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Stealth--the combat 'ace': a fighter pilot is considered an 'ace' after downing five enemy aircraft. Stealth aircraft have now participated in five combat actions--Panama, the 1991 and 2003 Gulf Wars, Yugoslavia and Afghanistan, so can perhaps be considered to have won 'ace' status.

Stealth aircraft have played a significant role in recent conflicts, albeit in small numbers. During the war against Iraq earlier this year, only four of the 51 bombers used by the US Air Force were Northrop Grumman B-2 Spirits, while only twelve of the 293 fighters were Lockheed Martin F-117A Nighthawks.

While stealth aircraft have carried a reputation for being maintenance hungry, this was not reflected in the mission-capable rates reported for the Iraqi conflict. Both the B-2 and F-117A achieved higher mission-capable rates than the best conventional combat aircraft--85.0 per cent for the B-2, compared with 79.4 per cent for the B-52, and 89.3 for the F-117A, as compared with 84.1 per cent for the F-15E.

The ability of stealth aircraft to operate with near-impunity over enemy territory remains unique, though it must be said that during the air campaigns against the former Yugoslavia, Afghanistan and Iraq, losses for all types of manned aircraft have been extremely low. For example. Iraq failed to down a single US or British aircraft during the long-running campaign of air strikes against that nation in support of operations of the northern and southern 'no-fly' zones. During the war, Iraqi air defences fired 1660 surface-to-air missiles and rockets, and the anti-aircraft artillery fired on 1224 occasions, yet the allied US losses to enemy fire were only four AH-64D Longbow Apache, two AH-1W Cobra and a single A-10A Warthog.

Carelessness?

The first-ever downing of a stealth aircraft on 27 March 1999 was a significant propaganda boost for the Yugoslavs during the Nato air campaign against that country. The F- 117A seems to have fallen victim to an S-125 (SA-3 'Goa') missile--the wreckage showed the type of damage which would result from a near-miss detonation of a blast/fragmentation warhead.

Press reports have suggested that the stealth fighter was downed by a lucky shot from an S-125 battery, which had obtained some idea of the aircraft's position from short-lived temporary tracks that had been established by widely-distributed radars or had detected the aircraft by using its back-up electro-optical tracking channel. The aircraft had just completed its attack, leading to speculation that the open weapon bay may have compromised the RCS for just long enough to allow the S-125 unit to begin tracking the stealth fighter.

Reports claimed that the US Air Force had grown careless in planning its F-117A missions, that the downed fighter had been using an aggress route which had been used before and that EA-6B Prowler jamming aircraft tasked with protecting the strike were too far from the scene to be effective.

One intriguing suggestion is that the aircraft's route may have taken it over a Yugoslavian test site used for radar or missile trials, giving experienced crews equipped with upgraded systems the chance to obtain a useful radar return.

Between 2000 and 2006, the F-117A fleet will be rotated back to Lockheed Martin to be updated under the F-117 Single Configuration Fleet (SCF) programme, which is intended to bring all the aircraft--which were originally delivered between 1983 and 1990--to a common standard. The existing radar-absorbent coating is being removed and replaced by a new coating with superior anti-radar performance and reduced maintenance requirements. Changes to the avionics include new cockpit instrumentation based on a new central processor and an LCD multi-function display.

The aircraft is also receiving the Raytheon Integrated Acquisition and Designation System (Iads), a new second-generation video tracker and associated system controller for the electro-optical targeting system.

Another upgrade is reported to allow real-time targeting information to be transmitted to and from the F-117A during flight, allowing aircraft to be diverted to alternative targets or tasked to attack newly-detected mobile or fleeting targets. This will require the use of an encrypted datalink system based on satellite communications.

Upgrades are also being applied to the B-2A fleet. By 2000, all had been modified to the Block 20 and Block 30 configuration. To help minimise RCS, and as part of the Block 30 upgrade, most of the edges have seen replaced and all surfaces treated, including control surfaces. When the B2 entered service, the US Air Force accepted that join lines in the skin--for example around access panels--had to be covered with tape before each operational sortie. By 2000, it was flight testing an improved magnetic radar-absorbing material known as Alternative High-Frequency Material (AHFM). This was designed to be sprayed onto access panels and fasteners to reduce radar signature.

