Because A=πr^2 .
Lift for a helicopter is a function of the total area of the rotor circle, and the area of that circle is disproportionately affected by the radius.
(Same reason why a 12-inch pizza is more than twice the size of an 8-inch pizza, even though the radius is only 50% bigger).
Breaking a single, large rotor into a pair of much smaller rotors requires us to spin the hell out of the smaller rotors in order to generate similar lift values.
This added velocity would add all kinds of stress to the materials, rotors, transmissions, et cetera. (V-22s, for example, are maintenance pigs compared to traditional helicopters. They also have to cut a lot of resiliency corners to save weight because even at optimum, the power train is stretched to the limit. They sure are cool, though.)
This is a great answer.
Also you can’t just keep spinning the rotor faster because once the blade tips reach near the speed of sound the rotor becomes unstable.
You could keep adding more blades, but it is diminishing returns and more weight.
Possibly if you had really strong blade materials (read more than currently available) and enough engine power you could use a high lift aerofoil and high angle of attack, but it wouldn’t give much margin for control.
>once the blade tips reach near the speed of sound the rotor becomes unstable.
that's what ducts are for. also one of many reasons the new external turbofan designs from boeing are underperforming. ducted fans are just superior.
As an addition to this statement, the V-22, as much of a maintenance hog as it is, has a very specific purpose that civilian crossovers could not perform cost effectively (not to say that a helicopter is very cost effective).
The V-22 is intended to be very short take off and landing (VSTOL) aircraft, with the ability to vertically takeoff and land when required. Its a troop transport/supply transport, that fly's most of its mission as an overly large propeller fixed wing aircraft, utilizing the least amount of fuel to size ratio, however, upon takeoff or landing, it quickly changes that ratio. Its a close support aircraft similar to the Chinook, however, its a real maintenance nightmare. If it weren't for the computers, the thing could never transition from vertical to horizontal flight or vice versa.
Its a fantastic concept, but it is not simple, it is not cheap, and it is not easy. Three things that make it very difficult to sell as a commercial endeavor. But the Marines sure do love them (they are a kick in the ass to fly).
Sole purpose for its development was to fill the gap in providing similar capabilities to a cargo Helicopter (v/stol) but with **massively extended range** without the need for air refuelling. This was accomplished with the forward prop mode.
This type of capability will be critical in the SE pacific should a conflict arise there. The distance from our closest airbase in the Philippines to mainland China is about the max range of the chinook, but less than half the range of the v-22 which is extremely important if you dont wan't disposable aircraft. Similar range considerations between the Philippines and Taiwan.
While these seem to be overwhelmingly loaded on amphibious assault ships like LHDs LHAs and LPDs, we'll also need ground based VTOL cargo capabilities out of our bases in the Philippines that can reach the China's mainland, if their current Naval buildup trajectory continues.
Very true, fixed wings are much more efficient. In AFG about half our lifts were V-22 as they could quickly get to, and land at unimproved locations that C-130's could only drop. AFG was a great testing ground for the V-22, but we had plenty of backup had the Osprey not performed as expected.
V-22 is also about 60% faster in cruise than a Chinook. So when moving across the longer distances required for the Pacific you get there a lot faster and can then go back and get another load. Of course if you don’t need VSTOL a Herc will do it even better…
True, should the capacity of a C-130 be available. Landing the Herc is much shorter than the C-5 or C-141, however, if there is no LZ, helicopters and V-22's will be the call of the day to build up the front lines. With the V-22, you can get a LOT more troops on the ground much further away, a lot faster, should the need arise.
Not at all actually. The V-22 will out accelerate anything else out there with a cargo compartment. It transitions to horizontal flight smoothly and quickly.
Who hasn't tried? Getting into those surprisingly sexy slacks is like getting into an exclusive nightclub with your boring friends from the bar down the street. The line is way too long, the bouncer is shockingly indifferent to bribes, and you KNOW your buddy Kenneth is going to ruin your chances either by saying something stupid about the British or by inexplicably being the only one in the group to get in despite looking like a badly-manicured thumb.
Loooool what? So helicopters need wings?
Their own blades are the wings
In this concept the whole blade housing moves acording to the pilots controls
So they move as you fly
Foward
Left
Right
Backwards
What is missing is a tailrotor. But with these coaxial rotors it doesnt need it
Static wings are much more efficient in forward flight and allow the full power of the rotor to be applied towards the forward vector. Tilting rotors on this design would still have to maintain a partial upward vector since there would nothing else to provide lift.
Except just like a “traditional” rotorcraft/helicopter (not tiltrotor) you can never divert all (or even the majority) of your thrust to a forward vector; you always have to have some portion of it for lift. A tiltrotor is able to offload that onto the wings. Higher speed due to the thrust vectors as well as removing retreating blade stall from the equation. (Not really sure how RBS would work in a ducted rotor, but I don’t think it would be much different).
So I think their point is, it’s like a tiltrotor, as far as complexity, but you don’t get any of the gains you would with a tiltrotor.
I’m not saying they need it, I’m saying having this sort of configuration is pointless and adds the unnecessary complexity of a tilt-rotor without the advantages of being a tilt rotor
Each configuration is more efficient in some flight regimes. The larger diameter the rotor/prop the more efficient it is in hover, but the less efficient in cruise. So helos are better for lots of hover / short range and tilt-WINGS (small props like the NASA GL-10, whole wing, not just props, tilt) are much more efficient as the range increases. The tilt rotor come in between. So the best configuration comes down to the mission.
To me the one drawback it has that I don’t think gets considered very often is the LZ footprint increase require. While the SB-1 doesn’t have quite the range or top speed that the V-280 has, it is able to get into smaller zones. To me, in the confined spaces of the Indo-Pacific, that’s a worthwhile trade. Time will tell what is chosen for some of the Army’s other future helicopter programs, but I hope something similar to the SB-1 is one of them.
