The future of rotorcraft?
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Dave,
Don't give up on the industry just yet ! There are still a few projects being worked on both sides of the Atlantic that represent significant developments.
As a follow-up to the Flight article, those with broadband (or dial-up connections and the patience of a newly-beautified saint) may also want to browse the helicopter section of the report to Congress recently submitted by the National Institute of Aerospace: NIA Aviation plan.
I/C
Don't give up on the industry just yet ! There are still a few projects being worked on both sides of the Atlantic that represent significant developments.
As a follow-up to the Flight article, those with broadband (or dial-up connections and the patience of a newly-beautified saint) may also want to browse the helicopter section of the report to Congress recently submitted by the National Institute of Aerospace: NIA Aviation plan.
I/C
Joined: Nov 2004
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From: Cambridgeshire, UK
Interesting thread. I'll scribble some comments to points raised:
Intermeshers are less aerodynamically efficient:
Realistically, you have to develope the whole package to gain the full benefit. I am astonished at how quickly the fuel in an R22 just dissappears. Even a transition from 10% loss to 5% loss is beneficial. Intermeshers are mechanically complicated, and have to justify this with better efficiency.
The ideal intermesher has to aim for:
Outboard/lower advancing - for most efficient downwash.
Feathered retreating (or ABC) - to avoid interference and tip stall.
Faired hubs - to minimise drag (coaxials cannot achieve this).
Variable blade twist - to optimise for flight condition.
Pusher prop - to keep both hubs at minimum streamline profile.
Variable RRPM - even though compressibility will eventually limit speed.
Any less, or any program not aiming to achieve all this, will not offer sufficient commercial advantage over a conventional. The above can be done in stages, since this program would be a serious undertaking. Ideally a development intermesher would sort out the handling issues of outboard advancing and gyro-aug contol system. Then the long-term project then develops pusher prop and aerodynamics (including v-RRPM).
Intermeshers require less pilot workload:
Not convinced. I can believe that the Husky and F-282 are easy to fly, but neither can hover close to ground hands off. Breastsroke rotation explains the ease of flight, As explained in my 9th May post in thread
http://www.pprune.org/forums/showthr...5&pagenumber=4
Hands-off hover is a must for the above program, as is lower advancing, and can only be achieved reliably/safely and cost effectively using the Lockheed Gyro mechanical augmentation system. With this an unstable helicopter (ie all of them in the engineering sense, since you always need the pilot) can be made neutrally stable. By neutral stability i means hands-off hover (ie stays at attitude it is put), not stable oscillation. Fixed wing positive stability can only be achieved with aerodynamic effects, and is ideally designed in after/with gyro-augmentation using (say) a T-tail.
The practical upshot is that initially investigating blades, then hub design is paramount. The next stage has to be gyro control system. Then intermeshing, since you already have component designs that would improve conventional helis.
Dave, i seriously suggest you look at the Schweizer/Hughes 300C hub - these are generally regarded as easier to fly than the R22. Also, The reason i suspect you will succeed in developing a carbon fiber rigid rotor may be found by clicking 2.3MW in the link:
http://www.bonus.dk/uk/produkter/index.html
Finally:
"They are all just variations on a theme. The quantum leap is only going to come when someone discovers some completely unheard of anti-gravity system..."
An interesting thought, RobboRider. This is neither the place nor the time, but i admit to having my reasons for wishing to understand the limits of helicopter technology...
Mart
Intermeshers are less aerodynamically efficient:
Realistically, you have to develope the whole package to gain the full benefit. I am astonished at how quickly the fuel in an R22 just dissappears. Even a transition from 10% loss to 5% loss is beneficial. Intermeshers are mechanically complicated, and have to justify this with better efficiency.
The ideal intermesher has to aim for:
Outboard/lower advancing - for most efficient downwash.
Feathered retreating (or ABC) - to avoid interference and tip stall.
Faired hubs - to minimise drag (coaxials cannot achieve this).
Variable blade twist - to optimise for flight condition.
Pusher prop - to keep both hubs at minimum streamline profile.
Variable RRPM - even though compressibility will eventually limit speed.
