The general objective was to collect and analyze aerodynamic stability and control data for the XV-4B, XV-5A, and P-1127 VTOL configurations. Correlation and analysis of existing model data were made to investigate hover and transition characteristics. Particular emphasis was placed on the aerodynamic power effects, sometimes referred to as interference effects. Other areas of investigation were sometimes referred to as interference effects. Other areas of investigation were nondimensional coefficients used to present VTOL data and wind tunnel test techniques. Wind tunnel tests were conducted using an inlet only model and a jet only model to investigate special test and analysis problems for these components. The agreement between different sets of XV-4B model data was, in general, found to be poor. However, the nondimensional coefficients used by Lockheed to reduce to XV-4B model data appear to be valid parameters for this category of VTOL airplane. The jet entrainment flow was shown by experiment to be the primary cause of the XV-4B power effects, and the XV-4B jet path was experimentally and theoretically determined.