The Unexpected Genius of Contra-Rotating Propellers

[@ZirothTech]

Play the incredible War Thunder game and click my link and claim your extra bonuses: playwt.link/ziroth Will these new innovations in the world of contra-rotating propellers bring them back to more applications?

[@dmytrobub]

Wartunder it's made by russian company Gaijin Entertainment, which, hiding from sanctions, moved russian programmers around the world and hide them as a non-russian company, while paying taxes in russia. So go fuck yourself with this advertising.

[@tonywilson4713]

Aerospace Engineer here: We've chatted a couple of times so I know your engineer and I'll hope you'll take this with the intent it is given. You and others need to stop putting up things like 116% efficiency or the 145% efficiency you had for the Fibonnaci turbine. I have seen a pile of this recently (most notably with heat pumps with insane claims) and we both know that there is simply no way in any engineered system to get mor than 100% efficiency. In fact if you have studied Thermodynamics then you know its fundamentally impossible in a engineered system because there's some loss somewhere that can't be recovered in every cycle. The problem isn't that you and I know what you mean that 116% means 16% above some other standard or reference. The problem is that people who ARE NOT engineers or have forgotten even their high school science class just think its possible. Where this becomes a massive problem is in dealing with the energy crisis. As an engineer I have to deal with it from a very pragmatic perspective. *First and foremost we have to do things RIGHT NOW that we know are going to work.* No matter what project you ever do you must start with something you know will work or have a very high level of confidence it will because the parts you are using are known to work in similar projects. Being honest I haven't always done that and its caused soe serious heart break at times. Here in Australia we are having this insane argument over nuclear power. No matter if we do or don't decide to go with nuclear it wont fix a damn thing RIGHT NOW because it takes time (a lot of time). We have the butt ugly situation of having power stations that we should have closed 5-10 years ago that are limping along because all of the public discussions are shitfests or stupidity fueled by armies of idiots stoking whatever their narratives are. Just this week I have saw a left wing think tanker claim that coal is NOT a mineral with the smuggest of looks on her face and NOBODY to correct it because it was here on her think tanks YT channel On the flip side we have the pro nuclear crowd telling so many lies its impossible to keep track and even more impossible to correct because they have mixed those lies in among actual facts. Do I think we will need nuclear? YES, the question isn't if we'll have it but when and what type and how much. Real Engineering did a great recent video on grid stability issue when you have a lot of wind feeding into a grid. Australia has an insane amount of wind available, but to make it work we need something to absorb the grid disturbances. Nuclear can do that and do it well but we can't even get a sensible discussion going. Just today I watched one of our Senators who was a test pilot and has a technical background in systems engineering and he mixed a staggering array of lie in among some important truths. I have the background to sort the lies from the facts most people don't. A week ago a neighbor of mine told me I had no idea what I was talking about because the Meisner Effect was the answer to everything. He had no idea that even if the Meisner effect (which is the effect of superconductors pushing away from magnets) has NOTHING to do with energy production and until we can use it practically it will have almost zero effect on energy distribution. BUT HE SAW the crap idiotic video by someone (I suspect 2 Bit Da Vinci) and now thinks he's an expert on energy. I have seen Thunderf00t's debunk of the 2 Bit video and its straight forward on how stupid that video was. I don't always agree with Thunderf00t, but most of the time he is spot on because like me he can see the lies through the crap. I think you have a great channel, but like a lot of younger people you haven't yet worked out just how problematic misunderstandings can become. These days we have so many people telling so many things that are simply wrong that its causing a lot of confusion and with that we can't have some of the very important things that need saying.

[@Era_SoNER]

Did you know that it doesn't have a functioning anticheat? despite being a PVP MOBA?

[@gae_wead_dad_6914]

Honestly it's not "unexpected" nor "innovative". It was known since 1907, and even used to some degree in WW2. I mean come on - this is obvious for anyone who has even the slightest idea of how newtonian fluids, and thus - air, work. The entire reason contra rotating propelles have become available was due to the increased HP of engines available. Back in WW2 the weight necessary to produce 2500 HP on an engine would far outweigh (literally) the meager benefits given by the contra rotating propeller.

[@Era_SoNER]

@@gae_wead_dad_6914 I think you responded to the wrong comment =s

[@papparocket]

In our research there are two major sources of noise, blade passage noise and tip vortex interaction. Blade passage noise happens when the wake off of a blade in the front prop strikes a blade in the rear prop. That wake causes an unsteady flow around the rear blade, which causes vortices to collapse and the blade to vibrate, both generating a broadband noise. When the number of blades in the front and rear prop are equal, like the Tu-114, all of the blades pass each other at the same moment and so all emit the noise at once. So the noise comes in two major bands, the high frequency broadband noise from vortex excitation frequency of the prop vibrating and the high intensity tone at the blade passage frequency. The solution is pretty straight forward and that is to make the number of blade on each prop a different number. Usually they only need to be one different, with one more blade on the front prop when the blade count is low, but two different when blade count on the front prop approaches ten blades. Then with unequal numbers of blades, only one set of front and rear blades are interacting at one time. This increases the blade passage frequency and dramatically lowers the amount of acoustic energy in each pulse. Higher frequencies being easier to attenuate and less energy in each sound pulse requiring attenuation make it substantially easier to reduce the amount of noise that penetrates into the cabin. A second mitigation strategy is to add sweep to the blades. In the Tu-114, the blades were perfectly straight, which means that the vortices off the front blade strike the leading edge of each of the rear blades along the entire leading edge at the exact same moment maximizing the amount of energy in that blade passage acoustic pulse. If the rear rotor blades had a bit of scimitar shape to them, then the vortex from the front blades would strike the leading edge of the rear prop at slightly different times and spread the acoustic energy generate over a broader and lower peak energy pulse. Both front and rear blades can have some sweep to them, which is especially helpful when applied to high subsonic propeller aircraft (usually called "open rotor" when the flight Mach number approaches 0.8). To maintain the acoustic reduction benefits, the rear blades just need to have a little more sweep than the front blades. The second major source of noise is when the tip vortex shed by the front prop strikes the tip of the rear prop. This interaction is so strong that it causes the entire rear blade to "ring". The obvious solution is to make the blades of the rear prop just slightly shorter so that the tip vortex of the front blades just passes over the rear blades with no tip interaction noise being generated. This solution does slightly reduce the efficiency of the combined propeller system since the vorticity at the tip of the front blade is not countered by the opposite vortex at the tip of the rear prop blades. But the loss in efficiency is minor and the reduction in noise is substantial. The combination of unequal blade numbers per disk, swept leading edges on the rear prop blades (or higher sweep than the front blades), and the reduction in blade length in the rear rotor combine to substantially reduces the noise from contra-rotating propellers.