Any less, or any program not aiming to achieve all this, will not offer sufficient commercial advantage over a conventional. The above can be done in stages, since this program would be a serious undertaking. Ideally a development intermesher would sort out the handling issues of outboard advancing and gyro-aug contol system. Then the long-term project then develops pusher prop and aerodynamics (including v-RRPM).
Intermeshers require less pilot workload:
Not convinced. I can believe that the Husky and F-282 are easy to fly, but neither can hover close to ground hands off. Breastsroke rotation explains the ease of flight, As explained in my 9th May post in thread
http://www.pprune.org/forums/showthr...5&pagenumber=4
Hands-off hover is a must for the above program, as is lower advancing, and can only be achieved reliably/safely and cost effectively using the Lockheed Gyro mechanical augmentation system. With this an unstable helicopter (ie all of them in the engineering sense, since you always need the pilot) can be made neutrally stable. By neutral stability i means hands-off hover (ie stays at attitude it is put), not stable oscillation. Fixed wing positive stability can only be achieved with aerodynamic effects, and is ideally designed in after/with gyro-augmentation using (say) a T-tail.
The practical upshot is that initially investigating blades, then hub design is paramount. The next stage has to be gyro control system. Then intermeshing, since you already have component designs that would improve conventional helis.
Dave, i seriously suggest you look at the Schweizer/Hughes 300C hub - these are generally regarded as easier to fly than the R22. Also, The reason i suspect you will succeed in developing a carbon fiber rigid rotor may be found by clicking 2.3MW in the link:
http://www.bonus.dk/uk/produkter/index.html
Finally:
"They are all just variations on a theme. The quantum leap is only going to come when someone discovers some completely unheard of anti-gravity system..."
An interesting thought, RobboRider. This is neither the place nor the time, but i admit to having my reasons for wishing to understand the limits of helicopter technology...
Mart
Last edited by Graviman; 15th May 2005 at 21:56.
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
I/C
Good. . However, if these projects include; Sikorsky's Reverse Velocity Rotorcraft, Piasecki's compound helicopter, Boeing's Canard Rotor/Wing or Carter's Gyro Transport, I would love to technically discuss any of them, particularly with the guy who developed the concept.
My concepts are open to public scrutiny, let them do the same.
Thanks for the reference to the NIA Aviation plan.
Unfortunately, it is only a request for funding. The rotorcraft portion of this proposal was developed by the four major US rotorcraft manufacturers and the three primary US rotorcraft universities. They are seeking funding from NASA. These seven entities just lost funding when NASA quit supporting rotorcraft.
Much of the American rotorcraft industry appears to be unwilling to pursue new viable configurations. Perhaps this is symptomatic of current US capitalism. Even the US Army is looking outside this 'cartel' seeking any wild and wonderful ideas that will give them second-generation VTOL craft.
The European rotorcraft industry appears to be more R&D oriented. No doubt, the Orient will be even more oriented.
Graviman;
There are 'ideas' looking for 'needs' to be satisfied, and there are 'needs' looking for 'ideas' to provide satisfaction.
If the only 'need' is stable hover then perhaps nothing can improve on the hot air balloon.
If the 'need' is a montage of; fast forward speed, high L/D ratio, stability, controllability, reliability, and cheapability, then the ultimate solution might be teleportation.
Dave J.
There are still a few projects being worked on both sides of the Atlantic that represent significant developments.
. However, if these projects include; Sikorsky's Reverse Velocity Rotorcraft, Piasecki's compound helicopter, Boeing's Canard Rotor/Wing or Carter's Gyro Transport, I would love to technically discuss any of them, particularly with the guy who developed the concept.My concepts are open to public scrutiny, let them do the same.
Thanks for the reference to the NIA Aviation plan.
Unfortunately, it is only a request for funding. The rotorcraft portion of this proposal was developed by the four major US rotorcraft manufacturers and the three primary US rotorcraft universities. They are seeking funding from NASA. These seven entities just lost funding when NASA quit supporting rotorcraft.
Much of the American rotorcraft industry appears to be unwilling to pursue new viable configurations. Perhaps this is symptomatic of current US capitalism. Even the US Army is looking outside this 'cartel' seeking any wild and wonderful ideas that will give them second-generation VTOL craft.
