The article studies feasibility of real cycles of combined power plants including gas turbine engines and Stirling engines. The authors consider variants of construction concepts for such power plants. The article presents the analysis of thermodynamic cycles and, as a result, provides dependences to calculate their basic parameters. On the research results the authors give the quantitative heat utilization estimates of the combustion products in the gas turbine engine for the Stirling engine. The study identifies the Stirling engine’s efficiency limits, power and combined power plant’s efficiency in general. The authors put forward proposals for the application and the empowerment of such plants as part of vehicles.