SSC-Natick Press Release
U.S. Army Soldier Systems Center-Natick
Public Affairs Office
Natick, MA 01760-5012
Contact: Jerry Whitaker -- Chief, Public Affairs Office
Date: September 15, 2004
Process clears supplies, equipment for airdrop
NATICK, Mass. -- Concerned manufacturer representatives, cringing at the thought of a new military vehicle undergoing airdrop certification at the Drop Tower, find that the nearly 13-foot plummet onto a concrete surface usually results in little, or more likely, no damage to their product.
The Drop Tower is one stop along the airdrop certification process managed by the Aerial Delivery Engineering Support Team at the U.S. Army Soldier Systems Center in Natick, Mass. Every piece of equipment or consumable product that the military delivers from the sky needs a stamp of approval that the cargo will safely and reliably reach the ground ready for combat.
"(Manufacturer representatives) have visions of wheels flying off and catastrophic failures," said George Moorachian, a senior aerospace engineer and manager of the five-person airdrop and helicopter sling load certification group. "We have pretty good success with things not breaking. It takes a lot of experience to learn how to do it without damaging the load."
With decades of know-how, engineers and technicians have tested everything from individual Soldier items, such as fully loaded rucksacks, to a pallet of rations to heavy construction vehicles with the Roller Load Test Facility, Drop Tower or both.
For cargo delivered on an airdrop platform, engineers begin by calculating the size and shape of a honeycomb kit based on weight and contours of the equipment, which they hope will allow for a soft enough landing to withstand damage.
Honeycomb kits consist of layers of 3-inch-thick impact-absorbing, disposable paper-named for its resemblance to the thin-walled cell structures made by honeybees-and custom-designed pieces of lumber needed to maximize the honeycomb crush.
Care is also taken to protect sensitive or delicate parts, such as guidance systems, hydraulics, glass and the oil pan of a truck.
Reusable aluminum platforms range from 8-32 feet and are extended in 4-foot sections. Once configured, a series of textile Dacron straps are tightened to meet various restraint G-forces in different directions. The mode of airdrop and weight determines the number and size of parachutes used on the load, according to Moorachian.
Platform rigged, the first stop is at the Roller Load Test Facility to check load distribution. The facility, the only resource of its kind, is capable of testing loads up to 40 tons, according to John Doucette, an engineering technician on the Aerial Delivery Engineering Support Team.
The facility has a 32-foot mock-up of the roller and rail system used in an Air Force C-141 to transport cargo, which can be either unloaded on the tarmac or dropped from the air with parachutes while the airplane is in flight.
A total of 136 instrumented rollers take force measurements of the cargo, and a computer-operated data acquisition system analyzes the results from the platform moving across the rollers. A hydraulic cylinder can simulate up to 50 tons of force on cargo pulled by parachutes.
"The Air Force has limitations on force ratings. We don't want to exceed those limitations of the rollers or we'll punch right through the floor," Moorachian said, adding that the C-141 is the test model because it's the weakest airframe in the Air Force inventory.
However, changes are on the way. With the upcoming retirement of the C-141, the facility will be upgraded early in 2005 with rollers and rails that can adjust to simulate other cargo aircraft, modern computing to speed data collection and two 30-ton capacity hoists.
The hoists bring a new capability to pick up the airdrop load in place and adjust it there instead of moving it outside to the Drop Tower hoist, which is time-consuming and delayed by wet weather, Doucette said.
After passing the roller load test, the platform moves to the Drop Tower for a Simulated Airdrop Impact Test (SAIT), more commonly known as static drop test, to determine if the product and honeycomb energy dissipation kit are ready for actual airdrop testing.
Strength of fittings, used to attach straps and parachutes, are also examined.
From a 1,600-square-foot pad, the cargo platform is lifted 12.7 feet from a 39-foot tall, 40-ton capacity crane with a weighted hook. The height at which the platforms are dropped gives 28.5 feet per second vertical impact velocity from acceleration due to gravity, Moorachian said, and except for the flat landing surface, it's the worst-case scenario for a parachute-controlled descent.
When the crane releases its hold, the platform's honeycomb kit crushes to protect the cargo that slams to ground. Instrumentation on the test load measures impact shock and video recording at 1,000 frames per second captures the event for later analysis.
"(The SAIT) is the way we verify the honeycomb works as expected. Maybe we'll find some weak points, and then we'll check for damage to the cargo," Moorachian said.
For testing paratrooper individual combat equipment, the Drop Tower has a 60-foot cable that descends at a 45-degree angle to simulate the "tumble and roll" of ground impact of items at the maximum allowed wind conditions on the drop zone for paratroopers. A required 27-34 feet per second velocity at ground impact is maintained with video analysis.
The Drop Tower crane also helps to certify vehicles or cargo for helicopter sling load missions. Doucette said they check to ensure lift points are strong enough and that the load is stable for a safe delivery.
Although weapon systems are tested with the Drop Tower, all munitions airdrop is tested at Yuma Proving Ground, Ariz. At Yuma and Fort Bragg, N.C., certification takes its final test step by conducting three successful airdrops.
Moorachian said sometimes his team might need to make a few adjustments to the rigging, parachutes or slings, or even start over. Once ready, he then writes a memorandum based on the test report certifying the item for airdrop, as long as the proper rigging procedure is followed.
For more information about the Soldier Systems Center, please visit our website at: http://www.natick.army.mil.