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 Unpublished.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