The dynamics modeling and payload adaptability of a light-weight flexible one-link manipulator are studied. Using the FEM (Finite-Element Method) model of a flexible manipulator, a lower order Linear Quadratic Gaussian compensator can provide satisfactory performance without controller/observer spillover. Moreover, the payload can be separated from the beam model, therefore, it is expected that the identification algorithm should have better robustness than the other schemes. The simulation results have shown that the proposed payload-adaptation synthesizer, which synthesizes a payload identifier and a nominal regulator/estimator interpolator to obtain a near-optimal compensator, has good adaptability with varying payload. And the resulting synthesizer also provides a near-optimal damping for this sensor-actuator noncolocated system.