A new method to estimate bending moments of a blade specimen having a constant cross section throughout was developed using fiber Bragg grating sensors. Based on theories of solid mechanics, strains of the simplified model of the specimen were evaluated for various pitching angles and the forces exerted. It was found by both theory and experiment that at least two FBG sensors are necessary to find out the magnitude and direction of the load acting on the specimen from measured longitudinal strain information. A method was also found to estimate the flatwise and edgewise bending moments from the measured strains. An experimental setup that enables pitching the specimen from $0^{circ}$ to $180^{circ}$ was used to experimentally verify the theoretical findings. The theory and the experimental results showed a fair agreement.