A flexible self-optimising propeller which combines the advantages of fixed-pitch and constant-speed units is being tested by US firm Global Aircraft of Starkville, Mississippi. Production of the Quasi-Constant-Speed (QCS) propeller, priced at $3,500, is set to start this month, initially aimed at experimental aircraft. Production of units certificated for general-aviation (GA) aircraft is due to begin in mid-1998.

The QCS has swept glassfibre-reinforced-plastic blades, which twist and flex predictably under load, providing performance approaching that of a constant-speed propeller without the mechanical complexity, says Global. Compared with fixed-pitch propellers, Global says that the new technology gives a 35% shorter take-off distance, 40% higher climb rate and 10% faster cruise speed.

Computer modelling has allowed blade aerodynamics to be optimised for the cruise, while aero-elastic properties are tailored for reduced pitch on take-off such that static thrust is some 20% higher than with a fixed-pitch propeller. Half of this is down to improved blade efficiency, while the rest results from the higher engine speed, says president Michael Smith.

NASA-sponsored ground tests of the initial 120kW (160hp)-rated propeller have shown noise reductions of 8-9dBA, says Smith, who adds that Global is taking orders for October delivery of the unit.

Source: Flight International