Fullscreen HTML5Med Res (??MB)HTML4

GLOBAL HAWK Part 2 in our UAV series By Bob Young a giant unmanned aircraft As we went to press in mid-April, the RAAF air base in Edinburgh, South Australia, was anxiously awaiting the arrival of one of the most unusual aircraft flying today. Soaring in from a non-stop, record-breaking flight across the vast Pacific Ocean, the landing of RQ-4A Global Hawk was set to mark the coming-of-age of the autonomous unmanned air vehicle, the UAV. P owered with a jet engine and with the wing-span of a Boeing 737, this is no miniature radio controlled aircraft. It has a maximum range of more than 25,000km, which is more than most commercial jet airliners and it can fly at 50,000 feet. After years of promising beginnings, disappointments, frustration and cancelled programs with UAVs, the success of Global Hawk is finally beginning to transform the military capability of unmanned air vehicles. However, as dramatic as the first flight of an unmanned air vehicle across the Pacific may prove to be, this flight is not about-record breaking. It is about proving the tactical and strategic value of long range UAVs. Deployed in Australia as part of a US–Australia Cooperative Project Agreement, Global Hawk will take part 4  Silicon Chip in a number of joint projects between April and June 2001. During the Australian deployment, Global Hawk will form the nucleus of a complex four-way partnership between the RAAF, USAF, DSTO and Northrop Grumman. The Australian project director is Dr Jackie Craig and the US project director is Col. Wayne Johnson. Australian interest in Global Hawk is aimed at investigating the compatibility of Global Hawk with existing defence and coastal surveillance systems. The Australian deployment begins with the historic flight on 21st April. It will then encompass 12 operational sorties aimed at demonstrating the capabilities of the aircraft in missions such as airfield surveillance, targeting and most important of all from an Australian point of view, coastal watch! Finally, Global Hawk will participate in Exercise Tandem Thrust. It is going to be a busy time for the Global Hawk flight and support team. The Global Hawk story The story of Global Hawk began back in 1993 with the pioneering work of Teledyne Ryan Aeronautical (TRA) when they conceived and began to pursue the idea of a high-altitude, long endurance (HALE) UAV. In 1994, the US Defence Advanced Research Projects Agency (DARPA) issued a request for proposals (RFP) for a HALE UAV. This request was prompted by the glaring shortfalls in real-time, consistent reconnaissance data which became obvious during Operation Desert Storm. Launching, operating and retrieving Global Hawk requires the use of a huge variety of communications, both direct to ground control stations and via communications satellites. It’s almost as complex as a space launch (some would say even more so!). The RFP called for an aircraft capable of carrying a 1000kg payload for more than 40 hours at altitudes of up to 65,000 feet (20,000m). In the peculiar jargon of the US defence forces, (sadly becoming all too common here) the successful proposal would be known as Tier 2 Plus and would be one of several UAVs planned by the US Defence Airborne Reconnaissance Office (DARO). The first of these, Tier 1, the General Atomics Gnat 750, was already in service with the CIA, peeping into hot spots in Bosnia. In May 1995, a TRA- lead team including E-systems as the sensor package supplier, won the Tier 2 plus competition and set about developing what has since become the Global Hawk. Originally budgeted to cost US$10,000,000 for each aircraft, based on a quantity of 20 units, cuts to the quantities ordered resulted in the current price of US$15,300,000 per airframe on seven aircraft delivered to date. This is still not a bad figure by modern standards, considering the complexity of the final system. As with all aircraft, the Global Hawk took shape out of a complex array of competing requirements. All were aimed at meeting the principal objective of flying at 65,000 feet for 24 hours. This is after covering 1,600nm (3000km) to arrive at the target, and with sufficient reserves to fly the 1,600nm back home. Stealth was not considered a major design factor as it was thought that the 65,000 feet altitude would provide sufficient protection against most ground and subsonic air-launched weapons. However, the relatively large sensor payload with the complex requirements governing the positioning of the sensor apertures certainly was most important. In the end, the airframe developed into a 35m (116 