Paul Lewis/FORT WORTH and NAS PATUXENT RIVER
Enhanced survivability is one of the key performance parameters of the Bell Boeing V-22 Osprey. By that measure, in the 12 years since the aircraft first flew, the V-22 has more than proved its worth. It has endured a succession of political, financial and technical blows that have threatened to terminate its development.
That the programme is now on the brink of full-scale production is largely down to a dedicated core of supporters who have never lost faith in what has become popularly known as "America's Airplane".
Eight years of engineering and manufacturing development (EMD) are winding down and industry eagerly awaits the results of the US Marine Corps/US Air Force Operational Evaluation (Opeval). This is the final hurdle before the V-22 can move from the current low-rate initial production (LRIP) to full-rate production starting in fiscal year 2001.
The Multi-Service Operational Test Team is close to completing its evaluation of the four remaining LRIP Lot 1 MV-22Bs. It stood down for two months after the 8 April crash at Marana, Arizona, which killed 19 marines. Delivery of the next seven LRIP 2 machines has begun and 18 more LRIP 3/4 tiltrotors will follow. With the planned start of full-rate production, this will increase to 16 USMC machines and the first four CV-22Bs for the USAF Special Operations Command (AFSOC), due for delivery in 2003.
USMC requirements call for the procurement of 360 combat assault MV-22Bs at $44 million each by 2012 to replace its ageing Boeing CH-46 and Sikorsky CH-53D helicopters. AFSOC plans to take 50 long-range special operations CV-22Bs by 2007 to supplant its MH-53Js and augment its fixed-wing Lockheed Martin MC-130s. The US Navy has pencilled in a need for 48 HV-22Bs in 2010 - 14 for combat search and rescue, logistics and special warfare.
The first 12 MV-22Bs are earmarked for the Marine Medium Tiltrotor Training Squadron (VMMT-204) at MCAS New River, North Carolina. The unit will also be equipped with the first of three new Level D full flight simulators from FlightSafety, plus flight training devices, cabin trainers and a suite of maintenance trainers.
"VMMT-204 will do all initial training, after which air force pilots go to Kirtland AFB, New Mexico, for advanced training," says Col Nolan Schmidt, USMC V-22 programme manager. The first of 18 US East and West Coast, Hawaii and Okinawa-based USMC MV-22 squadrons will stand up in March 2001. AFSOC's first operational unit will form at Hurlburt AFB, Florida, in 2004.
This is a far cry from the original V-22 programme timetable, which envisaged the tiltrotor making its US military debut in 1991. A hostile defence secretary bent on cancelling the programme, political infighting over funding and the loss of two prototype tiltrotors during full-scale development (FSD) conspired to keep the V-22 never far from the news headlines and out of the military's reach for another 10 years.
Ahead of its time
The intervening decade was not wasted, however, and the tiltrotor that has emerged from EMD is a considerable improvement on the original FSD model. In many respects, the V-22 was ahead of its time, pioneering not only tiltrotor technology, but an all-composite fuselage, fly-by-wire flight controls, a fully integrated glass cockpit and 345bar (5,000lb/in²) hydraulics.
"While the use of glass was not brand new, this was not a 767 with pretty displays and buttons," says Tom Macdonald, V-22 integrated test team chief test pilot. "We had integrated a lot in there with forward-looking infrared, a night vision goggle cockpit, helmet-mounted head-up displays and full military type mission management avionics."
Macdonald joined the V-22 programme in October 1991 during the final 12 months of FSD when flight testing was split between Boeing's Wilmington centre in Delaware and Bell's Arlington field in Texas. With EMD came four new test V-22s and a programme dovetailing Bell, Boeing and US Government test activities into an integrated effort centred on Naval Air Systems Command's home base at NAS Patuxent River.
The contractors, reeling from a $300 million overspend on the $2.2 billion fixed-price FSD contract, were offered a cost-plus deal encompassing a 5% fixed fee plus a 6% award fee. The latter performance-related payment was broken down into 10 six-month award fee periods during which Bell and Boeing were judged on meeting four major criteria - programme management, design to cost (DTC), technical and logistics.
