  Flapping Wing Micro Air Vehicles (FWMAV) are highly manoeuvrable,
bio-inspired drones that can assist in surveys and rescue missions. Flapping
wings generate various unsteady lift enhancement mechanisms challenging the
derivation of reduced models to predict instantaneous aerodynamic performance.
In this work, we propose a robust CFD data-driven, quasi-steady (QS) Reduced
Order Model (ROM) to predict the lift and drag coefficients within a flapping
cycle. The model is derived for a rigid ellipsoid wing with different
parameterized kinematics in hovering conditions. The proposed ROM is built via
a two-stage regression. The first stage, defined as `in-cycle' (IC), computes
the parameters of a regression linking the aerodynamic coefficients to the
instantaneous wing state. The second stage, `out-of-cycle' (OOC), links the IC
weights to the flapping features that define the flapping motion. The training
and test dataset were generated via high-fidelity simulations using the overset
method, spanning a wide range of Reynolds numbers and flapping kinematics. The
two-stage regressor combines Ridge regression and Gaussian Process (GP)
regression to provide estimates of the model uncertainties. The proposed ROM
shows accurate aerodynamic predictions for widely varying kinematics. The model
performs best for smooth kinematics that generate a stable Leading Edge Vortex
(LEV). Remarkably accurate predictions are also observed in dynamic scenarios
where the LEV is partially shed, the non-circulatory forces are considerable,
and the wing encounters its own wake.
