Parks College Parachute Research Group

The Improved Ideal Parachute Model and its Application to the Study of Inflation Dynamics of Slider-Reefed Ram-Air and Round Parachutes

T. Perschbacher and J. Potvin - Parks College Department of Physics

Presented at the 15th AIAA Aerodynamic Decelerator Systems Conference, Toulouse, France, June 9-11, 1999




Abstract

We present an improved version of the Ideal Parachute Model, a numerical scheme that simulates the inflation of slider-reefed parachutes without the use of empirical input information. The improvements aim at relaxing some of the approximations that were used to derive a simple version of the Model, such as the assumption of a vertical descent trajectory prior to and during the inflation of the parachute, or that of a drag area ratio being much smaller than the velocity-squared ratio, namely (t)/0 << ( v(t)/v0 )2 where the "0" subscript refers to initial values (i.e. a time just prior to slider descent). The improvements also aim at generalizing the equations of motion of the Model to allow its use to parachutes other than ram-air parachutes, namely those of circular geometry such as solid round parachutes, ringslot parachutes, cruciform parachutes, etc. The paper will discuss the results of hundred of numerical simulations performed over the past year, focusing on the following topics:

1) comparison of generic inflation characteristics of slider-reefed round parahutes and slider- reefed ram-air parachutes;

2) comparison of inflation properties (mainly scaling laws) obtained from the simple and improved Ideal Parachute Models (ram-air parachutes);

3) comparison of generic inflation characteristics between deployments carried out along a purely vertical trajectory and a ballistic trajectory;

4) demonstration of the existense of a "open - no open" phase diagram, a graph that displays in parameter space the location of parachute characteristics that will allow short, moderate or asymptotically slow inflations sequences. The improved Model is now detailed enough to be able to predict whether the slider will descend or not in terms of parameters such as slider grommet-line friction coefficient, slider surface area, canopy initial surface area, parachute descent velocity, etc.

Acknowledgements

The authors are grateful to the U.S. Air Force Office of Scientific Research which has provided financial support for this work. The also acknowledge many fruitful discussions with Mr. Richard Benney and Calvin Lee from the U.S. Army Natick Research, Development, and Engineering Center, Mr. Glenn Brown and Roy Haggard from Vertigo Inc., Mr. R. Alamat from Paranetics Technology Inc. and Mr. G. Peek from the Parks College Parachute Research Group.

References

1. See for example the press release appearing in FLYING, October 1998.

2 See for example the press release appearing in SKYDIVING, October 1998.

3. Potvin, J.; "Deployment Model for Slider-Reefed Ram-Air Parachutes"; AIAA-95-1564.

4. Potvin, J.; "Testing a New Model of Ram-Air Parachute Inflation"; The Aeronautical Journal, Vol. 101, pp. 299-313, 1997.

5. Lingard, S. J., ; "Ram-air Parachute Design"; 2nd ADS Technology Seminar; 13th AIAA Aerodynamic Decelerator Systems Conference, Clearwater Beach FL, May 15, 1995. Unpublished.



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