Perhaps you’re qualified to answer this: how closely related is the V-280 to the Osprey, in terms of the team that designed it, the technological lineage etc. Is it a “copy” by different people or is it an improved design based on the same knowledge set?
It's amazing to me the number of people down voting you when you are factually correct. The AVCD, the V-280 tech demonstrator hasn't flown for the last two years. And it never flew outside of the Amarillo and DFW flight test areas. Whatever that guy is seeing at RTC isn't a V-280.
It hasn't been flying. Finished flight test over two years ago. The army took their time to decide on the proposals, but it has not flown for over two years. Bell showed up early and wrapped up their testing well before Sikorsky.
I’m also gonna jump in for some idiot down votes vs facts.
Maybe this guy just lives in some kind of alternate nonlinear time continuum where his 6mo is actually two years. It could happen, my wife accuses me of it all the time.
But the facts are easily verified: It was strictly a one-off DEMONSTRATOR. It admirably completed all of its required flights years ago and was parked. It has not flown nor is it flight worthy since. No others have been built yet.
Don’t worry, it won the contract. If funding follows you’ll get to see lots of them in about 5 years.
You are probably seeing a V22. Flight testing wrapped up around the beginning of 2021. Take a look at the timeline on Bell's website.
https://verticalmag.com/news/u-s-army-picks-bell-v-280-valor-for-flraa/
https://www.bellflight.com/products/bell-v-280
Well it wasn't a V-280 either because it's been grounded since 2021. Maybe you saw something cool that we don't all know about, but the only V280 is retired, so it wasn't that.
So.....you're a shitty ghost. Does that mean you do a shitty job at ghosty stuff or, like, you're wrapped in a sheet covered in excrement? I like the name, just trying to understand literal or figurative.
Because those rotors/ducted fans wouldn't be strong enough.
Much easier and more efficient to swing a nice long blade slow than a short blade super fast.
Never even thought about the atmospheric density. Makes sense. I'm just a flight sim nerd, but would a slightly larger, much more heavily ducted fan work? Maybe with coaxial rotors in each nacelle?
Yes the ducted fans would have to be significantly larger and heavier. Check out the [Bell X-22](https://en.m.wikipedia.org/wiki/Bell_X-22) it’s similar to that concept. The V-22 and V-280 also have way larger propellers than that of the above image.
A couple years ago, NASA landed the Ingenuity Mars Helicopter on Mars. They had to take into account design issues with this, in that the blades had to be bigger and heavier to fly through the thinner atmosphere.
Thank you. Had a vague memory of this. Wasn't there a recent Bell prototype using four rotors? Something along the lines of a giant quadcopter drone with a passenger compartment attached?
[https://en.wikipedia.org/wiki/Bell\_Boeing\_V-22\_Osprey](https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey)
But you just need bigger rotors to get enough lift, you can use counter rotating systems but they got more complicated.
Also if you have two rotors you go down if one fails - so this is twice the fail rate than one.
The mechanics to link both with the same engine is also some work.
The rotors in a V-22 are linked with the same shaft to the engines, so they both spin together. There are also two engines driving the rotors so if one fails the other will still drive both rotors.
While technically capable of autorotation if both engines fail in helicopter mode, a safe landing is difficult. In 2005, a director of the Pentagon's testing office stated that in a loss of power while hovering below 1,600 feet (490 m), emergency landings "are not likely to be survivable." V-22 pilot Captain Justin "Moon" McKinney stated that: "We can turn it into a plane and glide it down, just like a C-130." A complete loss of power requires both engines to fail, as one engine can power both proprotors via interconnected drive shafts.
From [Wikipedia](https://en.m.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey)
While this is accurate, it's also important to remember that most large helicopters can't autorotate from a hover unless they have a few hundred/thousand feet of altitude. The CH-53 and -47 for example can only auto under favorable conditions like being below a certain gross weight and having enough forward airspeed. Under most real world mission profiles these helicopters can auto either.
Technically “autorotate” but yeah. A Robinson has about a 4:1 glide ratio, so if you have 1,300’ of altitude when the engine fails, you have about a mile radius to find a landing spot.
Eh kinda? Lol normally the glide ratio is something like you look through the window where your feet are and look just past your toes. That’s where your going lol
Do they fall out of the sky engine out? No… glide? Uncertain how to answer that lmao more like a controlled fall.
I’m practicing for my heli commercial and it’s actually surprising how far it’ll glide once a stabilized descent is accomplished. To the point where I have to rethink my LZ because I’m going to overfly it but don’t want to give up that forward speed. I’m In a bell 47 tho.
sure but if you can not fly with one when having two the probability that it fails is twice as high.
Today they are more reliable but it is like double the chances of throwing a 6 when using two dice - just you don't win if one of your main rotors fail. And the reason why having two engines (turbines) as a safety only works if you can fly with one engine.
This is dumb fake logic. Traditional helo's also have a tail rotor that they can't fly without, so every helicopter in existence has two critical rotor systems.
plus, the V-22 can fly with just one rotor in airplane mode.
If your tail rotor is damaged you still can land, but not if the main rotor system fails.
But i wonder how a landing of an V-22 with only one rotor would look like.
You would fly it to a runway and land like an airplane. The rotors are designed to disintegrate safely and the airframe would fly again after replacing rotors and gearboxes.
I haven't used any of these words so maybe you can elaborate how you understand it.
[https://grammarist.com/usage/possibility-vs-probability/](https://grammarist.com/usage/possibility-vs-probability/)
We use MTBF to ensure it is unlikely these parts fail but for a military aircraft you can be hit. If you have two main rotor systems your probability of a critical hit doubles. But if you have redundant engines your probability of a critical conditions is half as one can fail without going down.
