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Sound Reduction Poster VA_BH

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Virginia Robinson

The document discusses research into reducing noise from small aircraft propellers. The goal is to minimize noise pollution without significantly reducing thrust. Various propeller designs were tested for sound pressure levels and thrust using equipment in a university's aerospace laboratory. Inspired by owl wings, modifications were made to propeller blades resembling an owl's comb-like leading edge and uneven trailing feathers. Testing found designs that drastically reduced sound levels while maintaining thrust.

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TEMPLATE DESIGN © 2008 www.PosterPresentations.com Sound Reduction Of Small Aircraft Propellers Virginia Robinson Braxton Harter Faculty Advisor: Dr. Nate M. Callender, Aerospace Abstract The source of thrust on most small aircraft provide by from propellers, rotating at high rpm. Propellers are durable and reliable; however, they produce high sound pressure levels preventing of stealth operation. The noise levels present the very real problem of noise pollution in populated areas. The purpose of this research is to find a way to minimize the problem of propeller noise. Research will be conducted to identify a propeller shape that will drastically reduce propeller sound pressure levels. The modifications must not significantly reduce propeller thrust. Measurements of sound pressure levels and thrust will be taken with equipment in MTSU's Aerospace Technology laboratory. To collect sound pressure levels, an anechoic chamber has been installed in house in which a digital sound pressure level meter in installed. An electric motor mounted inside will rotate a propeller at fixed RPMs while the sound meter records sound pressure levels. These measurements were collected by DataLogger computer software. Several blade designs were found to drastically reduce sound pressure levels emitted by the propeller while maintaining thrust. Research, designs, and testing continue to be conducted in order to gather the most paramount propeller design. Propeller Design Sound Testing Method References ResultsDesign Theory Once the propellers were created to desired specifications, testing began for each propeller. Each propeller had two strips of reflective tape attached to the tip of the blade on the backside to measure rpm using a tachometer. Next, the propeller was attached to the motor in the anechoic propeller chamber. The battery’s voltage was examined with the handheld voltage checker. If the battery had acceptable voltage, it was attached to the motor. If the battery did not have acceptable voltage, it had to be charged. Using the motor controller, the desired rpm would be acquired. While altering rpm’s, the tachometer had to be held 90 degrees relative to the spinning propeller to read the rpm. Once the desired rpm was obtained, the sound produced had to be obtained by the Sound Datalogger program on the computer. The microphone had to be securely tightened to its post. A USB cord went from the computer to microphone for data acquisition through a hole in the anechoic propeller chamber. Once the program was pulled up on the computer, desired settings had to be set in the program. The program was setting to a sampling rate of 50 milliseconds and decibel sound retrieval. A red button on the bottom of the microphone had to be held for 5 seconds until three consecutive lights were displayed on top of the microphone (red, yellow, and green). Once the Sound Datalogger program was obtaining data and the propeller was operating at the desired rpm, the anechoic propeller chamber top of the box was secured on top to allow for a sound proof testing environment. Propellers were tested three to five intervals ranging from 2000 to 8000 for about 2-5 minutes to obtain a reliable average. Biomimicry