By Patty WelshJuly 15, 2008
NATICK, Mass. - Helicopters have long played a role in getting needed supplies to Soldiers in the field. One way this is accomplished is through sling loading. Sling loading is where a helicopter hovers while some type of cargo, whether it is food, ammunition or other needed equipment, is attached underneath. The load is fastened to a cargo hook via a sling set.
A few years back, during Operation Iraqi Freedom, air assault troops noticed a problem with sling load operations during brownouts, when blowing sand significantly decreased visibility for aircrews and ground personnel.
Scott Ullery, project officer, U.S. Army Natick Soldier Research, Development and Engineering Center, said that it can be difficult for pilots to hover and hold steady enough for ground personnel to connect a load to the cargo hook. In brownout conditions, with no visual references, hovering over the load can be extremely dangerous. NSRDEC is a subordinate element of the U.S. Army Research, Development and Engineering Command.
Air assault troops attempted to fix the problem using an existing polyester round sling as a pendant, providing additional separation between the helicopter and the traditional sling set attached to the load. The configuration allowed the helicopter to land beside the load but lacked the required strength and durability.
"It turned out to be a viable concept, but the material was not very durable. It was catching and tearing," said George Moorachian, senior aerospace engineer, NSRDEC.
Other approaches were examined but an early solution using a braided line didn't hold up well against sand. After a source selection process, development resulted in a more viable pendant design that used stronger materials and an extruded outer shell to protect it from foreign debris.
Soon a new problem arose. The initial delivery of the newly developed pendant failed first article testing. The production pendants were not able to meet the required strength level, which the design exceeded during development.
"The situation was, the unit had an urgent need and the first contract lot was not deliverable," said Ullery. "Once we realized there was a problem, [everyone] tried to react as quickly as possible."
As the pendants were for the 101st Airborne Division, the contracting had been done out of Fort Campbell, Ky. The contracting officer and the subject matter experts agreed that it wasn't feasible to cancel the contract and try to select a new manufacturer. Ullery said they realized by the time a new source selection could be done, it was possible the unit could be back from their deployment.
Therefore, it was decided to look at all information available, and use Lean Six Sigma process and statistical tools to try and determine where the problem might be.
"We looked at the actual [strength] testing process from beginning to end," Ullery said, "and had an independent lab conduct additional tests." Results varied, he continued, and we were able to statistically prove that the initial results were incorrect. The pendants, however, still did not meet the strength requirements.
The manufacturer and the subject matter experts also reviewed every step involved with the production of the pendant.
"We looked at production process areas where defects might inadvertently be introduced," stated Ullery. Areas such as machinery, linking items together, anything where there might be potential to have something not work, were observed, evaluated, and improved.
One area identified as potentially contributing to the reduced strength was found where production personnel were stripping some polyurethane off the eye area of the pendants using a knife. This posed a risk to the underlying fibers.
Ullery said they used a LSS tool called, 'Poke-yoke." Basically, Poke-yoke is mistake-proofing your process. We found an alternate way to remove the polyurethane so that there would no longer be the potential for the fibers to get cut, commented Ullery.
It's an iterative process, and as the pendants were produced, we continued to test and monitor the batches to find out where the strength was. The end result was that the pendant met its strength requirement and the 101st Airborne Division received what they needed for deployment.
"The item is much more reliable for the user," Ullery said. "The design of the pendant was proven, and what we found is that the problem was a production issue that we were able to find and correct using the tools of Lean Six Sigma."
He also commented that they wouldn't have been able to uncover the problem if the manufacturer hadn't been so willing to participate. "They stepped up and it was really beneficial," he said.
Moorachian commented that although there is a tradeoff with the pendant, because the load is further back so it projects more drag and reduces fuel efficiency, overall the general feedback from the users has been pretty good.
The U.S. Army Combined Arms Support Command is currently examining user requirements for improving helicopter operations, including sling load operations. "It [the pendant] is something the user is happy with," said Moorachian.
Ullery said, "Everyone worked together to ensure success."