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On the Mark
Written by Peter Buxbaum
It is no coincidence, then, that the armed services, under the Army’s leadership, have accelerated the development of high altitude precision airdrop systems in recent years.
“Six aircraft were hit during a ninemonth period in Afghanistan in 2006,” said Richard Benney, an aerospace engineer in the Warfighter Protection and Airdrop/Aerial Delivery Directorate at the U.S. Army’s Natick Soldier Center. “There has been a big push to go high.”
“With standard airdrops, you need to fly aircraft fairly low to get cargo into tight areas,” said Gary McHugh, business development manager at Airborne Systems North America. “You need to use a round parachute, and a round parachute is at the mercy of wind conditions. When you bring the aircraft down low, it also pays to have a fairly large drop zone.” Over the past four to five years, investments in aerial delivery have proceeded “in leaps and bounds,” McHugh added. “Precision drops at higher altitudes are out of reach of ground fire and reduce the size of the drop zone required to get payloads to the troops on the ground.”
The key program that came to answer warfighter requirements for aerial delivery was the Joint Precision Airdrop System (JPADS). All JPADS payloads are required to be airdroppable from 25,000 feet.
“Twenty-five thousand feet is not the limit, but it is a relatively safe altitude for C-130s and C-17s,” said Benney. “The eventual objective is 35,000 feet. The idea is to drop and forget.”
JPADS was first deployed to Southwest Asia by U.S. forces in 2004. Air delivery of supplies in Afghanistan has since grown from 2 million pounds in 2005 to 16.6 million pounds in 2008, according to Benney.
JPADS includes several payload weight classes of self-guided and non-steerable systems, navigation aids, and a common JPADS mission planner. JPADS has also spawned a number of ancillary developmental programs, including a Marine Corps program that seeks to drop extra-small payloads from helicopters to experiments with systems that could accommodate extremely weighty payloads such as vehicles or fuel tanks. One way to accomplish the goal of a precision airdrop is to have ground units equipped with a radio frequency signaler for which payloads aim. The U.K. Ministry of Defence has acquired such a beaconed controlled system.
The U.S. military rejected this approach, said Benney, because many precision airdrop scenarios involve providing supplies in advance of the arrival of forward troops to the drop area.
Instead, the U.S. approach opted for the control of the payload through mission planning and aerodynamics. The mission planner gathers information on atmospheric conditions; aircraft altitude, airspeed, heading and pitch; payload weight; and parachute type, and calculates a roll-out point.
Aerodynamics are provided by high-altitude high-opening (HAHO) rectangular airfoil, or ram air, parachutes, best thought of as a wing or a glider. The airfoil actually flies, rather than drops, to the target. A typical glide ratio of three to one in low-wind conditions means that the payload will be gliding three feet in the horizontal for every one foot it is dropping vertically. If dropped at a 25,000- foot altitude, this means that the roll-out point must be 75,000 feet, or around 25 kilometers, from the intended target.
“The Ram air parachute has forward speed and the ability to penetrate wind conditions,” explained McHugh. “It can maneuver better than a round parachute.” After exit from the aircraft, in the case of guided systems, an airborne guidance unit (AGU), which includes a GPS signaling system, flies the airfoil on automatic pilot, controlling its course by means of two pulleys on either side. The AGU continues to monitor conditions during flight and makes adjustments as needed. Non-guided JPADS systems use high-altitude low-opening parachutes to hit their marks.
“One of biggest challenges is in handling different wind environments,” said Alexandre Cote, Sherpa product manager at Mist Mobility Integrated Systems Technology Inc. “That is where you move from unguided to guided systems. Guided systems once deployed can overcome wind changes and find targets successfully.”
How successfully? Mist Mobility’s Sherpa, which was one of the first guided systems to be deployed to Southwest Asia, can land within 100 meters of an intended target 50 to 80 percent of the time, according to Cote. “The results resemble a bell curve,” he said.
The Sherpa’s guidance system, which is common to the three weight-category systems—below 1,000 pounds; between 1,000 and 2,200 pounds; and up to 12,000 pounds—Mist Mobility supplies the U.S. military, allows users to choose, not only a target point, but also an approach heading. That way, for example, if a payload is to be dropped on a beach, the airfoil will be guided to glide parallel to the water before landing so that, in case of an overshoot or undershoot, the cargo does not end up in the drink.
The Sherpa may also be used in unguided mode with its HALO capability. “The system allows the payload to free-fall to a preprogrammed altitude and then have the parachute open,” said Cote.
All of the JPADS programs, whether using guided or unguided systems, use a common mission planner that is provided by QinetiQ. The JPADS mission planner provides atmospheric modeling, airdrop planning and modeling, aircraft tracking using a Windows-based map overlay, and a predicted delivery footprint.