Insitute . (2008). Wing Feathers Enable Near-Silent Flight: Owl . Retrieved from Ask Nature: Strategy Griffith, E. (1974). Low Noise Propeller Demonstration. Lockheed California Company: United States Airforce, Air Force Aero Propulsion Lab. Springfield, VA: NTIS U.S. State Department of Commerce. NASA Langley Research Center. (1991). Aeroacoustics of Flight Vehicles: Theory and Practice (Vol. 1). (H. H. Hubbard, Ed.) Hampton, VA: NASA Reference Publication. Theodorsen, T., & Regier, A. A. (1946). The Problem of Noise Reduction with Reference to Light Airplanes. National Advisory Committee for Aeronautics, Langley Memorial Aeronautical Laboratory. Hampton, VA: Library NASA. Owls continue to be noticed for their stealth predatory flight. The wing and feathers construction cohesively compel the surrounding air to mask the sound of the predator. The leading edge of the owl’s wing consists of strong flexible comb-like edges as shown below in Figure 1. The comb like edges force the air going on either side of the feather to separate into smaller wakes. A feather of the same composition would have one large wake turbulence on either side of it. Figure 1. Leading Edge Comb The trailing edge of the feather consists of and uneven thin feathering as shown below in Figure 2. The thin feathering disrupts already small wake turbulences coming from the leading edge comb into miniscule vortices. Since sound produced by a wing are small pressure waves of air, when the air vortices and wake turbulences are reduced to such an insignificant size, the pressure waves are so small that the owl is mostly silent. In theory, if a propeller is modified to resemble an owl feather, the sound produced by the propeller will be reduced greatly (Biomimicry Insitute , 2008) Figure 2. Trailing Edge Uneven Feathering 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 RPM Sound (dBA) Propeller 1 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 2 Propeller 4 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 5 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 6 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 3 Propeller 4 Efficiency Testing Propellers were modified using exceptionally sharp hand held carving tools as seen below in Figure 1 generally used on wood with a lathe. The carving tools had a round sharp edge at the end of the tool. On the desired edge of the blade, slight pressure would be applied at an angle to the blade edge by the carving tool. The applied pressure of the curved carving tool created winglets on the propeller edge that resembled eyelashes. After extensive practice, including cutting my finger and nail in one cut, a method was created that permitted the design to be able to be modified to desired specifications. The method established a way to make each eyelash to be created deeper or shorter, wider or skinnier, and curl back greatly or very little. In theory, the modifications would resemble the leading edge comb of and owl wing and fringe of the trailing edge A parallelogram thrust box was used to test the overall efficiency of the propellers. The battery and receiver were taped together as one with the parallelogram thrust box cradle. The motor was screwed onto the cradle mount. The motor was turned on with the controller. At every 5 degrees the rpm of the propeller was measured using the tachometer. At about 45 degrees the propeller hit the top of the box creating a frightening sound and ruckus. So after rpm was logged at 35 degrees the motor was turned off slowly and testing ceased for the propeller. 0 1000 2000 3000 4000 5000 6000 7000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 RPM THRUST (LBS) Propeller 1 Propeller 2 Propeller 3 Propeller 4 Propeller 5 Propeller 6 Graph 1. Propeller 1 vs Propeller 4 Graph 2. Propeller 2 vs Propeller 4 Graph 3. Propeller 3 vs Propeller 4 Graph 4. Propeller 5 vs Propeller 4 Graph 5. Propeller 6 vs Propeller 4 Graph 6. RPM vs Thrust

