Pilot-free fighters. (Armed UAV).

Recent advances across a broad spectrum of technologies, coupled with the development of highly effective air defence systems and a growing reluctance to risk human lives, has encouraged leading nations to investigate the feasibility of Ucavs (Unmanned Combat Aerial Vehicles) performing the Sead (suppression of enemy air defences) role. They may prove suitable for more general air-to-ground/surface attacks at a later stage, and possibly air combat in the very long term. However, carrier-based operations by Ucavs pose special problems.

The Pentagon is expected to spend almost $ four billion on Ucavs over the next six years. For the designer of combat aircraft, the need for a human pilot has always been a major drawback, involving massive weight and cost penalties. This may be illustrated by considering a ground attack aircraft that is designed to deliver a number of anti-radiation missiles over a specified radius of action. Its take-off weight is made up of two types of elements. The first consists of items such as fuel, airframe structure and aircraft systems, all of which (for a given sortie profile) represent fixed percentages of takeoff weight. The second category might be termed the 'operational load', and consists of the specified warload, the necessary sensors and communications equipment, and all pilot-related elements, which together allow the task to be accomplished. The pilot-related elements of the operational load are the flying gear and ejection seat, a share of the environmental control system, the cockpit displays, the cockpit itself and the surrounding structure, windscreen and canopy, and of course, part of the fuel used to lift this 'penalty'. Depending on the sortie profile, the take-off weight will be five to ten times this operational load.

It is important to realise that if an existing aircraft, such as a Lockheed Martin F-16, were to be converted to a drone by removing the pilot and ejection seat and installing a few black boxes, the improvement in radius of action would be minimal. However, if an equivalent attack aircraft were designed from scratch as a Ucav, the reduction in size could be dramatic.

The pilot-related weight elements total approximately 1500 kg for a single-seater, hence the take-off weight might be reduced by 7500 to 15,000 kg. Likewise, if those pilot-related elements represent 25 to 40 per cent of the total operational load, the Ucav might be similarly lighter than the equivalent manned aircraft. If conventional (manned aircraft) structural safety factors and systems redundancy are relaxed in the design of the Ucav, then further gains will be realised.

Costs

Nobody would suggest that a 40 per cent lighter aircraft would, in turn, be 40 per cent less expensive to produce, but the flyaway cost is only a fraction of life-cycle cost, and the Ucav offers the prospect of large-scale reductions in operations and support costs.

It appears that US Air Force plans for Ucavs were initially aimed at rather small vehicles that would not really be equivalent to manned fighters in terms of warload radius performance. For example, the US Air Force/Boeing X-45A demonstrator has an empty weight of around 3630 kg (half that of a Gripen), and is powered by a 28 kN non-afterburning Honeywell F124 turbofan. The US Air Force goal was to achieve a flyaway unit cost of $ ten to twelve million (less than 50 per cent of the cost of an F-16 Block 50), and a 20-year operations and support cost equal to 25 per cent of that for the F-16. In terms of total life-cycle cost, the service was thus presumably looking for a Ucav that would be only one-third as expensive as an admittedly more capable manned fighter.

The US Navy hopes to have a Ucav-N that has a flyaway cost of between 11 and 15 million dollars and a 20-year operations and support cost no greater than 50 per cent of that for a Boeing F/A-18C. The reason that this percentage is so high (in Ucav terms) is that, unlike early US Air Force plans (which would have kept the vehicle in peacetime storage), the Navy plans a dual-role design that would be employed routinely to provide surveillance around its carrier vessel, in addition to its wartime strikes. The US Air Force and Navy are now under pressure to jointly develop follow-on Ucavs.

The cost advantage of a Ucav clearly depends on a number of factors, notably the basic concept of operations and the assumed attrition rate (due to accidents--which may be expected to occur at least ten times as frequently as for manned aircraft--and enemy action). The US Air Force envisaged that in peacetime these vehicles could be stored in relatively small, sealed containers for up to ten years. The containers would be designed to allow six (recently reduced to four) to be carried in a C-17.

Another key element in US Air Force cost-reduction plans is that, whereas a conventional fighter needs a pilot who has to fly over 200 hours each year to remain proficient, as well as requiring service and maintenance personnel, the Ucav would need a relatively unskilled operator who could deal with up to four air vehicles simultaneously, and would rely largely on simulator training.

However, the present Bush Administration now appears to be asking the Pentagon to regard continual high-tempo operations as the norm, hence the US Air Force may have to ditch the idea of a Ucav-in-a-box.

