The UAV noise problem…
The opportunities with UAVs and their applications are extensive, commercially and recreationally, but noise issues have to be solved.
A 2016-2017 National Aeronautical and Space Administration (NASA) study https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170005870.pdf, suggested, “In a short while, communities across the US will be inundated with new classes of noise due to (UAV) operations that they had not before encountered.”
One of its conclusions was that, “This result casts doubt on the idea that (UAV) operators can expect their operations to be greeted with minimal noise-based opposition as long as the sound of their systems are “no louder than” conventional package delivery solutions.”
At Dotterel we have invented, researched and demonstrated technologies that significantly cut UAV noise – delivering enhanced opportunity for UAV operators.
What is Dotterel doing to help fix the noise problem? Link to Cutting UAV Noise page (see below)
Cutting UAV noise with Dotterel technology
Dotterel has designed, manufactured and demonstrated working prototypes which have reduced perceived noise below the UAV by 40%, or 4 dBa.
Our ongoing development and demonstration programs target a 6-10 dBa reduction. This reduction opens up new applications such as (list or link to new applications/demo library..).
Our Noise Reduction Suite has three components:
- Acoustic Shroud: Redirects noise generated by the UAV propellers and engines away from the ground. It also absorbs a portion of the noise in the speech range.
The majority of a UAV’s noise is generated by its propeller tips. Rapidly rotating, they generate tip vortices that disrupt airflow and cause blade turbulence. This turbulence creates sound, and causes the blade to flex, reducing propeller efficacy.
Our shrouds reduce the generating of tip vortices and directs focus sound up and away from the ground.
In addition, less propeller vortices not only reduce sound but also increases the efficacy of UAV flight, retaining as lift energy that would be lost through turbulence. This additional lift of up to 30% helps offset the weight of the propeller shrouds.
Sound absorption in the dominant speech frequencies maximised by using novel nanofibre materials in the propeller shrouds.
- Low-Noise Propellers: These are purpose-built to work within the acoustic shroud.
Most of the noise from UAVs is generated by its propellers. Dotterel designs and uses low-noise propellers with edge modifications that work with the shroud to produce more easily cancelled sound frequencies.
- Audio Filtering Technology: Software that cleans up audio recorded in-flight on the UAV.
In concert with acoustic shrouding and low noise propellers, we are also developing on-board hardware and software based audio-filtering technology to clean up audio recorded from the UAV in-flight.
Using a field programmable gate array, we separate noise from speech frequencies (already partially cleaned by using selective sound absorptive nanofibres) to deliver clean audio from the UAV.
Our lightweight microphone arrays and signal processing algorithms filter drone rotor noise from target audio sources to provide clean audio transmissions and recordings in real time.
- Our UAVs
30″ Behemoth – QHL2
• Fully shrouded 30” blades
• 105 kg (231 Ib) thrust motors
• 20 kg (44 Ib) payload capacity
• 15 min flight time
• 64 dB at 10 metres.
15″ Audio Class – AC3
• Real-time audio capture
• Pre-mission adjustable directivity
• Streams either beam-formed or filtered audio
• 15” blades
• 30 min flight time
• HD video.
More products coming soon