Males poised to go high and away. (Unmanned Flight).

Piston-engined unmanned aircraft with long-span wings can fulfil a need for affordable, semi-attritable surveillance vehicles that can remain at medium altitudes for twelve hours or more, providing target imagery and designation facilities, and even a limited ground attack role. The US has led in this field, but Israel and the major European nations are now following suit.

Although US surveillance flights over the Soviet Union and China had been discontinued in 1960 and 1971 respectively, the CIA needed to acquire information about other countries which could still be overflown. The Agency thus appears to have provided initial funding for a comparatively low-budget project that could carry sensors to medium altitudes and remain on station for extended periods. The piston-engined General Atomics Aeronautical Systems Gnat-750 first flew in 1989, providing an endurance of over 24 hours and a service ceiling of 25,000 ft, although it is normally operated at around 15,000 ft. The Gnat-750 is believed to have a wingspan of around eleven metres and a normal take-off weight of 517 kg with a 150 kg payload. It carries three EO/IIR sensors in a chin turret, but other options include a synthetic aperture radar (Sar) and ECM and ESM payloads. In addition, the Gnat has been photographed with a pylon-mounted dorsal fairing, housing a satellite communications (satcom) dish.

Based on the Pentagon's post-conflict analysis of the 1991 Desert Storm war and on unsatisfactory experience with established UAVs in early operations over the former Yugoslavia, the Joint Chiefs of Staff launched an urgent programme to provide a four-tier family of long-endurance intelligence-gathering drones, the first of which corresponded to the Gnat-750. To ensure rapid availability, this project was left in the hands of the CIA.

Tier I

Operated by the CIA, the Gnat-750 has been deployed on several occasions to conflict zones, beginning in early 1994, when two UAVs and a satellite communications ground station were transported to Albania. Subsequent deployments in that region used bases in Bosnia and Croatia.

However, by-passing the normal procedure for drafting requirements had its drawbacks. For example, in operations over the Balkans, surveillance data had to be relayed to the ground station via a manned aircraft (a Schweizer RG-8), which--due to the distance from its base--could remain on station for only two hours out of its eight-hour endurance. It was thus impossible to exploit the long sortie capability of the Gnat (seen here in the title photo). A second problem was that, lacking normal service inputs at the requirements stage, the Gnat was highly susceptible to moisture ingress.

The Gnat has gone through several stages of development, including the Gnat-750-45 Lofty View, Gnat-XP and I-Gnat, this last example providing an endurance of more than 40 hours and the option of five hardpoints for external stores, plus the payload capability was increased to 225 kg. The Gnat is also in service with two publicly unidentified international customers (believed to be Turkey and Britain), and may still be in production. It is reported to have a unit price of $1.2 to 1.8 million, depending on aircraft model and sensor fit, while the ground station costs $ 5 to 6 million, implying a system cost of $ 8.6 to 13.2 million. Evidence of continuing use by the CIA was provided in March 2002, when a Gnat-750 operated by the Agency crashed off the Philippines during anti-terrorist operations.

On 12 September 2002, an automatic landing system developed by General Atomics was successfully demonstrated with an I-Gnat using differential GPS for positional measurements. An automatic taxi and take-off system is also being developed and will be applied to other members of the company's UAV family. In parallel with this work, General Atomics is conducting trials with the Sierra Nevada Ucars (UAV Common Automatic Recovery System), which employs millimetric-wave radar.

Predator

The Pentagon's Tier II (intended for use over 'moderate-risk' areas) was to be represented by the General Atomics RQ-1A/B Predator, a larger, heavier and better-powered derivative of the Gnat series. Its 30-month Advanced Concept Technology Demonstration (ACTD) phase ran from January 1994 to July 1996, with first flight on July 3, 1994. A Predator system was deployed to Albania in July 1995 to support United Nations operations in Bosnia. Deployments to Hungary began in March 1996, likewise for use over Bosnia, and (in the series' seventh US service deployment) Predators were sent to Afghanistan in October 2001.

