Unsteady in-plane forces, also referred to as 1P loads, area critical aspect in open rotor propulsion systems due to theirinfluence on vibration, aeroelastic stability, and structural fatigue.Their accurate quantification is therefore fundamentalfor both aerodynamic performance evaluation and structural design.This study presents a methodology for assessing 1P loadsand their structural implications using an open-rotor geometryrepresentative of modern open-fan concepts. High-fidelityfull-annulus CFD simulations were performed for take-off andcruise conditions, using dedicated meshing strategies to resolveunsteady flow features at angles of attack of up to 30° and 6°, respectively.The global loads are decomposed into thrust and inplanecomponents, with a focus on the 1P harmonic. Unsteadypressures are then projected onto the first bending mode of theblade to obtain modal forces, which are coupled with a singledegree-of-freedom oscillator to predict vibration amplitudes andalternating stresses. Results show that the projection step is critical,as global force harmonics alone fail to estimate the effectivedynamic excitation. The approach enables a direct evaluation ofvibration amplitudes, indicating that oscillation amplitudes remainbelow 1% of the blade span. This approach provides areliable method for the detailed design and fatigue assessment ofopen-fan blades.