An accurate aeroelastic assessment of powered HALE aircraft is of paramount importance considering that their behaviour contrasts the one of conventional aircraft mainly due to the use of high aspect-ratio wings with distributed propulsion systems. This particular configuration shows strong dependency of the wing natural frequencies to the propulsion distribution and operating conditions. Numerical and experimental investigations are carried out to better understand the behaviour of flexible wings, focusing on the effect of distributed electric propulsion systems. Several configurations are investigated, including a single propulsion system (composed of the electric motor, propeller, and the wing-propulsion mounting POD) installed at selected spanwise positions, and configurations with two and three propellers. References: Amato, E.,Polsinelli, C.,Cestino, E.,Frulla, G.,Carrese, R.,Marzocca, P. (2016). "Elasto-static and modal modeling on flexible wings carrying multiple external stores", Proceedings of the 30th Congress of the International Council of Aeronautical Sciences (ICAS 2016), Daejeon, South Korea, 25-30 September 2016 An, Sui. "Aeroelastic design of a lightweight distributed electric propulsion aircraft with flutter and strength requirements." PhD diss., Georgia Institute of Technology, 2015. K. Abbas, Q. Chen, P. Marzocca and A. Milanese, “Nonlinear Aeroelastic Investigations of Store(s)-Induced Limit Cycle Oscillation,” Part G: Journal of Aerospace Engineering, Vol. 222, No. 1, 2008, pp. 63-80. E. Cestino, G. Frulla, E. Perrotto and P. Marzocca, ”Experimental slender wing model design by the application of aeroelastic scaling laws”, Journal of Aerospace Engineering, Vol. 27, No. 1, 2014, pp 112-120.