QinetiQ’s system starts with pre-mission route planning. Weather forecasts for the flight and drop zones are updated by data from a meteorological device called a sonde, which is dropped 50 kilometers from the intended drop point.
“We take the data from the sonde and assimilate it with forecast data to look ahead in space and time to model the wind field in the mission area,” explained Andrew Rogers, director of survivability programs at QinetiQ North America’s technology solutions group. “This provides the air crew with a computerized release point, a flying vector, and the optimum standoff distance from the drop zone to ensure accuracy.”
Airborne Systems was awarded two major programs of record by the U.S. Army to provide two weight classes of JPADS systems, the 2,000-pound Firefly and the 10,000-pound Dragonfly system, which is expected to be fielded by the end of 2010. Airborne Systems also provides the 500-pound Microfly system to selected U.S. Army units.
Also in the works are the Megafly and the Gigafly, which are being funded by a Department of Defense science and technology program, which will take JPADS into the 30,000- and 40,000-pound ranges respectively.
“We successfully produced a system that carried a 42,000-pound payload,” said McHugh. “We dropped this several times as a proof of concept. This holds the record for a ram air parachute drop. The airfoil was over 10,000 square feet in size, and it had a bigger wing span than a C-17.”
These heavier-payload systems could be used for specialized missions, such as standing up a desert aircraft refueling position, delivering a specialized—for example, a mine clearing—vehicle, or delivering large quantities of ammunition, McHugh said.
A new system called Universal Precision Air Drop, or UPADS, is also in the works and is designed to deliver payloads of between 700 pounds and 10,000 pounds using either a ram air or a round parachute. “This is actually a modular system,” said Vincent Juchniewicz, director of program management at Capewell, the developer of the system. “It has a guidance unit and a control unit that snap together. Depending on the mission, you can change the control unit for a tighter configuration.”
Capewell’s system is able to steer round parachutes, which Juchniewicz said could be advantageous for use in mountainous regions. “We have been steering round chutes for a number of years,” he said. “It has a low glide ratio and horizontal offset. Especially in mountainous regions, an airfoil can catch the wind off the mountain and stay aloft for quite some time.”
Using round chutes also allows the military to make use of its current large inventory of G-12 and other standard parachutes right off the shelf. UPADS also uses the JPADS mission planning system and includes a single guidance system for all payload weight classes.
UPADS is in development under a Capewell contract with the Natick Soldier Center. The system could be fielded as early as 2010, depending on budgeting decisions, according to Juchniewicz.
EADS North America, a division of the aeronautics and space company based in the Netherlands, is working on an ultralight precision airdrop system on behalf of the U.S. Marine Corps. At demonstrations that took place in 2007 and 2008, the EADS system proved to be more accurate than those of its competitors.
The Marine Corps is interested in such a system for the resupply of small forward units, according to Aaron Johnson, EADS North America’s director of business development. “The Marine Corps saw what was going on with JPADS,” he said. “Natick was starting with systems for 2,000-pound and bigger payloads.”
The Marine Crops was interested in lighter weight systems and was designated by the Army to take the lead on an ultralight airdrop system. “We’re talking about sustainment of groups on the move and especially for the resupply of ammunition,” he said.
Johnson believes that EADS’ greater precision in the ultralight system demonstrations is connected with the company’s aerospace experience. He also said that EADS has been improving the system based on feedback from the Marine Corps.
“It probably has something to do with the variables you encounter in flight,” he said. “Each company has a different methodology. Some units take measured values and insert those into the autopilot. Others like ours take measurements as the parachute comes down and compensate for conditions.
“Some systems may have different flight profiles and may dissipate energy at different points in the flight,” Johnson added. “Each company, based on its own experience, will make different autopilot decisions.”
When UPADS will transition to a program of record is at this point unclear. The Marine Corps has been postponing issuing a request for proposal for the ultralight system for the last two years, said Johnson. The latest word, he said, is that the Marine Corps will proceed later this summer.
The next big push for precision airdrop systems, from the perspective of the Natick Soldier Center, is going to be improving guidance, navigation and controls for the JPADS. “There is a significant effort in the Army to improve navigation and control,” said Benney. “We want to establish communications among the airdrop units so that they know where each other is in air and space. We’re looking at systems that will supply terrain data so that the airfoil will know where mountains are and won’t fly into them. We are also looking at developing a controlled flare approach that airplanes have that would allow the parachute to make a dynamic maneuver just before landing to bleed off some velocity and decrease the impact of touchdown.”
The program Natick is working on will seek to develop, integrate and test advanced sensors, guidance approaches, and control system technologies relevant to all weight classes of JPADS. “The result of this research,” said Benney, “will be greatly improved delivery accuracy of airdropped payloads.” ♦