Theoretical predictions, based on a pilot-aircraft system, of root mean square control response, root mean square heading response and minimum pilot gain were found to correlate well with pilot opinion assessments of the directional control and response requirements for flight of simulated V/STOL aircraft in turbulence. The comparisons were made for two visual flight tasks, a circuit including approach and landing, and precision hovering in a simulated wind, for four values of the weathercock stability parameter. Pilot assessments of the pitch, roll and yaw control sensitivity and control power requirements for manoeuvre in calm air for visual circuit and hover tasks were compared for two aircraft weighing 2, 900 lb. and 15, 000 lb. The results did not agree with the predictions of the existing requirements for scaling control power with weight, indicating a trend opposite to that of the present recommendations. Preliminary results from this investigation, which include simulated turbulence, as well as results from previous experiments, suggest that scale effects are overshadowed by the requirements to ensure satisfactory flight in turbulent conditions. To be presented at the 27th meeting of the flight mechanics panel of the advisory group for aeronautical research and development, NATO, in Rome, October 11-12 1965