On October 26, 2002, the Predator reached 50,000 flight hours, half accumulated in combat area deployments. Operations were initially performed by the US Army, but in September 1996 the Predator was re-assigned to the US Air Force Air Combat Command. The 11th Reconnaissance Sqn was commissioned in July 1995, followed by the 15th RS in August 1997 and the 17th RS in March 2002. The home base for all three is at Indian Springs, Nevada. The US Air Force active force inventory is given as 48 air vehicles.

At least 79 Predators have been ordered for the US Air Force, Navy and the CIA, with seven more on option for the Air Force. Reports indicate that at least 25 have been lost in accidents or as a result of enemy action. Five have been ordered for the Italian Air Force (Aeronautica Militare), with three more on option. Initial operational capability with the Aeronautica is scheduled for the second quarter of 2003, to be followed by full operational capability in 2005. Four of the Predators will be assembled by the Meteor division of Galileo Avionica. The Aeronautica is considering advanced radar proposals from General Atomics and Northrop Grumman. The service is hoping to be able to operate its Predators in civil airspace and has specified that the ground control station should also be suitable for installation on a ship.

Reports of the cost of the Predator vary, but the US Air Force Fact Sheet quotes $ 40 million in 1997 values for a system of four air vehicles, a ground control station (GCS) and a Predator Primary Satellite Link (PPSL), which is also referred to as the Trojan Spirit II satcom and carried in two Hummer vehicles. The system requires 55 personnel for continuous operations.

The RQ-1A has a wingspan of 14.84 metres and is powered by a 63.3 kW Rotax 912 four-cylinder engine--in the RQ-1B replaced by a turbocharged 75 kW Rotax 914. It has a gross weight of 1020 kg with 300 kg of fuel and a payload capacity of 205 kg. The RQ-1B also features an 'ice-mitigation' system (presumably giving a limited capability to operate in icing conditions), an ARC-210 radio and an APX-100 IFF/SIF with Mode 4 codes.

The Predator has a maximum endurance of over 40 hours and is capable of remaining on station at 750 km radius for 24 hours. It has been flown to 30,000 ft, but a typical mission is reportedly flown for 16 to 20 hours at 13,000 ft and 450 km radius. Every nine kilograms of payload in addition to the basic EO+IR sensor-fit reduces time on station by one hour. The Predator is operated from runways at least 1525 metres long, but for emergency recovery carries a parachute (which can be replaced by 41 kg of fuel).

Changes from the Gnat series include the replacement of the pylon-mounted satcom antenna by a front fuselage hump. It retains the Gnat's inverted-vee tail, which also serves to protect the pusher propeller from contact with the ground. The fuselage contains the engine, sensor payload and fuel. Although not designed as a stealth aircraft, the Predator has a relatively small radar response due to its small size, clean lines and use of composites.

The baseline fit includes GPS/INS navigation and a nose camera, which is used primarily for flight control and is effected via a C-band line-of-sight datalink or Lockheed Martin Unisys Ku-band satcom that can also transmit imagery at 65 Mb/sec. In addition to the electro-optical and infrared sensor suite in the Versatron Skyball 18 turret, the Predator can carry a Northrop Grumman Sar for all-weather coverage from above clouds, but not all three sensors can be used simultaneously. High-resolution near-real-time video or synthetic aperture radar still-frame imagery can be transmitted to commanders on the ground.

The synthetic aperture radar can be replaced by an Aurora hyperspectral sensor, developed by Advanced Power Technology and providing the ability to distinguish between different types of vegetation, soil and building materials in searching for camouflaged and hidden targets.

General Atomics offers the APY-8 Lynx Ku-band radar, which weighs 52 kg and has been tested on both the I-Gnat and Predator. It can interleaf real-time MTI and Sar modes, the latter giving in 'stripmap' mode and in dry air a 30 cm resolution at 54 km, reducing to 33 km in precipitation. In 'spotlight' mode the Lynx can provide 10 cm resolution at 39 km in dry air, reducing to 28 km in precipitation. Existing capabilities include 'coherent change detection' in near-real-time, whereby the ground station compares newly received synthetic aperture radar images with stored data to identify small differences, such as footprints on grass.

