A160 Hummingbird rigid rotor design
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A160 Hummingbird rigid rotor design
The A160 has thick tapered carbon fiber blades to operate at 140rpm. Are the blades designed to be very stiff to avoid coning at 140rpm?
In other words, do the blades flap on the A160 the same as any other rigid or hingeless rotor?
Or in other, other words, is this a new type of rigid rotor that really is rigid?
thanks
slowrotor
Rotor head photo at this site: http://www.boeing.com/news/frontiers...r/ts_sf04.html
In other words, do the blades flap on the A160 the same as any other rigid or hingeless rotor?
Or in other, other words, is this a new type of rigid rotor that really is rigid?
thanks
slowrotor
Rotor head photo at this site: http://www.boeing.com/news/frontiers...r/ts_sf04.html
Last edited by slowrotor; 23rd Dec 2006 at 21:36. Reason: add website
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IDR gave the best description a couple of years back:
The unique and Frontier-patented feature central to the A160 is that the revolutions per minute of its main rotor can be reduced to as little as 40% of its maximum value, reducing drag and fuel consumption by half. This cannot be done with a conventional articulated rotor because it would lead to catastrophic vibration, so the A160 has a fully rigid rotor. The blades change in pitch, but the blades and hub are hingeless and stiff in the flapping plane - the hub is a solid forging from AerMet 100 high-strength steel - so that the aircraft is controlled as much like a fixed-wing aircraft as a helicopter. Roll and pitch moments are transferred directly from the rotor to the vehicle.
Reportedly, tip speeds dip as low as M0.25. The A160 can operate at a range of rotor RPMs: the original three-blade carbon-graphite optimum speed rotor spanned 150-350 rpm, while the new four-blade OSR system runs at 200-400rpm.
The other interesting part of the program is the ultra-efficient 650shp coupled diesel being developed: see OPOC thread.
I/C
The unique and Frontier-patented feature central to the A160 is that the revolutions per minute of its main rotor can be reduced to as little as 40% of its maximum value, reducing drag and fuel consumption by half. This cannot be done with a conventional articulated rotor because it would lead to catastrophic vibration, so the A160 has a fully rigid rotor. The blades change in pitch, but the blades and hub are hingeless and stiff in the flapping plane - the hub is a solid forging from AerMet 100 high-strength steel - so that the aircraft is controlled as much like a fixed-wing aircraft as a helicopter. Roll and pitch moments are transferred directly from the rotor to the vehicle.
Reportedly, tip speeds dip as low as M0.25. The A160 can operate at a range of rotor RPMs: the original three-blade carbon-graphite optimum speed rotor spanned 150-350 rpm, while the new four-blade OSR system runs at 200-400rpm.
The other interesting part of the program is the ultra-efficient 650shp coupled diesel being developed: see OPOC thread.
I/C
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I think that both answers are correct. I.e. the ability to widely vary the RRPM without damaging oscillation, plus the ability to operate at very slow RRPMs without excessive coning.
The related patent is US 6,007,298. As I recall, Karem also received a later patent that is almost identical to this one, except that it is for a tiltrotor.
slowrotor,
The idea could well be a good one, however it may not be meet your objectives. I believe the intent is for this rotor to operate near the optimum lift/drag ratio. This maybe ideal for an unmanned UAV but the increased possibility of stalling the rotor is probably not too attractive for a maned craft.
Dave
The related patent is US 6,007,298. As I recall, Karem also received a later patent that is almost identical to this one, except that it is for a tiltrotor.
slowrotor,
The idea could well be a good one, however it may not be meet your objectives. I believe the intent is for this rotor to operate near the optimum lift/drag ratio. This maybe ideal for an unmanned UAV but the increased possibility of stalling the rotor is probably not too attractive for a maned craft.
Dave
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How do they do it???
Are we seeing the first of the "intelligent" blades that will accomodate pitch changes along their length by variable twisting? Interesting times.
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Interesting times indeed.
