Aerodynamic Design of Nacelle-Mounted Sails for Flight Test Demonstration on the V-22 Osprey Tiltrotor

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Why is it important?

This paper details the aerodynamic design and wind tunnel testing of the nacelle-mounted sails for the V-22 Osprey tiltrotor aircraft. Several Boeing wind tunnel tests dating back to the early 80’s have shown great potential for improving the tiltrotor aerodynamic efficiency in cruise using nacelle-mounted sails. In 2008, a Boeing wind tunnel test of a 15%-scale model V-22 provided data on the effects of various sail design parameters. These included incidence, dihedral, and position on the nacelle. The goal of the test was to demonstrate that a set of full-scale representative sails would provide the target level of drag reduction on a flight test aircraft. The test also provided the opportunity to optimize a configuration that provided the best lift-to-drag ratio in cruise flight, therefore reducing the amount of flight testing that would be needed. The optimum design tested in the wind tunnel was a set of three sails per nacelle that provided an 8 percent increase in the cruise lift-to-drag ratio. On an aircraft, this improvement would yield a cruise drag reduction of approximately 10 percent. This improvement would amount to a nearly 5 percent increase in the performance margin for the Marine and the Air Force Self Deployment range capability. Data from the flight test is expected to provide design guidance for production implementation.