[@papparocket]

Here is a link to a presentation of the results of a test campaign in our 9 foot by 15 foot acoustic wind tunnel where the bottom line is that contra-rotating swept open rotor with unequal number of blades per rotor and shorter blades in the rear rotor reduces noise by around 21 EPNdB compared to historical single rotor propeller noise for the same net thrust level, all while being more efficient. ntrs.nasa.gov/citations/20160014870 And here is a link to a presentation that used acoustic capable CFD models to compute what the models predict the noise would be and compares them to the actual wind tunnel data. ntrs.nasa.gov/citations/20130000424

[@RePeteAndMe]

Hi, Papparocket. There's a much better way. A direct drive prop/fan sits in front of an open-nosed plane. The engine bay is cone-shaped. The base of said cone is as big as the plane's fuselage. The engine bay also functions as a stationary nose cone for a planetary gear driven prop/fan that operates at about 1/10 the engine's RPM. The cone pressurizes, spreads, and smooths the small-and-fast front prop/fan's wake while entraining surrounding air, feeding the big-and-slow rear fan/prop just what it needs. Yep, planes will need tall landing gear. So what? We need quiet planes with off the charts efficiency. The system I'm designing should approach 2/3 efficiency during high altitude cruising, including the engine (Carnot's equations seriously favor very cold environments)

[@benjaminmiddaugh2729]

@@RePeteAndMe I'm a bit skeptical, but seeing that it's been around 80 years since any serious research was done on using the plane's fuselage as any kind of assistance to prop-based airflow I'm glad that someone is exploring similar territory.

[@nutmeggaming11261]

A reduction in noise would also increase efficiency, since less energy is being wasted to generate vibration

[@RePeteAndMe]

​​@@benjaminmiddaugh2729You should be way skeptical since nobody has built a 2/3 efficient engine, let alone a propulsion system. Heck, I have doubts, but stretch goals are both fun and productive (why DID Moore's law drive chip development for decades?) Anyway, the front fan's vortices are consumed by air entrainment that's forced by the nose cone, leaving a large, pressurized, and smoothed rotating wake. Or so I think. Fortunately I live next to UCIrvine and they have a little wind tunnel. I'm drawing the latest version of the engine right now. When I'm done I'll head across the street

[@kirkwaggoner7328]

When I joined the Navy back in the '70's there were old torpedoes all over the place. Most that I recall had contra rotating propellers that still turned. The clearance between them was tight enough to do damage to an errant finger in the wrong place, a lesson most only had to learn once before knowing enough to not play with them.

[@jamesoshea580]

They used two propellers to reduce noise I believe.

[@bobsmith3983]

@@jamesoshea580 They used counter rotating propellers to prevent the torpedo from spinning due to the counter torque.

[@sinewave999]

@@jamesoshea580 did you even watch the video????? that's not how it works XD

[@HarmonRAB-hp4nk]

that was so they went straight.... one prob tends to torque it sideways tiny bit :-(

[@sjoormen1]

@@HarmonRAB-hp4nk and spining as that would also reduce the range too, not only true running.

[@Petriefied0246]

One way to reduce noise with contrarotating propellers is to have one odd and one even numbered prop so they don't pass each other at the same time. Also, the rearmost propeller needs to be slightly smaller so that its tips aren't passing through the tip vortices of the foremost propeller.

[@klausnielsen1537]

That might work. Du you know if this has been done?

[@matthewday7565]

I was thinking the same, just like PC fans have an odd number of blades and an even number of supports (also curved supports) to reduce chop noise

[@kuhhnt]

Came here just for this thought.

[@bartlettdieball2678]

@@klausnielsen1537 Yes it has Look at the AN-70 cargo aircraft out of Ukraine it has 8 and 6 blade combos

[@samsungtvset3398]

@Petriefied0246 That has a conceptual similarity to a vernier scale on a caliper or slide rule.

[@tomscott1159]

Geared reduction drives have proven notoriously difficult on small piston-engine aircraft. Placed between an engine going bang-bang-bang and a propeller with relatively huge rotational inertia, the gearbox walks a fine line between being strong enough to withstand the shocks and light enough to be practical. On electric motors and turbines they may prove much more useful.

[@piconano]

Isn't that what the flywheel is for? Doesn't the prop act like a flywheel by itself?

[@tomscott1159]

@@piconano The prop is a huge flywheel which wants to move steadily round and round. The Pistons go bang-bang-bang. There may be a heavy flywheel on stationary engines, but in airplane engines it's reduced to the barest minimum because of weight. In between are the crankshaft going flex-flex-flex and a reduction box going clank-clank-clank on the smallest lightest possible gear teeth. Long ago Continental (see Tiara engines) realized that 2/1 was a bad reduction ratio because the same teeth were pounded over and over, even with a damper added. By the time all was said and done, the Tiara line was no lighter, enjoyed shorter TBOs, were more expensive to build and overhaul, and burned more fuel. Almost 20 years later Porsche learned similar lessons.

[@piconano]

@@tomscott1159 So all these experimental aircraft home builders are screwed? Some use Mazda rotaries or Subaru engines with reduction gearbox. I've never heard of this and I got my private pilot's license in San Diego in 2000. Where can I read more about what you're saying?

[@tomscott1159]

@@piconano Anything can be made to work more or less, but historically, certified geared light general aviation applications have not proven particularly successful. Both Lycoming and Continental brought out geared lines in the 1950s which proved to have no particular weight or performance advantage over slighly larger displacement direct drive competition. The Continental GO-300 in the Cessna 175 would not survive the Lycoming O-360 engines, for instance, because the 300 had shorter TBOs and required a bit more operator finesse to reach them. Likewise in the upscale twin market, the geared Lycoming 480 and 540 series were notorious for demanding smooth and minimal numbers of power changes to preserve gearbox life. Professional corporate pilots fared better at reaching TBO than owner-operators. When small turbines became available they rapidly shrank the market for larger piston twins, with the King Air essentially replacing the Queen Air, for instance. Continental tried a new line of geared engines in the mid 1960s, but they offered no significant advantages to offset greater cost, greater fuel burn, and shorter TBO. Porsche worked with Mooney in the late 1980s to introduce a 200 HP class geared flat six. Less than 50 were installed before Porsche left the market and eventually surrendered the type rating to the FAA. Too heavy, expensive, with short TBO, poor fuel specifics. Today there are several series of small-displacement geared engines available to homebuilders and even a few which are now certified. Most of these are water cooled which makes it a bit easier to build a light-weight high-speed core. Yet by the time the system is complete and installed in an airframe with all accessories and coolant, these rarely offer a huge weight advantage over basic direct-drive air-cooled installations. Smoothness and automated controls are typically the main advantages of these new types. But even in these cases the gearbox is an additional point of failure and a costly component to purchase and overhaul.

[@UncleKennysPlace]

Yep. Torsional vibration is real; designing for maximum torque without considering TV (which forces can be quite spectacular) has caused many a redrive to become scrap.

[@poneill65]

Sharrow: "Our revolutionary Toroidal propellers greatly increase efficiency and reduce noise" Everyone: "Cool, can we have some figures please?" Sharrow: "No, go away. Here's a promotional video" Color me sceptical, but I smell a monorail salesman.

[@leifvejby8023]

Me too - from the public available data I calculated an efficiency of up to 124%, thought hogwash, and left.

[@gr3g0snz]

yeah and US$9k for a set to go on a existing duo prop legs yeah no thankyou

[@kittengray9232]

There is a video of a guy who tested RC boat with 3D-printed propellers. With GPS, hdr camera and so on... Toroidal designs had no advantage or slight disadvantage. 2 long thin blades has the upper hand!

