Way to go and return! The manner in which unmanned aircraft are launched and retrieved has a major impact an the overall performance and operational flexibility of the system, in addition to dictating response and turn-round times and the likelihood of damage during recovery.

Most mini- and micro-drones are operated like hobbyists' model aircraft, with a hand launch and soft horizontal landing. The main need of forward troops and special forces is simply to look 'beyond the next hill', without attracting attention to their positions.

However, urban warfare raises problems in hand-launching a drone with a wingspan of over one metre, if the launch is to take place in a narrow street or from the window of a building. This line of thinking led Rafael to develop for its SkyLite project a transport/launch canister from which the drone is ejected with wings folded. The SkyLite was not accepted by the Israeli Army therefore Rafael switched to a catapult launch for SkyLite-B. However, the canister concept may be offered for future products.

Hand launching is the simplest possible approach but restricts the weight of the drone, which in turn limits its payload and flight duration and thus its value as a reconnaissance asset. Hand launching also constrains the wing loading of the drone, and hence its maximum cruise speed.

For example, the hand-launched AeroVironment RQ-11A Raven, which is a lighter derivative of the company's Gulf War-era 3.76-kg Pointer, weighs only 1.9 kg and typically carries a 0.75-kg pay load. It has a speed of 32 to 82 km/hr and an endurance of up to 90 minutes.

Whereas the Pointer makes a soft horizontal landing (facilitated by having the propeller in a pusher arrangement behind the high-set wing), the Raven is recovered by inducing a deep stall, leading to a vertical landing. The same technique is used for AeroVironment's Puma, which at 5.5 kg is among the heaviest hand-launched drones available today.

A deep stall recovery allows the drone to be retrieved accurately, which is vital in special operations. In the case of the 5.6-kg hand/bungee-launched Israel Aerospace Industries (IAI) Bird Eye 400, which is a flying wing configuration with a ventral sensor, a deep stall is used to initiate an inverted descent, impact being cushioned by overwing shock absorbers.

To illustrate the hand-launched micro-drone sector, the AeroVironment Wasp has a span of only 41 cm and a gross weight of 275 gm. It has a speed range of 35 to 65 km/hr and an endurance of up to 50 minutes. The basic Wasp makes a conventional landing, but a naval version weighing 290 gm can be recovered as a seaplane.

Catapults

The reliability of hand launching is clearly reduced as weights and wing loadings increase, and in gusting conditions. Several mini-drones, such as the 2.8-kg AeroVironment Swift, are therefore offered with the options of hand- and bungee-launch. The latter (using elastic shock cord) ensures a higher release velocity but may well require more personnel.

A bungee launch is standard practice for such drones as the 3.2-kg Lockheed Martin Desert Hawk (referred to by US Air Force Central Command as the Force Protection Aerial Surveillance System) and the 2.7-kg AeroVironment Dragon Eye, which is being used by the US Marine Corps.

The next step beyond the simple bungee is to launch from a short ground-mounted rail, laterally stabilised by a bipod and incorporating some form of catapult. This is the technique used by the 4.5-kg Mission Technologies Buster, which employs a joined-up tandem wing configuration and is recovered by parachute. Whereas all the drones discussed so far have been electrically powered, the Buster has a reciprocating engine, making possible a 1.35-kg payload and an endurance of over four hours. The Buster is currently used by the US Army as a sensor testbed and is being evaluated by the Canadian forces.

Other drones catapulted from a short rail include America's Advanced Ceramics Research Silver Fox and Israel's Aeronautics Defense Systems Orbiter, BlueBird Aero Systems BoomerangV2 and the Rafael SkyLite B.

The 6.0-kg SkyLite B, developed with assistance from BlueBird Aero Systems, is recovered by parachute, with air bags to cushion the impact. It was designed for operation in winds up to 55 km/hr and in a demonstration tour in Australia and New Zealand in 2006 survived gusts of over 100 km/hr.