I notice that the Program Manager Steve Glusman worked on Comanche. This head looks roughly how i envisioned that head to look, from various descriptions. From the TV program "Ultimate Helicopter" i remember freeze framing the image, but never seeing a pitch link system. At the root is a "damper system", which looks to me as if it also acts as an electric pitch actuator. That ring at the base is either an azimuth sensor, power slip ring (either DC brushed AC brushless) or both.
I gather it can also absorbs blade flexural modes, so maybe blade torsional wavespeed has been tuned to to equal blade centrifugal tension wavespeed at midrange rpm. This means that through active pitch control the blade dynamics can be damped down at the aerodynamic source - this requires intense real-time computational modelling of blade dynamics. Alternately there may just be a damping system built into the blade root.
Since Comanche achieved either 12% or 15% effective offset hinge (i forget which), then Nr change induced coning could be accomodated by blade flexure alone. The Nr range would allow efficient silent hover, while beeping up for forward flight or manouvre.
----
Ian, somehow i missed that OPOC thread. Don't quite see/remember how crank mech works, but it is this designs best feature. The debate about 2-stroke vs 4-stroke is an old one, and for my money 4-stroke wins. The power advantage for a given displacement is at best x1.5, which becomes less as turbo charging does more of the compression (since turbine captures more energy in 4-stroke). Also at high RPM 2-stroke scavenging struggles, so the power advantage is further reduced.
This design will suffer from the 2-stroke need to lubricate the piston rings, so that you cannot help but let oil into combustion chamber or exhaust. The emission standard is not quoted, so i can only assume they are relying on helicopters having loose standards. This is the main reason 2-stroke are being dropped for land/sea machines (although there are some interesting designs carried over for historical reasons). Partially burnt oil is absolutely fowl, believe me.
Mart
I gather it can also absorbs blade flexural modes, so maybe blade torsional wavespeed has been tuned to to equal blade centrifugal tension wavespeed at midrange rpm. This means that through active pitch control the blade dynamics can be damped down at the aerodynamic source - this requires intense real-time computational modelling of blade dynamics. Alternately there may just be a damping system built into the blade root.
Since Comanche achieved either 12% or 15% effective offset hinge (i forget which), then Nr change induced coning could be accomodated by blade flexure alone. The Nr range would allow efficient silent hover, while beeping up for forward flight or manouvre.
----
Ian, somehow i missed that OPOC thread. Don't quite see/remember how crank mech works, but it is this designs best feature. The debate about 2-stroke vs 4-stroke is an old one, and for my money 4-stroke wins. The power advantage for a given displacement is at best x1.5, which becomes less as turbo charging does more of the compression (since turbine captures more energy in 4-stroke). Also at high RPM 2-stroke scavenging struggles, so the power advantage is further reduced.
This design will suffer from the 2-stroke need to lubricate the piston rings, so that you cannot help but let oil into combustion chamber or exhaust. The emission standard is not quoted, so i can only assume they are relying on helicopters having loose standards. This is the main reason 2-stroke are being dropped for land/sea machines (although there are some interesting designs carried over for historical reasons). Partially burnt oil is absolutely fowl, believe me.
Mart
Last edited by Graviman; 24th Dec 2006 at 17:44. Reason: General tidy up for readability only.
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Thanks Ian,
I wonder if the A160 rotor has large tip weights to help add centrifugal force at the low rpm.
With no flapping, the dissymetry of lift in forward flight must be equalized solely with cyclic pitch.
Also, why not make the forged steel rotor head larger to save weight?
Dave,
I think low rpm is good for efficiency and needed for entry level rotorcraft. The cruise speed would be slow. The helo would not be for transportation, but only sport and training or other local uses.
Thanks,
slowrotor
I looked at the patent and found the blades do not have tip weights. The patent is for a rotor blade design that is thick and stiff and light but apparently requires a hingeless hub flexbeam (at least thats how I interpret the patent legal jargon) Thank you Dave,, for the patent number
I wonder if the A160 rotor has large tip weights to help add centrifugal force at the low rpm.
With no flapping, the dissymetry of lift in forward flight must be equalized solely with cyclic pitch.
Also, why not make the forged steel rotor head larger to save weight?
