IN-FLIGHT ESTIMATION OF HELICOPTER GROSS WEIGHT AND MASS CENTER LOCATION

The ability to compute the weight and balance of a helicopter in flight under general conditions is an enabling technology for future condition based maintenance systems as well as advanced automatic flight control systems. This paper creates a real-time weight and balance estimation algorithm using an extended Kalman filter framework. To highlight estimation characteristics, the algorithm is exercised on the OH-6A helicopter in a variety of flight regimes. The algorithm is shown to work well in hover and forward flight as well as situations where loads are dropped and picked up in flight. Typically the algorithm quickly estimates station line and butt line mass center position (1 sec) and more slowly converges on helicopter weight (10 sec). To estimate helicopter waterline, the algorithm requires maneuvering flight where non zero roll rate is present. The algorithm is also shown to be reasonably robust to sensor and model errors. NOMENCLATURE zyx,, : Components of helicopter mass center position vector in an inertial frame.,,φ θ ψ: Euler roll, pitch and yaw angles of helicopter.,,u v w: Components of mass center velocity of helicopter in the helicopter reference frame.,,p q r: Components of angular velocity of helicopter in the helicopter reference frame.,m W : Mass and weight of helicopter. HI: Inertia matrix of helicopter about its mass center. BI: Flapping inertia of rotor blade.,,X Y Z : Total force on the helicopter in the helicopter reference frame.,,L M N : Total moment on the helicopter about the mass center in the helicopter reference frame. HT: Transformation matrix from inertial reference frame to helicopter reference frame