Son of CV-22B Osprey: Air Force Research Lab contracts Bell for high speed VTOL study

autoeac

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I like the idea of electric motors for the rotors. Battery weight is still an issue but the jet engines could recharge the batteries while inflight. I also think the plane could take off vertically tethered to an electric or a fuel line until it's 50 or 100 feet in the air. Hovering, the line replenishes the fuel and then the plane is released.


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Well, great minds think alike...sorta! This is even a better idea. My concept was to provide more fuel at that critical stage when the engines are using the most.
 

yasotay

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Floating (movable) refuel stations are much harder to target than a 10,000 foot (~3.5 km) runway attached to equally massive tarmacs with a fat fuel farm associated with it. In environments where there is more water than land this also gives you flexibility. Would be even more difficult to target if they are (semi) submersible.
 

shin_getter

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Submerged fuel (with detachable ballast to float), prepositioned by UUV, supporting on seaplane/vtol tanker aircraft is exactly what is needed to penetrate A2AD. No technical breakthrough is needed either.
 

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If the base aircraft have decent range (but safe bases are further still), a large area can be used for resupply and only one location needs to have workable sea state. If the entire area of operations is under a storm or something, well sometimes operations just have to wait.
 

yasotay

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If you are dealing with Sea State 3 and above then as mentioned above you are going to have to have contingencies in place. There are technologies than can mitigate some of the (lesser) sea states around the system and generate electrical power as well. I am not sure that I would expect to see these sort of thing on the high seas, but more likely closer to land but able to be moved if they cannot move themselves.
 

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now that i think about it..... how many pounds of thrust would it take for military grade VTOL??? i need some math help here. i have an idea but i need those numbers. it would have to be able to lift an M1A1 at the very least.
 

TomcatViP

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now that i think about it..... how many pounds of thrust would it take for military grade VTOL??? i need some math help here. i have an idea but i need those numbers. it would have to be able to lift an M1A1 at the very least.
1.4 T/W ratio usually. Less will restrain your ability to operate freely.
Think also that your blade loading will tend to increase that value as it raises (and reciprocally).
 
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stealthflanker

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now that i think about it..... how many pounds of thrust would it take for military grade VTOL??? i need some math help here. i have an idea but i need those numbers. it would have to be able to lift an M1A1 at the very least.

At very least 1.05 as what Harrier did but as Tomcat said above.. more would be better.

The challenge would be what kind of speed you want. If your requirements dictates low speed maybe something as fast as Helicopters, large helicopters would suffice or Multirotor like Mil Mi-12. Or if you can build a very large single blade to give the best (means low) disc loading, it will require less power to produce the required thrust and more importantly more efficient in hover (lesser fuel burn)

Anything faster like if you want to match military transport at mach 0.6-0.9 range will immediately increase the technical complexities. Lift jets are the simplest yet have very high fuel burn. One may also ended up having to resort to multiple engines. Like lifitng a fully operational Abrams with weight of say 65 metric tonne fully VTOL + your plane & fuel may require about 100 Metric tonne of thrust to take off. and This is kinda hard, with current jet engine. You may need at least 3 Trent XWB engine, maybe 4th engine for balancing purpose.

The giant helicopter solution, with single rotor will net you about requirement of 62 m diameter rotor, with power requirement of somewhere around 33000-47000 SHp but it will be bit slow, with all up weight of 150 metric tonne, disc loading of 50 Kg/sqm. It's big but propwash hazard is minimum. it can safely overfly tent or public place without making anything fly.

To reduce the fuel burn (SFC) one have to resort on larger fan which lowers the disc loading but give you problem on where to stow the fan and whether it can contribute to the propulsion or it will be a deadweight instead.
 

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would it be possible to downscale the Pratt & Whitney JT9D-7A? and put it in a better housing? it would work. it has the thrust capabilities with two even if they are downscaled a bit. you could have the same tilt system it wouldnt matter. and i was also thinking you could put some sort of gyro in it to assist with VTOL?
 

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I wonder how they will deal with the air flow effects of the blade twist at high speed in relation to the nacelles and the wing joint.

Since the rotors are used for a much smaller flight corridor (essentially only hover & transition and not full high speed flight) the twist required in the blades would be considerably less than a conventional proprotor, and therefore more suitable for folding conformally to a pylon and into the slots Bell seems to be illustrating.

The bigger problem is turbulence when in the folded state. I wouldn't want to be the guy having to justify the fatigue/dam tol of the folded rotor for the high speed turbulence case. Not sure I'd even want to be the static stress guy on that job.