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Sound Reduction Poster VA_BH

  • 1. TEMPLATE DESIGN © 2008 www.PosterPresentations.com Sound Reduction Of Small Aircraft Propellers Virginia Robinson Braxton Harter Faculty Advisor: Dr. Nate M. Callender, Aerospace Abstract The source of thrust on most small aircraft provide by from propellers, rotating at high rpm. Propellers are durable and reliable; however, they produce high sound pressure levels preventing of stealth operation. The noise levels present the very real problem of noise pollution in populated areas. The purpose of this research is to find a way to minimize the problem of propeller noise. Research will be conducted to identify a propeller shape that will drastically reduce propeller sound pressure levels. The modifications must not significantly reduce propeller thrust. Measurements of sound pressure levels and thrust will be taken with equipment in MTSU's Aerospace Technology laboratory. To collect sound pressure levels, an anechoic chamber has been installed in house in which a digital sound pressure level meter in installed. An electric motor mounted inside will rotate a propeller at fixed RPMs while the sound meter records sound pressure levels. These measurements were collected by DataLogger computer software. Several blade designs were found to drastically reduce sound pressure levels emitted by the propeller while maintaining thrust. Research, designs, and testing continue to be conducted in order to gather the most paramount propeller design. Propeller Design Sound Testing Method References ResultsDesign Theory Once the propellers were created to desired specifications, testing began for each propeller. Each propeller had two strips of reflective tape attached to the tip of the blade on the backside to measure rpm using a tachometer. Next, the propeller was attached to the motor in the anechoic propeller chamber. The battery’s voltage was examined with the handheld voltage checker. If the battery had acceptable voltage, it was attached to the motor. If the battery did not have acceptable voltage, it had to be charged. Using the motor controller, the desired rpm would be acquired. While altering rpm’s, the tachometer had to be held 90 degrees relative to the spinning propeller to read the rpm. Once the desired rpm was obtained, the sound produced had to be obtained by the Sound Datalogger program on the computer. The microphone had to be securely tightened to its post. A USB cord went from the computer to microphone for data acquisition through a hole in the anechoic propeller chamber. Once the program was pulled up on the computer, desired settings had to be set in the program. The program was setting to a sampling rate of 50 milliseconds and decibel sound retrieval. A red button on the bottom of the microphone had to be held for 5 seconds until three consecutive lights were displayed on top of the microphone (red, yellow, and green). Once the Sound Datalogger program was obtaining data and the propeller was operating at the desired rpm, the anechoic propeller chamber top of the box was secured on top to allow for a sound proof testing environment. Propellers were tested three to five intervals ranging from 2000 to 8000 for about 2-5 minutes to obtain a reliable average. Biomimicry Insitute . (2008). Wing Feathers Enable Near-Silent Flight: Owl . Retrieved from Ask Nature: Strategy Griffith, E. (1974). Low Noise Propeller Demonstration. Lockheed California Company: United States Airforce, Air Force Aero Propulsion Lab. Springfield, VA: NTIS U.S. State Department of Commerce. NASA Langley Research Center. (1991). Aeroacoustics of Flight Vehicles: Theory and Practice (Vol. 1). (H. H. Hubbard, Ed.) Hampton, VA: NASA Reference Publication. Theodorsen, T., & Regier, A. A. (1946). The Problem of Noise Reduction with Reference to Light Airplanes. National Advisory Committee for Aeronautics, Langley Memorial Aeronautical Laboratory. Hampton, VA: Library NASA. Owls continue to be noticed for their stealth predatory flight. The wing and feathers construction cohesively compel the surrounding air to mask the sound of the predator. The leading edge of the owl’s wing consists of strong flexible comb-like edges as shown below in Figure 1. The comb like edges force the air going on either side of the feather to separate into smaller wakes. A feather of the same composition would have one large wake turbulence on either side of it. Figure 1. Leading Edge Comb The trailing edge of the feather consists of and uneven thin feathering as shown below in Figure 2. The thin feathering disrupts already small wake turbulences coming from the leading edge comb into miniscule vortices. Since sound produced by a wing are small pressure waves of air, when the air vortices and wake turbulences are reduced to such an insignificant size, the pressure waves are so small that the owl is mostly silent. In theory, if a propeller is modified to resemble an owl feather, the sound produced by the propeller will be reduced greatly (Biomimicry Insitute , 2008) Figure 2. Trailing Edge Uneven Feathering 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 RPM Sound (dBA) Propeller 1 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 2 Propeller 4 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 5 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 6 Propeller 4 0 1000 2000 3000 4000 5000 6000 7000 8000 60 65 70 75 80 85 90 95 RPM Sound (dBA) Propeller 3 Propeller 4 Efficiency Testing Propellers were modified using exceptionally sharp hand held carving tools as seen below in Figure 1 generally used on wood with a lathe. The carving tools had a round sharp edge at the end of the tool. On the desired edge of the blade, slight pressure would be applied at an angle to the blade edge by the carving tool. The applied pressure of the curved carving tool created winglets on the propeller edge that resembled eyelashes. After extensive practice, including cutting my finger and nail in one cut, a method was created that permitted the design to be able to be modified to desired specifications. The method established a way to make each eyelash to be created deeper or shorter, wider or skinnier, and curl back greatly or very little. In theory, the modifications would resemble the leading edge comb of and owl wing and fringe of the trailing edge A parallelogram thrust box was used to test the overall efficiency of the propellers. The battery and receiver were taped together as one with the parallelogram thrust box cradle. The motor was screwed onto the cradle mount. The motor was turned on with the controller. At every 5 degrees the rpm of the propeller was measured using the tachometer. At about 45 degrees the propeller hit the top of the box creating a frightening sound and ruckus. So after rpm was logged at 35 degrees the motor was turned off slowly and testing ceased for the propeller. 0 1000 2000 3000 4000 5000 6000 7000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 RPM THRUST (LBS) Propeller 1 Propeller 2 Propeller 3 Propeller 4 Propeller 5 Propeller 6 Graph 1. Propeller 1 vs Propeller 4 Graph 2. Propeller 2 vs Propeller 4 Graph 3. Propeller 3 vs Propeller 4 Graph 4. Propeller 5 vs Propeller 4 Graph 5. Propeller 6 vs Propeller 4 Graph 6. RPM vs Thrust