Suspension Line Length Research Articles

Computational and Experimental Study for Reducing Forebody Wake Effect by Proper Designing of a Slit cut Square Parachute used for Sonobuoy Drop

This paper discusses the design of a square parachute based on classical approach, computational analysis and experimentation. This parachute will be used to drop directional sonobuoy on the sea to locate and classify the submarines. Design improvements are brought out by providing slits into a solid square canopy of parachute to bring in more stability and minimum drift during descend. Specifically, the effect of upstream sonobuoy, RANS model, suspension line length, canopy size and slit size in flow structure were considered. The predicted drag coefficients obtained from CFD for square canopy with slit-cuts compared with the results of wind tunnel experiment and found that the increase in the suspension-line length and/or of the surface area of the parachute canopy helps in better stability and results in the minimum drag loss.

Fluid-Structure Interaction Modeling of Spacecraft Parachutes for Simulation-Based Design

Even though computer modeling of spacecraft parachutes involves a number of numerical challenges, advanced techniques developed in recent years for fluid-structure interaction (FSI) modeling in general and for parachute FSI modeling specifically have made simulation-based design studies possible. In this paper we focus on such studies for a single main parachute to be used with the Orion spacecraft. Although these large parachutes are typically used in clusters of two or three parachutes, studies for a single parachute can still provide valuable information for performance analysis and design and can be rather extensive. The major challenges in computer modeling of a single spacecraft parachute are the FSI between the air and the parachute canopy and the geometric complexities created by the construction of the parachute from “rings” and “sails” with hundreds of gaps and slits. The Team for Advanced Flow Simulation and Modeling has successfully addressed the computational challenges related to the FSI and geometric complexities, and has also been devising special procedures as needed for specific design parameter studies. In this paper we present parametric studies based on the suspension line length, canopy loading, and the length of the overinflation control line.

Experimental Investigation of Three Rotating Parachutes

INCE they were first invented, parachutes have been widely used to lower men and goods to the ground safely, and to decelerate aircraft, race cars, etc. Although new types of parachutes were designed, this mission remained the same for years. During the last decades, new tasks began to be given to parachutes. These tasks are related to controlling the trajectories of their payloads and following complex flight patterns to carry out defined flight requirements. Today, rotating parachutes are a means of introducing dynamic maneuvers to their payloads to follow a predefined flight path and/or traces on the ground. In the design of a rotating parachute-payload system, the appropriate parachute system can be found by studying the aerodynamic properties of rotating parachutes in wind tunnels. While different types of parachutes are designed and studied in a windtunnel[1],thesameparachutecanalsobetestedbychangingits geometrical parameters such as suspension line length and staggering distance [2–6]. Inthisexperimentalstudy,threerotatingparachutesweretestedin a wind tunnel. Each canopy had the same surface area but had a different shape. The affects of the canopy geometry and the physical parameters (suspension line length and staggering distance) on the tangential force coefficient and the spin rate were studied [7]. Because the same size cross canopies and the same canopy fabric materialwereused,thespinrateandtheforcecoefficientresultswere compared with the corresponding results of the experimental studies found in the literature. During the tests, the oscillations of the configurations constructed from their symmetry axes were also observed, and different dynamic behaviors were classified.

Lateral stability of gliding parachutes

The lateral stability of a gliding parachute or other lifting surface with a suspended payload is analyzed to determine the relationship of aerodynamic and inertial parameters to stability characteristics. The system is represented by a rigid wing with a suspended payload in a steady glide. As with conventional fixed-wing aircraft, the lateral response is characterized by an oscillatory response mode and a spiral divergence. The stability boundary for spiral divergence can be prescribed analytically. Calculations show that there is a minimum effective anhedral angle required for absolute stability. Increasing suspension line length is stabilizing for spiral divergence, whereas increasing the glide slope is stabilizing for both spiral divergence and oscillatory response.

Stabilization parachutes: A rigid body treatment

Rigid body dynamics are used to describe the motion of parachute-payload systems released from aircraft. Two models are developed to describe the transitional and rotational degrees of freedom using the dynamical equations of Newton and Lagrange. The latter mechanics treats the parachute and payload as two rigid bodies in contact, while the former mechanics treats the entire system as a single rigid body. Finally, the equations of motion deduced from the Newtonian approach are numerically solved for a stabilization parachute to show the effects of wind and of suspension line length on damping.

Reductions in parachute drag due to forebody wake effects

An experiment was conducted to evaluate approximate analytical methods for predicting the reduction in parachute drag due to forebody wake effects. The drag of a 20/sup 0/ conical ribbon parachute was measured at several axial stations behind an ogive-cylinder forebody with and without fins. The same parachute was tested in undisturbed flow (where wake effects were negligible) so that the effects of suspension line length on parachute drag could be separated from the drag losses caused by the turbulent wake. Total head pressure surveys were made across the forebody wake and integrated across the canopy skirt area to determine the effective dynamic pressure acting on the parachute. Experimental results confirmed the validity of the underlying physical model of the parachute/wake interaction: the ratio of parachute drag behind a forebody divided by wake-free parachute drag is equal to the ratio of effective dynamic pressure acting on the parachute divided by freestream dynamic pressure.

Prediction of the Drag Coefficient of a 20' Conical Ribbon Parachute

An empirical formula for the steady state drag coefficient of a 20 degree conical ribbon parachute is developed. The derived expression takes into account the effect of suspension line length and geometric porosity within the limits of practical design. Also included are factors which provide drag reduction due to skirt reefing and the wake behind a primary body. The calculated values are in agreement with the available experimental results.