[@GundamReviver]

​@@kittengray9232that dude hasn't tested counter rotating ones yet has he? Was quite an amusing view with his viewer entered designs!

[@davidaugustofc2574]

​@@kittengray9232 3D printed samples cannot be trusted for fluid dynamics experiments unless the surface is really polished, so I'd rather not gonna take your or his word for it unless a proper test is conducted by a qualified person.

[@dfgaJK]

You could've put a huge ad read at the front of the video and I wouldn't have cared... I was too distracted trying to spin my fingers in opposite directions 😂

[@kevindevlieger300]

It's really frustrating. 😛 I tried for a few minutes. I just can't do it. Trying to figure out in my mind how I should do it. Sometimes my one hand suddenly starts spinning the other direction. Sometimes Im not even making circles anymore. 😅

[@PanzerBuyer]

I'm sure it can be done with practice. Reminds me of the guy that could control each of his eyes separately to read two different documents.

[@kevindevlieger300]

@@PanzerBuyer probably. Im getting a little closer to doing it. Right hand small circles. Left hand bigger circles with intervals inbetween. With training it'll possible for sure.

[@lucbloom]

The trick is: make 2 half circles. Really try it. Make a half circle in the opposing direction, stop and repeat but switched. Now keep doing that with shorter stops each time, but keep the 1/2 circle in mind.

[@kensmith5694]

I can do it easily. I can do it where the fingers move at different speeds. That version is hard. Don't look at your fingers. Touch your forefingers together and move your arms up and down. Count off 1,2,1,2 Stop doing that and move your right hand forward and pull in your left like you are punching with alternating fists. Count off 1,2,1,2 Switch back and forth between the two. Then when you can do it easily do both together and there you are.

[@davidmartin3947]

Candela hydrofoiling boats have small, low noise, highly efficient, zero maintenance sea water cooled contra rotating propellors operating right now on their hydrofoils in their C-Pods. Each pod contains two motors, one for each propeller. This seems to me the best and most obvious example of the use of the tech.

[@RenanDavidSoriaAhumada]

dude that sound awesome

[@davidmartin3947]

@@RenanDavidSoriaAhumada They are flying across the water right now in the Stockholm peninsula and elsewhere. Check out the videos. I can't post a link, or the spam filters will kill the post. Almost no wake either, so that they are being introduced in, for instance, Venice.

[@OliverFLehmann]

The dual-motor Dornier Do 335 was an attempt for a practical implementation with one motor at the front and the other, counter rotating, at the end. Being a development of WW2, it was never sent to the battle theater, but test flights showed its benefits and disadvantages.

[@kkobayashi1]

CFM Rise seems to be the best of both - it uses fixed blades behind the propeller (unducted fan) to clean up the airflow without the mechanical complexity of counter-rotating propellers.

[@dm45lm]

I saw a video recently about a new open rotor jet engine being designed by GE and Safran where they have decided to use a hybrid design. Instead of a second counter rotating propeller they use a set of fixed, adjustable blades that act to straighten out the airflow without creating all the noise.

[@gotherecom]

@dm45lm Perhaps set the leading boat prop at the front of a laminar flow tunnel with a trailing prop in the exit of the laminar flow tunnel. The added friction would be more than offset by increased efficiency of the trailing prop, which could also operate at higher rpm's

[@wagnerrp]

There's no such thing as an "open rotor jet engine". That's an oxymoron. You can have an open rotor gas turbine (a.k.a. a turboprop), but the shroud is what makes it a "jet". No shroud, no jet, no jet engine. Turbofans already use adjustable vanes for exactly this purpose. There's nothing new here. The only difference between the turbofan and the "propfan" is that you're running up against the boundary between the shroud being beneficial for eliminating tip losses, and the shroud being detrimental due to skin friction and weight. As you reduce the specific power of the engine, the trades say you should eliminate the shroud. Using vanes versus a contrarotating rotor does not fundamentally change the amount of noise you make. You still have blade interaction regardless, and that blade interaction makes a tremendous amount of noise. There's a lot of complex construction in the shroud of a turbofan to damp the noise output of that system, and when you take the shroud away, you eliminate all those mitigation efforts. This will be loud. The real reason they went with static vanes instead of a rotor is because a rotor is hard and expensive. You can add a gearbox and deal with all the problems PW has had with the GTF, or you can add a third spool and deal with all the complexity and cost of a RR Trent for an aircraft a third the size, or you attach the prop directly to the turbine without needing a shaft in a pusher configuration (see GE36). No one wants a pusher configuration, because no one has an aircraft design that would accept a pusher configuration.

[@andrewday3206]

The Kuznetsov NK-93 Contra-Rotating ducted fan is highly efficient. It has 8 propellers in the front and 10 propellers in the back. It has a 17:1 bypass ration. This design was dropped as funding dried out. It did deal with the noise effectively.

[@tomduke1297]

now that everything is going electric, i can totally see just 2 motors behind each other turning opposite directions, making the gears unnecessary. 15% higher efficiency is worth quite a bit.

[@TheDerperado]

My thoughts exactly aswell.

[@kittengray9232]

You're losing some efficiency from double the electronics and smaller motors. Benefits have to even that out. Same with mechanics. Turbines just position static blades after rotating ones.

[@tomduke1297]

@@kittengray9232 my guess would be that loosing that massive gearbox and its maintenance alone would pretty much make up for it.

[@Axiomatic75]

So a smaller shaft inside a bigger one or how would it work?

[@tomduke1297]

@@Axiomatic75 yes, the front-motor would have a hollow axle.

[@crazymonkeyVII]

The CFM Rise engine solves the mechanical complexity problem by using static blades with a spinning blade behind it. Possibly interesting for a future video?

[@ShuRugal]

the toroidal prop is going to have a real challenge finding a spot in fixed-wing aviation. Virtually all high-performance prop systems use variable-pitch propellers to allow the AoA of the prop to be adjusted by a prop governor to match the relative airflow and transmit the power produced by the engine efficiently into the air at any given combination of airspeed and engine speed. I don't see how the toroid prop COULD be configured to be variable pitch, which would limit the application to uses currently suitable for fixed-pitch props, which basically means low-performance training aircraft and some cheap personal commuter planes.

[@BOBK-jf4qx]

One day, they'll invent lab grown shark cartilage toroidal props that organically change shape under a small current from solar panels... ... but it's going to be the day before a giant asteroid hits the Earth. :D

[@Triple_J.1]

Toroidal propellers are unlikely to ever reach the level of efficiency necessary for economical flight. Their wild popularity only shows the general ignorance of the wider population as well as MIT undergrads on what actually makes an efficient propeller...efficient. Efficiency is defined as thrust horsepower ratio to net horsepower output. Toroidal are about 50% efficient. A good fixed-pitch is 90% efficient and the best are >91%~

[@alphaomega154]

a pair of 2 contra rotating propellers would need different aero design each. or the rear one must have lower RPM speed. this is due to how the air get carried into the first propeller's momentum and rotating towards the first propeller direction so it will hit the second propeller with more energy, making the second propeller, albeit it running at the same RPM speed as the first, to seem to have more velocity in relation to the flow coming towards it. and if both propeller have identical design, if the first propeller works the aero perfectly it will be off efficient when the flow hits the second. so the second propeller must have an individual design for its purpose that to deal with the higher velocity coming, and produce efficient flow and thrust. remember, the flow of the air from the first propeller not only faster towards the rear than what the first propeller is feed into, but also rotate the flow in OPPOSITE to the second propeller rotation. i prefer to have a pair of 2 uniformly rotating propeller with each has different aero design purpose. the first propeller act as the "setup" to condition the flow for the second propeller. not to produce power. then the second is acting as the main propulsion which i believe would works better. and the goal design is to produce ultra high RPM without causing any turbulence breaks between the blades. counter rotating propeller in tandem is tricky to make it fully efficient.