Dave,
I think low rpm is good for efficiency and needed for entry level rotorcraft. The cruise speed would be slow. The helo would not be for transportation, but only sport and training or other local uses.
Thanks,
slowrotor
I looked at the patent and found the blades do not have tip weights. The patent is for a rotor blade design that is thick and stiff and light but apparently requires a hingeless hub flexbeam (at least thats how I interpret the patent legal jargon) Thank you Dave,, for the patent number
Last edited by slowrotor; 24th Dec 2006 at 18:18. Reason: additional findings from patent
tt strap
To me, it looks like a tension torsion strap sticks out of the hub to restrain the blades from flinging off, while allowing the blade to pitch, The root end of the blade just pivots on bearings which are housed in the part of the head you can see. I'm guessing the pitch horn is on the root end of the blade. You can see the swashplate in a fairly conventional position.
This is different from Commanche, which was a bearingless MR design. All the classic degrees of freedom are achieved through a flex beam.
A rigid rotor doesn't flap, except by aeroelastics. It is hardly a new idea. The first was probably Juan de la Cierva's early autogyro, which tended to roll over and crash as speed increased. This ulitimately led to the invention of the flap and lead-lag hinges, much to the benefit of helicopters to follow. Additionally, the Sikorsky XH59 (ABC) had fully rigid rotors.
It will be interesting to see how well the Hummingbird works in forward flight. In a coax, like the ABC, the dissymetry of lift is canceled between the rotors, so it doesn't roll into the ground with increasing speed. Recently, the Phantom Works balled up the second Canard Rotor Wing, another rigid rotor. I wonder if they didn't have enough cyclic to counter the rolling moment from the rigid rotors, and merely did a historic reenactment of Juan de la Cierva's early work. In theory, you can stick in enough cyclic to make up for the missing flapping hinge, though in practice rotor flapping does an awful lot to equalize the dissymetry of lift.
-- IFMU
This is different from Commanche, which was a bearingless MR design. All the classic degrees of freedom are achieved through a flex beam.
A rigid rotor doesn't flap, except by aeroelastics. It is hardly a new idea. The first was probably Juan de la Cierva's early autogyro, which tended to roll over and crash as speed increased. This ulitimately led to the invention of the flap and lead-lag hinges, much to the benefit of helicopters to follow. Additionally, the Sikorsky XH59 (ABC) had fully rigid rotors.
It will be interesting to see how well the Hummingbird works in forward flight. In a coax, like the ABC, the dissymetry of lift is canceled between the rotors, so it doesn't roll into the ground with increasing speed. Recently, the Phantom Works balled up the second Canard Rotor Wing, another rigid rotor. I wonder if they didn't have enough cyclic to counter the rolling moment from the rigid rotors, and merely did a historic reenactment of Juan de la Cierva's early work. In theory, you can stick in enough cyclic to make up for the missing flapping hinge, though in practice rotor flapping does an awful lot to equalize the dissymetry of lift.
-- IFMU
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That'll learn me IFMU - something about keeping it simple. 
I'm still puzzled, since i can't see any pitch links in there, and the root seems to have more going on than just attachment to the hub via tension-torsion straps.
Mart
I'm still puzzled, since i can't see any pitch links in there, and the root seems to have more going on than just attachment to the hub via tension-torsion straps.
Mart
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Mart,
APT is developing the OPOC engine for FEV Engine Technologies, so FEV’s website might provide some additional insight into the type of supporting tech you'll see going into the powerplant. As if the OPOC design, the converted 4cyl & 6cyl Subaru boxer engines and Pratt’s PW207 turbine weren’t enough engines for one program, there is a fourth manufacturer developing a 6-cyl diesel for the Hummingbird: Nivek R&D.
Re: Comanche, as IFMU states the rotor system was designed around a composite flexbeam which allowed all but the thrust bearings to be eliminated. Pitch control rods were retained. IIRC, the offset hinge was 15%.
Slowrotor,
Can’t answer whether or not the A160 uses heavy tip weights. I know the team has emphasized the fact that the tip of the rotor is more flexible than the root in terms of flap, lag and torsion.
