Muscles & brains: often overlooked when discussing unmanned vehicles are their engines and sensors, although Armada has recently visited these two aspects in past issues (1/2007 for the engines and 2/2002 for the payloads). However, since developments are going apace, this is an update on available systems.

Small turbojet engines in the 4.5 to 23-daN thrust range are available from companies such as JetCat Germany. Developed for acro modellers, they are used in the Eads/Dornier DT25/35 target drones series. Spain's Artes Jet Microturbines and AMT Netherlands are developing military turbojets of 35 and 67 daN thrust respectively.

The Elbit-owned UEL produces most of the rotary engines used in drones, from the 28.3-kW AR731 to the 67.1-kW AR682R. The 40.4-kW Diamond Engines IAE 50R powers the Schiebel S-100.

There is more variety in piston engines. The 85.5-kW BRP-Rotax 914F has enjoyed considerable success in the Predator series but has been replaced by the Thielert Centurion 2.0 heavy fuel engine (HFE) in the Warrior development.

Italy's Zanzottera Technologies began with engines for the Meteor target series; now produces the 29-kW 498ia and is developing a 60-kW HFE. Germany's Hirth is developing a 20 to 80-kW family of two-stroke HFEs, and a Denel-modified 37-kW Limbach L550E is used in the former company's Seeker II drone.

For lightweight drones, hobbyists' piston engines are available from manufacturers such as America's Desert Aircraft. Germany's 3W Modellmotoren, China's GMS and JBA, the Czech Republic's ZDZ, Italy's SuperTigre and Japan's OS Engines.

In aiming for extreme endurance, AV and Boeing (possibly Northrop Grumman) are working on piston engines that burn liquid hydrogen fuel.

Thanks to advances in brushless motors and rechargeable batteries, electric power (giving silent operation) has become a realistic option in both cost and weight terms for small drones. Whether it is a good approach for lightweight Vtol drones is more controversial.

Lithium polymer (Li-Po) batteries are the current standard in hobbyists' model aircraft, but it is noteworthy that a lithium-ion (Li-ion) battery by Telcordia Technologies is used in the Wasp micro drone. Near-term battery material developments include bi-polar lithium-ion and lithium sulphur (Li-S).

The quest for longer sorties is driving designers toward combinations of different powerplant types. For lighter drones, Bental is developing hybrid units, with an internal combustion engine of high power/weight for take-off and cruise, during which it charges the batteries, and an electric motor for quiet operation in the target area.

Israel's Bental is to unveil at Idef in Ankara in May its latest propulsion system for drones up to eight kilograms. Featured in this subtitle picture, it weighs only about 450 gm but delivers 1200 Watts. For large drones with endurances of days, solar power will in the longer term be combined with fuel cells.

Radar Sensors

Drone sensor types cover a broad spectrum, from LTA radars with football field-size active electronically-scanned arrays (Aesa) to air-sampling 'sniffers' for mini drones. This subject was reviewed in our previous issue (Armada 2/2007), and the following notes are intended only to recap on a few highlights.

In the field of aerostat radars, Northrop Grumman took the sensor used in the F-16A/B as the basis for its APG-66SR used in Tcom's 32-metre aerostats sold to Italy. Northrop Grumman is also responsible for the TPS-63 and the improved E-Lass radars. Some US Air Force Tars (described earlier) are being upgraded from the Tcom 71M aerostat with E-Lass to the Lockheed Martin 420K aerostat with the same company's L-88(V)3 radar, with an 5.2 x 8.8-metre antenna.

Lockheed Martin is also the contractor for MDA's HAA airship radar, while Raytheon is responsible for the US Army's Jlens radars.

Israel's contribution is the Elta Systems Aerostat Programmable Radar (ARP), which was designed specifically for installation on the Tcom 71M. The ARP is derived from the ground-based EL/L-2080 Green Pine radar. It is believed that both the ground-borne and airborne systems have been purchased by India.

In the Sar (synthetic aperture radar) fixed-wing drone field, the most significant developments are the Northrop Grumman/Raytheon MP-Rtip (Multi-Platform--Radar Technology Insertion Program) for the Global Hawk Block 40, and the Tips (Transatlantic Industrial Partnership for Surveilance) Tcar for the AGS version of RQ-4, based on MP-Rtip and Sostar-X technology.

However, lighter drones can also be equipped with effective Sars. The General Atomics Lynx radar has been selected by the US Air Force for the MQ-9A and by the US Army for the Warrior. The German Army's 30-kg EMT Luna drone has been tested with a Misar (Miniature Sar) developed by Eads Defence Electronics.

Likewise, the Selex PicoSar, weighing less than ten kg, has been tested on the 320-kg Falco drone and the MiniSar developed by Sandia Laboratories and produced by Rockwell Collins has tested on Lockheed Martin's 82-kg SkySpirit.

The turreted sensor systems produced by companies such as Denel, Elbit, Flir Systems and Sagem were reviewed in our previous issue.