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Traditional helicopters and tilt-rotor vertical take-off and landing (VTOL) models such as Bell’s Boeing V-22 Osprey offer considerable mobility to troops operating on land or at sea, but have a major vulnerability: the enormous amounts of noise they produce.
Researchers from the U.S. Army’s Combat Capability Development Command Army research lab teamed up with engineers from Uber Elevate and academics from the University of Texas at Austin to experiment with building the ” a possible new generation vertical take-off and landing (VTOL) aircraft capable of operating. quietly using distributed electric propulsion.
Future planes, which are expected to use significantly smaller rotors than traditional helicopters, are seen for the huge advantage they can bring to the battlefield in missions such as cargo transport or surveillance, according to the researchers.
Engineers don’t expect experimental rotor designs to run completely silently, with electrically powered rotors showing a tendency in experiments to generate more “broadband noise”, i.e. load noise caused primarily by the ingestion of turbulence by a rotor.
The researchers supposedly assumed, then confirmed in their field studies, that broadband noise becomes the main source of noise when the rotors are reduced. The study would have included examining a variety of electric VTOL rotor configurations, with a series of nine microphones recording noise generated both above and below a rotor hub.
Engineers then analyzed the noise produced using two custom computer programs, which measured the aerodynamic loads on the rotor blades in various settings, as well as the actual noise generated.
George Jacobellis, a research engineer in the Army Research Lab, explained to Army.mil that “the noise you hear from these smaller rotors is generated by fundamentally different physical mechanisms” compared to traditional and proven designs. main rotor and tail rotor. “Traditional modeling techniques need to be improved to take into account all the noise generated so that vehicle designers can be aware of what will actually be heard,” he said.
Jacobellis stressed that “more work” would be needed to get “more accurate acoustic predictions” and compare model simulations with field experiments.
Based on their studies, researchers have so far found that stacked rotors (i.e. coaxial and co-rotating rotors) with equally spaced rotor blades create the lowest level of noise – equivalent to that of a traditional rotor. Engineers plan to continue experiments with axial spacing in hopes of producing a stacked rotor configuration that emits lower noise levels than conventional rotors.
The team published their findings in the 76th Annual Vertical Flight Society.
The noise generated by approaching helicopters is one of the main potential weak points for highly mobile and technologically advanced armies such as the United States, particularly in the face of a peer or near-peer adversary armed with radar and anti-aircraft systems. – advanced aerials. Pentagon planners first experienced the limits of airmobile warfare in Vietnam, where the US military lost more than 5,600 helicopters to North Vietnamese forces and the Vietnamese guerrillas in eight years.
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