With regards to the rotor head, everything about this vehicle has been specifically designed to meet very exacting long-endurance goals, so lower drag was traded-off wherever possible. Airflow interference with the mast-mounted mission pod probably also influenced the numbers. As Dave Jackson notes, it’s a very mission-specific design.
Another supporting technology publicly revealed by the DoD is the use of “high-speed electrical actuators [which, in combination with the hingeless rotor] allows for precision control and improved performance in turbulent flight conditions.”
I/C
APT is developing the OPOC engine for FEV Engine Technologies, so FEV’s website might provide some additional insight into the type of supporting tech you'll see going into the powerplant. As if the OPOC design, the converted 4cyl & 6cyl Subaru boxer engines and Pratt’s PW207 turbine weren’t enough engines for one program, there is a fourth manufacturer developing a 6-cyl diesel for the Hummingbird: Nivek R&D.
Re: Comanche, as IFMU states the rotor system was designed around a composite flexbeam which allowed all but the thrust bearings to be eliminated. Pitch control rods were retained. IIRC, the offset hinge was 15%.
Slowrotor,
Can’t answer whether or not the A160 uses heavy tip weights. I know the team has emphasized the fact that the tip of the rotor is more flexible than the root in terms of flap, lag and torsion.
With regards to the rotor head, everything about this vehicle has been specifically designed to meet very exacting long-endurance goals, so lower drag was traded-off wherever possible. Airflow interference with the mast-mounted mission pod probably also influenced the numbers. As Dave Jackson notes, it’s a very mission-specific design.
Another supporting technology publicly revealed by the DoD is the use of “high-speed electrical actuators [which, in combination with the hingeless rotor] allows for precision control and improved performance in turbulent flight conditions.”
I/C
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It appears that the rotor may have individual blade control, by electrical rotary actuator.
..
slowrotor,
A potential advantage of 'Absolutely'
rigid rotors for your objective is that the craft should perform as an airplane if it stalls. In other words, if there is sufficient elevation, the nose will drop and RRPM will then increase.
This may necessitate twin main-rotors. However, twin main-rotors offer many advantages;
Here is an serious concept;
An interleaving rotorcraft with very rigid rotors.
..
Mart;
The intermeshing offers many advantages, however the attractiveness of the interleaving increases as one looks deeper and deeper into it.
Dave
..
slowrotor,
A potential advantage of 'Absolutely'
rigid rotors for your objective is that the craft should perform as an airplane if it stalls. In other words, if there is sufficient elevation, the nose will drop and RRPM will then increase.This may necessitate twin main-rotors. However, twin main-rotors offer many advantages;
Here is an serious concept;
An interleaving rotorcraft with very rigid rotors.
- Slow RRPM rotors, with small aspect ratio blades to minimize the length of the braces between the rotors and the fuselage.
- Conventional pitch-arm and swashplate flight-controls. No active blade twist.
- Implement the simple ABC concept to minimize the downwash on the fuselage and braces.
- Arrange the power-train so that a pusher-prop could be implemented in the future, if desired.
- Etc.
- Etc.
- Etc.
..
Mart;
The intermeshing offers many advantages, however the attractiveness of the interleaving increases as one looks deeper and deeper into it.
Dave
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Dave,
This is what the picture looked like to me. Maybe this is the trial of Ian's "High speed electric actuators". Maybe the resolution is just too poor, but i wondered about that cable.
If a heli rotor stalls you fall from the sky like a stone - there is NO mode of recovery. The only way to avoid this would be designing a "pushable" collective for -ve pitch to force rotation (like windmilling a prop).
At the serious risk of threadjacking an already interesting subject:
I am a believer in identifying the problem before attempting to design the solution. Coaxial is the most flexible system but intermeshing has hub packaging and possible shaft weight advantages. I champion neither, but recognise both as solutions to the problem of high speed heli flight. Remember my interest here has always been to identify the technological lmlitations of future helicopter development.
----
All fellow Rotorheads,
Have a Merry Xmas, and thank you for developing my understanding of rotorcraft!!!
