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This article was Originally Published on Jul 10, 2003 in Volume: 2  Issue: 3

Dull, Dirty and Dangerous

Next generation of UAVs hover on the horizon.

By Larine Barr

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The Air Force Research Laboratory (AFRL) is developing the next generation of unmanned air vehicles (UAV) with an eye on enhancing the effectiveness and affordability of the systems.

Engineers and scientists with the AFRL Air Vehicles Directorate, Wright-Patterson Air Force Base (AFB), OH, are concentrating their efforts on technologies for Strike unmanned air vehicles, directed energy integration and SensorCraft to enhance the warfighter’s capabilities.

According to Gary Dale, UAV lead for the directorate, researchers are homing in on the three areas to help focus the technology developments on conceptual vehicles and capabilities. Over the next several years, AFRL will combine the innovations into one or several platforms and perform flight tests on a prototype as early as 2011. The directorate spent an estimated $7 million in 2003 on UAV technology research and expects to spend a similar amount in 2004.

“It’s important that we advance this research because UAVs may offer the warfighter capabilities beyond what manned systems do or, operating together with manned systems, may enhance the warfighter’s total capability,” said Dale.

Dull, Dirty and Dangerous

According to Dale, UAV missions are most often characterized as the “dull, dirty and dangerous.” Dull—as in patrolling no-fly zones or very long intelligence, surveillance and reconnaissance (ISR) missions; the UAV is just as alert in the last hour of its patrol as it is in the first hour. Dirty—as in operations in airspace potentially contaminated with biological or chemical weapons. And dangerous—as in electronic attack missions, often performed early in a battle while the enemy’s air defenses pose a serious threat.

The technology advancements AFRL scientists are exploring range from adding advanced sensors to facilitate automatic collision avoidance, integrating the propulsion system with the airframe to reduce size, and developing mission control capabilities that will enable multiple UAVs to operate as a cooperative group.

Along with these advancements, the directorate is developing on-vehicle control capabilities to enable UAVs to be as safe and effective as manned assets, but at a reduced size, weight and cost. Technologies in development include photonic vehicle management systems, intelligent reconfigurable control, prognostic health management, automatic collision avoidance and automatic air refueling.

Focusing on the three development areas also guides scientists into designing UAVs that are capable of certain feats. These major enabling thrusts are preemptive and reactive suppression of enemy air defenses using strike UAVs; efficient and effective integration of directed energy weapons into tactical UAVs; and increased endurance permitting longer range and more complex ISR missions.

Breaking from Paradigms

In the realm of airframe concepts, researchers are breaking from current air vehicle design paradigms to structurally embed and integrate antennas, arrays and subsystems into the wings and fuselages of UAVs. “This will enable researchers to design vehicles around the mission’s sensor requirements rather than designing the sensors to fit the constraints of the vehicle,” Dale said.

Towards that effort, AFRL researchers are exploring a concept for the warfighter, called SensorCraft, a futuristic ISR UAV. The SensorCraft integrates sensing devices, information technologies and new propulsion systems into an airframe capable of revolutionary ISR capabilities.

“The directorate is investing considerable resources on adaptive structures, active flow control, and ultra-lightweight airframe concepts specific to high altitude airfoils to enhance aerodynamic efficiency of concepts such as the SensorCraft,” said Dale. This increase in endurance would allow the system to fly longer range, and more complex missions or loiter time, which could result in fewer vehicles needed to maintain a continuous presence over the battlefield.

Though there are many technology hurdles to jump, directorate officials said a full-scale SensorCraft platform could be ready for flight tests in eight or nine years. Platforms with smaller subsets of technologies could be ready for tests as early as 2008.

In addition to SensorCraft, the Air Vehicles Directorate is exploring a concept that combines helicopter and plane-like characteristics. Called SkyTote, the craft has counter-rotating propellers and will be able to accomplish vertical take offs, landings and hovers. Once airborne, SkyTote can transition to wing-borne flight with its advantage of higher speed and increased range. The directorate is conducting flight tests on SkyTote this year.

Superior Sensors

While Air Vehicles Directorate scientists work on new platform designs, researchers at the Sensors Directorate at Wright-Patterson Air Force Base are incorporating a suite of specialized sensors to augment future UAV capabilities. These sensors would provide large area surveillance to dramatically increase combat identification capabilities for the warfighter.