It looks like Bell has some patent applications for retention clamps that appear to be intended to stabilize the blades in the folded state by grabbing the tabs on the blade trailing edge (you can see if you look closely in the video), which would help with flutter and high cycle fatigue. There was also another version of the same application with pneumatic bladders to squeeze the blade tabs as well.


US20210094683A1-20210401-D00007.png
 

steelpillow

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even cast irons and pigs could fly

Here is a French flying flatiron from 1937:

nimbus-fanpy.jpg

More seriously, I have to wonder whether a tiltrotor with additional jet engines for forward thrust makes any sense. The rotor is used for lift, but then why not just run up the jets, stop the rotor and fold it away like any carrier-borne chopper? Why all the tilt-everything-in-sight-first malarkey? Makes no sense to me, someone appears to be throwing out absurd concept artwork, but whether through ignorance or malice aforethought I neither know nor care.
I'd as likely bet my money on Professeur Nimbus there; he at least flew, if only as nose art on DH 88 Comet F-ANPY (formerly G-ACSR).
 

Spyclip

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even cast irons and pigs could fly

Here is a French flying flatiron from 1937:

View attachment 664681

More seriously, I have to wonder whether a tiltrotor with additional jet engines for forward thrust makes any sense. The rotor is used for lift, but then why not just run up the jets, stop the rotor and fold it away like any carrier-borne chopper? Why all the tilt-everything-in-sight-first malarkey? Makes no sense to me, someone appears to be throwing out absurd concept artwork, but whether through ignorance or malice aforethought I neither know nor care.
I'd as likely bet my money on Professeur Nimbus there; he at least flew, if only as nose art on DH 88 Comet F-ANPY (formerly G-ACSR).

The "stowed rotor" helicopter concept is nothing new. The issues are that it requires a rotor stiffness far in excess what is reasonable or feasible due to all sorts of structural, weight, and aeroelastic concerns. Sikorsky came to this conclusion a half century ago, which is why we ended up with ABC aircraft when CARA flopped. CL-945 was also a neat bit of absurd concept art.

S-57-10.jpg
EdifO2uWsAY4AgO




The stiffnesses of a conventional gimballed proprotor found on tiltrotors, especially if you were to lock out the gimbal at low rotor speeds as Bell describes, is leaps and bounds beyond what can be accomplished on a larger diameter single rotor helicopter. Folding in the chord plane 2 comparatively smaller diameter rotors is completely feasible, as evidenced by the full scale wind tunnel tests from 50 years ago.
 
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steelpillow

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
 

yasotay

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
While I am not prepared to argue that your concept is not viable, has there been anywhere near the amount of work done by Bell? "Practical" is based on requirements. The USAF, having realized that runways are likely to be akin to the Maginot fortifications in the coming years has started looking far and wide for means to offset a perceived vulnerability. "Practical" will end up being the project with the highest Technical Readiness/least risk approach weighted against which company is coming to an end on production cycle.
 

Foo Fighter

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Sea life appropriating these floating platforms could be a problem.
They might be able to lie, err, I mean mollify animal interest groups by allowing for part of these platforms to be available to wild life. Possibly even some of our politicians could be allowed on.........
 

coanda

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I wonder how they will deal with the air flow effects of the blade twist at high speed in relation to the nacelles and the wing joint.

Since the rotors are used for a much smaller flight corridor (essentially only hover & transition and not full high speed flight) the twist required in the blades would be considerably less than a conventional proprotor, and therefore more suitable for folding conformally to a pylon and into the slots Bell seems to be illustrating.

The bigger problem is turbulence when in the folded state. I wouldn't want to be the guy having to justify the fatigue/dam tol of the folded rotor for the high speed turbulence case. Not sure I'd even want to be the static stress guy on that job.

It looks like Bell has some patent applications for retention clamps that appear to be intended to stabilize the blades in the folded state by grabbing the tabs on the blade trailing edge (you can see if you look closely in the video), which would help with flutter and high cycle fatigue. There was also another version of the same application with pneumatic bladders to squeeze the blade tabs as well.


US20210094683A1-20210401-D00007.png
I wish them luck, they're gonna need it!
 

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
What is the design of a practically-usable sized 2 bladed rotor for something like that? A rigid 2 bladed rotor that size that would be able to lock would have absurd hub moments, and sizing anything like that up to a realistic scale would require enormously heavy structure.

You need to get well beyond the idea of simply scaling up prototypical RC quadrotors or similar as the same rotor stiffness required at feasible scales are totally unrealistic.

I also think you do not appreciate that the folding mechanism on Bell's HSVTOL concept is not a huge weight penalty - the fold is accomplished using the existing swashplate actuators. The only added hardware is a gimbal lock and linkage within each grip to convert vertical swashplate motion from feathering to folding. It looks rather elegant.

