English: The Dryden C-140 JetStar during testing of advanced propfan designs. Dryden conducted flight research in 1981-1982 on several designs. The technology was developed under the direction of the Lewis Research Center (today the Glenn Research Center, Cleveland, OH) under the Advanced Turboprop Program. Under that program, Langley Research Center in Virginia oversaw work on acoustics and noise reduction. These efforts were intended to develop a high-speed and fuel-efficient turboprop system. NASA's Dryden Flight Research Facility (later the Dryden Flight Research Center, Edwards, CA), in co-operation with the Lewis Research Center, investigated the acoustic characteristics of a series of subscale advanced design propellers in the early eighties. These propellers were designed to rotate at a tip speed faster than the speed of sound. They are, in effect, a "swept back wing" version of a propeller. The tests were conducted on Dryden's C-140 Jetstar, seen here on a research flight over the Mojave desert. The JetStar was modified with the installation of an air turbine drive system. The drive motor, with a 24 inch test propeller, was mounted in a pylon atop the JetStar. The JetStar was equipped with an array of 28 microphones flush-mounted in the fuselage of the aircraft beneath the propeller. Microphones mounted on the wings and on accompanying chase aircraft provided far-field acoustic data. In the 1960s, the same JetStar was equipped with an electronic variable stability flight control system. Called the General Purpose Airborne Simulator (GPAS), the aircraft could duplicate the flight characteristics of a wide variety of advanced aircraft and was used for supersonic transport and general aviation research and as a training and support system for Space Shuttle Approach and Landing Tests at Dryden in 1977. In 1985, the JetStar's wings were modified with suction and spray devices in a laminar (smooth) air flow program to study ways of improving the flow of air over the wings of airliners. The program also studied ways of reducing the collection of ice and insects on airliner wings.