Читать книгу Introduction to UAV Systems - Mohammad H. Sadraey - Страница 62

We call a UAV “medium” if it is too large to be carried around by one person and still smaller than a light aircraft. (As with all of these informal size descriptions, we do not claim rigorousness in this definition. Some attempts at standardized and universal classifications of UAVs are described later in this chapter.)

The UAVs that sparked the present resurgence of interest, such as the Pioneer and Skyeye, are in the medium class. They have typical wingspans of the order of 5–10 m (16–32 ft) and carry payloads of from 100 to about 200 kg (220–440 lb). There are a large number of UAVs that fall into this size group. The Israeli–US Hunter (retired!!) and the UK Watchkeeper are more recent examples of medium‐sized, fixed‐wing UAVs.

There are also a large number of rotary‐wing UAVs in this size class. A series of conventional helicopters with rotor diameters of the order of 2 m (6.4 ft) have been developed in the United Kingdom by Advanced UAV Technologies. There are also a number of ducted‐fan systems configured much like the CyberQuad Mini but having dimensions measured in meters instead of centimeters. Finally, we mention the US Boeing Eagle Eye, which is a medium‐sized VTOL system that is notable for using tilt‐wing technology.

The RQ‐2 Pioneer is an example of an AV that is smaller than a light manned aircraft, but larger than what we normally think of as a model airplane. It was for many years the workhorse of the stable of US tactical UAVs. Originally designed by the Israelis and built by AAI in the United States, it was purchased by the US Navy in 1985. The Pioneer provided real‐time reconnaissance and intelligence for ground commanders. High‐quality day and night imagery for artillery and naval gunfire adjust and damage assessment were its prime operational missions.

The 205‐kg (452‐lb), 5.2‐m (17‐ft) wingspan AV had a conventional aircraft configuration. It cruised at 200 km/h and carried a 220‐kg (485‐lb) payload. Maximum altitude was 15,000 ft (4.6 km) and endurance was 5.5 hours. The ground control station could be housed in a shelter on a High Mobility Multipurpose Wheeled Vehicle (HMMWV) or truck. The fiberglass air vehicle had a 26‐hp engine and was shipboard capable. It had piston and rotary engine options.

The Pioneer could be launched from a pneumatic or rocket launcher or by conventional wheeled takeoff from a prepared runway. Recovery was accomplished by conventional wheeled landing with arrestment or into a net. Shipboard recovery used a net system.

The BAE Systems Skyeye R4E UAV system was fielded in the 1980s and is roughly contemporary with the Pioneer, with which it has some common features, but the air vehicle is significantly larger in size, which allows expanded overall capability. It uses launchers similar to the Pioneer but does not have a net‐recovery capability. It uses a ground control station similar in principle to that of the Pioneer. It is still in service with Egypt and Morocco.

The Skyeye air vehicle is constructed of lightweight composite materials and was easy to assemble and disassemble for ground transport because of its modular construction. It has a 7.32‐m (24‐ft) wingspan and is 4.1 m (13.4 ft) long. It is powered by a 52‐hp rotary engine (Teledyne Continental Motors) providing high reliability and low vibration. The maximum launch weight is 570 kg (1,257 lb) and it can fly for 8–10 h and at altitudes up to 4,600 m (14,803 ft). The maximum payload weight is about 80 kg (176 lb).

Perhaps the most unique feature of the Skyeye when it was fielded was the various ways in which it could be recovered. The Skyeye has no landing gear to provide large radar echoes or obstruct the view of the payload. The avoidance of a nose wheel is particularly significant as a nose gear often obstructs the view of a payload camera looking directly forward, precluding landing based on the view through the eyes of the camera. However, it can land on a semi‐prepared surface by means of a retractable skid located behind the payload. This requires the landing to be controlled by observing the air vehicle externally during its final approach. This is particularly dangerous during night operations.

The landing rollout, or perhaps more accurately the “skid‐out,” is about 100 m (322 ft). The Skyeye also carries either a parafoil or a parachute as an alternative recovery system. The parafoil essentially is a soft wing that is deployed in the recovery area to allow the air vehicle to land much more slowly. The parafoil recovery can be effective for landing on moving platforms such as ships or barges. The parachute can be used as an alternative means of landing or as an emergency device. However, using the parachute leaves one at the mercy of the vagaries of the wind, and it primarily is intended for emergency recoveries. All of these recovery approaches are now offered in various fixed‐wing UAVs, but having all of them as options in one system still would be unusual.