[@kittengray9232]

Rear propeller can have different angle at attack. Even different shape and radius might help.

[@gotherecom]

Now, take it to the next level. The leading boat prop is always turning in water traveling at the speed of the boat. The trailing prop is always turning in water traveling at the speed of the boat PLUS the added prop wash of the leading prop. Therefore, the trailing prop should turn much faster than the leading prop to take advantage of the already moving water.

[@bbqchezit]

If RPM was the only variable you'd be spot on

[@GundamReviver]

Was my thought aswell that you would need different blade designs if you want them to move at the same speed (better option) or different speed with two the same blades (worse idea) My gut feeling would be that the first blade could be Conventional, and the second blade made submarine style or torroidal to counter the higher intake speed cavitation/vibration.

[@piotrprs572]

EXTREMELY WELL done video. In this 11 min. I learn everything I know about this two types of propellers!! GREAT JOB Man!!! Rly great job.

[@billywild5440]

You have a great voice for your videos. Makes it easy to concentrate on the subject matter. Keep up the good work.

[@mrxmry3264]

years ago i went to a museum in germany where they have an antonov 22. i took one look at that bird and i knew that it had counter-rotating props. on one engine the blades were spaced out evenly, one blade every 45 degrees. but on the other engine it was more like 30-60-30.

[@mikemondano3624]

Not sure what that means. A degree is not a measurement of space.

[@mrxmry3264]

@@mikemondano3624 degrees can be a measurement of temperature or, in this case, angle.

[@mikemondano3624]

@@mrxmry3264 Indeed. But the angles need to begin somewhere, have an origin. And angles have nothing to do with spacing. From where are they being measured?

[@mrxmry3264]

@@mikemondano3624 where do you think they are being measured? From one blade to the next, of course,

[@mikemondano3624]

@@mrxmry3264 In a box on the floor?

[@ShuRugal]

@1:50 - i feel a need to point out that spiral slipstream is WAY less of a factor in power-induced-yaw than the effect known as 'p-factor' if you're not familiar, p-factor refers to the prop disk itself producing asymmetric thrust due to the plane's Angle of Attack. At high cruise speeds, p-factor is negligible because the AoA will be only a few degrees. However, at lower speads, a higher AoA is required to obtain the same lift. This results in the relative airstream arriving at an angle to the propeller disk. Because of this offset angle, blades on the ascending side of the disk see a reduced AoA, and blades on the descending side see an increased AoA. With a conventional right-turning engine, this means that the blades on the right side of the disk produce more thrust than the blades on the left side. This effect can be pronounced enough, by itself, to result in loss of rudder authority before the wing actually stalls out, especially in some twin-engine designs operating with one failed engine. p-factor is a much stronger effect than spiral wash, even though spiral wash is the one everyone always worries about.

[@mikemondano3624]

Thank God! The voice of a real person using human diction. Guard your health, please.

[@jacobsmithjr]

I don't watch AI voiced videos. I leave a comment and give the video a thumbs down. If more people did that those videos would go away.

[@mikemondano3624]

@@jacobsmithjr I doubt very much that it is AI. It's a simple text-to-speech program.

[@sergiogcollado]

😂👍🏻

[@mikemondano3624]

@@jacobsmithjr I kind of doubt it. People can automate the making of such videos. They get money if people watch them and since they are free (of work or money) to make, even if 1 out of 100 makes money, it's worth flooding YT with them. KZbin could require that they be flagged, however.

[@sanderbenson1550]

I love contra-rotating propellers, because you don't have to deal with such. In fact, I had been obsessed because to me, it's like fulfilling the need to have one full set of wings to correct the errors one might encounter with one single wing, or other means of propulsion fitting in this case. One thing I would add to the design I suggested in your video about propellers following the tubercle effect was the one detail I completely forgot about until this one. The propeller I had in mind was also one of contra-rotating design.

[@philleasthouse3791]

I'm always fascinated by new (and not-so-new reused) technology. Your enthusiasm for the obscure is palpable. One personal criticism refers to the "soundtrack" - I'm not sure if I'm the only one who hates the use of "interrupted cadence" "music" (deliberately put inverted commas) as it is hugely distracting and harmonically unbalanced, almost to the extent in my case of wanting to close the video. This is, I know irrelevant to the content😢.

[@BulletproofPastor]

I would like to see some study in applying contra-rotating propellers in a ducted fan configuration. The ducting might reduce tip vortices or perhaps damage the enclosure and prove disastrous. Either way, it would be an interesting study.

[@jamesogden7756]

You might be able to find old Navy research using your described method applied to an older generation of torpedoes.... 😉

[@wagnerrp]

It's fairly typical for modern engines to have counter-rotating spools, as they eliminate at least half a stage, and potentially more as that first rotor can be made considerably more aggressive.

[@wrd777]

Ducted, contra-rotating toroids?

[@Triple_J.1]

@@wrd777 toroidal propellers are about half the efficiency of a properly designed propeller.

[@nigelwilliams7920]

Great thanks! With electric drives, you would dispense with the gear box, and just run two motors feeding a shaft within a shaft for the two props. There would I am sure be useful benefits in being able to actually rotate the props at different speeds for certain flight regimens and of course stepper motors are king at that sort of duty. Perhaps one prop off for cruise (say the front prop feathered), and differential speeds for assisting or even replacing roll control. For noise reduction a different number of blades on each shaft has helped, but a 2-3 or a 3-4 or 3-7 beat might still be a bit odd.

[@elonmuskes4874]

There exists a plethora of planes with counter rotating propellers (well almost). Pretty much all turbies use stators in combination with their rotors to counter the rotation of the air flow. It gives (almost) the same efficiency gain without any extra moving parts. In modern jets the stator also act as connecting rods between the casing and the rotor shaft which doubles as a shock dampener af helps with vibration (noise).

[@JoshWalker1]

Also the engine used in the F22 and F35 actually doesn't have static stators (lol). Instead the compressor shaft spins one way and the stator the other, via (afaik) planetary gearbox. This solves a huge problem where rapid changes in thrust or compressor stalls / unstarts jerk the aircraft. This movement was responsible for putting F14 (A model especially) into nearly irrecoverable flat spins

[@erich930]

Counter-rotating is not the same thing as contra-rotating, don't get the terms mixed up!

