Tilt Could Get Twisted as Test Flights Continue

 - May 7, 2008, 5:28 AM

While the immediate effect on the ongoing tests of the MV-22 Osprey tiltrotor is questionable, the U.S. Navy’s Office of Naval Research (ONR) has reportedly awarded Boeing a $10.25 million contract to look into the workability of a reconfigurable rotor-blade design as part of the overall reevaluation of the troubled convertiplane. Such a blade would use advanced shape-memory alloys to alter the twist of the blade during different flight regimes. One of the principal criticisms of the MV-22 is that in helicopter mode, its rotor diameter is too small and hence its rotor disk loading too high. Conversely, in straight-and-level flight, the proprotor diameters are too large, developing too much drag in proportion to their forward speed. According to a Marine Corps statement, “Shape-memory actuators integrated into the proprotor spar would enable the proprotor spar’s twist to be decreased or increased from the present 47-degree root-to-tip twist. A decrease would improve hover efficiency, while an increase could boost the MV-22’s forward-speed performance enough to allow transport of as much as 3,000 lb of additional payload or as much as 30 kt more forward speed.

Meanwhile, flight test of the first low-rate initial production MV-22 has resumed at Bell Helicopter’s Amarillo, Texas tiltrotor assembly center. This particular MV-22, also known as aircraft number 21, had just begun flight tests when such flights were suspended in December 2000 following a pair of fatal accidents and a widespread program scandal within Marine Corps management. That aircraft is scheduled to join the Marines’ flight-test program at Marine Corps Air Station New River, N.C., this month. Eventually the flight-test program is expected to employ eight prototype MV-22s. The two flying MV-22s are focusing on tiltrotor performance during high rates of descent and evaluation of aircraft behavior in settling-with-power conditions, also known as vortex ring state. Flight tests intended to verify tiltrotor performance within the boundaries of this phenomenon will continue for several months according to Michael Tkach, vice president and director of the Bell-Boeing joint program office.

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