GB1266854A - - Google Patents

Abstract

1,266,854. Air cushion vehicles. NATIONAL RESEARCH DEVELOPMENT CORP. 17 March, 1969 [15 March, 1968], No. 12716/68. Heading B7K. A gas cushion vehicle has at least one substantially vertically disposed fin 15a mounted on the vehicle for rotation under the action of wind forces about a substantially vertical axis 18, and means 16a automatically to adjust the incidence of the fin with respect to the relative wind direction, whereby to render the vehicle substantially neutrally stable for a majority of relative wind directions. Tab 16a is hinged to fin 15a at 17, and carries a follower 20 which co-operates with a cam 19, so that as fin 15a is rotated by a relative wind the incidence of tab 16a with respect to fin 15a changes, causing fin 15a to come to rest at an angle to the relative wind. A yawing moment is thus generated by the fin on the vehicle which, with a suitable cam profile, opposes the yawing moments generated by the wind on the remainder of the vehicle. To ensure that there is always a moment about the vehicle centre of gravity for all relative wind directions, at least two spaced fins 15a are required. Fig. 9 shows an arrangement which provides positive stability, that is allows a heading to be maintained relative to the wind direction; a first tab 16a maintains the vehicle neutrally stable as above, while a second tab 16b is controlled by a frusto-conical cam 19b initially centred on shaft 18. Cam 19b is moved horizontally to move tab 16b, and then vertically to restore the tab to its initial position; since cam 19b is then not centred on shaft 18 any change in fin position moves tab 16b to maintain the vehicle heading relative to the wind. In a further embodiment, Figs. 13 and 14 (not shown), hydraulic jacks (30), (35) are used to move a cam (19) both vertically and horizontally to assist manoeuvering the vehicle, the cam also having a profile which renders the vehicle neutrally stable to relative winds. The tabs used may be replaced by jet flaps or boundary layer control arrangements, and these aerodynamic control means could be governed by any mechanism for sensing relative wind directions. The fins are preferably situated clear of any slipstream from the main propulsion system of the vehicle.