Controlled opening method for clustered parachutes

This paper presents a method for achieving simultaneous opening of clustered parachutes. The method involves connecting and partially reefing the parachutes in a cluster during the initial stage of the opening so that they open together as a single parachute; they are then disconnected and disreefed at almost full inflation, thereby controlling and opening the parachute simultaneously. This method, called the controlled opening method, was tested with clusters of 64-ft-diam G-12 cargo parachutes, 100-ft-diam G-ll cargo parachutes, and 28-ft-diam C-9 personnel parachutes. Their openings were significantly improved when compared to the openings of these clusters without using the controlled opening method. LUSTERED parachutes offer several advantages over a single large parachute. The important ones are shorter opening time and distance, easier fabrication and ground re- covery, and more stable descent. The major difficulty of clus- tered parachutes is that parachutes in a cluster generally open randomly and unevenly; the random opening results in a large variation in opening times and an uneven distribution of open- ing forces among the parachutes. Consequently, the lead- opening parachutes are often damaged, resulting in an un- satisfactory airdrop operation. In view of the importance of uniform opening of clustered parachutes, some fundamental studies of flowfields and open- ing of clustered parachutes were conducted by Braun and Walcott,1 Heinrich and Noreen,2 Heinrich et al., 3 Wolf and Spahr,4 and Nicuum and Kovacevic.5 Current techniques for improved cluster opening are generally those used for con- trolling the opening of a single parachute. They include reef- ing the canopy skirt, adding a secondary chute at the skirt, introducing a pull-down centerline, and applying tension force at the apex by a drogue chute. These techniques generally modify the opening of a single parachute, but they do not necessarily improve the opening of a cluster as a whole. This is evidenced by the current problems in opening 100-ft-diam standard U.S. Army G-ll cargo parachute clusters6 and the great difficulties in opening 137-ft-diam developmental cargo parachute clusters.7-8 Most recently, Johnson9 developed a central reefing/disreefing system that addressed the opening of a cluster as a whole. His system improved the opening of a cluster of three 52.5-ft-diam parachutes. This paper presents a method for improved opening of clustered parachutes. The method was tested extensively with clusters of various size and number of parachutes. Test results demonstrated that the method improves their opening significantly.