Sky-high stakes

When the US government decides later this year which Joint Strike Fighter it wants, it will set off a production line that will see thousands of the combat aircraft take to the air across the world.

This autumn the US Department of Defence, aided and abetted by the UK Ministry of Defence, will make a decision that will shape the aerospace industry for the next 40 years. It is due to select the winner of the Joint Strike Fighter competition in October.

Around 3,000 JSFs are expected to be supplied to US and UK forces and another 2,000 to export customers. It is the biggest military procurement programme in history, and no other future combat aircraft is likely to be produced in such numbers. The JSF will be the mainstay of the US Air Force, Marine Corps and Navy, a feat achieved previously only by the classic McDonnell Douglas F-4 Phantom.

The JSF will be a single-seat, supersonic aircraft incorporating stealth technology, and will be built in three distinct variants. The conventional take-off and landing (CTOL) aircraft will replace the USAF’s Lockheed Martin F-16s and Fairchild A-10As, and will be the basis for the majority of export aircraft. The CV variant is for the US Navy and will be able to operate from its aircraft carriers, replacing the Boeing F/A-18 Hornet.

But the most interesting version technically is the short take-off and vertical landing (STOVL) aircraft being developed for the US Marine Corps, the Royal Air Force and the Royal Navy. It will replace F/A-18s and Boeing/BAE Systems AV-8B Harriers in the US Marines, and probably BAE Systems Harrier GR7s in the RAF and Sea Harrier F/A-2s in the Royal Navy.

Although the UK is likely to take around 150 of the STOVL aircraft as a replacement for the Harriers and Sea Harriers, a final decision has not yet been made. However, earlier this year the MoD signed a commitment to join the engineering and manufacturing development phase. This will cost £1.3bn ($2bn) plus another £600m for UK-specific work. Total JSF development costs are around $25.5-28.5bn. The JSF competitors Boeing and Lockheed Martin are already test flying their concept demonstrator aircraft, the X-32 and X-35 respectively. Their machines’ performance will decide the winner.

Both STOVL versions have passed crucial programme milestones in recent weeks, demonstrating their short take-off capability, and their ability to switch between level flight and hovering, and land vertically.

Earlier this month the Boeing variant completed all the government-defined flight test requirements in the programme, while Lockheed Martin’s demonstration flights are continuing.

Engineering and manufacturing development, the next phase of the programme, is set to begin in November. Service entry is planned for the end of this decade.

Reducing the cost

The JSF programme can trace its roots back to the late 1980s and a host ofsingle service programmes. Using a single design as the basis for the three variants is an attempt to reduce the cost of combat aircraft. Measured in 1998 dollars, the target costs of each variant are $28m for the CTOL, $30-35m for STOVL and $31-38m for the CV aircraft. The USAF’s Lockheed Martin/Boeing F-22 Raptor cost more than double these figures.

Not only has JSF evolved into a tri-service programme, it also has international participation. The UK is the only full-scale participant, but Canada, Denmark, Israel, Italy, the Netherlands, Norway, Singapore and Turkey have all contributed various levels of funding to the concept demonstrator phase. The UK, as the only ‘collaborate development partner’, has handed over $200m and provided some core technology, particularly associated with the STOVL aircraft. The UK is the only international concept demonstrator participant to have a say in which aircraft is selected for the next phase.

The MoD, in announcing its agreement to join the next phase, said 5,000 jobs at 70 UK companies would be sustained. Lockheed Martin claims that if it is selected its JSF production will support 8,400 jobs directly.

UK companies are playing key parts in both the Boeing and Lockheed Martin teams. BAE Systems is involved with both. As British Aerospace it allied itself with Lockheed Martin and Northrop Grumman, while Marconi Electronic Systems – the other element of the new BAE – was part of the Boeing group. BAE Systems Avionics is now also a Boeing team member. The JSF is expected to give BAE a £2bn boost to its order books.

Rolls-Royce is also a participant on both teams, as are a number of others. A list of UK firms involved in the JSF reads like the Who’s Who of British aviation: Claverham, Flight Refuelling, Martin Baker, QinetiQ (formerly the Defence Evaluation and Research Agency), Smiths Aerospace, and TRW Lucas Aerospace, to name a few.

With many of these companies, in addition to BAE and Rolls-Royce, contributing major elements to both competitors, it has been necessary to build ‘walls’ between teams and establish carefully monitored rules on interaction. This is not a new problem, since separating competing teams within the same company has become commonplace following consolidation in the aerospace and defence industry.

The process is helped to some extent by the physical distance between participants. For instance, BAE’s team on the Lockheed Martin grouping is based at Warton near Preston, whereas its Boeing team is sited at Rochester, Kent. Many of the engineers are also seconded to work in integrated teams at the US manufacturers’ facilities.