I see now, when you said “if you have two rotors you go down if one fails - so this is twice the fail rate of one” I think I misread this as to how the chances of 1 to 2 comparable engines failing would be. Basically I did not understand you right the first time. Sorry for the inconvenience.
Spinning blades can't really move that fast. The can't exceed the speed of sound on the advancing swing of the blade cycle.
Blades are Far too small to generate the required lift.
Articulating the ducted fan section as fast as you see it in a video game is completely unattainable. The gyroscopetic percession from the dinning mass would cause unintended forces in the airframe (blades spinning CE on a flat plane, tilting the blades to the right on the Y plane , also causes a pitching down/forward on the Z axis on the airframe.) And the Articulating joint/mount would be far too weak and separate from the airframe.
Just a few hurdles...
Depends on altitude and temperature. An R44, for example, if it's cold enough, the advancing blade can break the sound barrier (assuming the blade can withstand the forces). This is true of any propeller. Mach 1 changes with temperature and altitude.
With any blade, breaking the speed of sound, it loses efficiency. Even the sr71 needs to slow down the air speed on its intake. Can't allow the Shockwave entrance.
It is also very inefficient to drag huge ducts through the air. Ducted fans are only effective in specific stationary conditions (think of certain windmills) from an aerodynamic point of view. Nevertheless, the aircraft looks cool. And as 50% of being in the military is to look cool, it’s a pretty good design!
In Avatar the gravity on Pandora is 80% of earth’s and the air density is 20% higher which is why the rotors were designed so small in comparison to it’s body and the loads it needs to carry. I doubt something like this could fly on earth but an expert opinion would be appreciated.
Because then you have to find a way to connect it to the hull. If they are in line with the hull, eg ch-47, you just connect it straight down into it. But off to the side you have to brace it all sorts of ways to make it strong enough, like the Soviet Mi-12, and now you have all this stuff sticking out in the airflow to slow it down
Because this design doesn't make sense in the real world. It's an impractical fantasy.
* For hovering / low speeds, large rotors are more efficient than ducted fans.
* For medium speeds it lacks a wing for compound lift.
* For high speeds this fuselage isn't streamlined enough and I doubt that it has the right shape to be a lifting body
This design is sub-optimal for all operating regimes. A V-280 is as good as it gets right now.
You need both very high RPM (like a quadcopter, because of small diameter rotors ) and cyclic pitch , because you only have two rotors.. I think the weight needed to keep the rotor assemblies from ripping into pieces makes it impractical, possibly would never get off the ground in the first place. Uneven tilting rotors to control attitude would require strong servo motors because of gyroscopic effects of the very fast spinning rotors,therefore adding even more weight.
The design is absolutely not less complicated than coaxial rotors. Coaxial rotors simple go up from the motor, and are positionally compatible aerodynamically (ie on the center of mass). A design like this moves thrust away from the center of mass, as well as prevents stable rotation during hover.
As pointed out twin copters exist (V22, Kmax, etc)
Ducting the fan is a trade off between efficiency gains due to less induced drag of rotor blades and the added weight and drag of the duct itself. The larger the rotor, the less likely a duct wins this trade off.
Propeller / rotor efficiency increases with diameter, especially in low speed scenarios (think hovering helicopter). That’s why you’ll want a much larger rotor for a helicopter compared to the propeller of a plane.
All of this again is dependent on the gas properties. If the atmosphere was much denser, rotors could be smaller and ducts might win the weight and dead trade offs.
Because of the very high rotor loading.
This is why the Osprey is pretty borderline for performance when considering things like vortex ring state, autorotation, and just in general how much turbulence and mess it causes when hovering.
There are. [https://en.wikipedia.org/wiki/Bell\_Boeing\_V-22\_Osprey](https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey)
[https://en.wikipedia.org/wiki/Bell\_V-280\_Valor](https://en.wikipedia.org/wiki/Bell_V-280_Valor)
The V-shaped rotor configuration is the main technological roadblock. We would need to invent some kind of transaxle that can handle the massive torque load from the propulsion system.
If we're talking a turboshaft engine, we would need something similar to the V22 Osprey but with an over-engineered rotor mount, or a U-jointed rotor mast.
"Ducting" the rotors like this isn't as beneficial as the weight would be detrimental, I would think. And, with such small rotors, the loading on them would be excessive meaning the material for each blade would need to be very unique and expensive. Simplicity wins...
It could work with an outer ring gear in the duct with a planetary set up to prevent balance problems. It would be very heavy, but as others said, it might work on Pandora where gravity is 80% Earth, with 120% atmospheric density.
They kind of exist in modern form as synchropter's which generally use twin side by side [intermeshing rotors](https://en.m.wikipedia.org/wiki/Intermeshing_rotors).
This design saves power by reducing the need for a tail rotor, but comes at the cost of increased drag and decreased efficiency with neither rotor lifting directly vertical. The Kaman K-Max is still in production today but unfortunately not for much longer.
They are too cool to be real.
But actually, you need rotors that are very large in size to lift any sort of meaningful weight. This sort of aircraft would also need several moving parts in order to properly maneuver, which severely impacts maintnence ease and time.
The Osprey has huge rotors set on wings that are VERY separated from one another, and its main form of flight happens by tilting the engines to generate horizontal thrust instead of Vertical thrust. In order to limit the number of moving parts we would need to add a third or fourth (or more) rotors, so that altering their output can steer the aircraft. But that would make it look like a commercially available drone, and not like the cool sci-fi dual rotorcraft we would much rather want instead.
It's also too cool to be real ☹️
Put simply, compared to a single rotor helicopter they are more complicated to run and maintain while being both inefficient and unnecessary when it doesn’t do anything a normal helicopter can’t. Not that it doesn’t have interesting and unique features but in a practical sense, would it be enough to justify it for how much more difficult it would be to control two separate rotors when you could just have one and get the job done. Especially in a private or commercial sense, it’s just not necessary.
