The study is part of a wider biomimetic investigation focusing on flapping wing in water - penguin wing. The long-term aim is to design a hybrid vehicle capable of flying in fluids with very different densities. The paper analyses the dynamic loads on an oscillating wing used for obtaining the trust generated throughout harmonic motion. The strength requirements for such wing have not been analysed up to now and this study is to be followed shortly by experimental simulation in a wind-tunnel. The acting forces in the current analysis were obtained through a potential flow based panel method computer program.