An experimental and computational investigation was conducted on the film cooling adiabatic effectiveness of a flat plate with full coverage film cooling. The full coverage film cooling array was comprised of ten rows of coolant holes, arranged in a staggered pattern, with short, L/D = 1, normal coolant holes. A single row of coolant holes was also examined to determine the accuracy of a superposition prediction of the full coverage adiabatic effectiveness performance. Large density coolant jets and high mainstream turbulence conditions were utilized to simulate realistic engine conditions. High-resolution adiabatic effectiveness measurements were obtained using infrared imaging techniques and a large-scale flat plate model. Optimum adiabatic effectiveness was found to occur for a blowing ratio of M = 0.65. At this blowing ratio separation of the coolant jet immediately downstream of the hole was observed. For M = 0.65, the high mainstream turbulence decreased the spatially averaged effectiveness level by 12 percent. The high mainstream turbulence produced a larger effect for lower blowing ratios. The superposition model based on single row effectiveness results over-predicted the full coverage effectiveness levels.