https://newatlas.com/aircraft/toroidal-quiet-propellers

Toroidal propellers: A noise-killing game changer in air and water
By Loz Blain
January 26, 2023

VIEW GALLERY - 7 IMAGES
These strangely-shaped twisted-toroid propellers look like a revolutionary (sorry) advance for the aviation and marine sectors. Radically quieter than traditional propellers in both air and water, they're also showing some huge efficiency gains.
Propellers are designed to take a fluid, generally air or water, and use a rotating motion to push that fluid through. They're evolutions, in a sense, from the Archimedes' screw, which was likely used in ancient Egypt thousands
of years before it was described by Archimedes in 234 BCE.

For devices designed to revolve, however, there's been little in terms of revolutionary design changes for an awfully long time; prop-driven aircraft still use twisted-aerofoil bladed props similar in design to the
bamboo-copters Chinese kids were enjoying 2,400 years ago, with surprisingly slim gains in efficiency over the wooden props the Wright brothers developed
in wind tunnels in 1903. Boats still use screw-style propellers, variants of which can be found as far back as the 1700s.

So we're fascinated to find a couple of groups claiming they've demonstrated significant advantages in both air and water using a markedly different
shape – specifically, strange twisted-toroid ring shapes that appear not
only to be much, much quieter than traditional designs, but so much more efficient, particularly in the marine space, that they could mark a profound leap forward.

MIT's super-quiet, 3D-printed toroidal propellers fitted to a commercial
drone for testing
MIT's super-quiet, 3D-printed toroidal propellers fitted to a commercial
drone for testingMIT Lincoln Laboratory
A potential game-changer in the air
One key issue with multicopter props is their annoying noise, which is often described as "whiny," because much of it sits right in the same frequency
range as a baby's cries. Humans tend to be most sensitive to sounds between around 100 Hz and 5 kHz. This makes evolutionary sense; it's where we hear vowel sounds that are key to verbal communication. But it's a key issue if multicopters are going to fulfill their potential and fill our skies with
fast, cheap, clean aerial delivery services. Residents and lawmakers don't
want to add more annoying noises to urban life.

A team working on a silent, ion-propelled plane at MIT's Lincoln Laboratory found itself wondering whether prop noise in multirotors could be mitigated with differently-shaped propellers.

"Propellers, as we know, are pretty loud," says Dr. Thomas Sebastian, a
senior staff member in the Lincoln Lab's Structural and Thermal-Fluids Engineering Group. "And we can look at wings to see how that works. Back
when people were coming up with all kinds of crazy ideas for airplanes in
the early 1900s and during World War 2, there were a couple of designs that were basically these ring wings. So I wondered what it would look like if
you took a ring wing and turned something like that into a propeller."

"We came up with this initial concept of using a toroidal shape, this
annular wing shape, to hopefully make a quieter propeller," Sebastian continues. "I had an intern of mine, who was just absolutely phenomenal, run with the idea. He took the concept and created a bunch of iterations using
3D printers."

The biggest noise reductions occur right where people will want them: in the 1-5 kHz frequency range
The biggest noise reductions occur right where people will want them: in the 1-5 kHz frequency rangeMIT Lincoln Laboratory
Within a few attempts, the team indeed found a design that reduced not only overall noise levels at a given thrust level, but particularly noise in the
1-5 kHz range.

Indeed, they sound more like a rushing breeze than a propeller, making a
much less intrusive sound. Anecdotally, according to the team, a drone
running these props makes a level of sound roughly as annoying as a regular drone about twice as far away. Have a listen in the video below:


"The key thing that we thought was making the propellers quieter, was the
fact that you're now distributing the vortices that are being generated by
the propeller across the whole shape of it, instead of just at the tip,"
says Sebastian. "Which then makes it effectively dissipate faster in the atmosphere. That vortex doesn't propagate as far, so you're less likely to
hear it."

Propeller noise can be somewhat addressed by placing rings of acoustic treatment around the circumference of a prop's path, which can also act as
prop guards from a safety perspective. But these add parasitic mass,
reducing battery life, and they can also catch the wind in outdoor
situations, making the drone work harder to stay stable.

The team analyzed these weird-looking toroidal props to see whether there
would be a thrust efficiency penalty. Apparently not: the team's best-performing B160 design was not only quieter at a given thrust level
than the best standard propeller they tested, it also produced more thrust
at a given power level – pretty remarkable given that standard props have
more than a century of development behind them and these toroids are at a
very early stage, with plenty of optimization yet to come.