In Afghanistan, a rapid-response programme designated Rover (Remote Operations Video Enhanced Receiver) 1 made it possible for AC-130H/Us to receive Predator imagery directly. Rover 2 is aimed at allowing troops on the ground to receive such imagery on portable displays.

Drones Turned Bombers

Following the introduction of a laser designator on Predators to assist in strikes by manned aircraft in Kosovo (Operation Allied Force), and Hellfire trials by the US Air Force, the CIA's MQ-1Bs have provisions for two of these anti-armour missiles. The Hellfire was used operationally from a Predator over Afghanistan in October 2001, and in Yemen in November 2002. The Air Force fact sheet refers to future Predators carrying the Raytheon AAS-52 Multi-spectral Targeting System (MTS), with Hellfire targeting capability and integrated electro-optical, infrared and laser facilities in a single sensor package. However, these UAVs will not be able to carry MTS and Sar simultaneously.

Replacing the smaller Skyball, the AAS-52 is a derivative of the AAS-44 turret, which was initially used on Predators for Hellfire trials. It features a third-generation thermal imager with a 640 x 480 element focal plane array, with a pixel-pitch that is claimed to provide better resolution than any other operational system. The AAS-52 also has an optical system with five fields of view, a colour television camera, a laser designator, a gimbal-mounted inertial sensor, a three-mode auto-tracker and integrated targeting modes for Hellfire. Following seven prototypes, Raytheon is building 69 production units and is offering the MTS to Italy as well as to American customers.

Armament plans include use of the Bat (Brilliant Anti-Tank) gliding submunition from a UAV Ejection Tube (Buet). The Bat has the attraction of being fully autonomous and weighs only 20 kg, which is less than half as much as the Hellfire. The use of Stinger air-air missiles is also anticipated. US Air Force plans include a Little Weasel Predator, equipped with elements of the Harm Targeting System (HTS) to locate and classify enemy air defence radars. In August 2002, a Predator released a 26 kg Finder (Flight Inserted Detector Expendable for Reconnaissance) mini-UAV, developed by the Naval Research Laboratory. The Finder performed a 25-minute flight under the control of the Predator ground station. The next phase will include the integration of the Aerospace SMC Piranha (Predator IR Narrowband Hyperspectral combat Assessor) sensor on the Finder for atmospheric sampling.

The principal reservations on the Predator's usefulness concern its long transit times, possible vulnerability to enemy defences and sensitivity to weather conditions. Operations can be cancelled because of icing, moderate precipitation and high surface winds. The crosswind limit for take-off and landing is 26 km/hr, and in winds over 56 km/hr it must be hangared, as it has no tie-down points.

Since the mid-90s the US Navy has had a Medium Altitude Endurance (MAE) UAV requirement, relating to operation from aircraft carriers and LHA/LHD amphibious assault ships. However, (following a Marinisation Study that ended in October 1996) it was decided not to proceed with a fully marinised Predator. Naval operation would have involved the development of a heavy fuel engine and systems for automatic launch and recovery, with ship-motion sensing. It would also have included modifications to shield the bird's electronics from high radiation levels and material changes to minimise salt-water corrosion. The USN study, based on three Predator systems with twelve UAVs and twelve carrier modifications, predicted non-recurring costs of $10.6 million, plus $15 million per year in operating costs. The study expressed reservations on the survivability of the Predator in a medium-to-high threat environment. However, it recommended trials at Fallon Naval Air Station in Nevada, and listed further possibilities that included Predator flight demonstrations from CV/CVNs, and the development of an MAE type from a VTOL-UAV.

Interest by the US Navy is evidenced by its Naval Air Warfare Center Weapons Division at China Lake funding for the Kill Assist All-weather Targeting System (KAATS). This combines the General Atomics Lynx radar, stereoscopic Sar processing and relative GPS algorithms to provide target co-ordinates with a three-dimensional accuracy better than one metre and high resolution (better than 10 cm) in all-weather conditions.

