<p>This paper studies the dynamic response of a telescopic beam with variable span length. The telescopic beam mechanism is modeled using a coupled double cantilever beam system, which consists of a host beam that is fixed at its root and a sliding beam that is fixed at its root to a slider that slides over the host beam. The sliding beam is also supported by elastic sliders at the tip of host beam to prevent jamming from large deflections during morphing. The cantilever beams are considered to be rigid and attached to a rotational spring at its root, having stiffness equivalent to the bending stiffness of the respective beams. Inertial and elastic coupling between the beams is captured in this proposed dynamic modeling. The governing equations reveal morphing-induced pseudo-damping, and time-varying stiffness and categorize the telescopic span morphing beam as a non-stationary system due to the changing span. Numerical simulations demonstrate complex dynamics, including energy transfer between beams and transient chaotic response during morphing transitions despite linear modeling. The non-stationary nature of the system parameters during morphing, due to the time varying span length, introduces nonlinear characteristics in the system. Time frequency domain analysis using STFT is performed to analyze non-stationary frequency content of the telescopic beam. Floquet theory is applied to assess stability, revealing destabilizing effects from cumulative disturbances over repetitive morphing cycles. Telescopic systems in practice undergoing repetitive morphing cycles may become unstable due to cumulative dynamic impacts, even if single morphing cycles appear to be stabilized. Effects of morphing speed and relative beam stiffness on dynamics and stability are also investigated. The findings provide insights into designing and controlling telescopic morphing beam systems to ensure stable operation.</p>