UAVs or drones are used in a number of applications worldwide. For the Silent Flyer we focus on applications where a silent and non-obtrusive device is proven to be needed. These are in the fields of government law enforcement and surveillance by government and private companies, military use, and wildlife photography & research.
Drones (Unmanned air vehicles (UAVs)) are evolving into important tools, not only for military covert operations, but also policing (citizen survey and safety) and wildlife conservation/surveillance. Nevertheless, their widespread implementation is restrained by the noise and obtrusive appearance limitations of commercialized technologies in either flight range or usability.

Unmanned air vehicles (UAVs), colloquially called drones, are defined as “an unmanned aircraft or ship that can navigate autonomously, without human control or beyond the line of sight” [1]. UAVs are nowadays evolving into important tools in different fields. However, their widespread implementation is restrained by the noise and obtrusive appearance limitations of commercialized technologies. They tend to live up to their names in that they emit a constant buzzing noise when in operation, created by several rotors and electric parts as well as conventional motors, with both fixed wing and rotorcraft UAVs. UAVs use propellers at a high rate of revolution, which are inherently noisy, highly annoying for the citizens (as confirmed my recent NASA studies) and harmful [2]. For this reason, new EU regulations are proposing noise caps on UAV [3]. They are also quite obtrusive and their operation in the sky is obvious to bystanders. The UAVs has been successfully applied for:
1. Military covert operations: Despite the widespread use of UAVs in the Governments and military, unobtrusive, covert operations such as surveillance, reconnaissance and special ops-led military endeavours require silent operation for mission success [4]. g., the noise from the Predator and Reaper UAVs that patrol in Afghanistan and elsewhere is audible on the ground as an incessant hum, leading locals to call them “machar” (mosquito) [5].

2. Policing (citizen survey and safety): Drone surveillance is the use of UAVs to capture still images and video to gather information about specific targets, which might be individuals, groups or environments [6]. However, the UAVs appearance and noise can affect this surveillance, by alarming citizens unnecessarily [7].

3. Wildlife conservation/surveillance/research: Studies have shown that UAVs can be more efficient than traditional approaches to wildlife monitoring and can provide more precise observational data. However, scientists have already stated that steps should be taken to ensure that UAV operations are not causing undue stress to animals [8] because of their noise and appearance.
For successful embracing of UAVs as military, surveillance and research operations by a variety of private and government institutions, a rotor-less operation combined with manoeuvrability and durability in challenging environments is needed. This will also cause minimum chances of personal injury from elimination of open rotors and propellers. It should also provide ease of launch and imbibing vertical take-off and landing (VTOL) ability. In addition, a truly unobtrusive appearance such as that of a flying bird can ensure operation at lower altitudes without standing out as an obtrusive element in the sky, which will not interfere with natural habitats of wildlife (during wildlife photography/surveillance) or get detected prematurely during police or military operations. In addition, such bio-form UAVs should have no or very little humming noise area. Any continuous “humming noise” > 85 dB is known to cause permanent hearing disability while <70 db is equivalent to the noise of an air conditioner or shower.
[1] What is a drone: Main features & applications of today’s drones, Dronelab, 2018
[2] NASA study confirms drone buzzes are more annoying than cars. The Verge, 2018
[3] Drone Noise – Is it a Problem? Atmospheric, 2017
[4] US military wants quieter drones. Talkuab, 2018
[5] The Sound of Terror: Phenomenology of a Drone Strike. Boston review, 2013
[6] Drone surveillance, Tech Target, 2015
[7] Global UAV Market Growth to $28.27 Billion by 2022, driven by civil, commercial, military & security sectors, Idst, 2017
[8] Using drones without disturbing wildlife, Science Daily, 2016
[9] Noise dose chart: Noise exposure limits, Noise Help, 2018
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