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For a design engineer strength calculation is a prerequisite for completion of design. The parachute designer however encounters great difficulty. Theory provides no means for calculation and almost no data is available of measurements under dynamic conditions to permit adequate strength calculation. The rapidly changing dynamic forces can vastly exceed the steady state forces. Great efforts have been made to predict stresses in a parachute canopy. The latest work for a parachute stress analysis was conducted by H.G. Heinrich and L.R. Jamison [1] and is a great advance. Contrary to former attempts it includes parachute shapes during inflation of the canopy. The great disadvantage of all theoretical attempts is that the actual stress distribution in a canopy is still unknown. No method has yet been found to measure stresses directly in many parts of a canopy.
An experimental investigation and correlative analysis were conducted to determine the pressure distribution over the surface of parachute canopies during the period of inflation for the infinite mass case and to correlate pressure coefficients with inflating canopy shapes. Parachute canopy models of Circular Flat, 10% Extended Skirt, Ringslot, and Ribbon designs were tested under infinite mass conditions in a 9 x 12 ft low speed wind tunnel. External and internal pressure values were measured at various locations over the surface of the model canopies throughout the period of inflation, and generalized canopy profile shapes were obtined by means of photographic analysis.
An experimental investigation was conducted to determine the differential pressure distribution over the surface of parachute canopies during the period of inflation under mass conditions. Full scale parachute canopies of the circular flat, 10% extended skirt, ringslot and ribbon types were utilized during the free-flight test program, and differential pressures on the gore centerline and on the cord line were measured by means of four pressure transducers distributed over the canopy in equal distances from the skirt to the vent. In order to analyze the relationships and dependencies between the pressure distribution, projected canopy area, canopy shape, generated force, and dynamic pressure, graphical displays of these quantities were made as a function of time for each type of parachute canopy. The results of the pressure distribution measurements permit a better understanding of the physical nature of the dynamic process of parachute inflation. The stress distribution in a parachute canopy can be calculated if the corresponding canopy shape is known. For this purpose, the evolvement of the canopy shape with the corresponding time is presented for each of the canopy types. (Author).
An experimental investigation and correlative analysis were conducted to determine the pressure distribution over the surface of parachute canopies during the period of inflation for the infinite mass case and to correlate pressure coefficients with inflating canopy shapes. Parachute canopy models of Circular Flat, 10% Extended Skirt, Ringslot, and Ribbon designs were tested under infinite mass conditions in a 9 x 10 ft low speed wind tunnel. External and internal pressure values were measured at various locations over the surface of the model canopies throughout the period of inflation, and generalized canopy profile shapes were obtained by means of photographic analysis. Pressure coefficients derived for the steady state (fully open canopy) are quite comparable to the results of previous measurements. Peak pressure values during the unsteady period of inflation were found to be up to 5 times as great as steady state values. The relationships between the pressure distribution and time for each of the canopy models deployed at free-stream velocities between 70 and 160 ft/sec. are presented.
An experimental investigation was conducted to determine the differential pressure distribution on the canopies of four types of parachutes (Circular Flat, 10 % Extended Skirt, Ringslot, Circular Flat Ribbon) during the period of inflation under finite mass conditions. In flight tests the differential pressure on the cord and the gore center line was measured with four pressure transducers distributed over the canopy in equal distances from the skirt to the vent.
An experimental investigation and correlative analysis were conducted to determine the pressure distribution over the surface of parachute canopies during the period of inflation for the infinite mass case and to correlate pressure coefficients with inflating canopy shapes. Parachute canopy models of Circular Flat, 10% Extended Skirt, Ringslot, and Ribbon designs were tested under infinite mass conditions in a 9 x 12 ft low speed wind tunnel. External and internal pressure values were measured at various locations over the surface of the model canopies throughout the period of inflation, and generalized canopy profile shapes were obtained by means of photographic analysis. Pressure coefficients derived for the steady state (fully open canopy) are quite comparable to the results of previous measurements. Peak pressure values during the unsteady period of inflation were found to be up to 5 times as great as steady state values. The relationships between the pressure distribution and time for each of the canopy models deployed at free-stream velocities between 70 and 160 ft/sec are presented in detail and correlated with changing canopy shape. A complete shape analysis is made and a mathematical model is proposed. (Author).
For the purpose of parachute canopy stress analysis during the period of inflation, the pressure distribution measured on a ring-slot parachute model is related to the instantaneous parachute force. The correlation of pressure and force data is based on test results established at the Deutsche Forschungsanstalt fuer Luft-und Raumfahrt (DFLR), Braunschweig, Germany. The final pressure-force-time relationship incorporate individual as well as averaged test data. A fair agreement could be shown between measured forces and those obtained from numerical integration of differential pressure over the canopy surface.
The Sandia Laboratories, Albuquerque, N.M., established wind tunnel data of 3 ft ribbon parachute models concerning canopy profiles, drag forces and pressure distribution during the period of inflation. The data were analyzed at the University of Minnesota and resulted in presentations of canopy profile coordinates, drag areas and pressure distributions versus time. Pressure integration about the canopy surfaces as given by the established coordinates provided calculated areas which agreed satisfactorily with measured drag areas. Also, radial force coefficients of the various configurations were established. The results of this study are intended to serve as background information for related investigations such as studies concerning parachute dynamics, stress analysis, etc.
The stresses occurring in the cloth of an opening parachute and at steady state are calculated. The method is based on assumed instantaneous and steady state shapes and related pressure distributions. It is general and may be applied to any type and size of canopy built out of solid cloth. The presented analysis is limited to canopies constructed of triangular gores, but can be extended to other gore patterns. A numerical calculation is made for the Solid Flat, Circular Parachute during the opening and at steady state.
During the period from 1965 to 1969, two new methods for stress calculations have been proposed and general remarks primarily concerning the elasticity characteristics of a parachute cloth and pressure distribution have been made. The conservative way of performing a parachute stress snalysis consists of first establishing the geometry of the parachute canopy and then applying a certain pressure distribution. Subsequently, the pressure distribution has been linked to the instantaneous parachute force which can be obtained from an opening shock calculation. In this manner one can possibly obtain closed solutions with a minimum of empirical factors. An example of this approach is presented in detail in the following chapters.