Mart
I am a believer in identifying the problem before attempting to design the solution. Coaxial is the most flexible system but intermeshing has hub packaging and possible shaft weight advantages. I champion neither, but recognise both as solutions to the problem of high speed heli flight. Remember my interest here has always been to identify the technological lmlitations of future helicopter development.
----
All fellow Rotorheads,
Have a Merry Xmas, and thank you for developing my understanding of rotorcraft!!!
Mart
Last edited by Graviman; 24th Dec 2006 at 22:36.
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Mart,
Not so fast. 
You recover from a stall in an airplane by lowering the pitch of the wings.
You recover from a stall in a helicopter by lowering the pitch of the blades.
Remember, the blades are 'Absolutely' rigid. They will not 'fold up'.
A possibility. Another possibility would be to install a rotor-governor and not let the rotors stall.
I looked at Nick's book 'No Free Lunch'. It says that all four configurations (Side-by-side, Interleaving, Intermeshing and Coaxial) have their pros and cons vis vie each other. It suggested getting a piece of paper and drawing four columns, then ........ 
Dave
If a heli rotor stalls you fall from the sky like a stone - there is NO mode of recovery.
You recover from a stall in an airplane by lowering the pitch of the wings.
You recover from a stall in a helicopter by lowering the pitch of the blades.
Remember, the blades are 'Absolutely' rigid. They will not 'fold up'.
The only way to avoid this would be designing a "pushable" collective for -ve pitch to force rotation (like windmilling a prop).
identifying the problem before attempting to design the solution.
Dave
Originally Posted by Dave Jackson
It appears that the rotor may have individual blade control, by electrical rotary actuator.
No way. They are flying the hummingbird, at least in hover. Individual blade control is still a couple of decades behind phasers and transporters. I'll believe in Santa Claus before I believe they are using IBC on that thing. Those wires are more likely instrumentation. With a prototype aircraft you are going to want to know the forces on this new rotor system.
The pictures are poor, but look at them and I'll try and clarify my guess as to how it bolts together. The tension torsion strap is secured to the head with one bolt, and to the blade with one bolt. When it is bolted into the head, it sticks out of the hole that you see in the end of the head, and goes out a few inches. You slide the blade over the end of the head, the tt strap slides into the blade. You sock the blade down to that rectangular fitting, the tt strap hole lines up with a hole in the blade root. Sock a bolt through said hole and the blade is restrained against CF. Now, I'm guessing that somewhere near the rectangular fitting is the pitch horn, or an attachment (read: threaded holes) for the pitch horn to bolt to. This pitch horn would be attached to the swashplate visible in the crappy picture with a very conventional pitch link.
Merry Christmas to all.
-- IFMU
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Originally Posted by IFMU
They are flying the Hummingbird, at least in hover.
Merry Christmas, Happy Hanukkah, Jolly Kwanzaa or whatever the locals are celebrating where you're flying today.
I/C
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----
Originally Posted by IFMU
No way. They are flying the hummingbird, at least in hover. Individual blade control is still a couple of decades behind phasers and transporters. I'll believe in Santa Claus before I believe they are using IBC on that thing. Those wires are more likely instrumentation. With a prototype aircraft you are going to want to know the forces on this new rotor system.
----
From earlier post - too much Xmas spirit.
Originally Posted by Ian Corrigible
...As if the OPOC design, the converted 4cyl & 6cyl Subaru boxer engines and Pratt’s PW207 turbine weren’t enough engines for one program, there is a fourth manufacturer developing a 6-cyl diesel for the Hummingbird: Nivek R&D.
Merry Xmas all!
Mart
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Stiff blades
I am still trying to figure out if the Hummingbird has an "absolutely rigid" rotor as Dave would say. Or does it have a hub flexbeam.
There is mention of a flexbeam in the patent. But why have a stiff blade and flexable hub? The patent also says the rotor works from 0 to full rpm. That would suggest an absolutely rigid rotor.
This is of interest to me as I am looking at the idea of an absolutely rigid rotor, a slow rotor that does not have much centrifugal force.