[@bryanst.martin7134]

@ 10:41- I was an electrician for Duckworth Steel Boats in Fl, USA. Wired as 154' Casino boat. But that isn't Fla background. The issue with this prop design is, it is constrained. It's use could be advantageous to trawlers and ferries. This due to inefficiencies elsewhere in the performance curves. That is a lot of rotational mass that eats energy when accelerating.

[@BrianStDenis-pj1tq]

In marine applications, contra-rotating props have been around for a LONG time. Both Volvo and Mercruiser make them and supply them to this day. However, in marine use at least, they lose efficiency at high speed so they are used mainly on heavier/slower boats and not used on high performance boats.

[@cheekarp2180]

I thought the green 3d print was amazing. When I was a kid we never even had home computers, now in my lifetime I not only saw original dot matrix printers but now 3D printers, it's mind-blowing and we are only a few years into the technology! I bet in a decade or so the 3D printers can do full colour prints, like you don't just print out a miniature for a board game and then paint it, it just comes out painted.

[@Misterspork57]

We already do have something akin to that. Several printers on the market can switch filament types mid-print, and so they can programmatically change colors and print a full color model. There's some issues, of course. One is plastic waste because models like the Bambu line use a single extruder for all the filaments, and so it needs to be purged of the old filament in order to change color. Another is just that they don't look as good as a properly painted model.

[@edbruder9975]

I spent some time as a trucker in Canada. In really cold weather we'd sometimes put cardboard in front of our radiators to keep more heat in the engine. I was warned by an old trucker once to keep the cardboard centred on the radiator, I only had the bottom half covered, because the different wind speeds between the top half and bottom half would cause flexing with every rotation and eventual failure of the fan blades. Is this a problem with contra-rotating propellors? I would think there'd be an increase of pressure between the two blades every time they pass each other.

[@JoeSEED]

You can have a related conversation on Propfans and the transition to Open Rotor jet engines. It's an old idea with some concepts havin contra rotating stages, some single and the latest seem to be single with a stator. They were always promising for fuel efficiency but died due to noise, until recently.

[@ryanjamesloyd6733]

seems to me that as they've already got drones with contra rotating props, printing torroidal props for them would be fairly simple and maybe a good way to test this.

[@texasranger24]

The new open fan engine designs for aircraft do have a fixed second row of "propellers", which have some of the same benefits without the complexity of two counter-rotating props.

[@iskandartaib]

4:05 - note that the A400M doesn't use contra-rotating props, instead, the props on each wing rotate in opposite directions (4 shafts, 4 propellers). I suppose this also does cancel out the spiral slipstreams to some degree. The contrarotating props on the Seafire 47 were supposedly to make the airplane easier to land on carrier decks (it was still not that good of a carrier-borne fighter with its long nose and low drag), it was something the Fleet Air Arm was pushing for towards the end of the war. Tail draggers with single props were notoriously hard to handle on the ground, you had to stand on the rudder to keep the nose from swinging duue to the spiral slipstream acting on the vertical stabilizer, and a contrarorating prop would eliminate this particular problem. They also make sense for torpedoes, since torpedoes don't have long/large surfaces to keep them from spinning in reaction to the propeller's torque.

[@sdas683]

Thank you very much for making this for our current and future generations of innovators and builders. Props.

[@catherinesarah5831]

When talking about propeller efficiency, another interesting topic you may wish to entertain is increasing the efficiency of full displacement hulls. As it was for the Wright Bros to overcome gravity by increasing lift & thrust, I’m sure it’s only a matter of time someone will break the 1.48 constant on full displacement hulls. Thank you. 🙏

[@MindCrime550]

Some thoughts i had: The forward blade is going to have more load because it's going to interact with relatively stationary or groundspeed air. The 2nd prop will intercept already accelerated air (lower load, less rotational torque) and this imbalance will scale/vary with airpseed, air density, and wind. So unless the differential speed/torque can vary between props accordingly this isn't going to happen... also this is higher drag.

[@andrerousseau5730]

What you completely failed to mention was that the trailing propeller in a contra-prop pair is operating in a faster slip-stream and therefore to obtain optimum performance it's design parameters must differ from the one in front, I.e. they're NOT interchangeable.

[@ED-es2qv]

It's incredibly obvious that one propeller is blowing air or water on the second, so mentioning it would be as dumb as pointing out that once a plane takes off, it's moving faster through the air than when it's parked. As for the different air speed requiring a different design, does that mean you need a different design to take off than to fly? Until you test it, I don't think you can make a definitive statement about it.

[@andrerousseau5730]

@@ED-es2qv The concept of "dumb" is riddled through your whole reply - you clearly don't know what you're talking about. take the time to study the DORNIER DO335 Pfeil. This issue was well understood by Dornier who designed the propeller speed reducer/blade pitch controls to accommodate the phenomenon. I think you need to see a doctor about your bout of arrogance as I think you'll find that most people are NOT aware of this issue, after all, that's the point of making an educational video, isn't it? ..to educate!!

[@AufBerghofNAM]

Great observation 😊

[@jamesshimmen7818]

Curiosity would this principle work for wind turbines as I heard they have to limit the amount of blades due to the turbanlance caused behind them

[@andrerousseau5730]

@@jamesshimmen7818 Probably getting in a bit too deep with the mechanical complexity required. Major servicing, e.g. blade removal would be a nightmare.

[@toi_techno]

I remember flying from Dublin to Frankfurt on a propellor plane in '93 It was unbelievably loud and turbulent (and kind of scary)

[@Petriefied0246]

That wouldn't have been a contrarotating propeller though. Lots of regional airlines are propeller driven because they're more efficient in short journeys.

[@douglee2438]

The Wright Flyer had contra rotating propellers. However they were not coaxial. They were driven off the same engine.

[@Zalex612]

If they are not coaxial they are referred to as counter-rotating.

[@ChrisTaylor-NEP]

I guess we're going to see more and more of these, however, one disadvantage with big ships using this will be the loss of transverse thrust, which is very useful for manoeuvring.

[@Llyd_ApDicta]

Don't big ship usually have maneuvering thrusters?

[@ChrisTaylor-NEP]

@@Llyd_ApDicta At the front, but not so often at the back

[@Llyd_ApDicta]

@@ChrisTaylor-NEP So what can't big ships do with these that they can with traditional propellers?

[@ChrisTaylor-NEP]

@@Llyd_ApDicta Traditional propellers can provide transverse thrust at the aft end of the ship if there are no after thrusters (which there rarely are).

[@Llyd_ApDicta]

@@ChrisTaylor-NEP Transversal thrust only works in one direction depending if it's a right- or left-handed propeller, and can work against you as well. I'm not quite sure what you think of as a "big ship" but in case of actual merchant ships this is a non-issue since you have tugs, on medium sized ship you can use maneuvering thrusters in combination with the rudder and on small boats with a outboard engine or a sterndrive, i.e. an engine where the propeller can rotate it easy to work around as well and well worth the increase in efficiency.

[@RedRouge-j4j]

One of your problems in outboard (or pod drive) props is when the electric motor is in line. A video of a pod drive (electric motor in-line) on KZbin shows it is a gyroscope. The boat was demonstrating rudder turns by switching off the motor, turning, and powering up again. The alternative was a near impossibility of turning the rudder/prop while driving. Motors use a lot of metal, that is a lot of gyroscope!

