The aim of this thesis was the design of a retractable, electric propulsion system forsailplanes, which could eliminate the main drawbacks of internal combustionengines. The design process was based on a number of modern sailplanes, withinthe 12 - 15 meter class, with sustainer operation in mind. One of the goals was tocreate a universal propulsion system that could be fitted to various aircrafts.The first part of the project concerned the selection of the key components of anelectric propulsion system. First, the required power and thrust were calculated, andbased on the obtained results a suitable electric motor was chosen. For this motor,an electronic controller was selected. Later, the estimation of propeller parameterswas performed. Finally, battery basics were discussed and a battery was selected.The second part of the project concerned CAD modeling of the retractable electricpropulsion system. The used materials were discussed in the beginning. The designprocess focused on two main assemblies: the propeller folding mechanism and theretractable structure. The complete result, the individual sub-assemblies and themost important solutions were presented. The use of composite materials was animportant point of this thesis. Performance analysis was done after the system hadbeen designed.The retractable electric propulsion system was designed with optimum results. A fullscaleCAD model was created. The designed propulsion system can be consideredas universal due to its relatively low weight, adequate power and compact size in theretracted position. Custom-made accessories facilitate mounting. A visit to the glidermanufacturer Allstar PZL was the source of information about possible mountingsolutions and battery placement options. The designed propulsion system can beused as a sustainer for all designated sailplanes. Self-launching proved possible incase of the lightest sailplanes. With similar power and flight duration, the electricpropulsion system should be able to compete with petrol powered sustainer systemswithin the same class.