The Genius of Cycloidal Propellers: Future of Flight?

The first cycloidal propellers were thought  up in the early 20th century. But now,  

the same principles are being repurposed  for modern vertical take-off and landing  

vehicles. Later we will be checking out the  company Cyclotech who are doing just that,  

and see if their idea is getting off the ground.  But first, let’s see how the cycloidal propeller  

works, and why it might be favoured  over conventional propeller designs.

The first notable design of something  resembling a cyclorotor is the "Samoljot"  

by Russian military engineer E.P. Sverchkov in  1909. This vehicle, featuring paddle wheels for  

propulsion, was a step in cyclorotor development  but did not achieve flight. Further advancements  

were made in the 1930s, notably by Adolf Rohrbach  in Germany. The DVL, who are the German Research  

Institute for Aviation, evaluated Rohrbach’s  design, but the foreign aviation journals of  

the time cast doubt on the design which meant  that funding for the project could not be raised.

I also found this ridiculous clip of something  resembling a plane by Jonathan Edward Caldwell,  

the plan was for the rotating wings  to cause the aircraft to fly like a  

goose. Mr Caldwell was later charged  with fraud and a working aircraft was  

never completed. I am sure you  are all as surprised as I am.

There was also the Schroeder S1 of 1930,  

a full-size prototype which used a cyclorotor  only for forward thrust and looks a bit like a  

flying combine harvester. I can’t find much  information about the Schroeder S1 online,  

but it represents an era of interest and  innovation in the early to mid-20th century  

as engineers sought new methods to achieve  better aircraft performance and capabilities

The first operational application of  cyclorotor technology was the Voith-Schneider  

Propeller (VSP), developed by Ernst Schneider and  enhanced by the company Voith. Unlike the other  

systems, this was built for marine propulsion  and was successfully tested in 1937.

The Voith Schneider Propeller, or VSP, is a  type of cycloidal propeller and was patented  

in 1931. This propeller revolutionised the way  ships could manoeuvre, offering unparalleled  

precision and control compared to traditional  propeller systems. The ability of VSP-equipped  

vessels to move laterally, rotate on the spot,  and provide accurate thrust in any direction made  

it particularly useful for tugs, ferries, and  other vessels requiring high manoeuvrability.

The VSP's potential was further recognized  during World War II, where the need for nimble,  

highly manoeuvrable vessels became apparent.  However, its widespread adoption in military  

vessels was somewhat limited by the war's  demands and the technology's novelty at the time.

In the post-war era, the Voith Schneider  Propeller found its niche in civil maritime  

applications. Its adoption was driven by the  growing recognition of its advantages in safety,  

efficiency, and operational versatility.  Ports, harbours, and the flourishing offshore  

industry saw the VSP as a solution to their  increasingly complex operational challenges.

Over the decades, Voith continued to  innovate and refine the VSP. Advancements  

in materials science, hydrodynamics, and  control systems significantly enhanced  

the performance, reliability,  and application range. Today,  

it is not only found in marine vessels but also  in dynamic positioning systems for floating cranes  

and even in renewable energy applications  such as tidal and river current turbines.

I found a few videos of these in action and  they are pretty incredible to watch. Out of  

the water they look like some kind of death trap,  but on a scale model of a tugboat you can see how  

it is able to easily move in any direction  without having to rotate the whole vessel.

The transition of the cycloidal propeller  concept that has been working in maritime  

applications for decades, into aviation, is a  fascinating example of technological adaptation.  

While the core principles are grounded  in the same theory, successfully using  

cyclorotors for aircraft involves significant  re-engineering to suit air instead of water.

Given the continued success of the Voith Schneider  Propeller, you can see why the pursuit for air  

bound cyclorotors continues. Engineers remain  understandably excited due to promises of enhanced  

manoeuvrability, and efficient thrust vectoring  - that being the ability to change the direction  

of thrust with ease. You can see this in action  from a test video from the company Cyclotech,  

where the direction of the outgoing  smoke can be precisely controlled.

To understand how this precise control  is possible, let’s take a closer look at  

how exactly this propeller works,  and then see it in an aircraft.

But before that, if you want to design propellers  of your own, or just about anything for that  

matter, you need to know about Onshape.  OnShape is a professional grade computer  

aided design software that is completely free  for all makers and hobbyists forever. It's  

even free for engineers and companies for  6 months so they can properly try it out.

What blows my mind is that you can set  everything up in 2 minutes without any  

downloads and start making stuff straight away,  like I have done for so many projects now.

Because OnShape is built with  a cloud native architecture,  

it enables features such as real time  collaboration, seamless integration with  

mobile and tablet use for iOS and Android,  and built in product data management. Cloud  

auto saving also means you won’t ever lose  all of your work half way through a project.

File sharing can also be as  simple as just sending a link,  

just like the ones in the description. OnShape  is also continuously adding new features,  

so make sure to get a free account  and start creating whatever you  

can think of using onshape.pro/Ziroth,  which is also linked in the description.

