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weapons used, men down, while also securing the perimeter. The operation is concluded when the hostage scene is secured and the rescue team account for all hostages, takers, weapons and rescue personnel.
UAS Class Selection
Budgetary constraints are always a concern when implement- ing any system, so we fi rst consider the smallest UAV in search of the least expensive, suffi ciently capable platform that will accomplish the mission.
The smallest UAV is the micro air vehicle, or MAV, which has a maximum physical length of up to 6 inches according to the De- fense Advanced Research Projects Agency (DARPA); although manufacturers claim MAVs can have a wing span up to 2.5 feet. Given the small size of the aircraft, generally less than half a pound, an MAV would be an excellent platform to satisfy our tactical requirement for stealth. However, their small size al- lows for little payload capacity for the sensors required. Their light weight and slow fl ight speeds make them particularly sensitive to gusts and turbulence.
Although a UAV in the MAV design class might provide a stealthy platform, it would be payload limited and unable to carry the EO sensors needed to fulfi ll the mission. Thus, an MAV platform is not adequate to fulfi ll a hostage rescue mission. The next class of UAS available is the small UAS, or sUAS, which range in weight from 1 to 55 pounds. The sUAS is the smallest UAV class that will be able to carry the appropriate sensors and fulfi ll the hostage rescue mission requirements and is thus an appropriate platform to imple- ment in this situation.
Fixed Wing Versus Rotary Wing
Our next consideration is whether to use a fi xed wing or rotary wing aircraft. Since the location is stationary, we do not need to be concerned with speed, either to dash to the location or to chase a moving target. More importantly, the mission requires a UAV with loitering capability, and a UAV that has hovering capacity is more useful than one that circles overhead. A hov- ering platform provides a stationary position from which to observe events inside the building and discern hostages, who will more likely be stationary, from the hostage takers, who are more likely moving. A fi xed-wing UAV (such as the ARA
Nighthawk) would have few benefi ts and more liabilities for this situation. One such benefi t is the ability to ar- rive on station quickly. However, this would require a launch site somewhat close to the hostage site and given the suburban location, fi nding a runway or open fi eld nearby from which to launch may be diffi cult. Once arriving on site, the Nighthawk would loiter by circling either overhead or at a standoff location. An overhead loiter would allow for the best sensing vantage point, but the platform would
18 LAW and ORDER I May 2016
The RAPTR helicopter. Photo courtesy of Tactical Electronics.
always be moving, making it more diffi cult to discern move- ment inside the house.
In addition, a person of interest, once spotted, may be lost be- hind an obscuring object such as a tree, a wall, or another person as the Nighthawk circled. Also important is the need for the UAV to remain undetected by the hostage takers. A Nighthawk circling overhead would likely be noticed from engine noise or movement of the aircraft. This would dictate that the Nighthawk loiters suffi - ciently distant from the scene to remain out of earshot and perhaps even visual range. This decreases the effectiveness of the sensors requiring a compromise between stealth and sensor performance. A rotary wing UAV such as a multi-rotor or helicopter pro- vides a platform that eliminates several of these concerns. It can be launched from any level platform with no runway, requiring only enough space to navigate safely through the trees. Launched from a lawn just out of eyesight, perhaps 100 yards away from the scene, a rotary wing UAV can be on scene within seconds and loiter by hovering just out of eyesight of the takers. A signifi cant concern is alerting the takers through the noise generated by the UAV. Blade rotation noise is audible, but electric-powered engines provide quieter operation than gas-powered engines. Research conducted by the Space and Naval Warfare Sys- tems Center found that of the UAV requirements, “The most signifi cant is the requirement to quiet the system. The problem was primarily caused by the engine exhaust noise. This may be even more of a problem for a smaller system depending on small two-cycle engines. High-energy density batteries and high-effi ciency electric motors may help with this problem.”
Although noise is a necessary by- product of any airborne asset, a noise generator such as a lawn mower or leaf blower can be used to mask the sound of the propeller blades and engines. Numerous small multi-copters are
The FLIR Quark 640. Photo courtesy of OEM Cameras.
specifi cally designed for use by law en- forcement entities. One such multi-cop- ter is the Draganfl yer X6, used by the
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