F
R

1
0
-
2
0
0
1

JSF: THE WINNER TAKES IT ALL

Over the next 30 years there will probably be only one new American fighter aircraft programme, the Joint Strike Fighter (JSF). "There are not many alternatives left," says Major General Michael Hough, JSF programme director, alluding to recent doubts as to whether the project will really go-ahead. "All our assets are old. The maintenance costs are eating us up."

For this reason present military planning in the USA and the United Kingdom envisages some 3000 JSF's entering service from 2008, at a cost of at least $200 billion - potentially the biggest contract ever to have been secured by a military aircraft manufacturer. The ground rules laid down by the US Congress are clear: winner takes all.

That there should be only one winner was recently confirmed in a report produced by the Rand Corporation that was commissioned by the previous Secretary of Defense, William Cohen. John Birkeler and his colleagues worked out the a special "break-even" programme under various scenarios. Their calculations were used to check whether, if the Department of Defense invested in a second JSF variant, it would be able to recoup the additional investment by being able to exert greater pressure on the suppliers to drop their prices. The study concluded that only if the competitive situation resulted in a 30% reduction in the JSF purchase price would parallel production pay off. According to Rand, this would be "difficult, if not impossible" to achieve.

However, on one point the study did come out in favour of retaining competing capabilities. When it came to development and integration of mission systems such as radar, IR sensors and electronic warfare (EW) equipment, it made sense to support a second supplier. Ultimately, like all fighter aircraft, the JSF will need to be upgraded several times during its service career.

Between the lines, it would appear that programme director Hough is also in favour of retaining a rival capability. "Competition will continue in the future to be the key (to technological product excellence). For that reason I would always try to maintain a competitive situation." At any rate there are already indications that the work may be shared out. At least, Phil Condit, President of Boeing, hinted as much in a recent interview.

For the moment, however, the question does not arise. "We do not intend to lose," says Condit, and at Lockheed Martin the mood is equally aggressive. The two companies have until the end of August to submit their final tender documents. These are largely based on the data generated during the flight test programme for the short take-off, vertical landing (STOVL) concept demonstrators. Demonstration of satisfactory performance during short take-off and vertical landing was the most difficult part of the flight trials. Precisely in this area the technical solutions offered by the two JSF teams are significantly different.

Lockheed Martin X-32B

There is no doubt that both the X-32 and the X-35 satisfied the expectations placed on them and that the resulting production models (PWSC = Preferred Weapons System Concept) meet the Pentagon's requirements. "But the critical issue here is not (flying) performance," says Major General Hough. "It was much more difficult to arrive at a set of requirements regarding the purchase price and the cost of maintenance. We wanted to achieve a 30% reduction in operating costs over the lifetime of the JSF." This includes, for example, requirements such as a maximum of 30 minutes per flying hour to maintain stealth coatings.

"The aim is to achieve the best value overall for the investment," says Hough. To this end thousands of parameters are defined in the RFP as minimum requirements and objectives. "We are considering only the threshold values," explains Hough. Boeing follows a similar line of argument and places the main emphasis on the cost-effectiveness of its approach, whereas Lockheed Martin is apparently taking the view that, despite cost pressure, it would make no sense to produce an aircraft with mediocre performance.

Boeing X-32B

Which of the rivals has best read the customer's mind will become apparent on Friday 26 October, when, according to present information, the Pentagon is planning to announce its decision, already postponed several times. As well as the assessment carried out by the JSF programme office, other considerations will flow into the decision, such as confidence in the contractor's ability to complete development and production on time and within budget.

Whether the $20-25 billion (DM 44-55 billion) engineering and manufacturing development (EMD) phase will then begin on 1 November is still unclear. The JSF programme office at any rate is expecting the first design review to take place at the end of 2002, with the Critical Design Review in mid-2003. The first JSF prototype is scheduled to take to the air four years after the start of EMD, followed at approximately three-monthly intervals by the STOVL and carrier-based (CV) variants. Altogether 15 flying prototypes are to be built, plus another seven aircraft for various other tests.

Deliveries to the US Air Force and the US Marine Corps will commence in 2008, with the US Navy and the Royal Air Force receiving their first aircraft in 2010. The Marine Corps, which has the most urgent requirement, should achieve initial operating capability in 2010. The target unit flyaway price remains at between $28 million and $38 million (1994 price levels).

Production of the JSF could rise to up to 196 aircraft per year and continue into 2026. Such figures are viewed as unrealistic by many, as even the Pentagon does not have unlimited resources and also has to pay for other programmes like the F-22 and F-18E/F.

These figures do not take into account possible exports. "With the JSF we are pushing technology forward by 10 years," believes Maj. Gen. Hough. "We are offering the world a splendid option." This view is shared by a number of countries. According to Hough, negotiations are currently under way with Italy, the Netherlands, Turkey, Canada, Denmark and Norway about participation in the programme.

Any country that wishes to be involved has until the end of the year to come on board. If JSF is developed as planned, it is clear at any rate that the international competition will be extremely tough from the beginning of the next decade. The manufacturers of Eurofighter, Rafale and the F-18E/F will do their utmost to get their products well-established by then. Arguments against JSF include uncertainties regarding the US government's willingness to export the stealth technology, excessive dependence on the USA and the fact that JSF is optimised for the fighter bomber role.

