Spacecraft mechanisms commonly undergo extended periods of storage, either on-ground, or in-flight and there are an increasing number of missions for which some element of long-term storage may be required. Despite the obvious potential for degradation of lubricants during storage which might impact mechanism functionality or life and so even become mission-threatening, today’s understanding of storage phenomena is rather incomplete. This paper provides consolidation and review of recent experimental studies in this area and considers the range of storage conditions and associated degradation phenomena which could impact different lubricants. Whilst some storage best practice guidelines exist, experimental verification of the impact of storage phenomena has rarely been carried out and test data is rather scarce and incomplete. Given the absence of comprehensive data to support design, lubricant selection or the development of storage protocols, it is shown that for all lubricant types careful control of storage and test environments combined with monitoring of the evolving tribological performance during periodic mechanism exercising are presently the most effective storage risk mitigations.
Water-tunnel experiments were performed to determine the free-stream characteristics of a series of 12 rudders with systematic variations in the amount of flap area and flap balance. The results include lift, drag, rudder moment and flap moment coefficients for a range of angles of attack and flap deflections. A comparison is made of the effectiveness of all-movable rudders, rudders with a fixed skeg and movable flap, and rudders with movable skegs and flaps. The latter were found to be by far the most effective. Rudders with fixed skegs are inferior to all-movable rudders unless the proportion of flap is very large. Flap balance does not appear desirable. Maximum flap moments, even with zero balance, are generally less than or comparable to the maximum moment of an ideally balanced all-movable rudder.
Water tunnel experiments were performed to determine the free-stream characteristics of a series of twelve rudders with systematic variations in the amount of flap area and flap balance. The results include plots of lift, drag, rudder moment and flap moment coefficients for a complete range of angles of attack and flap deflections. A comparison is made of the effectiveness of all-movable rudders, rudders with a fixed skeg and movable flap, and rudders with movable "skegs" and flaps. The latter were found to be by far the most effective. Rudders with fixed skegs are inferior to all-movable rudders unless the proportion of flap is very large. Flap balance does not appear desirable. Maximum flap moments, even with zero balance, are generally less than or comparable to the maximum moment of an ideally balanced all-movable rudder.
Abstract-The experimental procedures developed to measure small forces generated by underwater vehicle appendages in a wind tunnel are described. These involve using precision load cell sensors arranged into a bespoke dynamometer, that has been integrated into a stand-alone wind tunnel rig. The set up is used to quantify performance of a scaled underwater glider hydrofoil, with particular care being paid to the effects of laminar and transitional flow features. Present data are benchmarked against similar measurements and simulations and it is shown that satisfactory results may be obtained with the current approach despite its simplicity and low cost. The apparatus is then used to show that the presence of laminar flow significantly affects performance of the considered foil at Reynolds numbers corresponding to a typical regime in which underwater gliders operate.
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