The RQ‐5A Hunter was the first UAS to replace the terminated Aquila system as the standard “Short Range” UAS for the US Army. The Hunter does not require a recovery net or launcher, which significantly simplifies the overall minimum deployable configuration and eliminates the launcher required by the Skyeye. Under the appropriate conditions, it can take off and land on a road or runway. It utilizes an arresting cable system when landing, with a parachute recovery for emergencies. It is not capable of net recovery because it has a tractor (“puller”) propeller that would be damaged or broken or would damage any net that was used to catch it. It also has a rocket‐assisted takeoff option to allow the launch to occur when no suitable road or runway is available.

The Hunter is constructed of lightweight composite materials, which afford ease of repair. It has a 10.2‐m (32.8‐ft) wingspan and is 6.9 m (22.2 ft) long. It is powered by two four‐stroke, two‐cylinder (v‐type), air‐cooled Moroguzzi engines, which utilize fuel injection and individual computer control. The engines are mounted in‐line – tractor and pusher – giving the air vehicle twin engine reliability without the problem of unsymmetrical control when operating with a single engine. The air vehicle weighs approximately 885 kg (1,951 lb) at takeoff (maximum), has an endurance of about 12 h, and a cruise speed of 120 knots.

The Hermes 450/Watchkeeper is an all‐weather, intelligence, surveillance, target acquisition and reconnaissance UAV. Its dimensions are similar to the Hunter. The Watchkeeper is manufactured in the United Kingdom by a joint venture of the French company Thales and the Israeli company Elbit Systems. It has a weight of 450 kg (992 lb) including a payload capacity of 150 kg (331 lb). The Watchkeeper was in service in Afghanistan with British forces late in 2011.

A series of rotary‐wing UAVs called the AT10, AT20, AT100, AT200, AT300, and AT1000 have been developed by the UK firm Advanced UAV Technology. They are all conventionally configured helicopters with a single main rotor and a tail boom with a tail rotor for yaw stability and control. The rotor diameters vary from 1.7 m (5.5 ft) in the AT10 to about 2.3 m (7.4 ft) for the AT1000. Speed and ceiling increase as one moves up the series, as does the payload capacity and payload options. All are intended to be launched by vertical takeoff and all claim the ability for autonomous landings on moving vehicles.

The Northrop Grumman MQ‐8B Fire Scout is an example of a conventionally configured VTOL UAV. It looks much like a typical light helicopter. It has a length of 9.2 m (30 ft) (with the blades folded so that they do not add to the total length), height of 2.9 m (9.5 ft), and a rotor diameter of 8.4 m (27.5 ft). It is powered by a 420 hp turbine engine. The Fire Scout is roughly the same size as an OH‐58 Kiowa light observation helicopter, which has a two‐man crew and two passenger seats.

The Kiowa has a maximum payload of about 630 kg (1,389 lb), compared to the 270 kg (595 lb) maximum payload of the Fire Scout, but if one takes out the weight of the crew and other things associated with the crew, the net payload capability of the Fire Scout is similar to that of the manned helicopter. The Fire Scout is being tested by the US Army and Navy for a variety of missions that are similar to those performed by manned helicopters of a similar size.

The tilt‐rotor Bell Eagle Eye was developed during the 1990s. It uses “tilt‐wing” technology, which means that the propellers are located on the leading edge of the wing and can be pointed up for takeoff and landing and then rotated forward for level flight. This allows a tilt‐wing aircraft to utilize wing‐generated lift for cruising, which is more efficient than rotor‐generated lift, but still to operate like a helicopter for VTOL capability.

The Eagle Eye has a length of 5.2 m (16.7 ft) and weighs about 1,300 kg (2,626 lb). It can cruise at up to about 345 km/h (knots) and at altitudes up to 6,000 m (19,308 ft). Some of these UAVs are shown in Figure 2.5.

The Bayraktar TB2 – as a precision strike MALE UAV – is developed by Baykar Makina, a Turkish company. It has a length of 6.5 m (21 ft), a wingspan of 12 m (39 ft), and a maximum takeoff weight of 1430 lb. The UAV is equipped with a 100 hp piston engine, carries a 330 lb payload (EO/IR/LD imaging and targeting sensor), and features four hardpoints for laser‐guided smart munition (missiles/rockets). The performance includes: (1) maximum speed of 120 knots, (2) range of 150 km, (3) service ceiling of 27,000 feet, and (4) endurance of 27 hours. As of July 2021, the TB2 UAV has completed 300,000 flight‐hours globally.