Tight deadlines for flight tests

At the end of July Boeing and Lockheed Martin both concluded flight testing of their JSF concept demonstrator aircraft. The last and undoubtedly the most exciting part of the tests was demonstrating the STOVL characteristics.

To achieve the short take-off and vertical landing performance required by the US Marine Corps and the Royal Air Force and Royal Navy in their Joint Strike Fighters, the rival bidders came up with very different design solutions.

Boeing has equipped its JSF with thrust-vectoring nozzles à la Harrier. They are accommodated on the fuselage side at the centre of gravity, directly behind the turbine section of the Pratt & Whitney JSF119-614S engine positioned much further forward. In the rear there is a rectangular thrust-vectoring nozzle which can be completely closed. In addition there are control nozzles on the nose, tail and wingtips, as well as cold air outlets beneath the fuselage. The latter are intended to prevent hot gases being sucked in through the air intake.

For short take-off, the swivelling nozzles are rotated downwards by 60-o. However, in the first acceleration phase the thrust goes through the main nozzle. Only when the aircraft is moving at a speed of about 130km/h does the pilot press a button and within a second the thrust is diverted through flaps to the lift nozzles. The aircraft takes off. It continues to accelerate while the lift nozzles are moved backwards to 45-o. At the click of a button, the jet is then directed back through the tail nozzle again.

The transition from horizontal flight to the hover entails the reverse sequence of events, and here the lift nozzles can be activated up to 450km/h. Below 110km/h the aircraft is largely dependent on its thrust. During the hover a total 33,000lb (146.6kN) of thrust is produced. With an empty weight of 12,200kg, around 2,760kg is therefore left for fuel reserves, weapons payload and pilot.

Boeing began flight testing with conventional trials on the X-32B. At Edwards AFB the transition to STOVL operating mode (thrust not through the tail but through the swivelling nozzles) was then tested at speeds of between 260 and 340km/h. Flight testing operations were then relocated to Patuxent River. There the speed and altitude in the STOVL mode were further reduced and some short landings were performed. On Sunday, 24 June the first hovering flight took place at an altitude of 60m.

Only three days later the first vertical landings followed from a height of 15m - initially over a pit covered over with a metal grate that was designed to eliminate the ground effect. Subsequently landings were performed on normal ground.

The short take-off demonstrations required by the programme office were completed on 1 July (approx. 170m rolling distance). These were followed by some tests of Boeing's, including supersonic flights following a short take-off late in the month.

Lockheed Martin achieved its "Mission X" (150m short take-off, supersonic flight, vertical landing) on 20 July, despite being initially a little behind due to problems with the lift fan. This is the central element of the X-35B's STOVL system. Mounted directly behind the cockpit, it delivers 17,000lb (75.5kN) of thrust and hence more than the downward vectored main nozzle in the rear (13,000lb/57.8kN). The control nozzles beneath the wings contribute another 4000lb (17.7kN).

The lift fan is powered by a continuously running shaft on the Pratt & Whitney JSF119-611. For the short take-off, the pilot moves the thrust-vectoring lever out of the idle position under static thrust, causing the various flaps for auxiliary air intakes, engine and lift fan to open. The D-shaped lift fan nozzle is rotated downwards 34-o and the main nozzle 22-o. It takes 15 seconds for the lift fan to get up to speed after engaging. The pilot now pushes the throttle and accelerates the aircraft. At around 110 km/h the two nozzles are vectored to around 60-o downwards and the X-35B lifts off. At 370 km/h the thrust vectoring lever is returned to the idle position, the lift fan is disengaged and the flaps are closed.

To land the aircraft vertically, the pilot first of all slows it down to 460km/h. The various flaps open up, the lift fan is engaged, the pilot reduces the thrust, slows down the aircraft and vectors the nozzles slowly into the vertical position for hovering flight. Rolling motion is controlled via nozzles in the wings, the angle of attack by the distribution of thrust between tail nozzle and lift fan and yawing by lateral movements of the tail nozzle. The thrust produced by the lift nozzle is regulated by guide vanes in the air intake.

According to Lockheed Martin the lift fan solution offers significant reserves of thrust. At sea level 37,700lb (167.5kN) of thrust are available - allowing a theoretical payload of 2,970kg, given an empty weight for the X-35B of 13,950kg.

These values were ascertained by the manufacture from 23 February, initially through static trials over a grate-covered "hover pit" in Palmdale, during which the X-35B was tethered to the ground by the landing gear legs. Installation and certification of a flightworthy propulsion system meant that the first hovering flight was deferred to 23 June. The next day the X-35 rose 7.5m above the hover pit and held its position for 35 seconds.

Altogether 18 hovering flights were completed in Palmdale before the aircraft was flown to Edwards AFB in the conventional manner. On 9 July Simon Hargreaves started up the lift fan for the first time at an altitude of 3,000m at 330km/h. During the same flight the X-35B achieved a speed of Mach 1.08.

The test team then felt its way with the lift fan activated at ever lower speeds, until on 16 July the first vertical landing was achieved at Edwards AFB. KARL SCHWARZ

From page 54 of FLUG REVUE 10/2001