The potential savings associated with Ucavs (based on earlier US Air Force plans) were illustrated by a Lockheed Martin study, comparing annual peacetime operating and support costs for a squadron of 24 current fighters (presumably F-16s) and those for a unit of 24 Ucavs. The conventional fighter squadron with 30 pilots, 34 operations support and 497 maintenance and support personnel, and flying 8300 hours per year was estimated to cost $ 50.4 million in FY1995 values. If the unit operated 24 fighter-based Ucavs (presumably F-16 drones) with 18 pilot/operators, 14 operations support and 41 storage and maintenance personnel, plus 260 reserve personnel for combat maintenance and support, the cost would be reduced by 80 per cent to $10.0 million, assuming 150 flight hours per year. However, using a Ucav designed as such from the outset, with nine pilot/operators, 13 operations and support and 39 storage and maintenance personnel, plus 142 Reserve combat maintenance and support personnel, the cost would be reduced by a further 38 per cent to $ 6.2 million, assuming 124 flight hours per year. The estimated overall cost reduction in peacetime operation and support cost would be almost 88 per cent, relative to a conventional fighter squadron.

Pros & Cons

Such contractor studies, followed by the CIA's successful use of the General Atomics MQ-1B Predator to launch laser-homing Hellfire missiles against ground vehicles in Afghanistan and Yemen, encouraged the leading armed services to investigate the potential of Ucavs. However, the point should perhaps be made that nobody is suggesting Ucavs can (at least in the short term) replicate the operational flexibility and air combat effectiveness of a manned fighter. It should also be noted that Ucavs would need in-flight refuelling to compete on radius of action. Nasa is working on an automated aerial refuelling (AAR) system for Ucavs.

The current argument for Ucavs is based on the idea that, for a sortie that demands nothing more than searching a pre-selected area of ground for a target such as a missile launcher, designating it by laser and then releasing a laser-homing weapon, the skill of a human pilot is not required. Likewise, the cost (both financial and in terms of the risk of death, injury and capture) of performing such a mission in a high risk environment with a manned aircraft is no longer justifiable, given modern technology. It is also arguable that it is more rational to use Ucavs (rather than the F-117A or B-2A) to attack known fixed targets using GPS-guided munitions. Finally, Ucavs will eliminate the future risk to crews of using DE (directed energy) and EMP (electromagnetic pulse) weapons.

The conventional manned fighter-bomber has the disadvantage of requiring support aircraft to jam enemy radar, strike at air defence systems, lay chaff corridors and provide escorts against hostile interceptors, although such requirements will be minimised in the case of stealth fighters such as the F-22 and F-35. If a manned aircraft is shot down, more lives must be risked in Csar (combat search and rescue) operations. In addition, Ucavs provide clear advantages over manned aircraft in operations in an NBC environment.

While increasing value is placed on human life, the effectiveness of air defences continues to improve, with the result that any major nation can now have a multi-layered air defence system that stretches more than 100 km beyond its borders, and that employs mobile launchers. Stealthy bomb-trucks such as the F-117A and B-2A currently offer the prospect of successfully carrying out the lethal Scad (or Dead: destruction of enemy air defences) mission, but some ground-based radars are already claimed to be able to counter stealth. In addition, it is clear that space-based radars will be able to detect stealth aircraft as black holes in ground clutter. There have also been reports of sensors that detect aircraft by the kinetic heating of their airframes, or by the turbulence in their wakes. Any significant decrease in the effectiveness of stealth measures would favour the use of large numbers of small Ucavs to swamp and destroy enemy air defences.

It should be emphasised that the term Ucav is employed here to indicate a reusable (if attritable) vehicle, which is intended to be employed in an attack mission in which the principal direct cost is that of the ordnance delivered. For example, a Ucav might release a Jdam combining an old Mk 84 bomb with a GPS-guided tail-kit costing around $ 22,000 in FY05 values, whereas a one-way (non-reusable) vehicle such as the Tactical Tomahawk would cost around $ 0.88 million, i.e., 40 times as much.

US Air Force

The US Air Force and the Darpa are working together on an ATD (Advanced Technology Demonstration) programme with an aim to developing and demonstrating a low life-cycle cost Ucav designed specifically for the Sead and strike missions, together with a multi-vehicle control station. Aside from investigating the feasibility of the basic concept, it is hoped to provide with 80 per cent confidence accurate estimates of what it would cost to acquire, operate and support a production derivative.

As mentioned earlier, the Boeing X-45A, which was selected as the basis for the 56-month, $ 256 million Darpa/US Air Force ATD programme in FY99, is a relatively small vehicle with a span of 10.30 metres. The first X-45A Spiral 0 had its maiden flight on 22 May 2002, followed by the second on 21 November 2002. Looking rather like a sawn-off B-2, the X-45A has a design that is consistent with stealth (e.g., in terms of wing plan-form and serpentine intake ducts), but does not incorporate all the LO (Low Observable) materials and features that would be used in a production derivative. It employs lateral thrust-vectoring for yaw control and electrical flight control actuators to avoid the maintenance demands of hydraulics.

Flight tests with the X-45As will first employ line-of-sight UHF control and a single vehicle, and later investigate the control of two vehicles in formation, leading to a Sead mission against a simulated Sam site. The aim is to lay the foundations for a low-risk EMD programme to start between 2005 and 2007. The US Air Force envisages that Ucavs would be used in conjunction with manned aircraft, and that a trio of Ucavs could passively locate an enemy ground-based emitter within 50 metres, with their synthetic aperture radar then providing sufficient imagry and target accuracy for attack with GPS-guided weapons.