feet) span wing with a stubby 13.5m (44 feet) long fuselage. The thin slightly swept wings (5.9° sweep angle measured at the 25% chord point), when combined with the fuselage fuel tanks, can accommodate 6.8t of fuel. When the wing tanks are fully laden with fuel (4000kg), the wings sag 0.3m at the tips. The wing is a lightweight structure constructed entirely of carbon-fibre-epoxy composites, with four shear spars and a high modulus composite skin. The laminar flow, super-critical wing has an area of 540 square feet and an aspect ratio of 25:1. Design lift/drag ratio (L/D) was 37 but flight-testing has shown that it is actually 33 to 34; still a very respectable figure, comparable to some modern sailplanes. Design changes to the wing section are under way to overcome this shortfall. The lift to drag ratio of an aircraft is a measure of the aerodynamic efficiency and any improvement in this ratio will result in increases in speed, range and/or loiter time. All of these factors are extremely important to Global Hawk so time and effort spent improving this area will be well rewarded. While the wing is composed of composite materials, cost factors dictated that the fuselage should be of conventional aluminium monocoque construction. The fuselage accounts for some 35% of the airframe weight. The main undercarriage is a standard Learjet 45 assembly and the nose gear is a two-position unit from a Canadair CF-5F. Here's Global Hawk’s notional “mission profile”. The first phase is getting it into the air and to its target. Second phase is the surveillance mission itself (which can last for 24 hours or more) while the final phase is the safe return and landing. MAY 2001  5 Some idea of the size and complexity of the Global Hawk can be gleaned from these drawings and – most spectacularly – from the detailed drawing overleaf. It needs a full-size airfield to operate from and remote control is not quite your hand-held radio control unit, as can be seen from the photos below! The unusual, high dihedral angle (50°) tailplane assembly was settled on as a compromise between a variety of factors which included ground clearance, weight, drag, and simplicity of engine exhaust ducting. The Rolls-Royce AE3007H turbofan engine was chosen for its excellent specific fuel consumption/thrust performance at altitude. It is also an engine with a “good heritage”, developed from a common core used in power plants for the C-130J (Hercules), Bell Boeing V-22 Osprey and a host of small commercial and business jets. The maximum operational altitude of the Global Hawk is limited by the engine developing surging at around 70,000 feet, therefore the service ceiling was set at 65,000 feet. The engine is programmed to perform a slow “roll back” to a lower throttle setting as maximum altitude is approached. The highest altitude achieved to date is 66,400 feet. In-flight operation Mixing manned aircraft with unmanned aircraft on international air routes has been one of the most pressing concerns for aircraft operators, as well as those entrusted with formulating the legislation and operating procedures. Interestingly enough, Australia, because of its long history with unmanned aircraft, in particular Jindivik and Aerosonde, has risen to the challenge of formulating operating procedures and has published draft legislation in the form of Civil Aviation Safety Regulation Part 101 (CASR Part 101). For those interested in more detail, www.casa.gov.au will provide all 6  Silicon Chip VEHICLE SPECIFICATIONS Fuselage   Width (ft) 4.8   Length (ft) 44.4 Wing   Area (sq ft) 540   Span (ft) 116.2   Aspect Ratio 25.0   1/4 Chord Sweep 5.9° V-Tail   Area (sq ft) (each) 42.8   Span (ft) (each) 11.4   Aspect Ratio 3.0   Dihedral Angle 50° Empty weight (lbs) 9,200 Fuel (lbs) 14,900 Take-off gross (lbs) 26,000 of the answers. Aeromodellers may also be interested in CASR 101 as this legislation also governs model aircraft as part of the broader UAV spectrum. As may be imagined, a considerable amount of effort has been expended on emergency procedures for Global Hawk, to cover the various contingencies that may arise. Broadly these are broken into four main categories: (a) Loss of the Command and Control link (C2). The aircraft is programmed to continue on course for 1.5 minutes before returning to base if no signal is pick-ed up. (b) Imminent or actual failure of a critical system. Return to base. (c) Engine flame-out. Global Hawk is programmed to search onboard memory for the nearest “friendly” alternative runway.    