Parks College Parachute Research Group

In-Flight Study of Cell Pressurization Inside Inflating Smokejumper Ram-Air Canopies

J. Potvin and G. Peek - Parks College Parachute Research Group

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




Abstract

We will report on the results of a series of in-flight measurements of the pressure distribution inside two inflating ram-air parachutes which are used by smokejumpers of the U.S. Bureau of Land Management (or BLM). The study focuses on the sensing of pressure differentials between selected points inside the rear and forward portions of the center cell and similar points located inside the tip cell as well as inside the quarter-span cell. This work represents the second phase of a larger study aimed collecting pressure profiles inside as well as outside of a large number of canopies during their inflation phase [1]. The hope is to eventually use such data to validate present and future CFD studies [2] and models of parachute unfolding [3,4].

Our technique involves using solid state differential pressure sensors embedded in the cells and linked via flexible tubing to selected ports (figure 1). Power and data signals are transmitted via magnet wire which is finger-trapped in an additional (non-load bearing) Dacron suspension line attached to the underside of the canopy and to amplifiers taped on the harness risers. As shown in reference 1, this arrangement is sturdy enough to have survived dozens of tight packings and violent deployments without any major breaks. (Photos of the canopy during inflation and the canopy in flight show some of the above mentioned configurations.)

Over the years, BLM smokejumpers have used two ram-air parachutes, namely the Goliath which is a 360 square foot seven cell design manufactured by Para-Flite Inc., and the Trilobe, a 320 ft2 seven cell parafoil designed by Quantum Parachutes. Compared to most ram-air parachutes in the market today (including the Goliath), the Trilobe features two oversized quarter-span cells that flatten the wing at mid-span. Given this difference in cell design between two such canopies that are otherwise similar, it will be interesting to see whether each display a different pressurization "signature" during inflation.

The paper will discuss the results obtained so far, including:

1) the pressure signatures of bag strip, early cell pressurization and slider descent stages for the Goliath and the Trilobe (see figure 2);

2) the value of the maximum pressure differentials experienced;

3) the time delays and spatial correlations of pressurization between selected pairs of ports;

Acknowledgements

The authors would like to thank Mr. Jim Raudenbush, Crew Supervisor, BLM Alaska Smokejumpers, and Mr. George Steele, Loft Manager, BLM Boise Smokejumpers for providing the necessary funding.

References

1. Potvin, J. and Peek, G.; "In-flight Study of the Pressure Differentials Near the Surfaces of an Inflating Ram-Air Parachute". AIAA-98-2529.

2. Garrard, W. L., Tezduyar, T. E., Aliabadi, S. K., Kalro, V., Luker, J. and Mittal, S. ; "Inflation Analysis of Ram Air Inflated Gliding Parachutes; AIAA-95-1565.

3. Potvin, J. ; "A Simple Description of Airflow Characteristics Inside an Unfolding Parachute". December 1997; submitted for publication.

4. Montanez, R., Potvin, J. and Peek, G.; "Wind Tunnel Investigation of Ram-Air Parachute Cell Pressurization"; AIAA-97-1524.



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