Preliminary Analysis of the Self-Tending Rigid Airfoils for the Hydrofoil Water Conveyance.

A theoretical analysis of the regions of stability and performance of the rigid-air-foil propulsion system for the hydrofoil sailcraft (discussed in reference (1)) is presented. The trailing-edge flap is either geared so as to move in proportion to the airfoil-axis or fixed (at negative camber) relative to the airfoil. A limited stability region in which the airfoils are self-tending is investigated using a flap-angle to airfoil-angle gear ratio(K) vs. distance of airfoil-mast behind the quarter chord (d) plot. The chordwise motion of the airfoil relative to the mast (pivot) is found to be essential. The stability is found to be better and overall aerodynamic performance is enhanced for higher apparent winds. Aside from the ability to point higher into the apparent wind (due to a larger lift-to-drag ratio), best overall craft performance is obtained on a beam reach. The broadest range of wind angles, for which the craft is self-tending, is obtained for a fixed positive flap angle (actually, a negative camber is thereby implied). (Author)