First revealed in October 2002, some four years after it first flew, Boeing's 'Bird of Prey' stealth technology demonstrator was seemingly intended to test new stealth technology. Privately funded by what was then McDonnell Douglas, it has a top speed of only 260 knots, which reflects its role as a flying testbed rather than the basis for a future combat aircraft. The wings are swept at around 65[degrees]. while the cockpit masks the inlet from the front view.

Some features of the design such as flexible hinge-line covers on the rudderons (a feature which would eliminate the radar 'hot spots' associated with skin gaps) have led to suggestions that the aircraft is intended to demonstrate RCS levels well below those of the F-117A, while the blue colour scheme has led at least one observer to speculate that the Bird of Prey had investigated techniques for visual stealth which might allow a future stealth aircraft to operate by day.

The Lockheed Martin F-22 Raptor is intended to combine stealth with traditional fighter manoeuvrability. It will also have a low IR signature; claims have been made that the fuel is used to cool the leading edges.

The work on F-22 signature control was done using full-scale models. Flight tests of the aircraft's stealthiness did not begin until several years into product development.

Seals

Emphasis has also been placed on maintainability. Wherever possible, service points are located within weapons bays or wheel wells, while panels and other parts which must be opened during servicing will have specially-designed seals and gaskets. To avoid the need to repair low observable seals and coatings in the field, the F-22 has almost 300 specially designed access points. These include quick-access panels, featuring positive locks, seals and gaskets.

Although the RAH-66 Comanche is intended to use stealth technology, earlier this year the General Accounting Office, the investigative arm of the US Congress, warned that the required RSC-reduction technology required additional development. The US Army was reported at saying that it expects this technology will reach maturity a year before the expected date of the production decision.

The first stealthy aircraft likely to be exported is the Lockheed Martin F-35 Joint Strike Fighter, but making this aircraft available to many of the operators of today's F-16 and F-18 will require a major relaxation of the rigorous export controls that apply to low observable technology today. Early in the programme, some observers speculated that the aircraft might be fielded in stealthy and unstealthy forms, but in practice such a move would be impractical. Stealth technology must be designed into an airframe--it is not something that can be added or removed as required.

Russian Plasma

Some Russians would argue that this is not the case. In the late 1990s came news of a new and novel technique for controlling RCS which could be fielded as all add-on or upgrade. Developed in Russia by the Keldysh Research Centre, it would protect an aircraft by creating an artificially generated plasma around it. Radar energy tends to pass around a plasma cloud rather than penetrate it, say the Russians, and the energy that does penetrate interacts with the plasma charged particles, and is partially absorbed. The hardware needed to create the protective screen weighs less than 100 kg, and consumes between one and ten kW of electrical power.

Ground and flight tests have shown that the radar observability of an aircraft can be reduced by a factor of more than 100, say the system's developers. This would reduce the radar cross section of a MiG-23 from around 6 sq metres to around 0.06 sq metres.

In 1983, the Russian Air Force released its requirement for an MFI (mnogofunktsionalnyy frontovov istrebitel = multifunctional front-line fighter). the resulting Mikoyan 1.44 twin-engined fighter was reported to make extensive use of radar-absorbent coatings, but development was protracted. Completed in 1991, it was placed in storage because the AL-41 engines were not ready. It did not fly until February 2000, by which time it was clear that the aircraft would never be placed in production.

In January 1999, Mikhail Korzhuyev, general director of what is now the Aviatsionnyi Nauchno-Promyshlennyi Komplex (ANPK) MiG, said that the aircraft would form the basis of "a new fighter that will be smaller and cheaper, but not worse, than the MFI".

Although the requirements for the new fighter are reported to have been published in 1998, as a result of Russia's economic problems, such as aircraft is unlikely to be built in the foreseeable future. It could fly some time later in this decade, but would be unlikely to enter production until some time after 2010.