Prowler II

The General Atomics Prowler II is a scaled-down Gnat with a wingspan of 7.31 metres, a gross weight of 385 kg, a payload of 50 kg and an endurance of over twelve hours. It makes use of the GCS and line-of-sight datalink developed for the Gnat, and was designed to provide a Low-Cost Tactical UAV. It has a maximum endurance in excess of twelve hours and is offered with the choice of an avgas-burning Rotax 582 or a heavy fuel engine.

Shadow 600

The Shadow series is produced by a company that was originally known as Aircraft Armaments Inc, and later diversified and was renamed AAI Corporation. Its association with UAVs dates from an agreement with IAI, under which Pioneers were supplied to the US Navy, Marine Corps and Army. These Pioneers flew more than 500 sorties during Desert Shield and Desert Storm (1990-91), but led to suggestions that a UAV with an endurance of 12 to 14 hours and a payload of 41 kg would be far more useful.

These demands were satisfied by the AAI Shadow 600, which introduced a 39 kW Norton AR801 engine, digital electronics and autopilot, a stronger nose undercarriage and long-life lithium batteries. The airframe makes extensive use of graphite composites. The Shadow 600 has a wingspan of 6.8 metres and a maximum take-off weight of 265 kg. Relative to the Pioneer, fuel capacity has been doubled to 96 litres by adding bladder tanks in the wings. Two batches have been produced for Romania, with an Inframetrics sensor package that consists of a daylight colour TV camera and a thermal imager. The standard fit includes a video recorder, allowing the Shadow 600 to operate beyond line-of-sight.

Lightweights

For a given endurance and aerodynamic efficiency, the size (and hence basic cost) of a Male drone is primarily a function of payload weight. As electronic components become progressively smaller and lighter, each succeeding generation of unmanned air vehicles in this category should logically become substantially more compact, improving not only unit price but also radar and infrared signature, and hence attrition from hostile actions. It is arguable that within the foreseeable future a useful wide-area surveillance capability may be provided by quite small aircraft, even if they rely on complementary larger vehicles to provide better imagery once a potential target is detected.

In February 2002, Boeing and the Insitu Group signed a 15-month agreement to develop a prototype Scan-Eagle, derived from the Insitu Seascan. The tailless Seascan is a ship-based vehicle for the fishing industry, which in 1998 performed a transatlantic flight of more than 3000 km from Newfoundland to Scotland. It has a wingspan of three metres, a gross weight of 15.4 kg and a maximum payload of 3.2 kg, including a steerable digital video camera with a downlink capability. It is launched from a pneumatic catapult and recovered by a patented SkyHook technique, with a wingtip hook engaging a vertical cable. The missionised ScanEagle first flew on June 19, 2002. It is hoped to eventually achieve an 8000 km range in a 72-hour flight.

Another American lightweight endurance drone is the D-1, of which 17 examples have been built by Dara Aviation of Seattle. The D-1 has a wingspan of 3.29 metres, a gross weight of 25 kg and a payload capacity of 2.0 kg. It first flew in September 2000, and Dara aims to achieve a basic unit price of around $50,000 including autopilot. The D-1 is offered with a range of engines from 0.9 to 2.9 kW, and is expected to achieve a 20-hour endurance with a 4.5 kg payload. It employs a tandem-wing configuration in which the wings are joined to the outboard vertical tails.

Another company that (like Boeing on the ScanEagle project) initially linked with Insitu is Australia's Aerosonde, whose Mk I became in August 1998 the first UAV to fly across the North Atlantic, taking 26 hr 45 min to cover 3270 km. The Aerosonde has a 1.25 kW engine and a twin-boom arrangement with an inverted-vee tail. It has a wingspan of 2.9 metres, a gross weight of less than 15 kg, can carry up to a 5 kg payload and flies with an operational ceiling of approximately 21,000 ft. The Aerosonde is normally launched from the roof rack of a moving car and landed on any level surface. It has gone through a series of developments, the current Mk III (which first flew in early 2001) being aimed at a range of over 4000 km and an endurance of more 40 hours. Australia's DSTO (Defence Science and Technology Organisation) has ordered six air vehicles for trials.

