Report presenting an investigation in the Langley Unitary Plan wind tunnel to determine the drag and static longitudinal and lateral stability characteristics of a model of the Grumman F11F-1F airplane at Mach numbers 1.56, 1.76, 2.06, and 2.53. The investigation included the effects on performance and stability of modifications, including a wing-root leading-edge fillet and horizontal tails with negative dihedral of 10 degrees and 30 degrees. Information regarding net external minimum drag coefficients, neutral points, directional stability, and positive effective dihedral is provided.

Part I of this report presents a brief review of methods available to the helicopter designer for obtaining desired stability characteristics by modifications to the airframe design. The discussion is based on modifications made during the establishment of flying-qualities criteria and includes sample results of theoretical studies of additional methods. The conclusion is reached that it is now feasible to utilize combinations of methods whereby stability-parameter values are realized which in turn provide the desired stability characteristics. Part II reviews some of the methods of predicting rotor stability derivatives. The procedures by which these rotor derivatives are employed to estimate helicopter stability characteristics have been summarized.