Because of this lack of blade flexibility, sharp maneuvers have caused new lightweight composite parts in V-22s to break during testing, so further tests were recently cancelled. The Fort Worth Star-Telegram published an investigative report on September 26, 2004 by Bob Cox on recent V-22 testing which noted: 

Some testing was done. But a series involving specific, sharp defensive maneuvers was skipped after Bell engineers warned that it would severely damage the rotors, according to a source within the testing program who asked not to be identified for fear of losing his job.

Several people told the Star-Telegram that the canceled tests are important.

Program officials feared the maneuvers would damage the aircraft.

Tom Christie, the chief weapons tester for the Pentagon, acknowledged to the Star-Telegram that the "most severe maneuvers" were not conducted during recent testing. When asked whether the skipped tests signal shortcomings that could affect the V-22's performance in combat, he did not answer directly.

"The tactical implications of this limitation have been carefully considered and will continue to be reviewed," he said.

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In short; the V-22 cannot perform combat maneuvers around an LZ, or turn sharply to avoid small obstacles in an LZ, lest it roll over and kill everyone.  When flying into unknown LZs at night or in poor weather, it is not uncommon for a helicopter crew to notice a fence, ditch, large hole, cow, telephone wire, or other things right where they want to land, so the pilots must make a sharp maneuver to land nearby, which may surprise other helicopters in a formation causing them to maneuver sharply.  

However, the V-22 is not a helicopter, it is more like a carrier aircraft.  It may look nimble during demonstrations when it has no payload and little fuel.  But when fully loaded, the V-22 must make an "approach" on a nice steady glide path.  If pilots attempt evasive maneuvers to avoid ground fire or obstacles, they may cause a rotor thrust imbalance and roll over, or may overstress the rotor system, causing something to break, resulting in an instant snap roll.  This tendency to roll over is deadly, and only occurs in tiltrotors like the V-22 due to the side-by-side placement of the rotors. 

So will the V-22 pass the current four months of operational evaluation?  Maybe, because this recent GAO report GAO Defense Acquisitions Assessments states that it may go through this final test phase with safety restrictions in place which limit the type of maneuvers pilots are allowed to perform.  And keep in mind the final V-22 design will not be complete until 2009 (or later) when the "Block C" design is ready, which calls for dozens of changes and weight additions; like the gun and external hoist.  

So when they state they are almost finished with testing, keep in mind they are really testing incomplete prototypes which may not be required to perform combat maneuvers. And they still haven't solved several subsystems issues.  For example, the engine oil cooling fan (blower) has been a critical problem since 2001, and it continues to fail so is replaced every 100 hours.  Apparently, the rotor downwash is so great that it becomes clogged and they have no solution.  

Three years ago, after over a decade of development, the V-22 was declared ready to resume flight tests after a 17-month stand down to redesign this aircraft after its fourth crash.  Marine Colonel Dan Schultz, the V-22 program manager, proclaimed: "All of the things that were wrong with this airplane have been fixed."  Yet we still see:

MV-22 STARTS OPEVAL AFTER DEALING WITH MORE GEARBOX PROBLEMS
Inside the Navy  Date: April 4, 2005

The V-22 Osprey program reached a watershed moment on the morning of March 28, when the Navy officially began the operational evaluation for the Marine Corps version of the aircraft, but not before the program wrestled a bit more with proprotor gearbox problems that resurfaced last month, shortly after a senior Navy acquisition official declared them resolved.
Bell Helicopter Textron is teamed with Boeing on the V-22 program, which is being developed primarily for the Marine Corps. The Osprey has the capability to take off and land vertically like a helicopter, but also to rotate its nacelles in flight to fly like a plane.
Ultimately, the proprotor gearbox problem was deemed a low risk in terms of safety of flight, clearing the way for the start of the operational evaluation, said Ward Carroll, the Navy’s V-22 spokesman. A Pentagon source confirmed that account.

The operational evaluation (OPEVAL), which is expected to run through the end of June, will determine if the Marine Corps MV-22 is operationally suitable and effective for military use. Two fatal crashes during operational testing in 2000 led the Pentagon to restructure the program. Since then, a lot of improvements have been made to the aircraft and the overall program, officials maintain. If the Osprey performs well in the new test phase, it will increase the likelihood the Pentagon will buy the aircraft in large numbers.

