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Aerocoustical engineer Rick Gaeta leads a team examining the different components of unmanned aerial vehicles and the specific sounds generated by each. Their main goal is to isolate the noise produced by the engine versus the propeller versus the exhaust on various UAVs. Once the current systems are well understood, this new knowledge can be used to reduce the sound as much as possible.
Isolating each component is proving difficult. In particular, it is very difficult to fully separate noise made by the engine from noise made by the propeller. The propeller system cools the engine as it operates. Using alternate cooling systems when the propeller isn't operating adds a great deal of unwanted noise to the equation. Both a quiet cooling system and a new load for the engine to spin are requirements to adequately test engine noise.
Researchers also need to consider the effect that quieter systems have on vehicle performance. It does no good to build an exceptionally quiet UAV if the noise damping degrades flight time or doubles fuel consumption. Gaeta and his team were able to utilize the Anechoic Flight Simulation Facility and the Static Jet Anechoic Facility at GTRI's Cobb County Research Facility to measure the performance and acoustic footprint of an engine and propeller system and determine a reasonable balance between the two competing needs.
Small changes to any one of the UAV component can have measurable effects on other components. The team is specifically monitoring infrared and radar signatures of UAVs and carefully ensuring that any changes they make do not adversely affect stealth capabilities in either of these areas.
The GTRI team has identified several ways to make quieter UAVs a reality through this testing process. They hope to build a prototype quiet UAV in the near future with an eye toward more extensive and more real world testing.
TFOT has previously reported on other stealth UAVs including the Boeing A160T Hummingbird helicopter UAV that's quieter than any known helicopter currently in use, a backpack-sized miniature UAV capable of deploying almost anywhere, and the X-47B, a new Navy stealth UAV designed to resemble a strike fighter. More recently TFOT reported on the “Stalker” - a mini UAV developed by Lockheed Martin, and “Skunk Works," a light, noiseless UAV designed specifically to be of use to the U.S. forces' Special Operations.
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