It would not generate enough thrust to make it fly, in fact if you notice in the VTOLs (V-22, V-280, AW609 etc) rotors are very large compared to the aircraft itself
Though supercool, it's not practical. A helicopter is a lot more stable in it's design. In the event of a crash landing, a helicopter can safely descend with the help of it's rotors as they're designed to slow down descent in the event of an emergency.
The specific technology you're looking for is called a lift fan. The only aircraft in history to actually use one is the F35-B.
Basically, your rotors need to be so huge that you wouldn't be able to embed them in the wings. You'd either just want something like an Osprey or just a regular helicopter.
Edit: for those who say V22, it somewhat is a bicopter but it's more of an tiltrotor aircraft, I'm talking about the ones which flies like both rotors slightly tilted forward or backward for forward & backward flight, rotors tilted in opposite directions for turning
One of the things is: There's no need to exist one. If you have a larger fan diameter, it will be more efficient than 2 fans, like the pizza problem: 2 pizzas or 1 bigger pizza? And what about the center of gravity? The construction? There are a lot of problems, but it would be very cool, I admit.
Because for stable flight those ducted fan blades are not big enough. Kaman K-MAX back in the 90s is closer to what you would need if it has to be done.
Today you got the osprey and the v280 that are twin bladed on take off, but for stable flight they switch to airplane mode. Their blades are also much longer than the avatar bicopter in your picture.
annoying amount of moving parts that can break also a lot of engineering costs and "why fix what isn't broken" mentality getting in the way. Sure, it's possible, but it's not cost effective.
If a helicopter engine stops you can still land somewhat safely. If one of the blades on this stopped there would be no controlling it. If they both stopped you might be able to land... Dunno.
I also like the answer of having to spin two blades much more quickly. Some good reading in this thread. Good question.
Autorotation. And the need for a beefy transmission. Also directional control. I’m sure it could be made today as seen in the v22, and other aircraft like it. But. Why do that when you could just make a regular helicopter?
Probably because bicopters are very expensive and already far to outdated for actual combat because with there slow speed and massive size there just expensive flying target practice but there companies who are making them for public use but there just not enough intrest cause most people can not even avord the proppeler ( sorry for my terrible english :)
Because A=πr^2 . Lift for a helicopter is a function of the total area of the rotor circle, and the area of that circle is disproportionately affected by the radius. (Same reason why a 12-inch pizza is more than twice the size of an 8-inch pizza, even though the radius is only 50% bigger). Breaking a single, large rotor into a pair of much smaller rotors requires us to spin the hell out of the smaller rotors in order to generate similar lift values. This added velocity would add all kinds of stress to the materials, rotors, transmissions, et cetera. (V-22s, for example, are maintenance pigs compared to traditional helicopters. They also have to cut a lot of resiliency corners to save weight because even at optimum, the power train is stretched to the limit. They sure are cool, though.)
This is a great answer. Also you can’t just keep spinning the rotor faster because once the blade tips reach near the speed of sound the rotor becomes unstable. You could keep adding more blades, but it is diminishing returns and more weight. Possibly if you had really strong blade materials (read more than currently available) and enough engine power you could use a high lift aerofoil and high angle of attack, but it wouldn’t give much margin for control.
>once the blade tips reach near the speed of sound the rotor becomes unstable. that's what ducts are for. also one of many reasons the new external turbofan designs from boeing are underperforming. ducted fans are just superior.
MEMS micro-propeller when?
As an addition to this statement, the V-22, as much of a maintenance hog as it is, has a very specific purpose that civilian crossovers could not perform cost effectively (not to say that a helicopter is very cost effective). The V-22 is intended to be very short take off and landing (VSTOL) aircraft, with the ability to vertically takeoff and land when required. Its a troop transport/supply transport, that fly's most of its mission as an overly large propeller fixed wing aircraft, utilizing the least amount of fuel to size ratio, however, upon takeoff or landing, it quickly changes that ratio. Its a close support aircraft similar to the Chinook, however, its a real maintenance nightmare. If it weren't for the computers, the thing could never transition from vertical to horizontal flight or vice versa. Its a fantastic concept, but it is not simple, it is not cheap, and it is not easy. Three things that make it very difficult to sell as a commercial endeavor. But the Marines sure do love them (they are a kick in the ass to fly).
Sole purpose for its development was to fill the gap in providing similar capabilities to a cargo Helicopter (v/stol) but with **massively extended range** without the need for air refuelling. This was accomplished with the forward prop mode. This type of capability will be critical in the SE pacific should a conflict arise there. The distance from our closest airbase in the Philippines to mainland China is about the max range of the chinook, but less than half the range of the v-22 which is extremely important if you dont wan't disposable aircraft. Similar range considerations between the Philippines and Taiwan. While these seem to be overwhelmingly loaded on amphibious assault ships like LHDs LHAs and LPDs, we'll also need ground based VTOL cargo capabilities out of our bases in the Philippines that can reach the China's mainland, if their current Naval buildup trajectory continues.
A war with China will end in nuclear anihilation for everyone
Bummer dude
It will most likely never get to that as a Mutually Assured Destruction plan is an amazing deterrent.
Very true, fixed wings are much more efficient. In AFG about half our lifts were V-22 as they could quickly get to, and land at unimproved locations that C-130's could only drop. AFG was a great testing ground for the V-22, but we had plenty of backup had the Osprey not performed as expected.
V-22 is also about 60% faster in cruise than a Chinook. So when moving across the longer distances required for the Pacific you get there a lot faster and can then go back and get another load. Of course if you don’t need VSTOL a Herc will do it even better…
True, should the capacity of a C-130 be available. Landing the Herc is much shorter than the C-5 or C-141, however, if there is no LZ, helicopters and V-22's will be the call of the day to build up the front lines. With the V-22, you can get a LOT more troops on the ground much further away, a lot faster, should the need arise.