The V-22 flies around with a discrete fold (for stow) motor/actuator and lock system per blade in the rotating system as part of the baseline design! Pound for pound an equivalent size HSVTOL rotor would possibly be lighter.
 
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Conspirator

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
What is the design of a practically-usable sized 2 bladed rotor for something like that? A rigid 2 bladed rotor that size that would be able to lock would have absurd hub moments, and sizing anything like that up to a realistic scale would require enormously heavy structure.

You need to get well beyond the idea of simply scaling up prototypical RC quadrotors or similar as the same rotor stiffness required at feasible scales are totally unrealistic.

I also think you do not appreciate that the folding mechanism on Bell's HSVTOL concept is not a huge weight penalty - the fold is accomplished using the existing swashplate actuators. The only added hardware is a gimbal lock and linkage within each grip to convert vertical swashplate motion from feathering to folding. It looks rather elegant.

The V-22 flies around with a discrete fold actuator and lock system in the rotating system as part of the baseline design! Pound for pound an equivalent size HSVTOL rotor would probably be lighter.
for some reason i did not know about that in the V-22. so you could build off of that and make it better and regularly operational. for some reason im seeing something along the lines of a Hurcules with VTOL capabilities. but scaled down quite a bit. bigger than an osprey but smaller than an AC130 unfortunately i dont have any 3D modeling software otherwise i would probably make a render. the wieght would be the issue with the design. but i would like it to have the capability to move heavily armoured vehicles. i mean a naval osprey can carry a stripped Humvee but not much else. that's why i was thinking jet engines. it would probably be better that way. the only issue would be noise. and throttle calibration. you could have better speed capabilities and possibly turning since you could control the gimbals. just some thoughts on this
 
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steelpillow

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
What is the design of a practically-usable sized 2 bladed rotor for something like that? A rigid 2 bladed rotor that size that would be able to lock would have absurd hub moments, and sizing anything like that up to a realistic scale would require enormously heavy structure.

You need to get well beyond the idea of simply scaling up prototypical RC quadrotors or similar as the same rotor stiffness required at feasible scales are totally unrealistic.

I also think you do not appreciate that the folding mechanism on Bell's HSVTOL concept is not a huge weight penalty - the fold is accomplished using the existing swashplate actuators. The only added hardware is a gimbal lock and linkage within each grip to convert vertical swashplate motion from feathering to folding. It looks rather elegant.

The V-22 flies around with a discrete fold actuator and lock system in the rotating system as part of the baseline design! Pound for pound an equivalent size HSVTOL rotor would probably be lighter.

By quadrotor, I am thinking of beasts like the 1956 Convertawings or the 1966 Bell X-22A, not the kiddies' "RC model" toys which you refer to.

By the way, the Osprey's fold mechanism is not flight-rated but is a lightweight system intended only for carrier stowage. Doing it for real is a very different kettle of fish.
 
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Spyclip

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Who says a stowed-rotor has to be a single rotor? Let's not pick impossible counterexamples just to big up a dubious one. How about a two-bladed quadrotor that simply locks its blades fore-aft, for example?
I still cannot accept that taking a complicated beast of an Osprey and loading it up with a hub folding mechanism and a couple of jets, is likely to create something with a practical payload.
What is the design of a practically-usable sized 2 bladed rotor for something like that? A rigid 2 bladed rotor that size that would be able to lock would have absurd hub moments, and sizing anything like that up to a realistic scale would require enormously heavy structure.

You need to get well beyond the idea of simply scaling up prototypical RC quadrotors or similar as the same rotor stiffness required at feasible scales are totally unrealistic.

I also think you do not appreciate that the folding mechanism on Bell's HSVTOL concept is not a huge weight penalty - the fold is accomplished using the existing swashplate actuators. The only added hardware is a gimbal lock and linkage within each grip to convert vertical swashplate motion from feathering to folding. It looks rather elegant.

The V-22 flies around with a discrete fold actuator and lock system in the rotating system as part of the baseline design! Pound for pound an equivalent size HSVTOL rotor would probably be lighter.

Thank you for your high ignorance of my knowledge. You also "need to get well beyond" being rude to people you don't know. Especially when, by quadrotor, I am thinking of beasts like the 1956 Convertawings or the 1966 Bell X-22A, not the kiddies' "RC model" toys which you refer to.

By the way, the Osprey's fold mechanism is not flight-rated but is a lightweight system intended only for carrier stowage. Doing it for real is a very different kettle of fish.

Please remind us all of the advance ratio of the Convertawings and whether or not a full size teetering rotor can fold up without CF applied. Also, the X-22 was a ducted propeller that also would never be able to operate stopped without ridiculous edgewise drag of the duct, so its not remotely germane to the discussion here.