But getting the new operational evaluation under way took a bit longer because of a recurrence of proprotor gearbox problems March 11, which prompted further investigation of an issue the Navy had described as resolved.  The gearbox is supposed to translate engine power into rotor torque. But the mechanism can fail if small bits of metallic particulate matter get into the Osprey’s engine lubrication system. For that reason, the proprotor gearbox is hooked up to a warning light that illuminates if chips of metallic particulate are detected in the system.

In January, the Navy announced VMX-22, the V-22 Osprey test squadron in New River, NC, had halted Osprey flights because several aircraft experienced gearbox problems. The program office said Jan. 18 that sensors had detected that problem six times, including three incidents “in the last month.” When encountered in flight, this kind of emergency requires the pilot to land as soon as possible. At the time, the program office blamed manufacturing errors for the problems, noting those causes had been identified and were being addressed.

Initial engineering investigations revealed two root causes, both relating to components in the proprotor gearbox, the program office said in a statement to the media. Investigators discovered “improper torquing of the planetary support bearing nut” occurred during the assembly of the proprotor gearbox. This “has been remedied by a modification of shop floor procedures affecting a stricter adherence to published torque specifications,” the statement said.

The second root cause was “improper chroming of bearings within the input quill during the bearing manufacturing process,” the program office said. The input quill is the first point of attachment between the proprotor gearbox and the engine’s drive shaft. Ultimately, the program decided to address this issue by having industry qualify, build and deliver non-chromed bearings.
But the statement failed to mention that one of the six incidents -- a Dec. 20 event that affected Osprey No. 41 -- had an unknown root cause. Carroll acknowledged this last week after being questioned by Inside the Navy.

“The third root cause was originally unknown and, due to the fact it had occurred only once, resolution was prioritized behind solving the chroming process,” Carroll told ITN last week.  By late February, the program and a senior Navy acquisition official characterized the gearbox problems as resolved. Thomas Laux -- the Navy’s program executive officer for air anti-submarine warfare, assault, and special mission programs -- issued a certification Feb. 24 declaring the V-22 Osprey program ready to begin an operational evaluation. This signaled Laux’s “satisfaction with the resolution” of the gearbox problems, a statement from the program office noted at the time.

But there was still the matter of the Dec. 20 incident with the unknown root cause. A reminder came March 11 when there was a seventh incident involving a gearbox problem that experts later decided was similar to the Dec. 20 event. Carroll acknowledged the March 11 incident for the first time in comments to ITN last week, noting pilots flying Osprey No. 56 had a chip caution light on the left-hand proprotor gearbox. The “initial teardown and metallurgical analysis” determined that that gearbox had also experienced a failure of the high speed planetary support bearing, he said. Further, the failure mode was identical to the “other unknown root cause,” he said.

  Rear Adm. David Architzel, commander of the Navy’s operational testing force, insisted on a complete root-cause analysis and sought assurance that the problems would present a low risk in terms of safety of flight, said a Pentagon source. Carroll said the engineering team’s focus “shifted to solving the previously unknown root cause.”  V-22 officials have since modified flight procedures during deceleration with the expectation that this will prevent the problem, said the Pentagon source. A long-term solution might involve changes for components in the gearbox, said the source.

Carroll said deeper investigation of in-flight data for these two occurrences revealed that “the most likely root cause was also an excessive axial load on the support bearing.” This was due to “a zero mast torque flight condition” (when the gearing has little to no friction and therefore is not providing torque to the proprotor) that engineers believe was caused by a routine procedure for V-22 pilots.  This procedure was an unloading on the assembly that occurred when the throttle was abruptly pulled to the aft stop and proprotor speed was increased from 84 percent to 100 percent, Carroll said.

For the time being, the V-22 test squadron and the program office have jointly developed a standardization manual change and flight clearance update to limit the zero torque condition. The safety assessment remains low risk, said Carroll.  Architzel and other defense officials held a V-22 meeting March 25 to discuss the gearbox problems and solutions, paving the way for last week’s announcement on the start of the operational evaluation.  The Air Force version of the aircraft, called the CV-22, is scheduled to undergo a separate operational testing phase late next year.

-- Christopher J. Castelli