“The sensor spectrum for UAVs is very comprehensive, ranging across both electro-optical and radio frequency spectrums,” said Paul Johnson, of the Sensors Directorate. “A prevailing theme is size, weight and power reduction through advanced technologies, paving the road to more prolific incorporation of multifunction capabilities. A primary example of this is our structurally embedded low frequency antenna technologies to enable respectable performance in areas of foliage penetration and airborne target tracking.”

Integrating Propulsion Systems

In addition to exploring new platforms and sensors, AFRL researchers are striving to integrate the propulsion system with the airframe of UAVs, which can have enormous payoff in vehicle size, weight and cost.

“UAVs are sized to three things: mission requirements (speed, range, etc.), payload (weapons systems, etc.) and a propulsion flow path length,” said Dr. Greg Addington, Air Vehicles Directorate program manager for propulsion integration. “The flow path must be sufficiently long to give good flow quality to the engine but twisting and turning to get around items installed in the fuselage. If we can make the highly offset inlet more compact, that sizing (especially length) requirement is cut proportionally. If air vehicle weight is proportional to the CUBE of the length scale—imagine the payoff. Additionally, vehicle cost is proportional to weight, so you get a smaller, lighter and less expensive air vehicle.”

According to Addington, the technology will reduce the length and diameter ratios of current ducts (F/A-22 and F-35 are both about 5) to about 2.5, but with flow quality (pressure recovery and circumferential distortion) equivalent to the fighters—or better.

Improved Safety and Effectiveness

Another goal pursued by AFRL researchers is to develop technologies to increase safety and effectiveness of UAVs. On a practical level, inventors are working on programs like the automatic air collision avoidance system and automated aerial refueling in which the vehicles, whether manned or UAVs, must talk to each other to formulate plans and intentions. “This could be done via data links or other methods, but they still must communicate,” said Bruce Clough, lead for Controls Automation, Air Vehicles Directorate. Clough stressed that autonomous UAVs must communicate and work with other UAVs and manned aircraft as an integrated team.

Clough said the directorate is researching—at the theoretical level—multiple characteristics of UAVs: how autonomous teams form; the internal knowledge needed to form these teams; when and what the UAVs discuss; the impact of command and control structure on this knowledge flow; and how UAVs can strike up conversations with their operator or human supervisor, to both aid the human’s decisions-making as well as build trust in UAV operations.

“The UAVs of the future will not just be passing knowledge, pictures per se, but they will use knowledge to think about what the pictures mean. If we trust the capability of the UAVs to generate and disseminate knowledge, then we reduce the need for pictures, videos, and the like and we can ultimately reduce our communication bandwidth requirements,” said Clough.

In concert with these advances, the directorate is pursuing a new generation of more unitized structures for UAVs that will reduce manufacturing costs and increase system readiness without weight or supportability penalties. The approach is to identify, develop and transition new structural design concepts and manufacturing methods for both metals and composites that place emphasis on reducing part count and the number of structural joints and fasteners.

Technology Assessments

To better understand the needs of the warfighter, the Air Vehicles Directorate, Subsonic Aerodynamic Research Laboratory, teamed with NASA Langley’s Advanced Instrumentation and Diagnostics Branch and the research organization Innovative Scientific Solutions Inc. as part of AFRL’s simulation-based research and development effort.

Dr. Charles Tyler, aerospace engineer with the directorate, said the goal is to provide multi-disciplinary technology assessment to technologists, managers and planners, so that high-payoff technology investment paths may be rapidly identified and communicated to the warfighter. In April, researchers conducted a test that deployed global diagnostics to measure surface pressures and test article geometry, while at test condition (under aerodynamic load).

“This test successfully demonstrated the first steps towards understanding and subsequently modeling aerodynamic cause and effect relationships,” explained Tyler. “In its ultimate embodiment the recovered information will be presented so that researchers—both experimentalists and computationalists—are able to integrate the data set into one solution or subsequent course of action, so-called useful knowledge.”

As AFRL researchers continue to push the envelope under the three-pronged UAV strategy, major breakthroughs are just over the horizon. “We could see combat UAVs—like our strike UAV concept—in operation by 2008,” said Dale. “The next major milepost will be testing an ISR platform by 2012 or 2013.”

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