[@gordowg1wg145]

That was very interesting, I had just thought of it being a torque reaction problem, but I learned a lot, thank you 👍😎 Regarding the noise, reportedly, the US was picking up the noise of the Russian "Bear" bombers with their submarine detection mic's on the sea beds.

[@Cynyr]

We basically already do this in turbofan engines.

[@cactus_cuber1589]

And on a lot of boat engines

[@johnmarkgatti3324]

this is why i am still cross that no body took up the Revetec trilobate crank engine for aero use ,it has two contra rotating three lobed central cranks ,the horizontally opposed pistons are linked across the central crank/lobes [the later version arranged two sets of linked pistons in an X making a bit of a radial look ]. The design has built in contra rotating inner and outer shafts .it also produced huge torque at low rpm ,just a perfect aero motor .Plus was as near to 40% actual fuel effeciency as .. could probably double the range of most sport planes .

[@Sythemn]

For EV, one might be able to just have two smaller motors on one controller which would keep them synchronized. The caveat being if one prop required more torque the motors may need to be different sizes to account for this which would make balancing everything an extra step at the design stage.

[@wagnerrp]

Why keep them synchronized? There's no reason to think synchronizing them would yield the highest performance or efficiency.

[@lloydevans2900]

Technically we did have a commercial aircraft with contra-rotating propellers more that 70 years ago in the early 1950s - well, almost: The Saunders-Roe Princess flying boat was designed to be a commercial passenger aircraft, was actually built and successfully flown, though didn't go into service. It was the largest flying boat design ever made and one of the largest non-military aircraft in existence at the time. It had 2 conventional single propellers and 4 sets of contra-rotating propellers, driven by a total of 10 Bristol Proteus turboprop engines. Each set of contra-rotating propellers was hence driven by a pair of engines, with each propeller in the set being driven by its own engine. A few years earlier, there was a piston-engine powered aircraft with a similar propeller arrangement: The Bristol Brabazon had 4 sets of contra-rotating propellers driven by 8 Bristol Centaurus radial engines, again with each propeller in a set driven by its own engine. This was also designed to be a commercial passenger aircraft, serving the luxury market, but again did not go into service. So the idea of using contra-rotating propellers is not a new one, even for non-military aircraft. The only new part is arguably making an aircraft fitted with them into a commercial success. Though having said that, both the Princess and the Brabazon were commercial failures for several other reasons, none of which had anything to do with their contra-rotating propellers.

[@KevinATJumpWorks]

From my POV, using contra-rotating propellers with electric propulsion (i.e. independent RPMs) combined with independent angles of attack is an interesting concept. This way, you can tune the rear prop to deal with the wake of the front prop at different speeds and altitudes.

[@lcambilargiu]

In wind turbines, efficiency drops when the airflow powering a turbine is more turbulent. There are algorithms to maximize farm output reducing power generation where the airflow from upwind turbines affect the downwind ones such that the upwind turbines operate at a lower capacity so that downwind turbines have less turbulent air. As such the whole farm outputs more power. That is only to point out that in the case of a counter-rotating propeller system, the second propeller is pumping turbulent air and therefore suffers an efficiency loss. I think a lot of the noise of the commercial plane using this design was due to that issue. The key would be to try to preserve laminar airflow if that's even possible. The rear mounted systems are likely best and rather than a counter-rotating system, perhaps a set of blades in a stator setup that can redirect air vortexes directly rearwards is a better design.

[@waynewhelan3069]

Good video. You need to mention the weight. Everything in aviation is affected by the weight. It would be great to have the efficency however the added weight will reduce your payload, therefore impacting efficency. The TU-95 you show, as well as the P-51 air racer use contra rotating props because a single prop can not absorb the power produced by the engines in those applications. They tolerate the added weight of the heavier gearbox, and extra prop so they can use the high power. Electification, new technology will not defeat the laws of physics. Every extra gram on an aircraft is 1 less gram you can carry. The Cessna 152 you showed as an example, has an inefficient fixed pitch prop, because an adjustable pitch (Constant speed) is heavier and would reduce the usable load, a contra rotating power on that aircraft would end up being a single seat plane with a 1/2 hour of range.

[@MichaelFlatman]

Interesting video, you've managed to get me excited about propellers somehow

[@jeffeloso]

There may also be a gyroscopic induced yaw when the aircraft pitches with a single propeller.

[@AZREDFERN]

Curious if you could make the system with a 2+3, 3+4, 4+5, 5+6, etc pro layout? That way it’s not nauseatingly loud. Every time the blades pass each other, they basically clap. When 3 blades match at the same time, you get a triple clap. If they’re off by 1, you’re losing some of the benefit, but smoothing out the sound.

[@AJTalks]

Ducted contra-rotating propellers get an even bigger efficiency bump from the ducts removing tip vortices. Studies about the optimized geometry for the ducts claim potentially huge efficiency if the geometry is right. The combination is almost necessary for EVTOLs which need every ounce of thrust they can get to offset the heavy batteries.

[@wagnerrp]

The only reason to have a shroud on an EVTOL is because you can't have large rotors, because you're intending to operate it in compact environments. The traditional helicopter is an efficient design. The modern multirotor exists out of brute force because power is plentiful, but it's not particularly efficient.

[@ricklewis4442]

Can you point me to those studies?

[@AJTalks]

@@ricklewis4442 1. Longfei Zhao and Sergey Shkarayev (2019) found that ducted contra-rotating propeller systems increased static thrust by up to 25% and power loading by 50% compared to open configurations (*International Journal of Micro Air Vehicles*). 2. Dudnikov, Kuznetsov, and Mel’nikova (2023) reported that two-row ducted counter-rotating propellers improved overall efficiency by mitigating flow swirl effects, achieving a measurable boost over single-row designs (*Russian Aeronautics*). 3. Hussain Nouri (2012) demonstrated that a ducted counter-rotating axial fan system achieved significantly higher efficiency than rotor-stator setups, maintaining up to 90% efficiency across varying conditions (arXiv).

[@AJTalks]

@@ricklewis4442 In 2019, Zhao and Shkarayev found that adding a duct increased static thrust by 25% and power loading by 50% compared to open systems, with optimal duct lengths between 28-53% of the propeller diameter. Building on this, Dudnikov's team demonstrated in 2023 that counter-rotating ducted propellers were 27% more efficient than single-row designs, mainly because the rear propeller helps correct the swirling airflow created by the front one. Earlier work by Nouri and colleagues in 2012 validated these benefits, showing that ducted counter-rotating fans maintained high efficiency across different operating conditions, and performed well even when the spacing between fans was increased.

[@AJTalks]

@@ricklewis4442 I tried, but the comments kept getting deleted. There are several, Perplexity or ChatGPT can easily find them for you.

