Tilt rotor aeromechanics phenomena in low speed flight

This work investigates important aeromechanics phenomena affecting the V-22 tilt rotor in low speed sideward flight or while hovering in quartering or crosswind conditions. These phenomena, such as pitch-up with sideslip and increased power required in sideward flight, were identified during V-22 critical azimuth flight testing and impacted handling qualities in this flight regime. High fidelity, dynamic, unsteady, Navier-Stokes computational fluid dynamics (CFD) calculations are presented and compared with flight test data. CFD predicts the flight test trends as a function of wind direction, in good agreement with data. Detailed investigation clearly shows the interaction of the rotor wake with the airframe as the major cause of the aeromechanics phenomena seen on the V-22. Identification of the underlying flowfield physics allows investigation of options for alleviation and prediction of future tilt rotor configurations.

1. Introduction

Tilt rotor aircraft are recognized for their significant potential impact on both military and civilian aviation. The range and speed of a turboprop airplane is augmented by the ability to operate in and out of confined areas like a helicopter. For civilian operations this means reduced impact on an overloaded airspace system and reduced infrastructure costs. For military operations, increased payload and range with reduced aerial refueling operations are possible when compared with helicopters currently performing the same remote area missions. Taking advantage of the helicopter mode capability allows tilt rotors to hover in place, maneuver around an airfield at low speed, and conduct shipboard operations with wind over the deck. The V-22 Osprey is the first production military tilt rotor aircraft.