While the MIT team hasn't spent much time optimizing these weird-looking
props for efficiency, they're already producing more thrust for a given
power level than standard DJI propellers
While the MIT team hasn't spent much time optimizing these weird-looking
props for efficiency, they're already producing more thrust for a given
power level than standard DJI propellersMIT Lincoln Laboratory
What's more, their looped shape not only adds structural stability, but decreases the chance of a prop cutting, clipping or catching on things it
runs into. You're still not going to want them hitting you in the face, but there's probably a marginal safety improvement there.

In terms of drawbacks, these are fairly complex shapes, so they're much
harder to manufacture than standard props using cheap and easy injection molding. They're probably the sort of thing you need to get 3D printed. But even if they double or triple the price of propellers, these are a low-cost part of a drone and the overall impact might not be that tough on the hip pocket.

It's unclear at this stage whether designs like this might be relevant at a larger scale, replacing traditional propellers on fixed-wing aircraft, or indeed on electric VTOL air taxis. The latter already appear to be significantly quieter than helicopters, but if they end up flooding the
urban airspace with fast, cheap, green aerial transport, every decibel of
noise will count when it comes to public and regulatory resistance. The question there, really, is what kind of frequencies these larger props will occupy in the audio spectrum, and whether the toroidal props shift the sound
in a human-friendly direction.

The team has patented the design, and while it's not clear whether there are plans to commercialize it, MIT appears to be prepared to license it to interested manufacturers.

Sharrow's aftermarket toroidal propellers for a range of outboard motors: expensive, but the claimed benefits are extraordinary
Sharrow's aftermarket toroidal propellers for a range of outboard motors: expensive, but the claimed benefits are extraordinarySharrow Marine
An even bigger advantage in the water
Drones and aviation are one thing, but aerodynamics and hydrodynamics are closely related, and it turns out there's already a product close to
production in the marine space that takes a very similar approach.

Sharrow Marine has been getting frankly spectacular results from boat propellers that use toroidal loops instead of standard blades. After several years of development, the company has now tested its props against hundreds
of standard propellers, and the difference is incredible. Sharrow's props simply don't create tip vortices – a major source of energy loss and a surprisingly large component in the overall noise of an outboard engine.

The gain in efficiency is ridiculous in the water at midrange RPMs, filling
in a pronounced hole in a boat's acceleration curve and conserving huge
amounts of energy
The gain in efficiency is ridiculous in the water at midrange RPMs, filling
in a pronounced hole in a boat's acceleration curve and conserving huge
amounts of energySharrow Marine
Vastly reducing the amount of fluid that "slips" out the sides of a
propeller rather than being pushed through, the toroidal props suck more
water through, and advance a boat further, per turn. They regularly double
the speed a boat can achieve at lower and mid-range RPMs, radically
broadening the effective rev range of the motor. And they reduce fuel consumption by somewhere around 20% – a seriously big deal given the huge energy requirements of propeller-driven boats and the scale of the industry.

Sharrow says they have the interesting effect of vastly reducing a boat's tendency to pitch backward as it accelerates; instead, the entire boat rises out of the water while staying much more level. On top of all this, the
effect on noise is absolutely profound, as you can see in the video below.


Standard vs Sharrow MX™ Noise Comparison
Indeed, the company says this is a propeller you can stick on more or less
any outboard motor, then blast along at 30 mph (48 km/h) quietly enough to
have a conversation on board without raising your voice. Remarkable stuff.

Sharrow is already selling its toroidal props, CNC machined to fit a wide
range of common outboard motors from most major manufacturers. The drawback here is price; they cost US$4,999 a pop regardless of which model, where a regular propeller might go for closer to US$500. But again, this is a pretty small component in the overall cost of many boats, and given their voracious appetite for fuel, the outlay may well pay for itself in short order as well
as making the ride a lot more comfortable for the people on board,
bystanders, and for marine life under the surface.

In the age of the energy transition, these things must also be of extreme interest to anyone making electrified boats, where a 20% boost in range from
a five-grand accessory would be an absolute no-brainer. Check out a fairly concise presentation from Sharrow in the video below.