The 5443 kg X-45A is to be followed by the much larger, full-stealth X-45C (Spiral 1) demonstrator, with a gross weight of 15,875 kg and a span of 14.63 metres. This may take from the intermediate-size X-45B (now cancelled) its larger weapons bay, designed to house twelve SDBs (Small Diameter Bombs), or two Mk 83 Jdams (Joint Direct Attack Munitions), a fuel tank or a directed energy payload. The US Air Force has budgeted for up to 36 Ucav systems to be delivered by FY2010 for operational assessment.

US Navy

Having cancelled the stealthy A-12, the US Navy has an obvious need for a first-day-of-war Sead capability, but is nonetheless trailing behind the US Air Force in Ucav development. The Navy hopes to benefit from US Air Force work, but has so far been thinking along very different lines. For example, the Ucav-N is to combine a Sead/strike capability with a twelve-hour endurance in the surveillance role. This must have come as an unpleasant shock for Northrop Grumman, having private-ventured the X-47A Pegasus around a low aspect ratio plan-form. The X-47A has a gross weight of approximately 2500 kg, and is powered by a 14 kN P&WC JT15D-5C turbofan. It first flew on February 23, 2003.

The Ucav-N is intended to be flown routinely in peacetime, and must fit in with the normal carrier operating cycle. Landings will make use of of a shipboard-relative GPS system, and the vehicle will be required to clear the arresting cable within 45 seconds. Another challenge is to produce a stealthy aircraft that can operate in a salt water environment without an unacceptable workload to maintain its LO characteristics. Despite all these potential problems, the US Navy hopes to fly a demonstrator in FY2006, start the EMD phase in 2010, and to deploy an operational Ucav-N before FY2015. The contenders will be the Boeing X-46 (presumably derived from the X-45 series) and a redesigned Northrop Grumman X-47B, which will be much larger than the current X-45A and will have folding wingtips. The Navy sees the Ucav-N as a 13,150 kg vehicle with a 15-metre span.

US Army

With the Ucar (Unmanned Combat Armed Rotorcraft) the US Army and Darpa are aiming at. a flyaway cost of 20 to 40 per cent of that of an RAH-66 and between 20 and 50 per cent the operating cost of an AH-64. Little has been published on this programme, aside from the fact that it is required for the armed reconnaissance and attack roles, and will not necessarily be a rotary-wing solution, although it will need Vtol capability. Four teams (Bell/Lockheed Martin, Boeing, Northrop Grumman and Sikorsky/ Raytheon) are competing. First flight is scheduled for FY2006, leading to an acquisition decision by FY2009. The Ucar is to have the highest-yet degree of autonomy, higher than even the US Air Force and USN Ucavs.

One of the contenders is the Boeing Canard Rotor/Wing (CRW), essentially a new variation of the old stopped-rotor concept, using bleed air from its Williams F112 turbofan to produce jets at the tips. Boeing is building two unmanned X-50A Dragonfly CRW demonstrators under a $ 24 million, 37-month programme. One contractor will build two Ucar-A vehicles to fly in FY06, leading to a 'missionised' Ucar-B demonstrator flying in FY08.

Rest of the World

Compared to the US programmes, the rest of the world appears to be spending little on Ucavs, perhaps because America has a massive lead in stealth technology, which is essential to this new concept.

Israel. the other world-leader in the broader field of UAVs. appears to be more concerned with using a long-endurance vehicle such as the company's Heron as a launch platform for the interception of tactical ballistic missiles in the boost phase. Although not a Ucav as defined in this review, the one-way Israel Aircraft Industries Harpy anti-radiation drone is worthy of mention, and not simply due to its having been exported to India, South Korea and possibly China. The Raytheon Cutlass (Combat Uninhabited Target Locate & Strike System) is a further development of the Harpy, proposed to the US Navy. It appears to add an electro-optical and infrared sensor as well as a datalink, providing for a wider range of targets and operator-control of the attack phase.

Several leading European nations are studying Ucavs. At Eurosatory 2002, Sagem exhibited a Sperwer LE, which was sporting new provisions for air-to-ground missiles. In July 2000, Dassault began flight trials with the 60 kg Petit Duc (scops owl) Ave (Aeronef de Validation Experimentale), paving the way for a family of larger drones and Ucavs, which will unsurprisingly be called Moyen Duc (eared owl) and Grand Duc (eagle owl). Incidentally, both French firms have recently signed an agreement under which their unmanned aircraft programmes will be managed by Dassault Sagem Tactical UAV.

On a similar timescale to the Petit Duc, Saab has been testing a sub-scale demonstrator named Sharc (Swedish Highly Advanced Research Configuration) with similar objectives. Germany's STN Atlas markets the Taifun anti-radiation drone, another one-way system. Britain's Future Offensive Air System (Foas) is expected to include a Ucav element and Rolls-Royce is studying a Small Commmon Core for future engines in the 20 to 40 kN range for Ucavs and large drones. Eads has exhibited models of stealthy Ucavs, reportedly as part of the Etap (European Technology Acquisition Programme).