[@captaincole4511]

1:14 Slight correction here. The left yaw motion from the torque of a propeller is a very minor force and acts int he direction of the propeller’s motion. For example, a clockwise rotating propeller rotating from the pilot’s perspective will provide a yaw to the right. The left yaw tendency of an aircraft on takeoff is due to the propeller slipstream hitting the vertical stabilizer, not the torque

[@garywhite2050]

Props👍🏼

[@samsungtvset3398]

I wonder if the two propellers would benefit by being driven from a differential gear setup so that they each received equal torque despite possibly seeing different loads. Any unequal load would make them rotate at unequal speeds, the sum of the two speeds being unchanged. Would help the torque reaction problem on a plane, but might partially undo the smoothed airflow exiting the rear prop.

[@tbird12yt]

Wouldn't it be better to have counter rotating blades close together side-by-side instead of inline? Then they will still cancel out the overall torque on the vehicle without having to change the direction of the air or water and push against each other.

[@michiganengineer8621]

Well, perhaps Veem will put out some numbers in a year or so since they're now milling Sharrow designed props in Oz. I know the NautiStyle channel is putting them on their new Bering. One surprise to me was seeing a Sharrow toroidal as a contra-rotating prop, those on a Merc 600 would be NUTS!

[@diGritz1]

Not sure what the increase in decibels for a smaller plane would be. But in the Tu-95, AKA: Bear, it was substantial. US fighter pilots would regularly intercept them flying up around the arctic circle, and could hear them before seeing them. An impressive feat, especially when you consider how loud a fighter can be. Had a low flying F-16 from the 180th FW and you could feel the sound in your chest. If I'm remembering correctly they were also able to track them using acoustic sensors used to track subs.

[@Demoralized88]

Tu-95 and a few other Prop planes throughout history were known for being insanely loud because the prop tips were supersonic. With large diameter props/fans this becomes a huge design constraint and one of the main reasons why jet airliners were able to cruise faster than turboprops and turbofan engines used today. The TU-95 is a funny example of accepting crazy noise to achieve faster speeds for a strategic bomber in a very Soviet way. I can't even imagine how loud they are in person

[@daemn42]

The noise really isn't about colliding tip vortices. It happens whenever there is any dirty air in front of a prop including that coming off the wing or fuse. This is why aircraft that use a pusher configuration are also very loud, like the piaggio p.180 which is incredibly efficient but banned at many airports. Putting one prop in front of another just means more dirty air and more noise, producing some of the loudest aircraft to have ever existed. The answer being investigated is to put variable pitch blades like stator vanes behind the prop that simply straighten the air out, without having to actually rotate.. increase deficiency without the added noise.

[@SFX95901]

Well from the initial graphic it’s clear that this uses simple sun & ring planetary gears. It’s fairly easy to harvest small ones from electric drills - I’m wondering why that wasn’t your 3D printing project? The planetary gear design could even be used to change the relative velocity between the two props enabling torque assisted maneuvering.

[@jagolago-bob]

The first time I ever flew as a child was on one of the Tupolevs. I still remember it being noisy. People should accept the slower speed of propellor-driven planes for environmental reasons. The airlines can supply us with noise-cancelling headphones to make it easier.

[@spdcrzy]

Counterpoint: a well-made, highly balanced toroidal prop setup requires far LESS maintenance than a normal shaft drive system would - in a marine application. Gearboxes would run smoother because the tolerances can be tighter because the props are balanced so you get less noise (which really is a symptom of wear and efficiency losses). A boat with two IPS (independent pod steering) drive units (engine + transmission) each with a set of contra-rotating toroidal props at the end with a hybrid electric driveline in parallel would be THE most maintenance-free boat. The upfront cost would be higher, yes, but in a marine environment, it's the maintenance costs and time losses that kill both your wallet and your passion. Not the actual cost of the boat.

[@JoeStoffa]

I'd say that almost all commercial airliners have counter-rotating engines. In a turbine engine, while the rotating blades/nozzles are all rotating in the same direction, the stationary buckets/vanes are redirecting the gas in the opposite direction. My layman's understanding is the efficiency is gained by having the fluid flow be perpendicular to the direction of travel, whereas a single blade is imparting some off-axis momentum to the fluid, and that smaller part of the vector isn't propelling you forward.

[@haxi52]

When talking about single engine (single prop) airplanes, P-Factor has a much greater effect on left turning tendencies than torque or slipstream.

[@ColinKlenner]

Recent research has indicated that in aircraft the trailing prop does not need to rotate at all for increased efficiency and thrust. Unclear how that translates to hydrodynamics yet.

[@Lord.Kiltridge]

I can contra rotate by hands with ease. I learned how to do it years ago.

[@macsnafu]

I have a $5 drone toy I bought at Family Dollar, and it has contra rotating propellors. I was wondering how the two propellers interact with each other. And also if contra-rotating propellers might make better fans. You just talked about airplanes and boats.

[@StaK_1980]

A contra-rotating Sharrow propeller? :-) I'd love to see that!

[@MisterDivineAdVenture]

Bummer no test results! Nice job.

[@larsmurdochkalsta8808]

I could be wrong cuz I've mostly looked into the efficiency of counter rotating ducted propellers, but when I did I was seeing significant decreases in efficiency. Like 15-30% less efficient than two separate propellers. This seemed to be due to a combination of drivetrain losses and the rear propeller engaging with turbulent flow. There's a lot of ways in which it is more efficient, like for a given swept area you get significantly greater thrust. But I'm wondering if your improved efficiency numbers are comparing contra rotating to idk synchronous rotating instead of more propellers with equal blade loading.

[@throttleblipsntwistedgrips1992]

Love the shot of the fairy gannet at 10:59

[@jaspertell6764]

You never talked about drones. A pretty famous counter rotating design would be ingenuity on Mars. Also I'm curious why there isn't a dual electric motor design? the axle could house the stator and the blade the rotor, something similar to what verge motorcycles is doing with their electric drive. I know there's added weight by having a second electric motor but eliminating the gear box, increasing reliability, and the potential for some interesting vortices precision control mechanics sounds like it'd be an interesting experiment in the least.. yet the internet hasn't shown me any examples.. why?

[@tsclly2377]

Penta-Volvo has made counter rotating marine propeller inboard and outboards designs for over 20 years.. the problem I deducted with these toroidal propeller designs work best in a small speed range on marine drives. So maybe for and ocean going tug or fast (17-19knots) bulk cargo ship of the twin shaft design..

[@erich930]

To add to your description of the turning tendencies: One of the biggest ones we feel is called P-Factor, which is where the downward moving propeller blade takes a bigger bite of air than the upward moving blade creating a thrust imbalance. This happens because the relative wind encounters the propeller disk from slightly below.

[@surajrao2889]

Next video should be on Hub and hubless conversion of Vehicles to Electric… Fuel to EV with the available kits in the market

[@thekinginyellow1744]

To contrarotate your fingers, start with one high and one low and then think about moving your fingers towards you then away. Makes it much easier ( though not easy)

[@Brainstrong2]

Rear propeller has worse airflow conditions compered to the first one. Two propellers have bigger drag then one big propeller. They use it only if there are no place for one big propeller or in very powerful single motor plane to compensate rotation. But even in such powerful planes as Corsair or thunderbolt they used one big propeller.

[@massimomaraziti5595]

Would a second (back) propeller spinning slightly faster that the first (forward) one make sense? The air flow would be accelerated faster by the second propeller, arguably improving efficiency.

