  Perching with winged Unmanned Aerial Vehicles has often been solved by means
of complex control or intricate appendages. Here, we present a simple yet novel
method that relies on passive wing morphing for crash-landing on trees and
other types of vertical poles. Inspired by the adaptability of animals' and
bats' limbs in gripping and holding onto trees, we design dual-purpose wings
that enable both aerial gliding and perching on poles. With an upturned nose
design, the robot can passively reorient from horizontal flight to vertical
upon a head-on crash with a pole, followed by hugging with its wings to perch.
We characterize the performance of reorientation and perching in terms of
impact speed and angle, pole material, and size. The robot robustly reorients
at impact angles above 15{\deg} and speeds of 3 m/s to 9 m/s, and can hold onto
various pole types larger than 28% of its wingspan in diameter. We demonstrate
crash-perching on tree trunks with an overall success rate of 71%. The method
opens up new possibilities for the use of aerial robots in applications such as
inspection, maintenance, and biodiversity conservation.
