Professional aerodynamic analysis of full aircraft and prediction of interactions between components are performed accurately and quickly, by our aerodynamic team. Some special tools that are developed within our many CFD experiences, analytical efforts and ESDU analysis, are utilized for aerodynamic coefficient calculations. Results of SIGMA fast methods have good agreement with flight test. of high aerodynamic efficiency airfoils is our skill. We have introduced and utilized a special airfoil in a demonstrative aircraft in Iran. Professional multi-disciplinary design of such airfoils with laminar flow transition control was leaded to maximum L/D more than 120 at low angles of attack. scientific practical procedure of pusher or tractor piston engine cowling design was developed by SIGMA Company. Many design aspects such as engine and its accessories limits, cooling requirements, minimum drag, inspection and accessibility, manufacturing technology, ice protection, safety and beauty are considered in this process. SIGMA Company has some successful experiences in cowling design, manufacturing and ground and flight tests. greatest challenge in aerodynamic and performance analysis of a piston-prop aircrafts is the propeller effect. Constant speed variable pitch propellers have more complex behavior to study. Computational fluid analysis of isolated and installed rotating propeller is our verified and dominant solution to study prop-wash effects, interaction with cowling, propeller efficiency and propulsion performance at various engine settings or flight conditions. Propeller simulation usually starts with geometry modeling using CMM or optic digitizers. Moving mesh, moving reference frame and sliding mesh are methods to solve simulated rotating propeller that one of them is selected according to special condition of each problem. expert and experienced CFD team is well known and unique group that have wined several projects in full detailed aircraft simulation. CFD analysis of part by part and combination of parts for an aircraft frequently has been performed in SIGMA Company. Using special localized correction factors has made them as pioneers. Moreover, SIGMA has been equipped by 64 node parallel processing computer to solve the large models faster. Airfoils, landing gears, external payloads, cowling, propellers, internal and external flow, low subsonic and transonic aircrafts analysis are some of our past experiences. Also, all of CFD projects were verified with standard models.