Introduction to Aircraft Aeroelasticity and Loads

14

Flight Mechanics Model for Dynamic Manoeuvres

In Chapter 13, the symmetric equilibrium manoeuvre calculations were considered, where the balanced/trimmed condition was sought and inertial axes fixed in space were used, with displacements and angles as unknowns. In this chapter, some basic concepts related to the large angle nonlinear flight mechanics equations of motion of the aircraft, when undergoing dynamic manoeuvres, will be introduced; this analysis will require a body fixed axes system moving with the aircraft, with velocities as unknowns. This is because, in industry, the flight mechanics equations (sometimes with flexible modes or quasi-flexible effects on aerodynamics included) are often used as the basis for performing flight dynamic manoeuvre calculations to determine loads (Howe, 2004) and to assess stability and handling, so assisting in design of the flight control system (FCS). Linearized versions of these equations are often used to enable basic mathematical treatment of the dynamic stability. In Chapter 15, the equations developed here will be applied to simple heave/pitch and roll manoeuvre conditions for both rigid and flexible aircraft. The nonlinear model with flexible modes is sometimes used for landing calculations (see Chapter 17).

The focus will be on ideas relevant to the response due to manoeuvres, and hence internal loads, for the aircraft and not particularly on performance or stability and control/handling issues. Other texts, e.g. Hancock (1995), ...