Parks College Parachute Research Group

A New Inflation Model for Low-Porosity Hemispherical Parachutes:

Validation and Implementation in PIMS V3.0

Jean Potvin, Jason Papke, Eric Brighton, and Mike Farmer
Saint Louis University
St. Louis, MO 63103, USA

Gary E. Peek
Industrologic Inc. St. Charles, MO 63301, USA

Presented at the 18th AIAA Aerodynamic Decelerator Systems Conference and Seminar, Munich, Germany, May 23-26, 2005, AIAA paper 2005-1687




Abstract

This paper discusses the fundamentals, validation and implementation of a new inflation model for low-porosity hemispherical parachutes, with or without drive-vents for gliding. The model is based on the explicit simulation of a two-stage inflation process, which begins with the canopy adopting a streamlined shape, be it a cigar-like or bulb-like shape, and ends as the parachute evolves into a near hemisphere. The simulation of the first stage is carried out with a new dynamical model based on the tracking of the acceleration of a series of air parcels interacting with the parachute, from a state of rest to a state of motion at the canopy's speed. Most importantly, the size of each parcel is made to increase with time, according to a prescription based on fixed-inflation distance theory and on the parachute systems' instant speed and acceleration. The model does not require specific canopy shape information other than a ballpark value of the steady-state drag coefficient corresponding to the mean parachute shape adopted during this first stage, and an initial projected surface area. On the other hand, the second inflation stage is modeled by Ludtke t6-t3's drag area law. This two-phase model represents a substantial improvement over using Ludtke's law for the simulation of the entire inflation process. Validation is discussed as well, with the comparison of selected simulations with test drop data obtained from several reefed and un-reefed military canopies, and from two civilian drive-vented canopies. The paper ends with a brief discussion of the implementation of the model in the Windows-based Parachute Inflation Modeling Suite program that is being developed with US Army funding.



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