A leaner, cheaper, V-22 tilt-rotor is taking shape, thanks to advances in manufacturing technology.

Graham Warwick/FORT WORTH

MAJOR PIECES OF THE FIRST production-representative V-22 Osprey tilt-rotor are coming together at Bell Helicopter Textron and Boeing Helicopters, and confidence is growing that the dramatic cost and weight reductions achieved so far will help secure the future of the once-endangered US programme.

This is a programme which seems to have been around for ever. The V-22 has its origins in a 1981 requirement for a joint-Services vertical-lift aircraft, but will not now enter service with the US Marine Corps until 2001. Preliminary design began in 1983, but a seven-year, $1.8 billion, full-scale-development (FSD) contract awarded to the Bell Boeing team in 1985 was never completed. Instead, it was replaced in October 1992 by a seven-year, $2.3 billion, engineering- and manufacturing-development (EMD) contract.

In effect, the V-22 was given a second chance. The aircraft had become branded as overweight and overpriced, but repeated cost- and operational-effectiveness analyses showed that the tilt-rotor transport was the best answer to the Marine Corps' needs. With the aircraft built during FSD as the starting point, the goals set for the EMD phase were to reduce the empty weight and unit cost of the V-22.

The aborted FSD phase is now credited with having demonstrated the tilt-rotor's capability and mission suitability, while EMD will demonstrate the producibility and affordability of the V-22. Six aircraft were built during FSD: five were flown, of which two crashed and two remain flyable. Four "production-representative" V-22s are being built in EMD. These will be used for operational testing.



Something of a revolution has taken place since the V-22 programme moved on from FSD to EMD. The aircraft has been totally redesigned to take advantage of manufacturing technologies not used in FSD. The results have been dramatic. Aircraft empty weight at the end of FSD was 15,830kg. Today, empty weight at the end of EMD is projected to be 14,800kg - more than the 900kg weight reduction targeted for EMD, and 240kg less than the specification empty weight agreed with the customer. "We are beating every one of our weight targets," says Bell's V-22 programme manager, Jack Gallagher, "and we will beat our performance targets," which are based on the specification weight.

Based on current plans to build 523 V-22s over 25 years, the flyaway unit cost of the FSD aircraft would have been $41.5 million. Today, the projected cost is $32 million. The goal for EMD is to reduce the cost to $29.4 million, a target which Gallagher says will be beaten when further cost reductions now in the pipeline are incorporated.

Cost estimates are based on a production rate which peaks at only 27 aircraft a year, as it is constrained by a $1 billion-a-year funding cap. Gallagher says that a report is due in February 1996 on the effects of increasing the V-22 production rate, which would require greater annual funding, but which would further reduce the unit cost. Four aircraft a month could be produced without needing additional tooling, he says.

The extent to which the V-22 programme, and the aircraft, changed with the transition from FSD to EMD cannot be understated. The new development programme is modelled closely on that of the Boeing 777, with integrated product teams and electronic product definition. The FSD aircraft was not designed on computer and the EMD "productionisation" process has included converting the entire design from paper drawings to the CATIA computer-aided design system.

In the process, each component has been re-examined to determine how it can be produced with fewer parts, less cost and lower weight. Gallagher says that the conversion to CATIA alone has saved $25 million, as the improved first-time fit of computer-designed parts, compared to those built to paper drawings, has reduced the design changes required. In addition, the CATIA system has enabled tooling to be designed, assembly sequences defined and the aircraft to be digitally pre-assembled on computer.

Manifold producibility improvements have been incorporated in the EMD V-22s, which will have 90% composite structures. Many are "systemic" - manufacturing technologies such as the automatic fibre-placement and tape-laying of composites which are widely used throughout the aircraft. Others are specific - components such as the wing-stow mechanism - and are redesigned to reduce complexity, cost and weight. Almost every part of the aircraft has been touched by the drive for producibility and affordability.

Examples abound both in the wing, which is produced by Bell, and in the fuselage, which is produced by Boeing. What Bell Boeing terms "design for manufacture and life-cycle cost" will reduce the cost of fabricating wing torque-boxes by $157 million over 523 aircraft. Wing skins, manually laid up during FSD, are being produced using automated tape-layup. The time taken to produce a skin has been reduced, from almost 1,250h to just under 840h, for a saving of $28 million.

Assembly-line fabrication of wing stringers using automated tape-layup will save another $24 million and a mechanised stringer-installation cell will save a further $12.5 million over manual placement. Spar webs are being produced using automated tape-layup, while wing ribs have been redesigned to require less shimming during assembly. A new wing-assembly concept is expected to save $52.5 million.

