  Tiny flying insects of body lengths under 2 mm use the `clap-and-fling'
mechanism with bristled wings for lift augmentation and drag reduction at
chord-based Reynolds number ($Re$) on $\mathcal{O}$(10). We examine wing-wing
interaction of bristled wings in fling at $Re$=10, as a function of initial
inter-wing spacing ($\delta$) and degree of overlap between rotation and linear
translation. A dynamically scaled robotic platform was used to drive physical
models of bristled wing pairs with the following kinematics (all angles
relative to vertical): 1) rotation about the trailing edge to angle
$\theta_\text{r}$; 2) linear translation at a fixed angle ($\theta_\text{t}$);
and 3) combined rotation and linear translation. The results show that: 1)
cycle-averaged drag coefficient decreased with increasing $\theta_\text{r}$ and
$\theta_\text{t}$; and 2) decreasing $\delta$ increased the lift coefficient
owing to increased asymmetry in circulation of leading and trailing edge
vortices. A new dimensionless index, reverse flow capacity (RFC), was used to
quantify the maximum possible ability of a bristled wing to leak fluid through
the bristles. Drag coefficients were larger for smaller $\delta$ and
$\theta_\text{r}$ despite larger RFC, likely due to blockage of inter-bristle
flow by shear layers around the bristles. Smaller $\delta$ during early
rotation resulted in formation of strong positive pressure distribution between
the wings, resulting in increased drag force. The positive pressure region
weakened with increasing $\theta_\text{r}$, which in turn reduced drag force.
Tiny insects have been reported to use large rotational angles in fling, and
our findings suggest that a plausible reason is to reduce drag forces.
