drag substantially in excess of 50% have been achieved. However, while the parent application indicates in general terms that such reductions in drag could also be achieved in a human powered vehicle, detailed structure and methods for the operation thereof in order to extend the teachings of the parent application to a human powered vehicle are not provided. Since a significant need exists for human powered vehicles for use in marine research, various military operations, recreation and other applications, and minimizing drag on such vehicles is critical, both for enabling the person powering the vehicle to be able to perform various projects before being overcome by fatigue and to minimize noise and turbulence from the vehicle so as to render the vehicle as noninvasive as possible in for example a research environment, a need exists for an improved, reduced drag human powered marine vehicles, and in particular for improved methods and apparatus for applying the teachings of the parent application to such human powered vehicles.