Velocity vector files from PIV measurements of the wake behind a flying beetle

These are the velocity vector files from the PIV measurements in the wake
of Batocera rufomaculata flying tethered in a wind tunnel. The data
correspond to the manuscript:  The aerodynamics and power
requirements of forward flapping flight in the mango stem borer beetle
(Batocera rufomaculata), by Urca et al. published by the journal
Integrative Organismal Biology.  The abstract of the coresponding
paper is:  The need for long dispersal flights can drive
selection for behavioral, physiological and biomechanical mechanisms to
reduce the energy spent flying. However, some energy loss during the
transfer of momentum from the wing to the fluid is inevitable, and
inherent to the fluid-wing interaction. Here, we analyzed these losses
during the forward flight of the mango stem borer (Batocera rufomaculata).
This relatively large beetle can disperse substantial distances in search
of new host trees, and laboratory experiments have demonstrated continuous
tethered flights that can last for up to an hour. We flew the beetles
tethered in a wind tunnel and used high-speed videography to estimate the
aerodynamic power from their flapping kinematics and particle image
velocimetry (PIV) to evaluate drag and kinetic energy from their unsteady
wakes. To account for tethering effects, we measured the forces applied by
the beetles on the tether arm holding them in place. The drag of the
flying beetle over the flapping cycle, estimated from the flow fields in
the unsteady wake, showed good agreement with direct measurement of mean
horizontal force. Both measurements showed that total drag during flight
is ~5-fold higher than the parasite drag on the body. The aerodynamic
power estimated from both the motion of the wings, using a quasi-steady
blade-element model, and the kinetic energy in the wake, gave mean values
of flight-muscle mass-specific power of 87 and 65 W kg muscle-1,
respectively. A comparison of the two values suggests that ~25% of the
energy is lost within the fluid due to turbulence and heat. The muscle
mass-specific power found here is low relative to the maximal power output
reported for insect flight muscles. This can be attributed to reduced
weight support during tethered flight or to operation at submaximal output
that may ensure a supply of metabolic substrates to the flight muscles,
thus delaying their fatigue during long-distance
flights.