"Neither we on the Bell Boeing side nor the government were very enthralled with fixed price because we had run out of money and were spending our own cash and they weren't getting the product," says John Buyers, Bell V-22 programme director. "The primary reason for the award fee was to motivate the contractor and provide Navair with the services and products it really wanted."
The transition from FSD to EMD had three main goals for the V-22 - cutting cost, shedding weight and addressing supportability. These aims led to the creation of integrated product teams (IPT), a concept that has since become an industry-accepted management standard.
IPTs served to break down the demarcation line of responsibilities and brought together design engineers, marketeers, manufacturers and logisticians into a single team that focused on a specific area. There were a total of 70 IPTs, of which Boeing's share of the fuselage, avionics and subsystems accounted for 52.
IPTs were given specific weight allocations to either stay within or trade off, and were required to brief and review design progress regularly with Navair. "One of the guiding principles of the IPT was to choose the right material for the right application and each team had the authority to do so," says Greg McAdams, Boeing V-22 programme senior manager.
The empty weight of the V-22 ballooned to 15,860kg (34,930lb) by the end of FSD, 1,520kg over the baseline specification. The excess weight was blamed on a mixture of factors, including the over-ambitious use of new materials and FSD flight test fixes. Examples of the latter included the addition of wing fences to improve airflow and hip-mounted strakes to reduce tail buffet at high angles of attack.
Boeing's main goals were to strip out 615kg of airframe weight and cut the fuselage DTC by 26% to $4.7 million. Its solution was to go back and reassess its earlier use of composites, which had extended beyond large sections of skin to include more intricate carbonfibre bulkheads and frames. These were not only more difficult to produce, but required a large number of attachment fasteners, which in turn added weight.
Return to aluminium
The introduction of numeric-control high-speed machining, married to a newly available digital definition of the V-22, made a return to traditional aluminium frames more financially attractive. "The composite frames each weighed 32.4lb [14.7kg]. We did some trials with aluminium frames and brought them in 6lb lighter, using just one part versus 39 and zero fasteners compared to 258," says McAdams.
Composites now comprise 43% of the V-22's airframe structure, down from an FSD high of 57%. Where the material is still predominant, such as the aft fuselage, the earlier hand lay-up processing has been improved radically with the arrival of fibre tow placement. The use of 3mm wide tow, with CATIA design data, has made automated lay-up of convex and concave structures possible.
As a result, where the V-22's aft fuselage used to comprise nine mechanically spliced skins, there is now a single-piece structure. Waste has been cut from 1.57kg to 0.57kg for every 0.45kg of material used. With composites costing about $70 for every 0.45kg, the knock-on effect is a 53% cut in costs.
Boeing reduced the number of fuselage parts by 36%, eliminated 18,500 fasteners out of nearly 55,000 used in the FSD aircraft, improved quality by 180% with better precision and fewer rejects, and slashed costs by 23%. In the end, the company shed 1,216kg from the airframe weight - twice its original goal.
Other major EMD changes included repositioning the V-22's Messier Dowty main landing gear to address a centre-of-gravity problem discovered during FSD testing. "The aircraft had a tendency to tip back on the ground, so we used the same design as in FSD, but flipped the gear 180í and moved it back 1.32m to solve the problem," says Tony Parasida, Boeing V-22programme manager.
More weight was saved by changing the aft loading ramp. After experimenting with a long and short single-piece ramp, the design team settled on a fully closing two-piece split door. This proved not only lighter, but was better for fast roping operations out of the rear without the lower ramp interfering with the vertical line.
Pilot ejection seats used in FSD were dropped from the EMD aircraft. "We already had done most of the critical envelope development we needed," says Buyers. At the same time, mechanically driven cabin escape hatches were replaced with pyrotechnic-activated panels.
EMD entailed a complete redesign of the FSD's bedframe and ballscrew-activated wing stow system. Boeing instead fitted the V-22 with a lighter flexring and hydraulic capstan cable drive to rotate the wing 90í between flight and stowage position. The ring is designed to flex between the wing and body attachment and reduce the effects of wing strain on the fuselage.
Further savings
Further weight and cost savings were generated by Bell with changes in wing, drivetrain and engine nacelle design. Multi-piece wing ribs were adopted to avoid time-consuming shimming, while a switch from machined-out nacelle castings produced combined savings of more than $170,000. Using a forged rather than machined swashplate cut weight by 51.7kg.