[@Bloodcurling]

I was hired at UTC Aerospace, (Hamilton Sundstrand), and they had the Sikorsky X2 project. Almost 15 years later and no production nor deliveries. Happy I left military contractors

[@Kram1032]

considering the propellers effectively mutually change the precise air flow of each other (especially the leading propeller for the trailing one but I imagine their proximity might be close enough that the trailing one has a direct effect on the leading one as well) I wonder if the optimal thing to do here (for efficiency or for sound) isn't two exactly equal propellers.

[@TheRojo387]

So how does a setup work that combines contrarotating propellers with toroidal shapes?

[@APMo2]

when my design enters prototype phase you'll eventually see how I combined these 2 into 1.

[@MindCrime550]

2:35 You can get the counter rotation perfectly efficient, the problem is the speeds between the two props will need to be dynamic, as the forward one speeds up or increases load the aft one isn't going to see the same loads increase (or decrease) proportional with a fixed gear ratio. There will be conditions where your aft prop is producing unessecary load/drag unless you can dynamically compensate for the changing "exhaust" of the forward propeller. And then as the aft/secondary propeller becomes more efficient the forward prop's dynamics change. This is gonna be tough for a human or a computer to perform better than a single prop. Maybe counter rotation is better in a ducted fan (turbo jets/fans don't (do they?))

[@ArunRamakrishnan]

Russian KA-52 copters use co-axial rotors to great effect. Maybe we can translate those benefits to the TU-95 bear style high speed contra prop setups.

[@UncleManuel]

Well, first of all the main reason why contra-rotating propellers were developed in WWII was the sheer torque the fighter planes had to deal with. Many pilots of Spitfires, Bf-109, P-47 and P-51 did flip their plane on the runway at takeoff - because they were applying the throttle too fast. 😁✌️ After WWII it was seen as a method to archieve more thrust. But realistically they only produced around 1.5x the thrust compared ti a single prop. Like others already wrote the main problem is that in most applications the same size propeller is used for the rear one. Many designers didn't optimize them for the faster airflow and vorticies that the front propeller is creating - thus the noise and efficiency losses. The Boeing 7J7 project had the same problems. This is the reason why the CFM RISE project does thing a bit different. 😉

[@infiniterats3870]

The greatest experimental aircraft of all time, the XF-84H Thunderscreech, used a contra-rotating propeller design.

[@alanchapman5806]

Boeing did do some Prop-fan designs concepts that used contra-rotating propellers, Boeing 7J7

[@anthonyellsmore4532]

Excellent program

[@andym4695]

The P-38 used counter-rotating props, though one engine drove each prop. This keyboard fighter jock loves the P-38. As far as the 110 dB of the Tu-114, I bring you the C-5, which I got to ride back from Europe. it doesn't have the niceties of sound insulation (that weighs a lot), and sounds an awful lot like being trapped inside a giant vacuum cleaner.

[@ZirothTech]

Sounds like quite the ride! Bet it was an awesome experience, even if your ears needed a rest afterwards 😂

[@LA6NPA]

This might work very well in an outboard motor, as that has a 90 degree gearing at the bottom already. Putting in your "half a differential" (basically) will not take up much more space and is a very simple solution. Engine manufacturers might not be ready for toroidal propellers, at the same time, but this should be very easy to implement. It should even be easy to implement for amateurs messing around in their garage! Problem is, a lot of the people who mess around with boat motors and gearing aren't the people who care about efficiency. So maybe start talking about a 15% increase in thrust? 😄

[@JonathanTamm]

The 2 gears on the prop shaft rotating in opposite directions are used to give reverse with contra rotating props a separate reverse is needed. so extra space is and parts are needed.

[@LA6NPA]

@@JonathanTamm Yes, but not much. You have interlocking, 1 horizontal and 1 vertical, gears. You basically only need to add a second vertical on a hollow shaft for the counterrotating (innermost) prop. This is in the little gear box in front of the prop.

[@0005yuki]

contra rotating my fingers makes my brain go numb

[@texmex9721]

It seems like you could simplify they seem a great deal just by spinning the inner and outer shafts with their own separate motor. That does not seem much more complex than a twin engine system, and provides some redundancy as the loss of one motor would not effect the other.

[@pbasswil]

Efficiency quotients above 100% make for enticing video taglines! (As do perpetual motion machines and the Tooth Fairy.)

[@portblock]

my 40ft carver sport fisher had this, it was nice as a single screw will walk at low speed when trying to dock

[@MrEo89]

It would’ve been a huge benefit to us “not” engineering minded if you had color coded the gear shaft and propellers! Whatever colors you want it would’ve made the visualization so much more intuitive!

[@rogerpha1398]

8:33 Thats definitely looks like the explosion of a shaped charge. No wonder those cavitation bubbles are so destructive. Focused blast

[@CC-iq2pe]

It is really interesting that these two technologies haven’t met with windmills to produce higher efficiency windmills which are more quiet and have impact due to low frequency sound waves.

[@darthnihilus511]

I doubt there is anything you can do to a windmill to make it a viable, reliable source of energy, we are finding out the hard way after all of that money wasted 😢

[@dianapennepacker6854]

​@@darthnihilus511lol, have you been living under a rock since 2000? Work for the oil industry? I don't think you know what you're talking about. Clearly you are ignorant on the subject. Wind is the cheapest form of new energy production now, and only getting cheaper. The percentage of total wind will rise significantly. There are literal swathes of areas running off of offshore or land based wind across the world. Any failures happen due to operator error or poorly designed grids. Like in Texas - but wind didn't just fail. Their gas plants also failed. Practical Engineering has a break down on what happened. Stop getting your information off tiktok or Fox News.

[@dianapennepacker6854]

When 3d printing becomes better then definitely for smaller blades. For grid? Right now cost is everything... It just wouldn't make sense when you can purchase much larger designs of a less efficent design for the same price. Afterall the bigger/taller the blade the more power you get by a big factor. It is why we've constantly pushed for bigger standard designs. For example the world's biggest design is coming out at 140m. Just making the blades 10m bigger of the previous record holder netted you 2 more megawatts. Once we hit the limit where going bigger is no longer feasible or wanted then definitely. When that happens I have no idea. China will launch a turbine with some truly monstrous blades at 140m and over 50 tons a piece. Generating like I said 18 megawatts total. Soon we will have ones that are skyscraper tall at 150m plus! Wild.

[@entelechy00]

​@@dianapennepacker6854a more feasible alternative would be a different approach to solar: instead of light changed to direct current electricity with a lot of heat inefficiency and about 5 years life, pull heat directly off man made objects creating the Urban Heat Island Effect (UHI), such as buildings and roads, and storing heat in heat batteries. A heat battery's life is measured in decades, not years, and the side effect of lower temperatures is what climate change activists want, right?

[@The8blackwidow8]

windturbines can only have a maximum efficiency of about 59% and the current designs are getting quite close to that. Having two rotors would be much more challenging and costly than the efficiency gains would ever yield.

[@generessler6282]

The Tu-95 would be an interesting add to this discussion.

[@JayFude]

I wonder about contra-rotating ducted fans / propellers. Ducting makes a normal fan / prop more efficient, and I would love to see a duel setup tested.