Restart by diving (wind-milling) is out of the question because the slow flying UAV cannot attain the required dive speed. Alternative restart options such as compressed air bottles and/or an auxiliary Global Hawk – System Performance Summary PROGRAM GOALS 14,000NMI 65,000 feet + 42 Hours 1 Loss in 200 Missions 1.5-50Mbps >50Mbps 1.0/0.3m resolution (WAS/Spot) 20-200km/10m range resolution EO NIRS 6.5/6.0 (Spot/WAS) IR NIRS 5.5/5.0 (Spot/WAS) 40,000 sq nm/day 1,900 spots targets/day <20 metre CEP CHARACTERISTICS PROJECTED PERFORMANCE Maximum Range 13,500NMI Maximum Altitude 65,000 feet Maximum Endurance 36 Hours Flight Critical Reliability 1 loss in 605 missions SATCOM Datalink 1.5, 8.67, 20, 30, 40, 47.9Mbps LOS Datalink 137Mbps SAR 1.0/0.3m resolution (WAS/Spot) MTI 20-200km/10m range resolution EO EO NIRS 6.5/6.0 (Spot/WAS) IR IR NIRS 5.5/5.0 (Spot/WAS) Wide Area Search 40,000 sq nm/day Target Coverage 1,900 spots targets/day Location Accuracy <20 metre CEP While not all of Global Hawk’s program goals have been met, they’ve come pretty close! Moves are currently under way to improve the maximum endurance to come close to the goal. power unit were ruled out on the grounds of weight, cost or complexity.     If there is no suitable alternative landing field within range, then Global Hawk is programmed to glide to one of several pre-determined optional points and “die”. As an interesting aside, an aircraft with an L/D ratio of 30 will glide almost 600km from an altitude of 65,000 feet. (d) Take-off and landing failures. Global Hawk has its own embedded reactive programming to cope with such emergencies. Take-off will be aborted if the aircraft deviates too far from the runway centreline or fails to reach V1 (decision speed).    On landing, an automatic goaround is initiated if the aircraft is not lined up with the runway correctly. There is no outside (landing) pilot associated with Global Hawk. All landings are carried out under auto-land protocol. Electronic systems Upon examining the on-board electronics of Global Hawk, it becomes immediately obvious why UAVs have taken so long to mature. From automatic take-off to auto land, the entire operation of any UAV relies completely on a host of complex electronic gadgets and support systems from the relatively simple air-data sensors to the staggeringly sophisticated array of GPS satellites. Much of the complex array of command and support equipment has only just matured in its own right and it has taken considerable effort Where Global Hawk goes, so does its Launch and Recovery unit (left) and the Main Mission Control unit (below). Transporting Global Hawk (and all its equipment) around the world takes about three Hercules Transport loads. to bring these elements together into a successful system. Global Hawk has a dual redundant flight control system (FCS) which is controlled by two onboard flight computers which receive constant input from the aircraft’s suite of navigation and air data sensors. This includes an inertial navigation system, inertial measurement unit and a GPS. The flight control computers are pre-programmed with a flight plan before departure. No flight commands are accepted by Global Hawk until after take-off. Once airborne, the flight is controlled and monitored by the launch and recovery element (LRE). The LRE is responsible for launch and recovery, mission planning and back-up control. The LRE is housed in a separate van to the MCE (Mission Control Element). The MCE is responsible for mission planning and control, sensor control, data links monitoring, imagery review and dissemination. These vans can be located almost anywhere in the world and do not need to be located in the same area as each other. The LRE communicates with Global Hawk via a line of sight (LOS) common data link (CDL) and then by Ku-band and UHF satcom. Once Global Hawk has settled into the climb and departure phase of the flight, the UAV navigates by GPS waypoints. There are several inbuilt default waypoints that are activated if necessary. Control is then handed over to the MCE for the actual task of completing the mission. Ku-band and CDL are mostly used for data transmission, including threat information and UAV status, while UHF is mostly used for command and control. As the UAV ascends and crosses controlled airspace, the LRE and MCE crews communicate with air traffic control via VHF/UHF radio. On one occasion a controller asked the duty crewman what was it like up there. To which the crewman stationed thousands of miles away on the ground stated simply “I don’t know – I am not up there!” Otherwise, the Global Hawk is treated the same as any other aircraft operating in controlled air