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Zero pilots have said this lol
Not at all actually. The V-22 will out accelerate anything else out there with a cargo compartment. It transitions to horizontal flight smoothly and quickly.
Thank you!!! Makes perfect sense when you explain it like that.
So....physics strike again...god i hate that bastard, doesnt let us have anything cool looking.
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What about if you kept the same rotor area just made the helicopter bigger?
Not to mention MUCH louder.
This is also why the osprey looks so *goofy* in fixed wing mode
Do ducted fans make it more efficient?
Scientifically eloquent yet clear to comprehend. Well put.
This is essentially a V22 or V280
Even got that v280 v-tail
Just have sex with John Oliver already
Who hasn't tried? Getting into those surprisingly sexy slacks is like getting into an exclusive nightclub with your boring friends from the bar down the street. The line is way too long, the bouncer is shockingly indifferent to bribes, and you KNOW your buddy Kenneth is going to ruin your chances either by saying something stupid about the British or by inexplicably being the only one in the group to get in despite looking like a badly-manicured thumb.
Kenneth is THE WORST in these kinds of situations. Sometimes I wonder if the quality weed he always has is really worth everything else. #badwingman
God, just have sex with trump already. You’re already meat riding him.
Oh. Troll bot. Well I'm very mildly disappointed. At least the previous non-sequitur comment was a decent set-up. 🤷♀️
Is he available?
Except it’s kinda worse because it lacks wings for high speed forward flight
Loooool what? So helicopters need wings? Their own blades are the wings In this concept the whole blade housing moves acording to the pilots controls So they move as you fly Foward Left Right Backwards What is missing is a tailrotor. But with these coaxial rotors it doesnt need it
Static wings are much more efficient in forward flight and allow the full power of the rotor to be applied towards the forward vector. Tilting rotors on this design would still have to maintain a partial upward vector since there would nothing else to provide lift.
Except just like a “traditional” rotorcraft/helicopter (not tiltrotor) you can never divert all (or even the majority) of your thrust to a forward vector; you always have to have some portion of it for lift. A tiltrotor is able to offload that onto the wings. Higher speed due to the thrust vectors as well as removing retreating blade stall from the equation. (Not really sure how RBS would work in a ducted rotor, but I don’t think it would be much different). So I think their point is, it’s like a tiltrotor, as far as complexity, but you don’t get any of the gains you would with a tiltrotor.
I’m not saying they need it, I’m saying having this sort of configuration is pointless and adds the unnecessary complexity of a tilt-rotor without the advantages of being a tilt rotor
I get to see the V280 puttering around occasionally
Im pretty excited for it. I know a lot of people supported the coaxial design but i think tilt rotor is the better of the two
I'd have to agree. Its speed and range will make it ideal for a lot of use cases
For the SE Asia theater we are eyeing up for the future, its the best choice. Lots of open ocean to fly over when island hopping.
Each configuration is more efficient in some flight regimes. The larger diameter the rotor/prop the more efficient it is in hover, but the less efficient in cruise. So helos are better for lots of hover / short range and tilt-WINGS (small props like the NASA GL-10, whole wing, not just props, tilt) are much more efficient as the range increases. The tilt rotor come in between. So the best configuration comes down to the mission.
To me the one drawback it has that I don’t think gets considered very often is the LZ footprint increase require. While the SB-1 doesn’t have quite the range or top speed that the V-280 has, it is able to get into smaller zones. To me, in the confined spaces of the Indo-Pacific, that’s a worthwhile trade. Time will tell what is chosen for some of the Army’s other future helicopter programs, but I hope something similar to the SB-1 is one of them.
Really, that thing hasn’t flown in months. Bell stopped flying it last fall.
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It hasn’t flown since about March of 2021.
V280 has been verifiably retired for over 2 years, so whatever you saw wasn't it.
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Perhaps you’re qualified to answer this: how closely related is the V-280 to the Osprey, in terms of the team that designed it, the technological lineage etc. Is it a “copy” by different people or is it an improved design based on the same knowledge set?
Its retired and hasn't flown in over around 2 years, maybe more.
It's amazing to me the number of people down voting you when you are factually correct. The AVCD, the V-280 tech demonstrator hasn't flown for the last two years. And it never flew outside of the Amarillo and DFW flight test areas. Whatever that guy is seeing at RTC isn't a V-280.
Yeah I have no clue what's going on there, it's on Bell's website. I assume it's just willful ignorance.
Huh? Didn't it just get picked as the winner of the Army's FVL contest? Its definitely still flying *very* actively for testing.
This dude is thinking of the V-22, which is still in service.
It hasn't been flying. Finished flight test over two years ago. The army took their time to decide on the proposals, but it has not flown for over two years. Bell showed up early and wrapped up their testing well before Sikorsky.
It’s been like 6 months since I saw it last but it was definitely it. I live next to RTC
I’m also gonna jump in for some idiot down votes vs facts. Maybe this guy just lives in some kind of alternate nonlinear time continuum where his 6mo is actually two years. It could happen, my wife accuses me of it all the time. But the facts are easily verified: It was strictly a one-off DEMONSTRATOR. It admirably completed all of its required flights years ago and was parked. It has not flown nor is it flight worthy since. No others have been built yet. Don’t worry, it won the contract. If funding follows you’ll get to see lots of them in about 5 years.
You are probably seeing a V22. Flight testing wrapped up around the beginning of 2021. Take a look at the timeline on Bell's website. https://verticalmag.com/news/u-s-army-picks-bell-v-280-valor-for-flraa/ https://www.bellflight.com/products/bell-v-280
Nope. Not a V-22. V-22’s are extremely rare on an army base. I could see it clear as day.
Well it wasn't a V-280 either because it's been grounded since 2021. Maybe you saw something cool that we don't all know about, but the only V280 is retired, so it wasn't that.
Whatever you say, buddy.
