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A simple, approximate model of parachute inflation is described. The model is based on the traditional, practical treatment of the fluid resistance of rigid bodies in nonsteady flow, with appropriate modifications to account for the changing shape of the canopy. Steady-flow, fixedgeometry correlations for the drag and radial force are required as input to the dynamic model. In a novel approach, the radial force is expressed in terms of easily obtainable drag and reefing line tension measurements. A series of wind tunnel experiments provides the needed correlations. Coefficients associated with the added mass of fluid are evaluated by calibrating the model against an extensive and reliable set of flight data. A parameter is introduced which appears to universally govern the strong dependence of the axial added mass coefficient on motion history. Through comparisons with flight data, the model is shown to realistically predict inflation forces for ribbon and ringslot canopies over a wide range of sizes and deployment conditions. Nomenclature C, = radial force coefficient C' = axial force (drag) coefficient d = constructed canopy diameter, ft F = force, lb g = gravitational acceleration, 32.2 ft/s2 k = added-mass coefficient LRL = unloaded reefing line length, ft LsL = suspension line length, ft m = mass, slug m ' = added mass, slug *

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A set of 6-ft-diam ribbon parachutes (geometric porosities of 7, 15, and 30%) was tested in various subsonic wind tunnels covering a range of geometric blockages from 2 to 35%. Drag, base pressure, and inflated geometry were measured under full-open, steady-flow conditions. The resulting drag areas and pressure coefficients were correlated with the bluff-body blockage parameter (i.e., drag area divided by tunnel cross-sectional area) according to the blockage theory of Maskell. The data show that the Maskell theory provides a simple, accurate correction for the effective increase in dynamic pressure caused by wall constraint for both single parachutes and clusters. For single parachutes, the empirically derived blockage factor KM has the value of 1.85, independent of canopy porosity. Derived values of KM for two-and three-parachute clusters are 1.35 and 1.59, respectively. Based on the photometric data, there was no deformation of the inflated shape of the single parachutes up to a geometric blockage of 22%. In the case of the three-parachute cluster, decreases in both the inflated diameter and the spacing among member parachutes were observed at a geometric blockage of 35%. Nomenclaturecanopy constructed diameter, 6 ft approx. K M = Maskell bluff-body blockage factor L r = riser length L s = suspension line length, 6 ft TV = number of parachutes in a cluster p = canopy surface pressure p s = freestream static pressure q -freestream dynamic pressure Subscript u = uncorrected for wall interference

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