The same situation applies to the government Joint Program Office based in the Pentagon, where personnel from the Royal Navy, RAF and MoD sit with their US colleagues. UK test pilots from BAE and from the MoD are integral to both flight test teams.

The X-32 and X-35 being used in the concept demonstration phase are not strictly prototype aircraft. Their role has been to prove critical elements of the design, including the STOVL propulsion system and the commonality between the three versions.

Each company has built two concept demonstrator aircraft. Boeing’s X-32A represented the CTOL and CV variants, with the X-32B presented as the STOVL demonstrator. Lockheed Martin’s X-35A flew 27 sorties and was returned to the company’s Palmdale, California factory, where it was converted to the X-35B STOVL aircraft. Its X-35C represented the CV version with its larger wings and tail surfaces necessary to meet the aircraft carrier landing-weight requirements.

Service standard

During the engineering and management development phase the winning bidder will produce the service standard or preferred weapon systems concept JSF, which is due to make its first flight around 2005.

Boeing and Lockheed Martin submitted their engineering and manufacturing proposals in early February, and final proposals, to include the data from the STOVL flight test programmes, are scheduled for submission on 15 August.

Lockheed Martin believes the EMD phase and production of 3,000 aircraft for the UK and US forces will be worth $27bn to the UK, with production of export aircraft worth another $24bn.

However, these figures could change. In theory, the programme at present is a winner-takes-all competition. Whichever company is selected for EMD takes the spoils, leaving the loser facing a stark future as a fighter manufacturer.

But many in industry believe the US government will be forced to hand about 30% of the programme to the losing bidder. This will ensure that there will still be two competitors for the next major combat aircraft programme, probably a bomber in the later years of the next decade.

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Hovering on the edge of thrust: Two routes to short take-off and vertical landing.

Development of the Harrier – which has been combat proven in the 1982 Falkands War, during the 1991 Gulf War and over various parts of the Balkans – has been restricted by the basic layout and by the thrust from the Rolls-Royce Pegasus engine.

In 1969 when the Harrier GR1 entered service, the engine produced around 19,000lb of thrust. Today’s Pegasus 11-61 pushes out 23,800lb, and significant improvements in fuel burn, and mean time between overhaul and failure rates have been achieved.

JSF is significantly larger and heavier than the Harrier, and the X-32 and the X-35 are powered by the Pratt & Whitney JSF119 engine, with its 40,000lb thrust. But Boeing and Lockheed Martin have taken very different STOVL approaches.

Boeing’s way

The company has followed the Harrier direct-lift route, with the Rolls-Royce supplied lift module adding two vectoring nozzles, compared with the Harrier’s four, immediately aft of the JSF119 and on its centre of gravity.

In STOVL mode, the JSF119’s thrust-vectoring cruise nozzle closes and butterfly valves in the lift module open, directing thrust to the lift nozzles.

Engine air is ducted to a Harrier-style attitude control system, with forward pitch nozzles under the inlet, aft pitch/yaw nozzles under the tail and roll nozzles near the wingtips. Air is also directed to a jet screen under the fuselage, forward of the lift nozzles. In hover mode, this forms an air barrier to prevent hot nozzle gases flowing forward and being re-ingested into the inlet, which reduces engine thrust.

Pros: Boeing, having taken over AV-8 manufacturer McDonnell Douglas, claims 30 years’ experience of direct-lift. It says its system minimises moving parts, which increases reliability and maintainability, thereby reducing support costs.

Cons: The hot jet efflux directed straight on to the runway or aircraft carrier deck causes damage, while the amount of jet-lift is limited to what the engine can provide and that this will vary with ambient air temperature. For a successful vertical landing of any jet-lift aircraft, the weight cannot be greater than the available thrust.

Lockheed Martin’s solution

The company has installed a Rolls-Royce lift fan just behind the X-35’s cockpit. This is driven by a shaft from the main engine, using a clutch to engage and disengage it. The two-stage, contra-rotating fan compresses air, which is then allowed to expand, producing thrust: it takes about 15 seconds for the fan to spool to full speed.

There is no combustion so the jet flow is cooler. The lift-fan thrust is balanced by that from the JSF119 engine directed downward through a three-bearing vectoring nozzle and roll posts installed in the wing. The nozzle and roll posts are also from Rolls-Royce. Varying the thrust split between the lift fan and engine controls pitch.

Pros: The advantage of Lockheed Martin’s approach is that together the fan and engine produce more thrust than the engine alone. It claims Boeing’s aircraft is working at the limit of thrust available and only achieved its vertical landing andhover performance with key components stripped out to save weight. Boeing has only conducted demonstration flights at sea level, whereas Lockheed Martin has demonstrated vertical landing capability at higher altitudes.

Cons:The shaft spinning at high speed and the need for the clutch to engage and disengage the lift fan represent added complexity. The lift fan and nozzles are a dead weight during flight and they take up vital fuselage space.