In 1995, Col. Gen. Peter S. Deinekin, who was at that time commander of the Russian air force, stated that the Tupolev Tu-22 Blinder bomber and the Sukhoi Su-24 Fencer would be replaced by a new 'multi-role strategic bomber.' Unofficial reports suggest that this could be a Sukhoi design designated T-60S or S-60, but virtually nothing is known of this project or its current status.

China

China has studied stealthy single- and twin-engine variants of its J-10A fighter. The Shenyang Aircraft Company has already been selected to lead research and development of a possible twin-engine heavyweight stealth fighter, and there have been suggestions that Chengdu might be ordered to work on a lighter single-engined design which could form the low end of a high/low mix of types.

In early 1999, trials were reported of a Shenyang Aircraft Corporation J-8 (Finback) with some parts of its structure covered in Xikai SF18 radar-absorbent material, along with proposals to fit the same material to the Xian Aircraft Company J H-7 heavy fighter-bomber.

Unmanned

The US Department of Defense is applying stealth technology to a new generation of unmanned combat air vehicles (Ucav). Boeing's X-45A is a stealthy design with rear-mounted swept wings. Under development for the US Air Force, it has two internal bays, one to carry a single 2000 lb (900 kg) bomb or precision-guided munitions, the other for avionics. The X-45A first flew in May 2003, and forms Spiral 0 of the Ucav programme. This was to have been followed in Spiral 1 of the programme by the X-45B, a design some 40 per cent larger than the--45A, but this configuration has been bypassed in favour of the X-45C, which will carry more internal fuel.

The US Navy plans to operate a Naval Unmanned Combat Air Vehicle (Ucav-N) from its aircraft carriers and has assigned the project to Boeing and Northrop Grumman, who are producing competitive designs. Boeing is offering the X-46, a design whose planform resembles that of the B-2 bomber. Northrop Grumman's X-47A Pegasus technology-demonstrator, which made its first flight in February 2003, is a stealthy design with a diamond-shaped plan form.

Work on stealth is underway in Europe. Germany independently developed the concept of faceting--as used on the F-117A--and started work on the Lampyridae (Firefly) programme in 1981. The resulting design used fewer facets than the F-117A.

A three-quarters scale model was test-flown in a wind tunnel, but although this system had the potential to be developed into an operational aircraft, the project was cancelled in 1987, apparently due to lack of funds.

Europe

In September 2000, Eads announced that it was studying a stealthy UAV configuration as part of the Future Airborne Weapon System (Faws) programme to study possible replacements for the Tornado fighter-bomber.

In the UK, British Aerospace (now BAE Systems) started work in 1994 on a project designated Replica. This resulted in the production of a full-scale model of low-RCS aircraft configuration, which was designed, manufactured, assembled and tested at the company's Advanced Technology Demonstration Centre at Warton, England. This model was subjected to an extensive RCS measurement programme, which showed that the design had achieved the signature targets.

France is engaged in several classified development programmes. In July 2000, Dassault Aviation began flight tests of Aeronef de Validation Experimentale (Ave), a scale model of a low-observable UAV design. While weighing a maximum of 60 kg at take-off, it is thought to be large enough to meet a French military requirement for a low-observable target that can be used to train airborne and ground-based radar operators. The company hopes that the Ave will be the first stage in the development of a full-scale UAV able to carry out reconnaissance or even combat missions.

MBDA-France has been developing active stealth systems that attempt to cancel the radar return from an airframe by transmitting a second signal of equal frequency and amplitude to the genuine return. Unlike Ram, this technique retains is effectiveness at low and medium frequencies, where the efficiency of passive stealth technology tends to decline.

In 1999, MBDA conducted ground tests using a C-22 target drone fitted with an experimental active-stealth system, and flight tests conducted using 'testbeds' (probably C-22s) were carried out at the Centre d'Essais des Landes range at Biscarosse in southwest France.