The Sharrow Propeller™ EXPLAINED
Sources: MIT, Sharrow Marine

VIEW GALLERY - 7 IMAGES

43 COMMENTS
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Tristan P JANUARY 26, 2023 11:00 PM
Now that does seem to be a significant improvement on designs used all aver
the planet!
windykites JANUARY 27, 2023 03:08 AM
Could the Sharrow props be metal-3D printed? Also what about shrouded props,
or jet boats? How efficient are they?
michael_dowling JANUARY 27, 2023 05:03 AM
I wonder if the Navy submarine service is using these props on their nuclear attack subs already-talk about the Silent Service! I don't understand why
they cost so much more than conventional props. As ???????????????????? comments,can't they be 3-d printed,saving a ton of money??
michael_dowling JANUARY 27, 2023 05:21 AM
Speaking of noise reduction in recreational drones,these toroidal props
should be about the same price as standard props,as ???????????????????? commented,as they can be 3D printed from the same plastic used already for drone props,if not by prop makers,then by anyone with a personal 3D printer. Come to think,prop makers would only have to 3D print the mold for plastic props,and start cranking them out for the same price as conventional props. Jinpa JANUARY 27, 2023 07:15 AM
Kitchen hood fans should be a lot quieter with this design. Current OEMs are indifferent.
CDE JANUARY 27, 2023 08:19 AM
I wonder if these toroidal propellers would be less damaging to marine life such as manatees and other small animals. I've seen manatees with an evenly spaced series of cuts on their backs where a traditional propeller has cut their skin as the blade tip acts like a rotating knife. Just a thought.
Robert JANUARY 27, 2023 08:21 AM
If those have been used on submarines, than maybe they are available to civilians due to submarine designers using some even better now. I wonder
what it might be.
ghouse52 JANUARY 27, 2023 08:22 AM
I really appreciate New Atlas' reporting. Interesting, accurate and educational. Thank you, thank you.
Rick Ferrier JANUARY 27, 2023 08:34 AM
It's obviously better for the environment regarding noise pollution and fuel consumption so why is the price so high if they would offer it to the public
at a cheaper price more people would use it ?
Expanded Viewpoint JANUARY 27, 2023 08:50 AM
I'm highly impressed with this advancement in prop engineering! Well done, Gentlemen, well done indeed! This is exactly the kind of stuff I look
forward to seeing in New Atlas. It gave me an intellectual rush like I would have when I got the latest copy of High Technology Magazine back in the
early 1980s! I'm sure that all of the other gearhead technoids here will appreciate this work as well.
DaveWesely JANUARY 27, 2023 09:14 AM
This is truly impressive! And the really big question is: Would it work on a wind turbine? Instead of three props, there would be two loops. Instead of
an abrupt end to the blade, it would be a sloped edge. Considering all the histrionics about bird and bat mortality, would birds and bats have an
easier time avoiding impact? With tip vortices almost eliminated, could turbines be placed closer together? Could these replace existing blades
without a complete nacelle redesign?
More pertinent to wind turbines, can the blades be trimmed (rotated to catch more or less wind)? If they can, would the amount of tower clearance be substantially difficult to engineer? If the loops are further from the
tower's downstream turbulence, could the loops be trailing instead of
leading? Could loops be angled away from the tower for better clearance
instead of parallel to the tower's plane?
How much heavier, or lighter, might they be for the same amount of energy production? Could the loops be a smaller diameter, allowing taller towers
with more of the loop diameter in prime wind space (with the same maximum height)?
So many questions, so little time.
Ronald Foust JANUARY 27, 2023 09:37 AM
Would these designs work for wind and water turbines?
CraigAllenCorson JANUARY 27, 2023 09:48 AM
How would a person go about investing in this? This will be HUGE!
jerryd JANUARY 27, 2023 09:50 AM
Too much surface friction in the water and too much weight in the air.
McDesign JANUARY 27, 2023 09:59 AM
This is just the coolest thing! I wonder about the recent article about unshrouding turbofan engines, and how this tech could work there.
Username JANUARY 27, 2023 10:17 AM
The reason they are so expensive is that they can be. Sharrow has the
patent. They make much more profit selling one of these at 5k than they
would selling 10 at $500. The author is off base saying that 5k is not a big percentage of the boat. And props need to be changed. For people with an
older leisure boat that's paid off or operate a boat where props often get smashed on rocks, 5k is a no starter.
Eggster JANUARY 27, 2023 10:19 AM
New, over-priced Dyson fan in 3 ... 2 ... 1 ...
1stClassOPP JANUARY 27, 2023 11:23 AM
I’m wondering why it’s taken so long for Sharrow marine propeller so long to
be featured in New Atlas. I’m sure I’ve seen these featured for a couple of years on Pinterest. By now the market should have been robust if there are
no negative issues to deal with. Also, they’ve been around long enough to be able to figure out a cheaper way to ass produce them.
guzmanchinky JANUARY 27, 2023 11:45 AM
That is just amazing all around. I had no idea that the prop could make such
a difference in noise on a boat (and I've been boating for decades)
Adrian Akau JANUARY 27, 2023 12:07 PM
Excellent article. Now if only car designers would get serious about
reducing the Cd (coefficient of drag) on cars, that would also be a good development.
oldpistachio JANUARY 27, 2023 01:20 PM
How about as the "blades" of generators? Do toroidal propellers work their efficient magic as passive pinwheels? I picture the tides funneled into
these. The article says toroidal propellers are even more efficient in
water.
jsopr JANUARY 27, 2023 05:40 PM
If he's going to praise the "phenomenal" intern, he should it by name. Delivering this whole video in the first person, and then giving unnamed credit, is just rude, especially for an academic.
Ranscapture JANUARY 28, 2023 12:45 AM
@jerryd did you even read the article? They’re MORE efficient by A LOT. christopher JANUARY 28, 2023 01:46 AM
"tested its props against hundreds of standard propellers" - shows a graphic
of just one single prop they tested, guaranteed to be the worst performer of all those 100... and you can absolutely guarantee they'll never show you
their results from the best (or even tell you if theirs even outperformed it
at all).