All I did was point out the fundamental flaws in your off-the-cuff suggestions that the HSVTOL concept is "absurd concept art" while subsequently proposing objectively more absurd alternatives.

The fact the Osprey fold system is not flight rated was essentially my point. It uses 6 heavy discrete individual blade actuators/motors per ship and carries that dead weight around, while the HSVTOL concept dual-uses the main flight control swashplate actuators to perform the fold - which would fly in the face of your claim that it would make for an unusable empty weight fraction.
 
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Fluff

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Did they ever consider a 4 bladed rotor, and just lower it onto the fuselage and wing - would seem a lot more straightforward than folding it, in flight, whilst transitioning, without FBW......I mean we are trying to be faster than a heli, not fast as a bizjet - right?

Hanging more engines, and blade folding on a bigger osprey doesnt sound very elegant.

Given electric power, and all the VTOL machines being considered, how about just sticking 6 fans in the wing of a mini-herc and calling it done?
 

yasotay

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Gentlemen/Ladies (one must not presume these days), it is wonderful to see your passion here, however verbally wagging fingers at each other gets tedious for the rest of us who are very interested in your engineering level knowledge. I would note that there are at least 30(?) entrants in the USAF HSVTOL effort that I believe is going through down select as we write. I suspect there are any number of variations of folding, stowing or other assorted means to make rotorborne aircraft into fixed wing 400 knot aircraft.

But, since I am not a moderator, do carry on if you must.

@Fluff - I suspect that many of the stability issues with the process could be dealt with by modern digital flight controls. The biggest challenge I suspect is the extra weight you are carrying around for all of the folding and idle rotors. Weight = cost, for most calculations (right or wrong), and this just did not make the platforms justifiable to those who funded these sort of thing. Today with composites and much improved metallurgy, along with electrical systems it might be viable now.
 
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Spyclip

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Did they ever consider a 4 bladed rotor, and just lower it onto the fuselage and wing - would seem a lot more straightforward than folding it, in flight, whilst transitioning, without FBW......I mean we are trying to be faster than a heli, not fast as a bizjet - right?

Hanging more engines, and blade folding on a bigger osprey doesnt sound very elegant.

Given electric power, and all the VTOL machines being considered, how about just sticking 6 fans in the wing of a mini-herc and calling it done?

1. Fan in wing designs have downright terrible disc loading and therefore hover efficiency and resultant control. To get a reasonable level of performance anywhere on par with what is commonly expected of a VTOL aircraft, the sizing of a fan unit is almost universally larger than the chord of the wing a designer would desire to install it within.

2. The larger manned HSVTOL variant concepts do not add engines.

3. With respect to the eVTOL electric paradigm, I suggest a wait and watch approach. What is being promised by each new config is so far out of bed with reality it makes for comic reading in the daily aerospace news blasts.
 

AeroFranz

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The Air force hasn't made up its mind regarding signature levels. There is much to be said about the low power requirements of open rotors, but if (and that's a big if) they decided that VLO was necessary, then fan-in-wing solutions would be appealing.
Another concern is speed. I listened to some of the AFWERX webinars and with regard to this, all they could say 'jet-like'.
Can you push a folded rotor at transonic speeds? sure, but you pay a progressively steeper price.
So I wouldn't rule out any configuration at this point, provided it closed. Air force CONOPS, once they make up their mind, will largely dictate the appropriate configuration.
edited: one word
 
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steelpillow

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Please remind us all of the advance ratio of the Convertawings and whether or not a full size teetering rotor can fold up without CF applied. Also, the X-22 was a ducted propeller that also would never be able to operate stopped without ridiculous edgewise drag of the duct, so its not remotely germane to the discussion here.
I was merely responding to your assumption that toy quadcopters were all that existed. Do not read more into these old machines than that.

All I did was point out the fundamental flaws in your off-the-cuff suggestions that the HSVTOL concept is "absurd concept art" while subsequently proposing objectively more absurd alternatives.
Nope. Not objectively, but subjectively more absurd - by your judgement, not mine.

The fact the Osprey fold system is not flight rated was essentially my point. It uses 6 heavy discrete individual blade actuators/motors per ship and carries that dead weight around, while the HSVTOL concept dual-uses the main flight control swashplate actuators to perform the fold - which would fly in the face of your claim that it would make for an unusable empty weight fraction.
Well, you swore with feeling when you made the comment, and that had to be redacted by an admin. And you failed to mention that it was not flight-rated. You must pardon others for not appreciating the intent you now explain. But at least we can now agree on something. And I take your point about the folding mechanism, but the main weight gain over the Osprey is in the extra thrust jets.
 

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