A numerical design tool was developed that greatly facilitates the design process of small UAVs. The integrated approach of the method makes it highly suitable for the aerodynamic needs of such small aircraft. Traditional design tools and methodologies are typically tailored for the design of larger aircraft, such as for general aviation, whose aerodynamics generally exhibit more linear behaviors. Building on this motivation, a user friendly integrated design tool was developed and validated in order to provide a more tailored approach to designing low Reynolds number aircraft. At the heart of the tool is a performance prediction that relies on a higher-order free wake potential flow aerodynamic code that employs viscous drag corrections. Subsequently, the method provides accurate characteristics for a wide range of Reynolds numbers and aspect ratio wings. In a validation process, the flight performance results of the method are compared with the results of other prediction methods as well as with several experimental flight test results. In general good agreement exists. The utility of the integrated design tool is demonstrated with the design application of a small UAV for a heavy lift competition. The design tool greatly streamlined the design process, limiting it to two weeks rather than the typical several months.