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The initial results of a program to investigate the sources of noise in unshrouded propellers under forward flight conditions are reported. Tests were conducted using a three-blade, full-scale instrumented propeller mounted on a twin-engine aircraft. Measurements included 1) farfield noise at fixed ground stations and at two aircraft wing tip locations, 2) blade surface pressures at seven locations on one of the propeller blades, 3) atmospheric turbulence encountered by the aircraft in flight, and 4) aircraft operating conditions. The results confirm that significantly lower levels of propeller noise are produced in forward flight than at static conditions. The most significant reductions occurred at mid-frequencies which dominate Perceived and A-Weighted Noise Levels. Blade surface pressure data showed the presence of disturbances in the propeller inflow under static conditions which were seen to disappear as the aircraft started its takeoff roll.

This paper presents the status of the airbreathing hypersonic airplane and space-access vision-operational-vehicle design matrix, with emphasis on horizontal takeoff and landing systems being studied at Langley; it reflects the synergies and issues, and indicates the thrust of the effort to resolve the design matrix including Mach 5 to 10 airplanes with global-reach potential, pop-up and dual-role transatmospheric vehicles and airbreathing launch systems. The convergence of several critical systems/technologies across the vehicle matrix is indicated. This is particularly true for the low speed propulsion system for large unassisted horizontal takeoff vehicles which favor turbines and/or perhaps pulse detonation engines that do not require LOX which imposes loading concerns and mission flexibility restraints.