NOVELTY - The arrangement has an arm (21) including opposed thrust bias units and return bias units to urge the arm respectively to a thrust position and a return position. The arm is associated with a thrust lug (22) and a return lug (25) to define the thrust position and the return position across a drive cycle with a thrust release finger (2) and a return release finger (5) associated with drive mechanism respectively arranged at limits of the drive cycle to alternately release the thrust or return bias units to orientate the arm toward the thrust or return position.    USE - Flow harness arrangement e.g. piston-type arrangement and rack and pinion arrangement, for extracting energy from fluid flows e.g. wind and water flows, using a flow harnessing element e.g. sail, paddle and wing/aerofoil to convert the flows to usable motions for electrical power generation or pumping in generators and flywheel to produce electricity.    ADVANTAGE - The arrangement allows a relevant torsion spring to drive a sail arm around an axis of the mechanism body when a carrier and mechanism assembly reach the end of a lift stroke or down stroke, so that relevant spring loaded neutral position retaining pin is engaged with the neutral position retaining slot in the sail arm and locks wing/aerofoils in neutral position resufts in a nominal zero angle of attack and zero camber, thus reducing forces exerted upon the device, and minimizing lift or down forces. The arrangement includes a carrier with realizing units to releasably secure the mechanism body and to prevent movement in relation to the carrier. The arrangement includes a frame that is secured so as to prevent rotation about the axis of a sail arm by supporting bars. The arrangement includes a spring loaded down stroke retaining pin so as to engage with the down stroke retaining lug effectively, thus preventing upward movement of the carrier. The mechanism assembly or wing/aerofoils critical components are provided with heating units so as to prevent ice formation in event of extreme low temperatures.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of an arrangement for energy harnessing of fluid flows.    Thrust release finger (2)    Return release finger (5)    Arm (21)    Thrust lug (22)    Return lug (25)    Thrust stroke sail (31)