Aside from providing a more positive launch, these short catapult systems (typically with rails of three or four metres) allow heavier drone and payload weights and higher wing loadings, in turn making possible faster response and greater wind tolerance. Both the Silver Fox and BoomerangV2 are in the 9.0-kg class.

The long endurance (15 hr) 18-kg Boeing/Insitu ScanEagle is launched by a pneumatic 'wedge catapult' and is recovered by a wingtip-mounted claw engaging a rope hanging from a pole.

Longer-stroke catapults permit heavier launch weights and thus more useful drones. For example, the 35-kg Elbit/Silver Arrow Skylark II, launched from a rail on a 4WD utility vehicle, has a maximum payload of nine kg and an endurance of up to six hours.

The EMT Luna, which has been used operationally by the German Army in operations from Kosovo to Afghanistan, employs a six-metre rail with a bungee-type catapult. This allows a 37-kg take-off weight, including a four-kg payload. The Luna has a four-hour endurance and a maximum speed of 160 km/hr. It is normally landed by parachute with impact dampers to reduce airframe loads but, alternatively, can use a recovery net.

The South African Army's 100-kg ATE Vulture is catapulted using a vacuum launch system from a truck-mounted rail. It carries a 25-kg payload for up to four hours--for recovery it is guided by a laser-tracking unit into a net, and then falls onto an airbag.

The AAI RQ-7B Shadow 200, which entered US Army service in 2002, has a rail-launched weight of 170 kg with a 27-kg payload. It has a maximum speed of 195 km/hr and an endurance of seven hours. It is landed on a runway; an airframe-mounted hook engaging arrester wires.

The same techniques are used by the 205-kg US Marine Corps RQ-2B Pioneer, which has been in use since 1986 and can employ either a conventional runway or rocket-assisted take-off. It has a 34-kg payload, a 205 km/hr maximum speed and an endurance of five hours.

The Sagem Sperwer has been operated for several years now by the Canadian forces (who have recently placed a repeat order) in Afghanistan, but is also operated by the services of Greece, France and the Netherlands (recently by the latter in Afghanistan). The 250-kg aircraft is catapult launched and recovered by parachute and airbags (the latter deflate upon impact to prevent rebound).

The IAI/Malat I-View series drones are launched by catapult and, interestingly, are recovered automatically by means of a parafoil, giving a precise landing without requiring a runway. The largest of the series is the 250-kg I-View 250A, which has the wing from the 426-kg Searcher II and was successfully proposed by Boeing Australia to satisfy that country's JP129 requirement. It has a maximum payload of 60 kg and an endurance of up to eight hours

The 275-kg Ruag Aerospace Ranger is catapult launched and recovered automatically to land on skids (which enables it to land on grass, snow or stony surfaces), tracked by a TV camera and laser ranger. The Ranger is used by the Swiss armed forces and has been exported to Finland. Automatic landing is effected with the Ruag-developed Opats (Object Position And Tracking Sensor), a laser-based system which takes over control of the aircraft in a 'window' and brings it down with high accuracy to the touchdown point just after shutting down the engine with the twin-blade propeller in the horizontal position. Ruag is promoting the Opats for other drones, as well as its Archer and DC4 launchers. The Archer can launch a 320-kg air vehicle at 32 metres/sec, while the DC4 increases these figures to 400 kg and 55 metres/sec.

Runway Operations

The use of a conventional runway (or a straight section of highway) removes catapult limits on launch weight. Examples in this category include the 816-kg Northrop Grumman MQ-5B Hunter (which uses a hook arrest), the 1020-kg General Atomics MQ-1B Predator-A and 4765-kg MQ-9A Predator-B and the 12,133-kg Northrop Grumman RQ-4A Global Hawk and 14,630-kg RQ-4B.

The 265-kg Flight Refuelling Falconet jet-powered target has a unique method of operation, taking off from a dolly running around a circular runway and landing by parachute on its frangible nose-cap.

