Introduction to UAV Systems. Mohammad H. Sadraey

air vehicles were generally conventionally configured oversized model airplanes or undersized light aircraft that tended to land and take off from runways if based on land, did not have any attempt at reduced radar signatures and little if any reduced infrared or acoustical signatures, and rarely had laser designators or any other way to actively participate in guidance of weapons.

      They generally did not explicitly include a large support structure. Although they required most of the same support as an Aquila system, they often got that support from contractor personnel deployed with the systems in an ad hoc manner.

      UAV requirements that have followed Aquila have acknowledged the cost of a “complete” stand‐alone system by relaxing some of the requirements for self‐sufficiency that helped drive the Aquila design to extremes. In particular, many land‐based UAVs now are either small enough to be hand launched and recovered in a soft crash landing or designed to take off and land on runways. All or most use the global positioning system (GPS) for navigation. Many use data transmission via satellites to allow the ground station to be located at fixed installations far from the operational area and eliminate the data link as a subsystem that is counted as part of the UAS.

      However, the issues of limited fields‐of‐view and resolution for imaging sensors, data‐rate restrictions on downlinks, and latencies and delays in the ground‐to‐air control loop that were central to the Aquila problems are still present and can be exacerbated by use of satellite data transmission and control loops that circle the globe. Introducing UAV program managers, designers, system integrators, and users to the basics of these and other similarly universal issues in UAV system design and integration is one of the objectives of this textbook.

1.5 Global Hawk

      1.5.1 Mission Requirements and Development

      The requirement for a Global Hawk type of system grew out of Operation Desert Storm (in 1991). The Global Hawk was intended to compliment or replace the aging U‐2 spy plane fleet. The Global Hawk is an advanced intelligence, surveillance, and reconnaissance air system (i.e., ISR mission). The strategy for this UAV program involved four phases, which were to be completed between 1994 and 1999.

      It flew for the first time at Edwards Air Force Base, California, on Saturday, February 28, 1998. The first flight of the Global Hawk became the first UAV to cross the Pacific Ocean in April 2001 when it flew from the United States to Australia. The entire mission, including the takeoff and landing, was performed autonomously by the UAV as planned.

      A total of 21 sorties of flight tests were conducted over 16 months using two air vehicles accumulating 158 total flight hours. It entered service in 2001 and reached the serial production stage in 2003. The Global Hawks, monitored by shifts of pilots in a ground control station in California, fly 24‐hour missions, and they are cheaper to operate than the manned aircraft Lockheed U‐2.

      1.5.2 Air Vehicle

The Global Hawk unmanned aerial system consists of the aircraft, payloads, data links, ground stations, and logistics support package. Global Hawk is the largest active current UAV with successful flights, and with a high altitude and long endurance (HALE). A Global Hawk (Figure 1.4) is equipped with a single AE 3007H turbofan engine – mounted on top of the rear fuselage – supplied by Rolls‐Royce. The engine is mounted on the top surface of the rear fuselage section with the engine exhaust between the V tail.

The wing and tail are made of graphite composite materials. The wing has structural hard points for external stores. The aluminum fuselage contains pressurized payload and avionics compartments. The V‐configuration of the tail provides a reduced radar and infrared signature. Some mass and geometry features as well as the flight performance of Global Hawk are provided in Table 1.1.

Figure 1.4 Global Hawk

      (Source: Bobbi Zapka / Wikimedia Commons / Public Domain)

Table 1.1 RQ‐4B Global Hawk data and performance

No.	Parameter	Value (unit)
1	Wingspan	39.9 m
2	Length	14.5 m
3	Maximum takeoff mass	14,628 kg
4	External payload weight	3,000 lb
5	Internal payload weight	750 lb
6	Turbofan engine thrust	34 kN
7	Maximum speed	340 knots
8	Range	22,779 km
9	Endurance	32+ hours
10	Service ceiling	60,000 ft

The prime navigation and control system consists of two systems, the Inertial Navigation System and the Global Positioning System (INS/GPS). The aircraft is flown by entering specific way points into the mission plan. The GCS consists of two elements, the Launch and Recovery Element (LRE) and the Mission Control Element (MCE). The LRE is located at the air vehicle base. It launches and recovers the air vehicle and verifies the health and status of the various onboard systems. The MCE is employed to conduct the entire flight from after takeoff until before landing.

      Many changes have been applied in the design of Northrop Grumman RQ‐4B Global Hawk as compared with RQ‐4A. For instance, the RQ‐4B Global Hawk has a 50% payload increase, larger wingspan (130.9 ft) and longer fuselage (47.6 ft), and a new generator to provide 150% more electrical output. Although RQ‐4B carries more fuel than RQ‐4A, it has a slightly shorter range and endurance, due to a heavier maximum takeoff weight.

      1.5.3 Payloads

      Originally RQ‐4A had three sensors (as payload): an Electro‐Optical/Infrared sensor and two Synthetic Aperture Radar Sensors – which are located under the fuselage belly in the integrated sensor suit – have been enhanced for RQ‐4B. The main thrust of the air vehicle changes over time has involved the sensors. The enhancement improves the range of both the SAR and infrared system by approximately 50%.

      1.5.4 Communications System

      The Global Hawk has a wide‐band satellite data link and a line‐of‐sight data link. Data is transferred by: (1) Ku‐band satellite communications, (2) X‐band line‐of‐sight links, and (3) both Satcom and line‐of‐sight links at the UHF‐band. The synthetic aperture radar and ground moving target indicator operates at the X‐band with a 600 MHz bandwidth.

The