Retraction softens equipment landings without honeycomb
Slamming into the ground at an average velocity of 28 feet per second, airdrops of vehicles and supplies suffer devastating damage if left unprotected.
Honeycomb cardboard has been used for as long as heavy cargo has been airdropped to absorb energy on impact, but new technology researched by the Airdrop Technology Team at the U.S. Army Soldier Systems Center (Natick) has led to systems that reduce impact velocity to the point where cushioning is unnecessary.
An airdrop with a 10,000-pound load was successfully tested in November at Yuma Proving Grounds, Ariz., using retraction, which decelerates the load to a survivable velocity immediately before landing. The next step is to test loads of 15,000-20,000 pounds.
“This year we’re getting closer to a production item,” said Brian Bagdonovich, project officer for the Rapid Rigging De-rigging Airdrop Systems. “It looks like we should be able to eliminate paper honeycomb for energy absorption purposes.”
That will be a relief to those who rig the equipment before it’s loaded onto an airplane and de-rig it once it’s on the ground, and benefit the Army in reduced logistics.
Soldiers in airborne units can spend up to eight man-hours rigging a Humvee onto a platform. This consists of packing parachutes, making honeycomb kits to be placed on the platform under the equipment, lifting the equipment onto the platform with a crane and then securing the equipment down to the platform with straps under the supervision of riggers.
“With downsizing, there is a reduction in personnel available to rig equipment. If you can just drive onto the platform, it’s much quicker,” Bagdonovich said.
On an imperfect landing on the drop zone, the honeycomb may not always crush uniformly and can become entangled in the vehicle. “It can take up to 20 minutes to de-rig if a vehicle’s stuck in the honeycomb,” he said. “We’d like to reduce de-rigging time to a minute so the soldier can just drive out of harm’s way.”
Honeycomb needs to be pre-cut, glued and stacked into custom kits for each piece of equipment. It’s lightweight but bulky, and is costly to purchase, store, transport and dispose. It is used only once, while the new retraction systems will be designed for 25-50 or more airdrops for vehicles, trailers, towed artillery or supplies to support units.
To move away from the passive protection of honeycomb, engineers designed two different retraction soft landing systems that dramatically slow the fall.
“We wanted a system that slows the descent rate down to 8 feet per second, which is the impact velocity a Humvee should handle,” Bagdonovich said. “An additional advantage is the payload won’t rebound and will have a lower tendency to rollover after ground impact, which can happen with honeycomb.”
The Pneumatic Muscle Actuator (PMA) is a silicone tube reinforced with a braided Vectran fiber that’s inserted between the cargo slings and the parachute confluence point.
A stick trigger hanging beneath the platform strikes the ground and activates a generator that expands the actuator with a hot gas. When the actuator is inflated at about 20 feet before impact, its diameter increases while its length decreases by 35 percent, pulling the cargo up toward the parachutes and reducing the cargo’s landing velocity.
“The PMA still requires extensive testing and refinement but has the greatest potential for the widest variety of applications for airdrop equipment,” he said.
Cable retraction is another way to rapidly decelerate cargo for a soft landing.
Soldiers would drive right onto a platform to be rigged. When the platform exits the aircraft, the parachutes open and 20-feet of steel cable releases through a pulley system.
A stick trigger activates a nitrogen gas charge at about 14 feet above ground that forces a piston to move the pulleys and reel in the 20 feet of cable. Similar to the actuator, the shortened cable creates an upward force on the cargo toward the parachutes and decelerates the load to 8 feet per second.
A preplanned product improvement program will be introduced as doctrine changes and technology matures to allow for the modernization of the system. Upgrades would support airdrop of vehicles that weigh up to 60,000 pounds at wider-ranging altitudes and at a higher airspeed.