A prototype unmanned air vehicle designed to be as quiet as possible is being planned by a team of Georgia Institute of Technology Research Institute engineers.
Funded by the institute's independent research programme and the US Department of Defense, the engineers want to use acoustic signature control to make UAVs as quiet as possible because they operate at low altitudes. Reducing noise would make a UAV less easily detected and improve the performance of its ground noise monitoring sensors.
The engineers have been characterising the acoustic signature of propellers' propulsion systems, which can be piston engines or a battery or a fuel cell. They have analysed the signatures of the institute's UAVs and some US military unmanned vehicles. The researchers have characterised UAV noise sources using ground-based and vehicle flight tests.
"Our next step is to put our findings into a prototype for testing. We believe that we have the means to make tactical UAVs much quieter," says senior research engineer Rick Gaeta.
Researchers needed to understand the noise from a piston engine's exhaust, which can be obscured by propeller noise. Tests included placing a mass on the engine shaft to represent the propeller, but without the blades' noise levels, so the engine's acoustic output could be monitored.
Researchers used two acoustic chambers at the institute's Cobb County Research facility - the Anechoic flight simulation facility and the static jet anechoic facility.