1. A Bioinspired Modification for UAS Propeller/Rotor Noise Reduction
Mark N. Callender
Middle Tennessee State University

2. Noise in Aviation Federal Aviation Regulations
Aircraft Certification (FAR 36)
Aircraft Operations (FAR 93)
Airport Planning (FAR 150)
Regulated to minimize SPL for people on the ground
Unmanned Aircraft Systems (UAS)
Previous Operation
Certificates of Authorization (COA)
Section 333 Exemptions
Current Operation
FAR 107 as of August 29th, 2016
The FAA chose not to regulate SPL of UAS

3. UAS Propeller Noise Reduction
Reduce RPM
Maximize the product: nSbCL
n – number of blades
Sb – blade area
CL – blade lift coefficient
Trailing edge serrations
Modify tip geometry

4. Owl Feather Characteristics
Comb-like leading edge
Hairy or porous upper surface
Downy trailing edge

5. Propeller Modifications
Full span
Carved to mimic the leading edge comb
Orientation
Tip-oriented
Hub-oriented

6. Extech Instruments USB Sound Pressure Level Datalogger
dB range
A and C weighting
Shielded 0.5” electret microphone

7. Sound Chamber 17” x 23.5” x 36” Foam padded interior
Multiple mounting locations for the SPL datalogger
Horizontal mounting post for electric motor

8. RCbenchmark Series 1580 Thrust Stand and Dynomometer
1 vertical member
5 kg maximum
0.5% tolerance
Torque
2 horizontal members
1.5 Nm maximum
Speed
13,000 rpm maximum
Controlled via software through USB connection to data acquisition card

9. Thrust Raw thrust data collected
Validated using parallelogram force balance
2nd order polynomial trendline applied

10. SPL Comparison Hub-oriented comb significantly reduced SPL
SPL reduction greatest at low rpm

11. Thrust Comparison
Hub-oriented comb was compared to a baseline propeller
Thrust was reduced by 10% over a large rpm range

12. Constant Thrust Comparison
SPL reduction must not adversely affect thrust
Constant thrust comparison
Given that thrust must increase, sound typically increases
SPL is still decreased

13. SPL Reductions Multiple constant thrust comparisons were conducted
SPL reductions across thrust levels
Increased SPL reduction as thrust demand decreases

14. Future Research Leading Edge Comb Upper Surface Treatment
Comb angle
Comb spacing
Upper Surface Treatment
Materials
Location on blade
Trailing Edge Tuft
Tuft length
Combinations of modifications
Incorporation into full scale propellers