High altitude span loader aircraft experience significant wing bending mainly due to turbulence of spanwise scale comparable to the wing. These moments are often the primary wingspar design loads. Spanloaders with a few concentrated loads on the wing are called semi-span loaders. Typical of this class is a family of unmanned solar-powered vehicles developed by AeroVironment of California, which have spans up to 250ft and flight speeds of about 30fts-’ equivalent. An aeroelastic model of the wing moments induced by turbulence varying in both spanwise and flightwise directions has been developed. The model treats flexural displacements and torsional deflection, runs rapidly in Excel® format, and can be used to study many different design and gust cases, thus it is a powerful tool for multi-disciplinary optimisation. The procedure was exercised for a generic semi-spanloader. Calculations were made for the effects of turbulent scale, of altitude, and of centrebody mass, all of which are shown to be small. Stiffness sensitivity calculations show that, although the composite wing is very flexible, the turbulence-induced moment is not greatly attenuated by flexibility. Effects of flexural deformation dominate the bending moments and torsional effects are very small. Seven different cases of the type used to define gust loads were examined. These indicated that gust models that do not contain spanwise variation seriously underestimate wing bending.