Osprey resumes flight test; tiltrotor future far from certain

 - April 21, 2008, 6:00 AM

With little fanfare and a lot of crossed fingers, flight test of the embattled Bell Boeing MV-22 Osprey resumed in the final days of May at the U.S. Navy’s Patuxent River Naval Air Station in Maryland. The first day’s flight test since the tiltrotor design was grounded 17 months ago ended on May 29 with 2.5 hr logged, during which gradual hover and gentle takeoff and landing maneuvers gave way to a full conversion from helicopter to fixed-wing mode and airplane flight at speeds up to 250 kt.

“The long awaited return to flight was a success,” reported Marine Corps Col. Dan Schultz, MV-22 program manager. “The Osprey not only performed what today’s test program called for but exceeded our wildest expectations. We are excited about being back in the flight-test business.”

Tom McDonald and Bill Leonard, senior Bell Boeing V-22 integrated test team pilots (with a combined total of 13,000 flight hours between them, both fixed- and rotary-wing time, and 500 hr each in the MV-22), spent a large portion of the flight-test day converting from helicopter to fixed-wing mode to record standard vibration measurements aimed at evaluation of the tracking and balance of each of the three blades on the Osprey’s two proprotors.

MacDonald and Leonard trained for their flight by means of a dress-rehearsal simulation in Bell’s flight simulator at Patuxent River. There the two pilots practiced the flight using the actual test cards they would later use, as well as procedures developed by the Bell Boeing telemetry room engineering team, the same team that directs actual test flights and monitors progress and performance in the control room.

Five Ospreys for Flight Test
Over an 18-month developmental flight-test period, a pair of engineering, manufacturing and development (EMD) MV-22s and three MV-22 production aircraft, all of which have been fitted with many of the improvements mandated by a military review panel and an independent NASA survey, will take to the air to evaluate those changes. The targeted total number of flight hours is 1,800. An upcoming landmark of the program will be delivery and first flight of the first Marine Osprey built from the ground up and incorporating the latest in required design changes, an event set to take place late next year.

While the Marines are testing their Ospreys, the U.S. Air Force is expected to resume testing of its Osprey variant, known as the CV-22, at Edwards Air Force Base this month. The Air Force has two EMD Ospreys it is developing for the special operations/combat search-and-rescue mission. That testing will focus mainly on terrain-following flight and electronic warfare.

“Now that we have an approved ‘way ahead’ plan, we return to flight with a methodical and event-driven test program that will deliver an aircraft to the fleet that is safer and more capable than ever before. ‘Event driven’ means the V-22 program progress is based on a clearly articulated set of accomplishments, not a date,” said Schultz. “The new comprehensive flight-test program will put ‘X’s’ in the outer corners of the flight envelope.”

Schultz stressed that the flight-test program just resumed will involve the most extensive testing of what’s known as the “vortex ring state” ever undertaken. It is this “settling with power” condition that is widely suspected as the cause of at least one of the two fatal Osprey crashes that largely led to the MV-22’s grounding a year-and-a-half ago. “In this regard, we will dedicate one aircraft for one year of high-rate descent testing and set the standard for flying every conceivable approach to this kind of situation,” he said.

Other flight regimes to receive special scrutiny will be formation flight, low-speed hovering and landings (with nacelles tilted slightly forward, the MV-22 can perform run-on STOL-type landings and takeoffs), icing, cargo-handling and radar warning systems.

Many Modifications
The MV-22 has undergone a broad range of modifications over the past 17 months, most of them as per recommendations from DOD and NASA panels. Chief among them are modifications to the convertiplane’s controversial 5,000-psi high-pressure hydraulic system and rerouting of electrical lines, especially in the proprotor nacelles where failures of chafed electrical lines contributed to wear and subsequent cracking of the Osprey’s hydraulic control lines. This wear is the suspected cause of the MV-22 crash that claimed the lives of four Marines early last year.

Fixes for these conditions include line-clearance modifications intended both to eliminate wear and make it easier to inspect those lines; additional clamps to reduce the effects of vibration; and more tape under those clamps to minimize wear.

Overall, the interior nacelle configuration is being redesigned in ways the Marines and the manufacturers have not yet announced.

Software for this fly-by-wire transport is scheduled to be upgraded, an ongoing process that will be a part of the next three Osprey production blocks.

Last spring the Bell Boeing tiltrotor team was awarded an additional $770 million earmarked for production of another 11 Ospreys, work that will, at the present low rates of production, keep the world’s only tiltrotor production lines busy until 2005. Sometime between late 2004 and early 2005 a final go/no go production decision on full-rate Osprey production is planned. At stake is a production run of as many as 360 tiltrotor transports and an estimated $40 billion in revenue.