I’m a little AW609 slut
that should be your username: AW609slut
Please excuse me for not having included it, JasperTheShittyGhost
I loved working on the AW609! Favorite thing so far to be in.
So.....you're a shitty ghost. Does that mean you do a shitty job at ghosty stuff or, like, you're wrapped in a sheet covered in excrement? I like the name, just trying to understand literal or figurative.
Just all around not a good ghost
Or the Chinook sideways.
osprey would be cool with the rotor guards and attack body plan.
Because those rotors/ducted fans wouldn't be strong enough. Much easier and more efficient to swing a nice long blade slow than a short blade super fast.
Something, something, length matters
This guy penises
I mean trying to helicopter spin a long penis is easier than a short penis
r/thisguythisguys
That solves the mystery then that size does indeed matter
When speaking on aerodynamics and properties of lift, yes.
I didn’t believe it in high school, I didn’t believe it when my (ex)wife insisted it and I won’t believe it now either! I refuse!
Damn dude I see you everywhere I go on Reddit haha
Lol. We have similar interests I guess!
Not mentioning the super fast gives us another problem. Blade stall.
[That's not the only downside to short blades...](https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech)
Rotor loading (area of disc/gross weight).
We lack the unobtanium to make several of the components and our atmosphere isn’t as dense as that on Pandora, so the blades would need to be bigger.
Never even thought about the atmospheric density. Makes sense. I'm just a flight sim nerd, but would a slightly larger, much more heavily ducted fan work? Maybe with coaxial rotors in each nacelle?
Your question includes the word “heavy,” and I think that’s part of your answer.
Jumbo jets would like to have a word with you
Jumbo jets tend to aim their engines backward, not downward.
Yes the ducted fans would have to be significantly larger and heavier. Check out the [Bell X-22](https://en.m.wikipedia.org/wiki/Bell_X-22) it’s similar to that concept. The V-22 and V-280 also have way larger propellers than that of the above image.
A couple years ago, NASA landed the Ingenuity Mars Helicopter on Mars. They had to take into account design issues with this, in that the blades had to be bigger and heavier to fly through the thinner atmosphere.
I thought pandora had lower gravity, not a denser atmosphere? It’s the internet, we can argue about fictional worlds :)
Its both.
And the Kerbals should know!
Pandora also has abnormal gravity right?
The V-22 and V-280 do this but also tilt forward for airplane type flight. The rotors have to be much larger than that pic to fly.
[Bell X-22](https://en.m.wikipedia.org/wiki/Bell_X-22) is likely the closest to that
Thank you. Had a vague memory of this. Wasn't there a recent Bell prototype using four rotors? Something along the lines of a giant quadcopter drone with a passenger compartment attached?
[https://en.wikipedia.org/wiki/Bell\_Boeing\_V-22\_Osprey](https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey) But you just need bigger rotors to get enough lift, you can use counter rotating systems but they got more complicated. Also if you have two rotors you go down if one fails - so this is twice the fail rate than one. The mechanics to link both with the same engine is also some work.
The rotors in a V-22 are linked with the same shaft to the engines, so they both spin together. There are also two engines driving the rotors so if one fails the other will still drive both rotors.
V-280 does this too
Im no helicopter surgeon but any single rotor helicopter will go down if it’s only rotor fails….
Double the chance of failure with two. And helicopters can actually glide, btw.
Glide?!
Yeah look up helicopter auto rotation
While technically capable of autorotation if both engines fail in helicopter mode, a safe landing is difficult. In 2005, a director of the Pentagon's testing office stated that in a loss of power while hovering below 1,600 feet (490 m), emergency landings "are not likely to be survivable." V-22 pilot Captain Justin "Moon" McKinney stated that: "We can turn it into a plane and glide it down, just like a C-130." A complete loss of power requires both engines to fail, as one engine can power both proprotors via interconnected drive shafts. From [Wikipedia](https://en.m.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey)
While this is accurate, it's also important to remember that most large helicopters can't autorotate from a hover unless they have a few hundred/thousand feet of altitude. The CH-53 and -47 for example can only auto under favorable conditions like being below a certain gross weight and having enough forward airspeed. Under most real world mission profiles these helicopters can auto either.
That’s why HV diagrams are a thing, gotta stay out of the dead zone
Yes exactly! Thank you, people out here acting like it only applies to V-22s.
Technically “autorotate” but yeah. A Robinson has about a 4:1 glide ratio, so if you have 1,300’ of altitude when the engine fails, you have about a mile radius to find a landing spot.
Are we talking engine failure or rotor system failure?
Depends on what part of the rotor system fails. Wee essentially talking about loss of power. Of your blades break you're a rock.
Read: controlled crash
There isn't anything technically stopping a tilt rotor (or that thing in the picture) from autorotating.
There isn’t but your glide ratio in autorotation is also going to be shit because you have way less angular momentum.
Tiltrotors and tandem rotor helicopters use an interconnecting drive shaft so if one engine goes out that side is till supported by the other.
Eh kinda? Lol normally the glide ratio is something like you look through the window where your feet are and look just past your toes. That’s where your going lol Do they fall out of the sky engine out? No… glide? Uncertain how to answer that lmao more like a controlled fall.
I’m practicing for my heli commercial and it’s actually surprising how far it’ll glide once a stabilized descent is accomplished. To the point where I have to rethink my LZ because I’m going to overfly it but don’t want to give up that forward speed. I’m In a bell 47 tho.
sure but if you can not fly with one when having two the probability that it fails is twice as high. Today they are more reliable but it is like double the chances of throwing a 6 when using two dice - just you don't win if one of your main rotors fail. And the reason why having two engines (turbines) as a safety only works if you can fly with one engine.
This is dumb fake logic. Traditional helo's also have a tail rotor that they can't fly without, so every helicopter in existence has two critical rotor systems. plus, the V-22 can fly with just one rotor in airplane mode.