Ok, now for the magic of Cycloidal Propellers. The  exact working principle of different Cyclorotors  

changes from system to system, but let’s start  with the similarities. As you have probably seen,  

the rotors have a number of aerofoils arranged in  a circular pattern around a disk. These aerofoils  

therefore generate lift and drag as the cylinder  spins around. However, in order to generate lift  

or thrust in a single uniform direction, these  aerofoils need to be at different angles of attack  

depending on where they are in the circular  loop. For example, if we want to go upwards,  

the leading edge of the aerofoil on the top would  need to point away from the centre of rotation,  

whereas the leading edge of the aerofoil on the  bottom would need to point towards the centre. The  

airfoils on the sides would therefore be tucked in  as they transition and try to minimise their drag.

The direction that these aerofoils point can be  used to quickly change the direction of thrust  

from the propeller. For example, to change the  direction downwards, the top aerofoil would have  

to point into the centre and the bottom  aerofoil away from the centre. This means  

the high pressure side of the airfoil is now on  the upper side, forcing it downwards. Similarly,  

the angle of the side aerofoils could  be altered for side to side movement.

A lot of cyclorotors use a mechanical linkage to  control the angle of attack of the aerofoils all  

together. This is a simple way to control  everything all at once and makes sure each  

blade rotates at the right point. This is  important because each blade must shift  

in orientation as it changes from being at the  top, sides, and bottom. Modern setups like the  

ABB Dynafin actually use individual servo motors  to control each aerofoil. Although this is more  

complex from a control point of view, it allows  more flexibility and likely higher efficiencies.

Due to the different properties of water  and air, the timings and angle of attack  

in cyclorotors for each application do vary. In  fact, some marine systems I have seen kick out  

one blade with such a high angle of attack it  seems to act as more of a paddle. Nevertheless,  

that is broadly how they seem to operate, which  brings me onto some other interesting benefits.

Unlike conventional propellers that  have tips which move much faster than  

the inner portions of the propeller, the  blades of cyclorotors all move at the same  

speed. This means the lift they generate is  uniform by default, but it also means they  

are quieter as they don’t create vortices and  loud noises from the rapidly moving tips. This  

reduction in noise could be a pretty serious  benefit if these were to be used in vertical  

take off and landing vehicles that would be used  for city transport, like cyclotech has planned.

Before looking at cyclotech, it’s worth noting  that these propellers aren’t all sunshine and  

rainbows however. Their unique blade movement  requires intricate control systems, which can  

increase the cost and maintenance requirements.  Additionally, the varying angles of attack  

and the dynamic nature of their operation subject  the blades and structure to significant stress,  

potentially leading to wear and tear or  even failure under harsh conditions. This  

is made worse by the fact the rotor is essentially  trying to pull itself apart the faster it spins.  

The size of cycloidal propeller systems are also  considerably bigger than conventional propellers,  

in turn increasing the weight. Even if a  cyclorotor’s thrust vectoring abilities make  

it more efficient in some scenarios, it might be  useless if the thrust to weight ratio is too low.

Thankfully, engineers are not ones  to give up quickly when things get  

complicated or even impractical. Flying cars  have been a childhood dream of so many of us,  

and I think part of the excitement around the  Cyclotech vehicle is based on the flying car  

feeling it gives off. This all electric  vertical takeoff and landing vehicle,  

or eVTOL, might be a while away from  taking me from my driveway into a big  

utopian city of opportunity. But what they  have achieved is still pretty incredible.

Cyclotech is an Austrian company that  has been working on their rotor design  

for over 15 years now, and just received  over $20 million of additional funding.

Their main test vehicle appears to be  a carbon fibre chassis with 4 of their  

cyclorotors attached. The vehicle weighs  just 83 kg, of which roughly half is the  

cyclorotors. Each cyclorotor spins up to  3100 rpm and they have successfully shown  

the ability for the vehicle to fly indoors  tethered up. However, following permission  

from the European Union Aviation Safety Agency  in 2023, they have also demonstrated the vehicle  

flying outdoors. There is no talk of the  flight time available here, but I imagine  

it’s very limited given that adding batteries  would quickly send up the weight of the system.

I do have to wonder if the cyclorotor will have  any substantial benefits over more conventional  

propeller designs in this use case. We have  already seen products like the Jetson One  

demonstrate it is possible to achieve a lot  of the aims of cyclotech using more mature  

technologies. The Jetson One is a similar weight  at 86 kg, but allows for another 95 kg in pilot  

weight on top of that with a flight time of  20 minutes. Man, I really want to have a go  

in one of these things. Think how easy it would  be to trim all the local hedges or lose an arm. 

As you’re still watching, please subscribe to the  channel, as I think you’ll enjoy some of the other  

videos, like this one about drones that can 3D  print houses. Your support helps the channel  

so much, and I’d love to hear your thoughts  on the future of cyclorotors in the comments.