Noise is a result of garbage prop design: go watch a self-launching glider
to see what a properly performing one sounds like (hint - if it flew past
100ft above you at the beach, you'd never know unless you looked up (true
story - literally happened to me) - those props are so perfectly designed they're all but silent).

Even an old school ruler is going to outperform and make less noise than a propeller - if you chose a garbage propeller to start with.

That's the problem with the tests this article references - the new prop
might be good, or maybe not - we cannot tell - because all the tests they
show and describe are against a garbage prop in the first place. No attempt
to select a good prop to test against has been made (and there's no
incentive either - nobody wants to publish a new design that underperforms against the best of current designs, right?)
Trylon JANUARY 28, 2023 06:17 AM
@Adrian Akau, we've known how to make cars very aerodynamic for the past 50 years. Blame American consumers for demanding big, boxy, heavy, gas-guzzling SUVs and pickup trucks.
Bob809 JANUARY 28, 2023 07:45 AM
You watch, the wheel will be next... The noise difference alone is amazing
in the boat video. I always thought the noise was from the outboard engines, just goes to show until someone else comes along with a new design, we think the current design is best. Well done team at Lincoln Lab, MIT.
Joy Parr JANUARY 28, 2023 08:18 AM
Fantastic, so now who will print me a set of eight 20mm diameter red racing ones for my nano, please? :-D
Steven Clarkson JANUARY 28, 2023 12:18 PM
@jerryd i agree, further i like the prop noise on multicopters, look if this design wasn't bulky which ot seems to be, and heavy which it seems to be
maybe use it in certain circumstances. I like the look of current mono plane props, simply add more blades and shape the tips for more silence.
Steven Clarkson JANUARY 28, 2023 12:29 PM
Around 5000 k is this a joke ?
Kenneth Jaworski JANUARY 28, 2023 01:21 PM
Ok so crazy idea here, if they are quieter in the water, and could prove to
be quieter for planes and drones in the air, what about windmills? Could the boost in RPM's create a windmill that generates more electricity, at a lower height, with shorter blades, then conventional commercially available windmills, and all while being quieter??

