Blade element modelling provides a quick analytical
method for estimating the aerodynamic forces produced
during insect flight, but such models have yet to
be tested rigorously using kinematic data recorded
from free-flying insects. This is largely because
of the paucity of detailed free-flight kinematic
data, but also because analytical limitations in
existing blade element models mean that they
cannot incorporate the complex three-dimensional
movements of the wings and body that occur
during insect flight. Here, we present a blade
element model with empirically-fitted aerodynamic
force coefficients that incorporates the full threedimensional wing kinematics of manoeuvring Eristalis
hoverflies, including torsional deformation of their
wings. The two free parameters were fitted to a large
free-flight dataset comprising N = 26, 541 wingbeats,
and the fitted model captured approximately 80%
of the variation in the stroke-averaged forces in
the sagittal plane. We tested the robustness of
the model by subsampling the data, and found
little variation in the parameter estimates across
subsamples comprising 10% of the flight sequences.
The simplicity and generality of the model that we
present is such that it can be readily applied to
kinematic datasets from other insects, and also used
for the study of insect flight dynamics.
