NATICK, Mass. (Sept. 10, 2013) – Among the many testing capabilities housed at the Natick Soldier Systems Center, the Roller Load Test Facility offers the unique ability to simulate the roller and rail systems used in aircraft to deliver cargo airdrops – all while still on the ground.
Recently, engineers at the U.S. Army’s Natick Soldier Research Development and Engineering Center used this facility to collect data samples taken during simulated roller load testing in an effort to develop the airdrop requirements of the Caterpillar 924H Wheel Loader — a multifunctional, front-end bucket loader used in the construction of airfields, roads, defensive berms, and demolition on the battlefield.
The facility allows engineers to see the force exerted on the rollers that move a cargo payload out of an aircraft during delivery. By recording and analyzing this force, engineers can identify the stressors placed on the rollers and determine if they meet the requirements to perform an airdrop of certain equipment payloads from various aircraft models.
Ultimately, the goal is to mitigate the force applied to aircraft rollers and airframe by the heavy equipment airdropped into combat theaters of operation.
However, that capability didn’t always exist at Natick.
The original facility, located offsite in Sudbury, Mass., was designed to simulate only the rollers found in a C-141 aircraft, which was known to have the weakest roller system at the time. The rationale was that if a payload didn’t pass the C-141 roller test, it wasn’t ready for the rollers of any other aircraft, and had to go back to the drawing board to recalculate its energy dispersion.
Even after the facility was moved to Natick in 1978, engineers found the computer and controls to be antiquated systems limited to the outdated testing parameters of the C-141 rollers.
They needed the capability to test the rollers used in newer aircraft in order to drop more robust cargo. The need for heavier equipment and advanced logistics on the ground called for new airdrop requirements, prompting an upgrade to the facility in 2006.
The new Roller Load Test Facility can simulate the platform and rollers of a C-17, C-17 Dual Row (logistical rollers), C-130H, and C-130J aircraft. With an expanded, 28 ft pallet and the added depth of 160 rollers that are placed every ten inches apart, the upgraded facility has an increased capacity for testing and recording roller loads applied by airdrop loads for customers across the Department of Defense.
“The old facility only had two positions to place the pallet on, that’s it,” said John Doucette, a systems engineer for the NSRDEC’s Airdrop and Aerial Delivery Directorate, who operates the facility on a daily basis. “You couldn’t get enough samples to validate the requirements. Now we have 22 positions, which yield a lot more samples.”
Collecting these data samples of the force on rollers demands precise measurements, and the Roller Load Testing Facility excels at this.
Sensors along the roller track send readings about the weight and force of the cargo load to the control room computer, which records them in a database. The computer screen shows rows of numbers corresponding to the rows of rollers on the roller bed. The numbers are in constant flux, displaying minute changes as the weight exerted on the rollers slightly moves. A row highlighted in green indicates it is currently within its weight capacity.
If the weight limit for a roller is exceeded, the row is highlighted in red to show the engineers exactly which roller(s) are over the limit. When this happens, engineers must recalculate the weight dispersal, which often means they must adjust the honeycomb structures they have placed at key contact points throughout the load to absorb the impact of the drop.
“A paratrooper can bend their legs and roll upon impact,” said George Moorachian, senior aerospace engineer with the Aerial Delivery Engineering Support Team, referring to the technique taught at the U.S. Army’s Airborne School to mitigate impact injuries of paratroopers jumping from aircraft.
“Inanimate objects can’t do this. So we need to find away to absorb that impact,” he said.
As the Group Leader for the Airdrop & Helicopter Sling Load Certification Team, Moorachian has been instrumental in improving this honeycomb technology at Natick.
While the military has been using honeycomb to dissipate cargo-ground impact for decades, Moorachian’s team must constantly look for better ways to utilize it with whatever requirement they are working. This means continually moving the material, which resembles a big, cardboard bees’ nest, around the platform to better protect the cargo.
“If there are issues, we have to manipulate the honeycomb to shift the load where it is required according to the sensors,” Moorachian said. “Then we take more samples until the load is deemed stable.”
Once the roller simulation testing is completed, the next step is to go through “tie-down” restraint development. This involves checking and rechecking all the restraint forces used in the trying, strapping, and taping of the equipment to the platform, which often can interfere with the suspension slings.
Securely strapped and tied down to the platform, rigged load data for the cargo load must be collected, having its height, width, and weight sampled, and center of gravity calculated. Only after the data is collected and validated, is the cargo load is ready for the next step — a Simulated Airdrop Impact Test — a new title coined by Moorachian to replace the old, inaccurate one of “Static Drop Test.”
SIMULATED AIRDROP IMPACT TEST DAY
Tucked into a grassy hill at the north end of campus, the Roller Load Test Facility building appears inconspicuous and mundane. Box-like in structure and painted a subdued tan color, the facility blends into relative obscurity amongst a sea of similar looking supply warehouses, garages and storage containers. Yet, the work that goes on there is vitally important to the Soldier on the ground.
It’s the starting point for determining how to best supply warfighters with the equipment they need to fight. And today, the NSRDEC will test the feasibility of that task.
Outside, the building and surrounding landscape is eclipsed by a 33-foot high drop test tower. From the mouth of the building, a track of rollers leads up to the tower, where engineers bustle around the Caterpillar 924H Wheel Loader hanging from suspension lines approximately 12 feet off the ground. They tighten and secure straps, fasten cables, check and recheck numbers on a laptop, and reposition the honeycomb that will absorb the impact of the drop.
A crowd of employees has gathered near the tower to watch the test. Most work for the Airdrop and Aerial Delivery Directorate and were invited by the engineers to come out and see the test live.
For many who work in supporting roles for the directorate, it’s a rare chance to see a live test. Since much of the live tests are conducted offsite during large scale airdrops in actual aircraft at locations and altitudes far from Natick, they must view the outcome of their collective work in videos taken on site. These videos are used as tools to both document and evaluate the performance of the airdrop, and are subsequently viewed countless times by the directorate’s staff.
The most successful airdrop videos, often shot at remote drop zones throughout Afghanistan, serve as a testament to the center’s relevancy to current operations in theater. Last year, approximately 88,000 cargo airdrops were conducted in Afghanistan. Every one of those drops kept Soldiers off of a resupply run, preventing countless casualties from enemy attacks.
Today they get to see something delivered from the air to the ground, even if it’s only a 12-foot, 7-inch simulation drop.
With the cargo secure, the engineers are finally ready to conduct the simulated airdrop. The countdown begins. Months of work hang — literally — from the tower. When the suspension cables are released, there is a second of silence as it drops and before it hits the earth with an enormous thud that echoes across the complex. Lunch time walkers, previously oblivious to the activity, let out a gasp as the noise is heard and impact felt by all in proximity.
“All clear” is sounded and engineers walk into the dust cloud enveloping the impact area, anxious for visual clues about the outcome. A preliminary inspection reveals the cargo to be intact, the honeycomb has compressed as designed, and initial figures on the computer are within range.
Over the next few weeks, engineers will scrupulously analyze the data and report their findings in an Airdrop Proposed Test Plan. But today, the test is a success, and the 924H Caterpillar can now be shipped to Fort Bragg, N.C., for further live testing.
When it ultimately arrives in the hands of Soldiers fighting in austere locations around the world, it will have been the work of the NSRDEC’s Airdrop and Helicopter Sling Load Certification Team at Natick’s Roller Load Test Facility that got it there.