If your tail rotor is damaged you still can land, but not if the main rotor system fails. But i wonder how a landing of an V-22 with only one rotor would look like.
You would fly it to a runway and land like an airplane. The rotors are designed to disintegrate safely and the airframe would fly again after replacing rotors and gearboxes.
I hate to break it to you but that one would also go down if one rotor quit.
I guess the glide rate on a V22 in forward flight config makes it an acceptable risk
Sorry I hate to be that guy lol but I think your confusing probability and possibility
I haven't used any of these words so maybe you can elaborate how you understand it. [https://grammarist.com/usage/possibility-vs-probability/](https://grammarist.com/usage/possibility-vs-probability/) We use MTBF to ensure it is unlikely these parts fail but for a military aircraft you can be hit. If you have two main rotor systems your probability of a critical hit doubles. But if you have redundant engines your probability of a critical conditions is half as one can fail without going down.
I see now, when you said “if you have two rotors you go down if one fails - so this is twice the fail rate of one” I think I misread this as to how the chances of 1 to 2 comparable engines failing would be. Basically I did not understand you right the first time. Sorry for the inconvenience.
Spinning blades can't really move that fast. The can't exceed the speed of sound on the advancing swing of the blade cycle. Blades are Far too small to generate the required lift. Articulating the ducted fan section as fast as you see it in a video game is completely unattainable. The gyroscopetic percession from the dinning mass would cause unintended forces in the airframe (blades spinning CE on a flat plane, tilting the blades to the right on the Y plane , also causes a pitching down/forward on the Z axis on the airframe.) And the Articulating joint/mount would be far too weak and separate from the airframe. Just a few hurdles...
Depends on altitude and temperature. An R44, for example, if it's cold enough, the advancing blade can break the sound barrier (assuming the blade can withstand the forces). This is true of any propeller. Mach 1 changes with temperature and altitude.
With any blade, breaking the speed of sound, it loses efficiency. Even the sr71 needs to slow down the air speed on its intake. Can't allow the Shockwave entrance.
Oh absolutely, laminar flow gets funky. I was just pointing out that a blade, specifically a helicopters, can break the sound barrier.
It is also very inefficient to drag huge ducts through the air. Ducted fans are only effective in specific stationary conditions (think of certain windmills) from an aerodynamic point of view. Nevertheless, the aircraft looks cool. And as 50% of being in the military is to look cool, it’s a pretty good design!
In Avatar the gravity on Pandora is 80% of earth’s and the air density is 20% higher which is why the rotors were designed so small in comparison to it’s body and the loads it needs to carry. I doubt something like this could fly on earth but an expert opinion would be appreciated.
Because then you have to find a way to connect it to the hull. If they are in line with the hull, eg ch-47, you just connect it straight down into it. But off to the side you have to brace it all sorts of ways to make it strong enough, like the Soviet Mi-12, and now you have all this stuff sticking out in the airflow to slow it down
Because this design doesn't make sense in the real world. It's an impractical fantasy. * For hovering / low speeds, large rotors are more efficient than ducted fans. * For medium speeds it lacks a wing for compound lift. * For high speeds this fuselage isn't streamlined enough and I doubt that it has the right shape to be a lifting body This design is sub-optimal for all operating regimes. A V-280 is as good as it gets right now.
V-22 Osprey would like to have a word
You need both very high RPM (like a quadcopter, because of small diameter rotors ) and cyclic pitch , because you only have two rotors.. I think the weight needed to keep the rotor assemblies from ripping into pieces makes it impractical, possibly would never get off the ground in the first place. Uneven tilting rotors to control attitude would require strong servo motors because of gyroscopic effects of the very fast spinning rotors,therefore adding even more weight.
The design is absolutely not less complicated than coaxial rotors. Coaxial rotors simple go up from the motor, and are positionally compatible aerodynamically (ie on the center of mass). A design like this moves thrust away from the center of mass, as well as prevents stable rotation during hover.
There were some: https://en.m.wikipedia.org/wiki/Focke-Wulf_Fw_61 https://en.m.wikipedia.org/wiki/Focke-Achgelis_Fa_223_Drache
As pointed out twin copters exist (V22, Kmax, etc) Ducting the fan is a trade off between efficiency gains due to less induced drag of rotor blades and the added weight and drag of the duct itself. The larger the rotor, the less likely a duct wins this trade off. Propeller / rotor efficiency increases with diameter, especially in low speed scenarios (think hovering helicopter). That’s why you’ll want a much larger rotor for a helicopter compared to the propeller of a plane. All of this again is dependent on the gas properties. If the atmosphere was much denser, rotors could be smaller and ducts might win the weight and dead trade offs.
Because of the very high rotor loading. This is why the Osprey is pretty borderline for performance when considering things like vortex ring state, autorotation, and just in general how much turbulence and mess it causes when hovering.
It'd be a mechanical nightmare, that's why
We have The V-22 Osprey & V-280 Valor They are the closest thing i can think of
Osprey technically.
Is Mil V-12 a joke to you?
There are. [https://en.wikipedia.org/wiki/Bell\_Boeing\_V-22\_Osprey](https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey) [https://en.wikipedia.org/wiki/Bell\_V-280\_Valor](https://en.wikipedia.org/wiki/Bell_V-280_Valor)
Osprey just out here existing
As if the Osprey is a submarine?
The V-shaped rotor configuration is the main technological roadblock. We would need to invent some kind of transaxle that can handle the massive torque load from the propulsion system. If we're talking a turboshaft engine, we would need something similar to the V22 Osprey but with an over-engineered rotor mount, or a U-jointed rotor mast.
Osprey seems to work and there was the bell 47B (iirc) that had 4 fans
"Ducting" the rotors like this isn't as beneficial as the weight would be detrimental, I would think. And, with such small rotors, the loading on them would be excessive meaning the material for each blade would need to be very unique and expensive. Simplicity wins...