Israel

Given Israel's pioneering efforts in the unmanned air vehicle field, it is hardly surprising that a number of products in the Male category are now being marketed. At the lower end of the scale, IAI's 426 kg Searcher II is described as an advanced fourth-generation ship. It is powered by a 54.4 kW engine, has a wingspan of 8.55 metres and a maximum payload of 100 kg. The Searcher II has an endurance of 15 hours and a ceiling of 20,000 ft.

The IAI E-Hunter is a long-span derivative of the Hunter that is operated by the US Army and the French Air Force using the wing, boom and tail assembly of the Heron (discussed below). The Hunter has two 50.7 kW engines, a wingspan of 8.9 metres, a gross weight of 727 kg and a maximum payload of 114 kg. It has an endurance of twelve hours and an operational ceiling of 15,000 ft. The Hunter has jet-assisted take-off provisions and the long-span E-Hunter an increased ceiling to 20,000 ft and maximum endurance of 20 hours. It first flew in 1995.

In developing a Male UAV in the same class as the Predator, IAI produced the Heron, which has a 75 kW turbo-charged Rotax 914 engine, a wingspan of 16.6 metres, a gross weight of 1100 kg and carries a maximum payload of 250 kg. It has a nominal endurance of 40 hours, but has already demonstrated 52 hours (presumably with zero payload). The Heron has a ceiling of 30,000 ft, and was designed to operate at up to 200 km radius using a line-of-sight datalink, or to 350 km using a drone signal relay, or at up to 1000 km while recording surveillance data. Like IAI's Hunter and Searcher, the Heron has an automatic take-off and landing system. It first flew on October 18, 1994. The Indian Army (which also has the Searcher II) operates the Heron, whereas the Indian Air Force operates the Hermes 450 (discussed below).

IAI's domestic competitor is Elbit/Silver Arrow, whose Hermes 450 is in broadly the same category as the Searcher II. The Hermes 450 has a wingspan of 10.5 metres and is powered by a single 38.8 kW UEL AR-80-1010 rotary engine, turning a pusher propeller. It has a gross weight of 450 kg and a maximum payload of 150 kg. Operational altitude is 18,000 ft, and maximum endurance is 20 hours. An automatic landing system based on DGPS is available. Typical payloads include the Northrop Grumman Tesar radar with synthetic aperture radar and ground moving target indicator facilities, the Controp DSP-1 day/night electro-optical turret providing real-time video imagery and the high-spec Elop Compass turret with forward looking infrared, colour CCD camera and optional laser ranging. The Hermes 450, which is in service with the Israel Defence Force, was exhibited at the 2001 Paris Airshow with a dorsal satcom antenna.

With a gross weight of around 1500 kg, the Elbit/Silver Arrow Hermes 1500 is considerably heavier than the IAI Heron, but it has two 75 kW Rotax 914 engines, a wingspan of 15 metres and a payload of 350 kg, providing real-time day/night imagery and Sar/GMTI radar facilities. The Hermes 1500 first flew on May 22, 1998.

Europe

Europe has trailed behind the United States and Israel in developing Male UAVs, leaving services to choose (at the upper end of the spectrum) between the General Atomics Predator and the IAI Heron. As noted earlier, the Italian Air Force chose the Predator, and more recently the French Air Force has selected the Heron, in the form of its Eads Eagle derivative. Reports indicate that the Eagle will introduce modifications to the Heron sensor fit and its automatic take-off and landing system. It will have a satellite link to allow operations at 1000 km radius from base, and clearance to fly in civil airspace. The Eagle is described by Eads as having a 16.3 metres span, a gross weight of 1150 kg, an endurance of 30 hours and an operating altitude of 25,000 ft. In July 2002, an Eagle was tested extensively by the Swedish Armed Forces and Space Agency.

Sagem's support for the Predator in the French contest was unsuccessful, but the company has produced a long endurance version of its Sperwer, with a span increased to 6.5 metres, giving flights of more than twelve hours and a ceiling of 20,000 ft. The gross weight of the Sperwer LE is 350 kg, and maximum payload is 100 kg. The bird is launched from a pneumatic catapult and recovered by parachute, both operations being fully automated.