Analysis of Deployment and Inflation of Large Ribbon Parachutes

Abstract

A method for predicting deployment and inflation of reefed ribbon parachutes is presented. The method is based on integration of axial and radial momentum equations developed in the paper. Axial and radial forces are assumed to be describable by drag and radial force coefficients. Computer solutions of the equations are compared to measured parachute loads and to parachute mouth and maximum diameters from tests of 23-and 76-ft-diam conical ribbon parachutes. Comparison of load histories indicates that snatch loads depend to a large extent on deployment bag design and packing influences. Computed loads and parachute size histories for the inflation process compared favorably with flight data. The concept of a radial force coefficient appears to have considerable merit as a means of computing inflation for most types of parachutes. Nomenclature B= apparent mass coefficient Co = drag coefficient based on inflated diameter CR = radial force coefficient D = drag, Ib e c = ratio of minor axis to major axis for canopy equals 0.6 constant F = force, Ib g -acceleration of gravity, fps 2 LI = arc length along inflated portion of canopy, ft L u = arc length along uninflated portion of canopy, ft / = suspension line length, ft m -mass, slug ra' = apparent mass, slug M = total mass, slug N = number of suspension lines q = dynamic pressure, lb/ft 2 R = radial dimension, ft S = reference area, ft 2 t = time, sec T -tension, Ib TRL -radial component of reefing line force, Ib V = velocity, fps x = coordinate along flight path, ft 7 = flight path angle, below horizontal, deg B c = inflated canopy half angle, deg BI -one-half suspension line included angle, deg B r = overinflation angle for reefed canopy, deg X g = constructed geometric porosity, percent Age = geometric porosity corrected for canopy strain, percent e = strain p = air density, slug/ft 3 p = density, slug/ft 3 Superscripts = first derivative with respect to time = second derivative with respect to time ' = designates apparent mass Subscripts

Aerodynamics of Parachute Opening

“…Studies and mathematical models for parachutes systems have been developed which acknowledge and account for the unsteady flow conditions that the canopy encounters during inflation (Wolf, 1974;McVey & Wolf, 1974;Purvis, 1982) but still do not provide much insight into the details of the flow field around the canopy itself.…”

A Discrete-Vortex Analysis of Unsteady Flow About Cambered Plates

“…dz The last term may be written as (2), and carrying out the • differentiation, the velocity of the km -vortex becomes Pzk P dc irkp b2)(cko + °C. dz + 2n Rgkp + nt)2 + b2 J2…”

“…The previous models of parachute loads are based by and large on empirical assumptions(see Heinrich and Saari [1], and Mcwey [2]). The apparent mass is assumed to be a function of canopy projected *Now Air Academy, Belbeis.…”

Simulation of the Dynamic Tensile Characteristics of Nylon Parachute Materials

“…Array of values for creep strain I -1, 6 rate. Used as the dependent J -1, 3 variable in creep model.…”

“…Array of ordinates for the six I = 1, 6 cord fixed knots in cubic spline fit lb/in for used to represent material unloadfabric ing characteristic.…”