The Unsteady Vortex-Lattice Method provides a medium-fidelity tool for the prediction
of non-stationary aerodynamic loads in low-speed, but high-Reynolds-number,
attached
flow. Despite a proven track record in applications where free-wake modelling
is critical, other models based on potential-flow theory, such as the Doublet
Lattice and thin-aerofoil approximation, have been favoured in fixed-wing aircraft
aeroelasticity and
flight dynamics. This dissertation presents how the Unsteady
Vortex-Lattice Method can be re-engineered as an enhanced alternative to those
techniques for diverse situations that arise in
flexible-aircraft dynamics. A historical
review of the methodology is included, with latest developments and practical applications.
Different formulations of the aerodynamic equations are outlined, and they
are integrated with a nonlinear beam model for the full description of the dynamics
of a free-flying
flexible vehicle, which furnishes a geometrically-nonlinear description
of both structure and aerodynamics. Nonlinear time-marching captures large
wing excursions and wake roll-up, and the linearisation of the equations lends itself
to a seamless, monolithic state-space assembly, particularly convenient for stability
analysis. The aerodynamic model and the unified framework for the simulation of
high-aspect-ratio planes are exhaustively verified by comparing them to lower- and
higher-fidelity approaches. Numerical studies emphasising scenarios where the Unsteady
Vortex-Lattice Method can provide an advantage over other state-of-the-art
tools are presented. Examples of this comprise unsteady aerodynamics in vehicles
with coupled aeroelasticity and
flight dynamics, and in lifting surfaces undergoing
complex kinematics, large deformations, or in-plane motions. Geometric nonlinearities
are shown to play an instrumental, and often counter-intuitive, role in the
aircraft dynamics. The Unsteady Vortex-Lattice Method is unveiled as a remarkable
tool that can successfully incorporate them in the unsteady aerodynamics modelling.