A further 88kg and $70,000 was saved by swapping from a mechanical bellow/deflector engine exhaust infrared suppressor to a Coanda effect deflector drawing on high-pressure compressor bleed air.
Elsewhere, improved prop-rotor gearbox lubrication, a reduction in the size of the engine conversion spindle following load tests, and a simplified cast titanium transmission support adaptor trimmed nearly 86kg.
Rolls-Royce's task in EMD was to achieve a 4% improvement in specific fuel consumption for each of the twin AE1107C turboshafts. "This was largely addressed through improved aerodynamics in the compressor and improvements to the hot section," says Greg Becker, R-R director of AE military turboshaft engines.
Engine maintenance procedures and costs were improved through lessons learned supporting the civil-derivative AE2100 turboprop and AE3007 turbofan. The AE1107 has also introduced the military, for the first time, to the concept of on-condition maintenance and a simplified two-tier support plan.
Other improvements made during testing included equipping the AE1107 with a particle separator screen, capable of filtering out 90% of particles 100Ám or larger. The elastomeric spindle bearing was made more robust with a change in rubber material, and the empennage and proprotors were strengthened against lightning strikes. "We found during testing, a number of areas we needed to improve and one was the composite empennage, where we were not sure of the path until we ran the test," says Buyers. "We also had to put some grounding straps on the blades, which are a little bit more difficult to fasten on because it is a composite rotor system and is spinning."
The vibration-suppression system was improved by replacing the FSD active damper with a 31kg lighter dual hydraulic Frahm damper in the nose. "We have two forms, 100% for helicopter mode and 84% for aircraft mode," says Buyers. "There is also a proposal for an electronic-tuned system which will save even more weight."
During EMD, the V-22's wiring was repackaged into flat ribbonised strips. Integrated wiring not only saved 50kg in weight, but by fixing a wire's location and organising signals for compatibility, helped ensure better protection from electromagnetic interference. The only drawback is that no new wires can be added without replacing the entire ribbon.
Fivefold improvement
In the cockpit, a new General Dynamics Information Systems mission computer was installed, providing a fivefold improvement in processing and memory power. The two 100 x 100mm (4 x 4in) monochromatic control display units fitted to the central console of the FSD aircraft were replaced by a single 150 x 200mm colour display.
A new digital standby flight display (SFD) was also added in place of many of the earlier pressure gauges. Displayed data includes nacelle angle, engine performance, hydraulic system health, flap angle and fuel quantity. Conventional airspeed, altitude, artificial horizon and compass instruments are retained.
"All displays in the cockpit, with the exception of the SFD, are driven by the avionics computer," says Dave Moorman, Boeing V-22 chief engineer. "The SFD is driven by the flight control computer, which is triple redundant. You can have a complete failure of the avionics systems and the flight control system will be able to provide enough information for the pilot to land in a worst case."
Planned product improvements call for the 150 x 150mm cathode ray tube multifunction displays to be replaced by four similarly sized active-matrix liquid-crystal displays from the 19th production V-22 onwards. The new displays are 15.9kg lighter, occupy less space and are more readable in sunlight as well as being night-vision-goggle-compatible.
The Dallas-based vendor is already supplying the V-22 digital mapping system and display unit keyboard. "They put together a heck of a proposal that saved us $1 million per aircraft if we bought the lot," says Buyers.
Telescopic boom
Also in the pipeline is a new retractable inflight refuelling probe from Flight Refuelling. The telescopic boom will replace the current 3.3m-long fixed probe, which its too big for the flightdeck elevators of the US Navy's LHA/LHD amphibious helicopter carriers. An earlier 1.5m-long probe was too short to be seen from the left-hand pilot seat.
The new probe will make way for the USMC to begin fitting the MV-22 with a chin-mounted gun turret. "We'll begin forward-fitting the probe starting FY2002. The gun goes in in FY2004," says Schmidt. "The real need is for the probe to work with the gun, so we're putting this in early and retrofitting the gun back to FY2002 aircraft."
