Session: 01-08 Propellers and Open Rotors I

Paper Number: 153414

Far Field Acoustic Comparisons of Commercial and Custom Propeller Mounted on a Boom With and Without a Motor Containment Box 

     Increasing interest in eVTOL and Advanced Air Mobility (AAM) has caused a new awareness of propellers.  As these vehicles often operate in populated environments, the need for quiet and efficient propellers is becoming more important.  It is especially important to understand how the propeller sound propagates to the far field.  A new propeller design, called a double break, has proven itself to satisfy being both quiet and efficient in the near field when compared to a commercial propeller of similar performance.  A hybrid propeller, with one high lift airfoil carefully chosen for the hub and another low drag airfoil for the tip, proves to be the best combination for the double break.  Testing this new design in the far field is the subject of this paper.

    A propeller with a SG6043 hub airfoil and a SG6041 tip airfoil was designed with a double break.  This custom propeller, 21.5 inch diameter, was compared with a commercial baseline propeller, the KDE CF215, a 21.5 x 7.3 propeller which is also 21.5 inches in diameter.  Both propellers were tested with a KDE 330KV motor mounted on a boom, such as would be seen on a quadcopter.  Pusher and puller configurations, simulating a propeller and motor mounted below or above the boom, were tested and sound pressure levels measured 50 ft from the propeller test stand.  At 50 ft the KDE pusher configuration was 2 dBA quieter than the puller configuration.  The custom propeller saw little change between the pusher and puller configurations but was another dBA quieter than the KDE pusher.   

    The sound spectrums showed there was a noticeable high frequency component, between 2,000 Hz and 4,000 Hz, present for all tests.  This was believed to be the contribution of the motor noise and a PLA box was constructed to shield the motor from the sound measurements.  Tests were run again for both propellers in the puller configuration only, with and without the box around the motor.  For the KDE propeller, the box reduced the SPL 1 dBA (front) to 4 dBA (side).  The data for the box/no box SG hybrid propeller had similar values for both tests but with all measurements being 1-2 dBA lower than the KDE propeller from 0 to 45 degrees and SPL values between the KDE box/no box measurements for 60 and 90 degrees.  For all measurements, the high frequencies were still present. 

Presenting Author: Kenneth Van Treuren Baylor University

Presenting Author Biography: Dr Ken Van Treuren is Professor Emeritus in Mechanical Engineering at Baylor University. In 1977 he earned his B.S. in Aeronautical Engineering from the USAF Academy studying gas turbine propulsion. He was then awarded a Guggenheim Fellowship to study hydrocarbon combustion for his M.S. in Engineering at Princeton University. After serving 10 years as a USAF pilot in KC-135 and KC-10 aircraft, he completed his DPhil in Engineering Sciences at the University of Oxford, United Kingdom in gas turbine impingement cooling. Dr Van Treuren returned to the USAF Academy to teach heat transfer and propulsion systems until his military retirement in 1998. At Baylor University for the past 26 years, he taught courses in fluid mechanics, energy systems, propulsion systems, heat transfer, and aeronautics. Research interests include renewable energy, small wind turbine aerodynamics, and noise generation as it applies to the urban environment. Currently, he designs small Unmanned Aerial System propellers, reducing noise and power requirements. He is a Fellow of the ASME and an Associate Fellow of the AIAA.

Authors:

Charles Wisniewski USAF Academy
Kenneth Van Treuren Baylor University
Devin O'dowd USAF Academy