space and possessing an IFF system. Monitoring Status Global Hawk carries a fault log computer that monitors and records any MAY 2001  7 8  Silicon Chip MAY 2001  9 Look at the detail available to military strategists in this EO (electro/optical) image taken in the Mojave Desert, California. Altitude was in excess of 62,000 feet and the slant range (ie, distance from aircraft to target) was 20.3km. Notice the “tiling” effect as the image is built up from multiple smaller images – so called “step stare”. problems detected during a mission. The results can be down-loaded for analysis after a mission. Real time monitoring is via discrete and continuous signal comparators. These provide preset upper and lower operational limits for every on-board system, ranging from engine pressures, temperatures and RPM, to hydraulic pressures, electrical voltage levels and airspeed. If any of the levels move outside the acceptable range, a red light comes on in the control centre and if the system is critical to the vehicle it will start flashing. At this point Global Hawk will call it a day and return home. Regardless of the complexity of the control and command electronics, it is the imaging electronics that really take one’s breath away. The quality of the images is stunning, from all three systems. These comprise an EO (electro/ optical), IR (infrared) and SAR/MTI (synthetic aperture radar/moving target indicator). These systems require extensive monitoring and account for the much larger size vans used by the MCE compared with the LRE. The SAR/MTI antenna is housed in a bulged fairing immediately behind the nosegear and provides real-time imagery of the ground in several formats. With a field of view of ±45° either side of the aircraft, the Raytheon X-band radar can cover up to 138,000 10  Silicon Chip This one is infrared imagery, again taken more than 61,000 feet above the Mojave Desert and more than 22km away from the target. One of the big advantages of IR imagery is that “cover of darkness”, so long relied upon by the world’s armed forces, has ceased to be a cover at all! IR relies on heat radiated from virtually everything! square kilometres per day in search mode from a range of 200km. In ground MTI (GMTI) mode the radar can search up to 15,000 square kilometres a minute, detecting any targets with a velocity of 4kt (7.5km/h) or more, from a range of 100km. With a 10m range resolution, the GMTI mode scans a 90° sector, and can be used to cover zones between 20km and 200km either side of the aircraft. Is it any wonder that the Australian Government should find Global Hawk very interesting in regard to coastal surveillance? The Raytheon supplied EO/IR system mounted in the chin of GH combines a Recon/Optical camera with a Raytheon IR sensor. The EO system uses a commercial 1024 x 1024 pixel Kodak CCD (charge-coupled device) while the IR sensor uses a 640 x 480 pixel 3-5µm indium antimonide detector derived from Raytheon’s common module forward-looking infrared (FLIR) system. Both EO and IR sensors are fed by a fixed focal-length reflecting telescope with a beam splitter. Neither of the systems has the 6,000-plus pixel width needed to provide the required 1m resolution in a single exposure so a “step-stare” system is used. The telescope scans continuously and a mirror back scans to freeze the image on the sensor. Thus the mirror returns to the same spot every 1/30th of a second, while the small patches are assembled to create a larger picture. To help keep the avionics warm at altitude and cool at lower levels, air temperature is carefully controlled in a pressurised section of the fuselage. Monitored autonomously by a Honey-well environmental control system built to Northrop Grumman specifications, the system uses the aircraft’s own fuel as a heat sink. Fuel is fed through tubing in the leading edge of the wing to the outboard tanks and gravity fed back to the centre fuselage tank. Two pumps feed the fuel to the engine and excess fuel, which is pumped around the equipment, goes to a fuel/air heat exchanger. At altitude, bleed air from the engine is used to warm the fuel which is then pumped around the compartment to warm it. All in all, Global Hawk is a very sophisticated aircraft and one that has already made its mark on aviation history. For more information, visit Northrop Grumman websites: www.northgrum.com or www.iss.northgrum.com Acknowledgement: We are grateful to Erroll Walker in the Canberra office of Northrop Grumman for his assistance in obtaining the images used in this feature. Like the Global Hawk, they flew half-way SC around the world!