There is mention of a flexbeam in the patent. But why have a stiff blade and flexable hub? The patent also says the rotor works from 0 to full rpm. That would suggest an absolutely rigid rotor.
This is of interest to me as I am looking at the idea of an absolutely rigid rotor, a slow rotor that does not have much centrifugal force.
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Slowrotor,
An absolutely rigid rotor is just not achievable, since we are dealing with large inertias at relatively high RPM. Comanche achieved 15% effective hinge offset, and has about the most rigid rotor practical. This reduces the azimuth lead angle from 90' to about 75', but we are still dealing with an aerogyroscopic system.
The flexbeams mentioned in the patent with be the tension torsion packs that IFMU discusses. These are basically a pack of steel laminate "feeler guages", which transfer bending loads and tension but allow torsional freedom. The result is a high effective hinge offset. The only potential downside is that they can suffer reduced fatigue life from lead-lag forces, since guages can buckle with in plane bending.
Aerokopter Sanka example mentioned under title "Rotor System"
Mart
An absolutely rigid rotor is just not achievable, since we are dealing with large inertias at relatively high RPM. Comanche achieved 15% effective hinge offset, and has about the most rigid rotor practical. This reduces the azimuth lead angle from 90' to about 75', but we are still dealing with an aerogyroscopic system.
The flexbeams mentioned in the patent with be the tension torsion packs that IFMU discusses. These are basically a pack of steel laminate "feeler guages", which transfer bending loads and tension but allow torsional freedom. The result is a high effective hinge offset. The only potential downside is that they can suffer reduced fatigue life from lead-lag forces, since guages can buckle with in plane bending.
Aerokopter Sanka example mentioned under title "Rotor System"
Mart
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IFMU,
You make good points. The blade root just seem to have a larger diameter than what should be required for the radial bearings or the blade strength. All very interesting.
Mart, 
Forget the generalistic 'statement of fact'. Please give a reason why a helicopter with 'absolutely' rigid rotors will crash into the ground.
HOW do you think autogyros spin up their blades before flying? (excluding prerotors)
What are you trying to say?
Who says that an 'Absolutly' rigid rotor is not achievable.
slowrotor,
Just an observation. The vertical distance from rotor to fuselage (center of gravity and drag) is decreased as the rotor's rigidity is increased. The picture of the Hummingbird shows a rotor that is very close to the fuselage.
I will list out a few reasons why the interleaving MAY be attractive.
Dave
You make good points. The blade root just seem to have a larger diameter than what should be required for the radial bearings or the blade strength. All very interesting.
Mart,
Dave, you recover from blade stall in a helicopter by crashing into the ground
Why do you think autogyros spin up their blades before flying?
A single teetering rotor has dihedral as a result of the aero-gyroscopic forces, and "rigid" rotors are not so far removed in behavior (but feel less stable). The only problem is rotor dynamic response, and the fact that the cyclic does not auto centre. The Honeywell SPZ7600 system Nick sited takes care of that.
An absolutely rigid rotor is just not achievable
slowrotor,
Just an observation. The vertical distance from rotor to fuselage (center of gravity and drag) is decreased as the rotor's rigidity is increased. The picture of the Hummingbird shows a rotor that is very close to the fuselage.
I will list out a few reasons why the interleaving MAY be attractive.
Dave
Last edited by Dave_Jackson; 25th Dec 2006 at 18:28. Reason: Politeness forbids a response.
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Dave,
Most of the development in very stiff rotor research , such as Sikorsky's ABC, was for higher cruise speed. But a stiff blade would also be needed for any rotor that has a low tip speed, such as the human powered helos. Most of the early designs did not use centrifugal force, they were wire braced.
I wonder if anyone has built a flying replica of the first helicopter?
Most of the development in very stiff rotor research , such as Sikorsky's ABC, was for higher cruise speed. But a stiff blade would also be needed for any rotor that has a low tip speed, such as the human powered helos. Most of the early designs did not use centrifugal force, they were wire braced.
I wonder if anyone has built a flying replica of the first helicopter?