The yet-to-be-selected weapon will be integrated with the flight control computer to ensure a safe field of fire, both in helicopter and aircraft flight modes. It is planned to slave the gun to a helmet-mounted sight and the Raytheon AAQ-27 FLIR, as well as to a manual track handle.
AFSOC has its sights on the gun, but has yet to find the extra funding. Instead, it is spending $7-8 million per aircraft on a new sensor package. This comprises the Raytheon APQ-186 terrain following/avoidance radar, a satellite communications terminal and ITT ALQ-211 electronic countermeasures, as well as the MV-22's Lockheed Martin AAR-47 missile warning receiver (MWR) and Raytheon AVR-2A laser warning system.
The ALQ-211 provides a passive radar warning receiver and active jammer. Threat information is colour-coded and displayed on a digital map and can be correlated with pre-mission data or mid-mission updates received via satcom. The CV-22 will also have up to six BAE Systems ALE-47 forward- and rear-firing buckets of flare/chaff expendables, compared to the current MV-22's two dispensers.
Critical mission requirement
The first eight CV-22s will be completed to a Block 00 configuration, after which production will switch to the Block 10, which will include new Northrop Grumman/BAE directed infrared countermeasures. With a software update planned every two years and a hardware upgrade every three years, attention has begun to turn to Block 20, says Schmidt.
AFSOC's critical mission requirement is to take off at 26,330kg, close to the tiltrotor's maximum gross weight, fly 925km (500nm), the last 550km at terrain following height with 18 troops aboard, hover out of ground effect at 915m for 1min, and return 925km. The CV-22, accordingly, will be fitted with eight more wing fuel cells and an aft sponson auxiliary tank, adding more than 3,400 litres (900 USgal) to the MV-22's baseline 4,290 litre capacity.
Full-time engineer
Other CV-22 modifications will include the permanent provision for a full-time flight engineer in the cockpit, an updated mission computer and map display, four Rockwell Collins UHF/VHF radios, a static parachute jump line and rescue hoist.
The rescue hoist must be capable of lifting 272kg but be small enough to stow internally because of proprotor clearance in forward flight mode, all of which has proved a challenge. A Breeze Eastern system has been fitted to an EMD machine, but the airframe is having to be modified to provide extra hydraulic power for the hoist.
CV-22 developmental test flying starts in September at Edwards AFB using two extensively modified EMD aircraft. The two remaining V-22s will stay at Patuxent River for post-EMD testing. The immediate focus is on completing icing trials, expanding the inflight refuelling envelope currently restricted to aircraft mode, improving the reliability of the wing fold system and exploring high sink rates following the Marana crash.
A follow-on test and evaluation programme will include flight testing of the new inflight refuelling probe and gun turret and, in the longer term, possibly improving the V-22's lift capability. A planned advanced technology demonstration of piezoelectric actuators has the potential to improve hover and forward flight blade efficiency by optimising proprotor twist.
In retrospect, the V-22 proved to be an ambitious leap in technology and was not without its setbacks, but Macdonald adds: "If we hadn't gone through that, you probably wouldn't today have tiltrotor." With Bell now channelling its energy into developing the BA609 civil tiltrotor and studying an even larger Quad Tiltrotor, it is clear "America's Airplane" has come of age.
| MV-22/CV-22 PROJECTED CAPABILITIES | |||
| Mission Radius | Key performance parameter | MV-22 projection | CV-22 projection |
| Pre-assault/raid (18 troops) | 370km | 485km | |
| Land assault (24 troops) | 370km | 425km | |
| Land assault (4,540kg load) | 90km | 100km | |
| Amphibious assault (24 troops) (radius) | 2 x 90km | 2 x 170km | |
| Amphibious assault (4,540kg load) | 90km | 210km | |
| Long-range strategic offensive forces missions | 925km | 930km | |
| Sepf-deploy (range with one aerial refuel) | 3,890km | 4,250km | 4,330km |
| MV cruise speed (at maximum continuous power | 240kt | 265kt | |
| CV cruise speed | 230kt | 246kt | |
| Survivability (calibre of round fired) | 12.7mm | 12.7mm | 12.7mm |
| VSTOL/shipboard compatibility | Yes | Yes | Yes |
| Aerial refuelling | Yes | Yes | Yes |
Source: Flight International
