Parks College Parachute Research Group

Wind Tunnel Study of Cruciform Parachutes Folded in Various Configurations

J. Potvin, L. Esteve, and G. Peek - Parks College Parachute Research Group
R. Alamat and J. Little - Paranetics Technology Inc.

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



Abstract

As part of the U.S. Air Force New World Vistas program, a series of wind tunnel tests was initiated in order to study the feasibility of a "drogue-to-main" cruciform parachute system, to be used in ballistic cargo drops of the HALO type [1, 2]. As first discussed by Farinacci and Bruner [2] for operations involving round parachutes, the drogue-to-main concept consists in using the main parachute as a drogue, by deploying it in a folded or reefed configuration which allows a stable, but rapid descent rate of the payload. Near its intended landing point, the main is then allowed to unfold at a preset altitude with the use of pyrotechnic cutters.

The main attractions of this concept resides in its simplicity and weight savings that result in using only one parachute system to carry out two important phases of a cargo airdrop. The recent interest of the U.S. Air Force in performing cargo airdrop operations at altitudes exceeding 20,000 ft has revived research in this area, as exemplified by the wind tunnel study discussed in this talk.

In this paper we present results collected during wind tunnel tests of the drogue-to-main concept as applied to cruciform parachutes. The results discussed here fullfill two of the three main objectives of this study, namely: 1) finding out those reefed or folded drogue configurations which are the most stable in the wake of a standard U.S. Army CDS container falling at near-terminal speed, and 2) selecting those configurations which feature the smallest drag area to provide the fastest fall rates. The paper will not discuss the third goal of the project which aims at singling out those configurations which yield the simplest, fastest and most reliable transitions from the drogue phase to the main chute phase.

The paper will discuss the following topics:

1) The drag area requirement of the drogue-to-main concept as applied to high-precision ballistic airdrops;

2) Wind tunnel description;

3) Tunnel systematic error description (model blockage and model inflated shape)

4) Comparison with test drops of the tunnel models from a flying ram-air parachute;

5) Sample reefed and folded configurations defining the drogue; values of the measured drag areas.

Acknowledgements

The authors are grateful for the invaluable help provided by Mr. M. Barcklage and Ms. B. Brocato. We are also grateful to Professor K. Ravindra and Mr. F. Coffey from the Department of Aerospace and Mechanical Engineering, Saint Louis University, for their aeronautical and tunnel expertise. We thank Dr. S. Lingard, Chief Systems Engineer, Martin-Baker Aircraft for sending us a copy of Maskell's classic (and hard to find) paper. We also want to acknowldge many useful discussions with Mr. R. Benney, A. Mawn and K. Stein from the U.S. Army Natick Research, Development, and Engineering Center. Finally, the authors want to thank the U.S. Air Force Office of Scientific Research for providing the financial support.

References

1. Barnard, G. A., Black, W. L., and Hawker, F. W.; "Development of a High-level Container Airdrop System"; AIAA-75-1386; and references therein.

2. Farinacci, J. R. and Bruner, D. B.; "High Level Container Airdrop System"; Technical Report 73-55-AD; Army Natick Laboratories, Natick, MA, 1973; and references therein.

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

4. Macha, J. M.: "An Introduction to Testing Parachutes in Wind Tunnels"; AIAA-91-0858.

5. Macha, J.M. and Buffington, R.J.; "Wall Interference Corresctions for Parachutes in a Closed Wind Tunnel"; AIAA-89-0900.

6. Maskell, E.C.; "A Theory of the Blockage Effects on Bluff Bodies and Stalled Wings in a Closed Wind Tunnel". Unpublished. Royal Aircraft Establishment, Report Aero. 2685; November 1963.



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