And would the circular nature of these "blades" be more stable, possibly lasting longer than the elongated blades that connect to nothing at their ends??
stevendkaplan JANUARY 28, 2023 02:20 PM
I wonder how well these new props will function if you stick them on a turboprop? Might this new prop shape finally be the key to unlocking a supersonic prop plane? Someone should license it and try it out!
soundnado JANUARY 28, 2023 04:01 PM
This will be good for jet planes or turbine planes.
Nobody JANUARY 28, 2023 04:36 PM
The efficiency graph leaves a lot out. Below 2000 rpm most boats would not
be on plane, at which speed, propeller efficiency does not look much better
on the graph nor is it much better at high rpm which would be the top speed
of the boat. My inboard cabin cruiser for best fuel consumption usually runs near the 2000 rpm range just above planing speed and my outboard ski boat
would normally run in the 3500 rpm range which coincidentally would be near
the same speed. My ski boat would probably gain efficiency but how much top speed would it lose? There is a lot that goes into what makes the best prop, hull design, weight and desired speed. That the boat doesn't pitch up as it accelerated with the new prop would seem to indicate that it doesn't
accelerate out of the hole as quickly. Trim tabs and motor mounts could have
a lot to do with that. $5 grand for one of these fancy props? Nope. $5 grand would buy a lot of fuel. Several seasons for me and by then I would probably need a new prop.
WireTalents JANUARY 28, 2023 05:32 PM
To all those grumping about the price, remember that Sharrow (and Dr. Thomas Sebastian) has put millions of $$ research into these.
Original thought & design, computer aided design & development, wind tunnel
& water testing in Labs & refining the design, boat testing & refining the design again.
Even I, as an electrician, can see that conventional machining techniques
are not going to work on this propellor and it always will be more
expensive.
3D printing has benefits but it's slooooooww. How much will 100 or 1000 3D printers cost that will do this job at marketable volumes.
This is an exciting new design and early adopters will see that and value
it. The price will settle down later.
I hope Sharrow has got rock solid patents because the Chinese will make it
out if sintered metal and 9 in 10 will outlast the warranty. Then you can
buy one for $500.
Well done to Dr. Thomas Sebastian and Gregory Sharrow for the design and persistence against all the nay-sayers as all great inventors do.
And well done to New Atlas for another great article.
Now, when can I put one on my Rotax powered Ultra-light aircraft :-)
itsKeef JANUARY 29, 2023 06:04 AM
such a pretty shape...geometry reveals another of its sublime secrets. So,
it appears the humble doughnut has been trying to tell up something all
these years....hmmm doughnuts!
TpPa JANUARY 29, 2023 03:39 PM
Well on any boat engine with less than say 300 hp would be foolish to spend
5 grand on a prop., so that rules out most of the boats you hear, the rest
are out in big water.
christopher JANUARY 29, 2023 04:50 PM
@Ronald - props are different to turbines, because of the betz limit
(59.26%) - if you try to extract too much energy, the flow simply goes
around your device, instead of powering it, plus it's the opposite reaction (slowing the flow, instead of speeding it up) - so no, this design isn't
going to improve any of that for a turbine.
George Fleming JANUARY 29, 2023 06:30 PM
This toroidal device reminds me of the Lily impeller:

https://www.paxwater.com/biomimicry

But the Lily is only a mixing impeller, This invention is a propeller. It appears to be far more important.
Martin Yale JANUARY 30, 2023 03:12 AM
How about going back almost 30 years - https://www.youtube.com/watch?v=TdcWQpN8hl4 dual prop versus single prop
Dual props were similarly touted to give amazing boosts to boats - perhaps comparing the sharrow to a dual prop would be interesting
HokenPoke JANUARY 30, 2023 08:19 AM
How about an update on the cyclocopter !
Craig Issod JANUARY 30, 2023 01:07 PM
Mass production will not be 3D Printed - once the design is locked down,
almost anything can be molded. What is most fantastic here is that DJI - a company known for fantastic engineering, did not fully exploit this years
ago! Then again, maybe they did (R&D on it) and we just don't know because
they didn't produce it yet?
CrookedGrin JANUARY 30, 2023 01:49 PM
Do these efficiency gains also apply in the opposite direction, i.e., using propellors to generate power in a turbine? If so, that could be a massive
win for things like hydroelectric systems, or even a nuclear generator that uses steam to drive a turbine. If the efficiency gain is from turbulence
that's just wasted energy, it would seem like it would translate. Is anyone looking at using these in power generation contexts?
ljaques FEBRUARY 1, 2023 07:23 AM
Wow, what a difference in noise level. I'd like to hear a quiet drone some
day, too. And a quiet range hood.
Both the brass and chromed models are absolute works of art as well. Shiny!

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