During FSD, one fixture was used to assemble almost 85% of the wing. This resulted in congestion and delays, Bell says, so a modular approach has been adopted for EMD in which one fixture handles about 40% of the assembly task. Major subcomponents are assembled in portable fixtures, called "bridges", which are then used to transport each completed subcomponent to the next fixture in the process.

By the time Bell mated the wing and nacelles of the first EMD aircraft in early November, the time taken to assemble the wing and nacelles was already more than 2,500h under budget. As the company moves towards mating its wing with the Boeing-supplied fuselage in December, it is now more than 3,100h under plan.

There are other signs that Bell Boeing's projections of cost and weight savings might yet prove conservative. One example is the composite "grip" at the root of each prop-rotor blade by which it is connected to its hub. The FSD grip was produced using filament winding; the EMD grip is produced using fibre placement. Bell projected a reduction in the time taken to produce the grip, from 1,825h to 890h, for savings of $64 million over 523 aircraft. In fact, grips are being produced in around 280h, Gallagher says.

The design change eliminates more than 1,000 Gerber-cut plies, he says, and requires only three major tools. Using a fibre-placement machine - Bell has two in-house - composite tows are wound on to a mandrel to shape the grip in one step. Fibre-placement is also being used by Boeing, to produce the entire V-22 aft fuselage on a single tool.


Important changes

Other notable design changes include the "stow ring" which allows the wing to be rotated to align with the fuselage for below-deck storage on US Marine Corps helicopter carriers. On the FSD aircraft this was a stationary fuselage-mounted ring weighing 550kg; on the EMD aircraft it is a wing-mounted "flexring" with a target weight of 370kg. "We have saved 350lb [160kg] and $350,000 [per aircraft]," says Gallagher.

Nacelle design improvements include laser-assisted layup of the pylon support, which is projected to save $11 million. CATIA design data are used to generate an outline which is laser-projected on to the tool to assist in ply location. A single-piece cast-titanium transmission adapter, which replaces a four-piece assembly, will save $25 million by reducing machining operations.

Automated production of "ribbonised-wire" harnesses is projected to save a remarkable $47 million. In FSD, each of the wires in a ribbon had to be stripped and crimped manually. For EMD, an automated cell has been developed for stripping, crimping and connector assembly, cutting the operation from almost 790h to just 100h.

In addition to these individual component improvements, there are other manufacturing changes which cut costs across a variety of parts. One example is the creation at Bell of a composite-cutting centre, which is expected to save $120 million. This is equipped for high-speed ultrasonic ply-cutting and includes tape-dispensing and ply-nesting systems which save both time and material.

Another cost-saving change to the V-22 programme was the decision to have just one final-assembly line, for EMD and low-rate initial production at least, located at Bell's flight-test centre in Arlington, Texas. The workshares are otherwise unchanged: Bell is responsible for the wing, overwing fairing, nacelles, propulsion, rotors, dynamics, empennage and ramp (the latter two subcontracted to sister company Textron Aerostructures), while Boeing is responsible for the fuselage, landing gear, avionics, electrics and hydraulics, as well as per- formance and handling qualities.

The EMD V-22 now taking shape at Bell is scheduled to be flown for the first time in December 1996. Operational evaluation is scheduled for 1997-8, using the EMD aircraft. Funding for low-rate initial production is expected in 1997 and initial operational capability is planned for 2001. The EMD and initial-production aircraft will all be MV-22A tactical transports for the USMC.

In May 1995, the EMD contract was amended to include development of a CV-22 special-operations version for the US Air Force. Work is now under way to define the required changes to the basic Marine MV-22. These centre on the integration of the Texas Instruments APQ-174C terrain-following/terrain-avoidance radar.

Boeing is leading the CV-22 effort, with 55% of the development work. The airframe and other hardware will be 90% common between the MV-22 and the CV-22, the company says, while software commonality ranges from 100% in the fly-by-wire flight-control system to 60% in the mission computer. A CV-22 is expected to cost about $4 million more than an MV-22.

In addition to the radar, the CV-22 will have radar warning and jamming, laser warning, satellite communications, ground collision-avoidance, covert radar-altimeter and crash-position indicator. Extra fuel tanks will be installed in the wings, sponsons and cabin, and an aerial-refuelling probe will be fitted.

Current plans call for just 50 CV-22s, compared with the 425 MV-22s planned, with production beginning in 2001. The US Navy's 48 planned HV-22 combat-rescue aircraft, which will make up the balance of the 523-aircraft production run, are expected to share some of the CV-22's special features.


Source: Flight International