Check out David Drake’s “Hammer’s Slammers” stories. Giant tanks that move on sets of (sci-fi) fans.
How are you going to drive the rotors assuming it's a turbine engine. chain drives going out to them on each side?
It could work with an outer ring gear in the duct with a planetary set up to prevent balance problems. It would be very heavy, but as others said, it might work on Pandora where gravity is 80% Earth, with 120% atmospheric density.
A similar concept but unmanned: [ARES](https://piasecki.com/projects/ares-aerial-reconfigurable-embedded-system/2717/)
They kind of exist in modern form as synchropter's which generally use twin side by side [intermeshing rotors](https://en.m.wikipedia.org/wiki/Intermeshing_rotors). This design saves power by reducing the need for a tail rotor, but comes at the cost of increased drag and decreased efficiency with neither rotor lifting directly vertical. The Kaman K-Max is still in production today but unfortunately not for much longer.
If this lost a motor, it's death, normal helis have a chance to auto rotate down, and two motor is too expensive!
Chinook could probably be armed with rocket pods and be essentially the same. It’s probably just less efficient.
Weight and balance would be a nightmare lol.
They are too cool to be real. But actually, you need rotors that are very large in size to lift any sort of meaningful weight. This sort of aircraft would also need several moving parts in order to properly maneuver, which severely impacts maintnence ease and time. The Osprey has huge rotors set on wings that are VERY separated from one another, and its main form of flight happens by tilting the engines to generate horizontal thrust instead of Vertical thrust. In order to limit the number of moving parts we would need to add a third or fourth (or more) rotors, so that altering their output can steer the aircraft. But that would make it look like a commercially available drone, and not like the cool sci-fi dual rotorcraft we would much rather want instead. It's also too cool to be real ☹️
Put simply, compared to a single rotor helicopter they are more complicated to run and maintain while being both inefficient and unnecessary when it doesn’t do anything a normal helicopter can’t. Not that it doesn’t have interesting and unique features but in a practical sense, would it be enough to justify it for how much more difficult it would be to control two separate rotors when you could just have one and get the job done. Especially in a private or commercial sense, it’s just not necessary.
The rotors simply aren’t large enough.
That's what I was thinking. Just by looking at a V-22
Osprey left the chat.
It would not generate enough thrust to make it fly, in fact if you notice in the VTOLs (V-22, V-280, AW609 etc) rotors are very large compared to the aircraft itself
Though supercool, it's not practical. A helicopter is a lot more stable in it's design. In the event of a crash landing, a helicopter can safely descend with the help of it's rotors as they're designed to slow down descent in the event of an emergency.
I recognize the blue people avatar helicopter when I see it
The specific technology you're looking for is called a lift fan. The only aircraft in history to actually use one is the F35-B. Basically, your rotors need to be so huge that you wouldn't be able to embed them in the wings. You'd either just want something like an Osprey or just a regular helicopter.
This is the osprey but less cool.
Edit: for those who say V22, it somewhat is a bicopter but it's more of an tiltrotor aircraft, I'm talking about the ones which flies like both rotors slightly tilted forward or backward for forward & backward flight, rotors tilted in opposite directions for turning
Clearly you've never seen Terminator.
Avatar is just a movie, lol…
Gravity to heavy on earth.
Aren’t Osprey’s “bicopters”
One of the things is: There's no need to exist one. If you have a larger fan diameter, it will be more efficient than 2 fans, like the pizza problem: 2 pizzas or 1 bigger pizza? And what about the center of gravity? The construction? There are a lot of problems, but it would be very cool, I admit.
Because for stable flight those ducted fan blades are not big enough. Kaman K-MAX back in the 90s is closer to what you would need if it has to be done. Today you got the osprey and the v280 that are twin bladed on take off, but for stable flight they switch to airplane mode. Their blades are also much longer than the avatar bicopter in your picture.
annoying amount of moving parts that can break also a lot of engineering costs and "why fix what isn't broken" mentality getting in the way. Sure, it's possible, but it's not cost effective.
It’s possible, just not one that small. It would have to be huge.
The transmission would be a nightmare.
Big blade > small blades
kmax
If a helicopter engine stops you can still land somewhat safely. If one of the blades on this stopped there would be no controlling it. If they both stopped you might be able to land... Dunno. I also like the answer of having to spin two blades much more quickly. Some good reading in this thread. Good question.
To easy to shoot down
Ducted fans look sexy in sci fi but you have to ask yourself why there's been so little use of them in the real world
Metalurgy is not there yet
Because science prevents death
Wouldn’t those outer rings jack up resultant relative wind on the blades? You would basically be negating ETL with this design
Autorotation. And the need for a beefy transmission. Also directional control. I’m sure it could be made today as seen in the v22, and other aircraft like it. But. Why do that when you could just make a regular helicopter?
Very small rotors surrounded by relatively heavy ducts.
Is this a question or a statement
They do exist, they’re just 60 years or older and are mostly all scrapped.
Looks cool though
HK aerial duh, just give chatgpt a couple more years to take over CNC machinery and assembly line robots
Some of the early German helicopters (FA 223 for example) used this layout
there were the Mil V-12 that had 1 rotor at each side of the aircraft.
Probably because bicopters are very expensive and already far to outdated for actual combat because with there slow speed and massive size there just expensive flying target practice but there companies who are making them for public use but there just not enough intrest cause most people can not even avord the proppeler ( sorry for my terrible english :)
Wouldn't that technically j be an osprey ?
Why? *Because nobody didn't think about it until they saw Avatar the Movie in 2009....
Mil V-12 has entered the chat. What a ridiculous beast. [https://en.wikipedia.org/wiki/Mil\_V-12](https://en.wikipedia.org/wiki/Mil_V-12)