A toroidal propeller is a type of

propeller A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working flu ...

that is ring-shaped with each blade forming a closed loop. The propellers are significantly quieter at

audible frequency An audio frequency or audible frequency (AF) is a periodic function, periodic vibration whose frequency is human hearing range, audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most deter ...

ranges, between 20 Hz and 20 kHz, while generating comparable thrust to traditional propellers. In practice, toroidal propellers reduce

noise pollution Noise pollution, or sound pollution, is the propagation of noise or sound with potential harmful effects on humans and animals. The source of outdoor noise worldwide is mainly caused by machines, transport and propagation systems.Senate Publi ...

in both

aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' include fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air aircraft such as h ...

and

maritime transport Maritime transport (or ocean transport) or more generally waterborne transport, is the transport of people (passengers or goods (cargo) via waterways. Freight transport by watercraft has been widely used throughout recorded history, as it pr ...

History

In the centuries after

Archimedes Archimedes of Syracuse ( ; ) was an Ancient Greece, Ancient Greek Greek mathematics, mathematician, physicist, engineer, astronomer, and Invention, inventor from the ancient city of Syracuse, Sicily, Syracuse in History of Greek and Hellenis ...

invented the

Archimedes' screw The Archimedes' screw, also known as the Archimedean screw, hydrodynamic screw, water screw or Egyptian screw, is one of the earliest documented hydraulic machines. It was so-named after the Greek mathematician Archimedes who first described it ...

, developments of propeller design led to the torus marine propeller, then described as a propeller featuring "double blades". It was invented in the early 1890s by Charles Myers from

Manchester Manchester () is a city and the metropolitan borough of Greater Manchester, England. It had an estimated population of in . Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92&nbs ...

affiliated with Fawcett, Preston and Company. The design was successfully trialed on several English steam tugboats and passenger ferries at the time. In the 1930s, Friedrich Honerkamp patented a toroidal fan, and Rene Louis Marlet patented a toroidal aircraft propeller. The marine propeller was patented again in the late 1960s by Australian engineer David B. Sugden affiliated with Robbins Company of Seattle. Overall, the relevant Cooperative Patent Classification category, B63H1/265 ''Blades each blade being constituted by a surface enclosing an empty space, e.g. forming a closed loop'', features over 160 patents in 120 years worldwide as of 2024. The technology was adapted for

fluid dynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...

in the 2010s by Gregory Sharrow with twisted loops instead of traditional blades. He patented propellers that addressed issues with rotary propulsion through the reduction of tip cavitation and vortices to increase performance in

boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size or capacity, its shape, or its ability to carry boats. Small boats are typically used on inland waterways s ...

s. Sharrow Marine argued that the benefits of lower fuel consumption, higher

efficiency Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste. ...

and reduced noise are even greater in water. Its MX propeller was recognized as one of ''

Time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...

'' magazine's "Best Inventions of 2023" for being more efficient and quieter than standard boat propellers.

Design and features

The design distributes

vortices In fluid dynamics, a vortex (: vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...

generated by the propeller along the entire shape of the propeller, which means that noise is distributed and damped more quickly without requiring components that add weight to increase overall power. It has similarities with the

closed wing A closed wing is a wing that effectively has two main planes that merge at their ends so that there are no conventional wing tips. Closed Wing configuration, wing designs include the annular wing (commonly known as the cylindrical or ring wing), the ...

, which is annularly shaped and therefore distributes the vortices generated along the entire shape instead of just at the tip. This decreases the probability that the spinning propeller will catch onto objects or cut surfaces. Drone propellers made according to this principle have been shown to emit a frequency between 1 and 5 Hz, which is outside the audible spectrum for humans.

In use

Toroidal propellers are most commonly used by the aviation and maritime industries. On drones it is used with thrusts comparable to multirotor drone propellers, and on boats with a notable increase in efficiency. Due to its inaudible frequency, the propellers have also been associated with quiet take off and landing protocols and

stealth aircraft Stealth aircraft are designed to avoid detection using a variety of technologies that reduce reflection/emission of radar, infrared, visible light, radio frequency (RF) spectrum, and audio, collectively known as stealth technology. The F-117 Ni ...

Unmanned aerial vehicles An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Dron ...

such as Amazon Prime Air, valkyrie drones, collision-tolerant drones and cargo drones have also been considered for use.

References

{{reflist Aircraft components Propellers