  Unmanned Aerial Vehicles (UAVs) are an important component of next-generation
wireless networks that can assist in high data rate communications and provide
enhanced coverage.Their high mobility and aerial nature offer deployment
flexibility and low-cost infrastructure support to existing cellular networks
and provide many applications that rely on mobile wireless communications.
However, security is a major challenge in UAV communications, and Physical
Layer Security (PLS) is an important technique to improve the reliability and
security of data shared with the assistance of UAVs. Recently, Intelligent
Reflecting Surfaces (IRS) have emerged as a novel technology to extend and/or
enhance wireless coverage by re-configuring the propagation environment of
communications. This paper provides an overview of how IRS can improve the PLS
of UAV networks. We discuss different use cases of PLS for IRS enhanced UAV
communications and briefly review the recent advances in this area. Then based
on the recent advances, we also present a case study that utilizes alternate
optimization to maximize the secrecy capacity for IRS enhanced UAV scenario in
the presence of multiple eavesdroppers. Finally, we highlight several open
issues and research challenges to realize PLS in IRS enhanced UAV
communications.
