Across the base, flight testing of the Bell Boeing V-22 Osprey tiltrotor transport is "on a critical path" leading to operational evaluation in 1999. Late delivery of the four development aircraft has left the integrated test team facing the challenges of meeting deadlines for sea trials, operational evaluation and testing of the CV-22 special-operations derivative - "-those dates are not slipping", says Phil Dunford, director of V-22 operations and flight test.
The testing pace is picking up after a period when the V-22s were grounded for modifications to bring them up to the latest standard. "The aircraft-are really starting to perform well," Dunford says.
To date, the V-22 has been flown to 342kt (630km/h), close to the specification speed of 345kt; reached the specification altitude of 25,000ft (7,600m); taken off at the specification maximum weight of 27,400kg; and, at 3.9G, exceeded the specification load factor of 3.8G.
Aircraft 7, the first of four "production representative" V-22s in the development programme, "-is on the critical path from a development standpoint", says Dunford. The aircraft must complete a formal flight loads survey and mission manoeuvre evaluation before becoming one of two aircraft in the CV-22 development programme. Aircraft 10, meanwhile, must be used for 120h of operational test pilot training before sea trials in January 1999 and operational evaluation later next year.
Aircraft 8 is heading into external loads testing, followed by evaluation of high AoA handling qualities and high altitude hover performance. After completion of development testing, aircraft 8 will be deployed to Nova Scotia, Canada, for almost six months of icing clearance tests, between 1999 and 2000.
Aircraft 9 is assigned to propulsion and systems testing. After development of the basic MV-22 transport variant of the US Marine Corps is completed, the aircraft will be remanufactured to the production configuration for the US Air Force's CV-22 special-operations version. Aircraft 7 and 9 will be deployed to Edwards AFB, California, for CV-22 development testing beginning in 2000.
PREVIOUS EXPERIENCE
Although the fixed deadlines for sea trials, operational evaluation and the start of CV-22 development do not give the test team much room for manoeuvre, it has the benefit of considerable flight test experience gained in two previous phases of the V-22 programme.
The original contract was awarded in 1986, and the first full scale development (FSD) V-22 flew in March 1989. Five FSD aircraft flew - and two were lost in accidents - before the contract was terminated in October 1992. It was replaced by a new engineering and manufacturing development (EMD) contract with two phases: risk reduction flight testing using two FSD aircraft; and EMD flight testing using four production representative V-22s.
The risk reduction phase covered 450h of tests to expand the flight envelope, measure flight loads, optimise flight controls and evaluate "high risk" issues such as proprotor downwash. "At the end of FSD, the flight envelope had lots of limits, and there were lots of loads issues," Dunford says. For example, he says, six aeroservoelastic issues were identified in FSD. These were fixed during the risk reduction phase with software changes to the triplex redundant fly by wire flight control system, "-and have not been seen in EMD".
One of the issues encountered during FSD was the severe tail buffet observed in wind-up turns at moderate speed. This was traced to airflow separation caused by stalling of the inboard wing, and was cured by fitting forebody strakes. An AoA limiter was added to the flight control system to provide additional protection. On 21 May, the team did its first test without the limiter "-and did not run into buffet until 4G, right in the corner of the flight envelope", he says.
Tailoring of the flight control system continues. A software upgrade is planned for June to overcome handling qualities issues uncovered during flight tests in conversion mode behind a KC-130 aerial refuelling tanker. "We hit the control limits and that needs a software fix, which should be in before the loads survey begins," Dunford says.
Flight testing of the V-22 is complicated by the need to evaluate the aircraft's performance in three different modes: helicopter, aeroplane and conversion. Aeroplane mode handling qualities are "excellent", Dunford says.
One major change between the FSD and EMD programmes was the creation on an integrated contractor/government test team comprising Bell Boeing, US Navy, Marine Corps and Air Force personnel, and both development and operational test pilots.
"It's a lot different to the way it was done," says Dunford's counterpart, government flight test director Lt Col John Rudzis. Compared to previous flight test programmes, "-the Government gets involved in the envelope development and structural validation of the aircraft, while the contractor gets more involved in operational concerns," he says. "The big driver is the savings in time and cost; the big advantage is that everybody gets a better look at the aircraft," Rudzis says,
Dunford agrees: "In the past, we did not get involved in operational stuff. Now the contractor gets a better handle on operational concerns, while the Government gets a better understanding of development issues. We've done a lot more operational work." Recent examples include night flying using the forward looking infrared sensor and night vision goggles.
Operational fleet pilots are being qualified to fly as copilots on development test flights. "This will allow them to get familiar with the aircraft before going into operational evaluation," Dunford says. The Marine Corps will soon take over maintenance of aircraft 10, which will be used for the operational evaluation, along with three low rate initial production MV-22s.
AGGRESSIVE SCHEDULE
Key to meeting the aggressive test schedule will be keeping the four development aircraft flying. "Productivity is not a good as we want to to be, "Dunford says. Reliability is mixed. "Aircraft 8 just flies and flies, while 7 is the least reliable," he says. Aircraft 8 and 10 have averaged 20h/m, compared with a budgeted 15h. "We've got to get all four doing the same," he says.
The next milestone will be the fourth block of operational testing, scheduled for September-October, using aircraft 9 and 10. Aircraft 10 is then scheduled for sea trials in January 1999 - initial sea trials having been performed in late 1990 using two FSD aircraft.
The need to release aircraft 7 and 9 for the CV-22 programme is also pacing the test effort. "This the critical path for both aircraft. The CV schedule is not slipping, "Dunford says. After completing loads testing, aircraft 7 will be fitted with the CV-22's terrain following/terrain avoidance radar, fuel system and radios for development testing. Remanufacturing aircraft 9 will take about a year, after which it will be used for radar qualification testing.
Keeping track of development test progress is vital, Dunford says. A database is used which turns test events into earned value. "It's the best database for tracking what we're doing, but you have to stay 100% on top of it," he says. "We didn't control the programme well in FSD, but we have as good a handle as we can on EMD."
Source: Flight International