Possible applications for active stealth measures include the nose, seeker, wing-leading edges and engine air inlets of future missiles. France hopes to use such technology on the mid-life update of the Scalp EG air-to-surface cruise missile, and in next-generation supersonic missiles. Studies have been underway since the mid- 1990s, when designers investigated a possible stealthy variant of the Apache with a redesigned fuselage of flattened triangular cross-section.

Sweden has been studying stealthy UAVs since the late 1990s. Saab Aerospace has flown a 50 kg subscale version of its proposed Swedish Highly Advanced Research Configuration (Sharc). A full-scale Share demonstrator would be 32 ft (10 metres) long, have a wingspan of 26 ft (8 metres) and a take-off weight of around 11.000 lb (5000 kg). However, there is currently no specific Swedish Air Force requirement for such a UAV.

A European stealth demonstrator could be created as a technology demonstration project or technology demonstration vehicles under the European Technology Acquisition Programme intended to explore key technologies for future joint European system for deployment in the period to 2020.

Alenia Aerospace, BAE Systems, Dassault Aviation, Eads, Saab and other major European aerospace companies all recognise that the long-term requirements identified by European governments must be developed and demonstrated jointly. Stealth is one of a number of areas in which they plan to co-operate, though British participation could be made difficult by the prior existence of US/UK co-operative agreements.

Other Applications--Ships

While stealth is most commonly applied to aircraft and missiles, ships or even armoured fighting vehicles are also candidates for signature-reduction measures. The Swedish Navy's new Visby-class 72-metre corvettes are constructed almost entirely from carbon fibre-reinforced plastic material and the superstructure is covered with Ram.

Shaping for low RCS will be taken even further in the US Navy's planned new DD(X) class of destroyers, whose profile is dominated by a large all-composite integrated deckhouse incorporating the ship's low-signature electronically steered antenna arrays and integrated multi-function mast. The new class is intended to have minimal radar, IR and magnetic signatures.

Applies to Guns Too

The United Defense Advanced Gun System, which will arm these ships, has a gun mount with steeply sloped sides and other features intended to give a low signature. Artist's impressions show that a faceted covering surrounds the barrel.

Signature-reducing modifications can also be applied to older weapons. For example, the variant of the Otobreda 76 mm/62-calibre SR (Super Rapid) naval gun mount selected for Norway's Fridtjof Nansen-class frigates and the Franco-Italian Horizon anti-air warfare frigates is shaped to reduce RCS.

Armour

The basic rules of RCS reduction are equally applicable to armoured fighting vehicles. All large flat surfaces should be angled to reflect radar energy away from the direct line back towards the enemy radar, surfaces should not meet at right angles in order to avoid creating corner reflectors, facets should replace curves wherever possible, and the traditional clutter which festoons an AFV must be ruthlessly eliminated to avoid the radar hot spots which they will inevitably create.

Giat of France has conducted experiments with an AMX-30 main battle tank whose turret and chassis were enclosed in a Ram covering shaped to reduce the RCS, while cold air was pumped between the covering and the hull in order to minimise the vehicle's IR signature. The project was funded by France's Delegation Generale pour l'Armement (DGA) defence procurement agency, which has also funded the creation of a similar modification for the Leclerc.

In Sweden, a number of companies such as Saab Barracuda, Saab Bofors Dynamics and Saab Tech Systems built the Sat/Mark (Signatur Anpassnings Teknik / Mark = Signature Management Technologies/Ground) stealth demonstrator. Based on the CV 9040 infantry fighting vehicle, this uses shaping and special materials to minimise the vehicle's visual, IR and radar signatures.

Having been combat-proven in five conflicts, stealth technology is slowly becoming an established military tool, and while the US has a massive head start in this 'black art', its monopoly is no longer absolute. As the Yugoslavian shoot-down demonstrated, stealth platforms are not invulnerable, but for the foreseeable future the technology will still give its user a massive edge in combat.
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Title Annotation:Technology
Author:Richardson, Doug
Publication:Armada International
Date:Aug 1, 2003
Words:2918
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