The need to find a runway to operate a drone is clearly undesirable in tactical operations, especially in undeveloped regions or areas constantly the target of mortar bombs. Rockets can be used to either shorten ground roll or achieve a zero-length take-off. The latter case is illustrated by the 161-kg Rheinmetall Defence Electronics KZO, which carries a 35-kg payload for almost four hours and has a maximum speed of 250 km/hr. It is launched from a container transversely mounted on a truck and is recovered by parachute, with airbags to soften the landing.

Moving Platforms

The discussion has so far been concerned with launching drones from the ground. However, some are released from moving vehicles, thereby eliminating the need to accelerate the drone to flying speed. For example, Canada's 635-kg Mmist CQ-10A SnowGoose leaflet-delivery system is equipped with an 80-kW engine and a parafoil and is normally launched from a moving Hummer. It can also be released in flight from a ramp-equipped transport aircraft such as a Lockheed Martin C-130 or Boeing C-17. Maximum payload is 260 kg and it can remain aloft with a 34-kg payload for up to 16 hours.

The SnowGoose is a powered derivative of the GPS-guided Mmist Sherpa, which has been employed by the US Marine Corps in Iraq to deliver payloads of up to 1000 kg, with releases from KC130Ts. A similar air release is used by the Atair Aerospace Onyx, which is being funded by the US Army as a means of precision delivery for vital loads. The Onyx employs a GPS-guided ram air parafoil to manoeuvre the load above the desired delivery location, switching to an unguided round parachute for a soft touchdown.

In a much lighter category, the 27-kg NRL-developed Finder drone has been released from a Predator in trials to assess its potential in atmospheric sampling. The Raytheon SilentEyes is an unpowered mini-drone designed for bomb damage assessment and is intended to be launched from an aircraft-mounted countermeasures dispenser. The lightweight Eads-Dornier DT55 target is released from the larger DT25.

The US Navy is interested in the concept of a surveillance drone that could be launched from (and recover to) a submerged SSGN submarine. The 4000-kg Lockheed Martin Cormorant project, aimed at such requirements, is currently at the risk-reduction demonstration phase.

VTOL 

A drone that can take off and land vertically can be operated almost anywhere, but requires proportionally more power. For a given payload and endurance, a Vtol drone is heavier and more expensive than its conventional counterpart.

Since the ill-fated 1155-kg Gyrodyne QH-50 torpedo platform of the 1960s there have been few rotary-wing drones. One success story is Austria's 200-kg Schiebel S-100, with orders now approaching 200 (with some 60 ordered from the United Arab Emirates with an option on a further 20 units).

The 1430-kg Northrop Grumman MQ-8B Fire Scout is scheduled to enter service with the US Navy in late 2008 (with up to three per Littoral Combat Ship) and with the US Army as the Class IV drone for the Future Combat System in 2014. In addition, the US Marine Corps plans to replace the RQ-2B Pioneer from 2015 with a new system designated Vuas, which may eventuate as the MQ-8B.

It is hoped that the 1950-kg Boeing A160 will provide a breakthrough in performance, using its patented Optimum Speed Rotor system. Others entering the rotorcraft field include Saab with the 150kg Skeldar V-150, Eads with the 680-kg Vertivision and lightweight 13-kg Scorpio, and by a team of Thales and Boeing with the Unmanned Little Bird.

Helicopter drones have limited forward speed, although it is hoped to exceed 260 km/hr with the A160. The tilt-rotor concept offers much higher speeds: the 1292-kg Bell Eagle Eye that was chosen by the US Coast Guard is expected to reach 390km/hr.

For front-line and special forces the smaller dimensions of a ducted fan may be preferable, although this requires more power, since it is dealing with a smaller mass flow. In May 2006 Honeywell was selected to provide the US Army's 6.8-kg Class I Organic Air Vehicle.