The European rotorcraft industry appears to be more R&D oriented. No doubt, the Orient will be even more oriented.
Graviman;
There are 'ideas' looking for 'needs' to be satisfied, and there are 'needs' looking for 'ideas' to provide satisfaction.
If the only 'need' is stable hover then perhaps nothing can improve on the hot air balloon.
If the 'need' is a montage of; fast forward speed, high L/D ratio, stability, controllability, reliability, and cheapability, then the ultimate solution might be teleportation.
Dave J.
Last edited by Dave_Jackson; 14th May 2005 at 21:15.
Joined: Nov 2004
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From: Cambridgeshire, UK
"There are 'ideas' looking for 'needs' to be satisfied, and there are 'needs' looking for 'ideas' to provide satisfaction."
Dave, I think you misunderstand the point of my last post. I am saying that the next gen rotorcraft needs to address all of the aerodynamic design points, to be commercially competetive. Ease of hover will then require augmented stability. I am suggesting practical and reliable ways to go about both.
"My concepts are open to public scrutiny, let them do the same."
The comments i often raise should be seen as constructive criticism. Rather than simply dismiss your ideas, i try to highlight what i see as good points while explaining my concerns with areas i see as bad points - hopefully to provide realistic engineering feedback.
Mart
Dave, I think you misunderstand the point of my last post. I am saying that the next gen rotorcraft needs to address all of the aerodynamic design points, to be commercially competetive. Ease of hover will then require augmented stability. I am suggesting practical and reliable ways to go about both.
"My concepts are open to public scrutiny, let them do the same."
The comments i often raise should be seen as constructive criticism. Rather than simply dismiss your ideas, i try to highlight what i see as good points while explaining my concerns with areas i see as bad points - hopefully to provide realistic engineering feedback.
Mart
Last edited by Graviman; 15th May 2005 at 08:52.
Thread Starter
Joined: Apr 2003
Posts: 1,635
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From: Vancouver, BC, Canada
Mono Tilt Rotor ~ Developed by Baldwin Technology
US Army could set up to $5 million aside to study unusual heavylift rotorcraft design.
________________________________
Graviman,
Perhaps augmented stability should be provided electronically. In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented.
Dave J.
US Army could set up to $5 million aside to study unusual heavylift rotorcraft design.
________________________________
Graviman,
Perhaps augmented stability should be provided electronically. In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented.
Dave J.
Joined: Nov 2004
Posts: 1,334
Likes: 0
From: Cambridgeshire, UK
"Perhaps augmented stability should be provided electronically."
Perhaps, but i am suggesting a method that is mechanically simple and has already been proven in the Lockheed CL475, 186 and Cheyenne. An aerodynamic variation was developed at Hiller, and all electro-hydraulic systems are based on the same idea of gyro feedback for attitude control.
"In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented."
Again perhaps, but i have not seen anything so far that leads me to believe that hands off hover can be achieved purely aerodynamically. The original De Bothezat heli had four rotors, with dihedral, and even this was unstable. I'm actually puzzled why you are so resistant to gyro-aug, when you were argueing for the gyro stability of intermeshers. I'm suggesting a simple way to achive one of your objectives, allowing greater freedom of design for aerodynamic efficiency.
Mart
Perhaps, but i am suggesting a method that is mechanically simple and has already been proven in the Lockheed CL475, 186 and Cheyenne. An aerodynamic variation was developed at Hiller, and all electro-hydraulic systems are based on the same idea of gyro feedback for attitude control.
"In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented."
Again perhaps, but i have not seen anything so far that leads me to believe that hands off hover can be achieved purely aerodynamically. The original De Bothezat heli had four rotors, with dihedral, and even this was unstable. I'm actually puzzled why you are so resistant to gyro-aug, when you were argueing for the gyro stability of intermeshers. I'm suggesting a simple way to achive one of your objectives, allowing greater freedom of design for aerodynamic efficiency.
Mart
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
Mart,
The Lockheed gyro system may be an excellent one. However, I have a phobia about adding 'gizmos' to any machine solely for the purpose of rectify a problem that the basic machine didn't, or couldn't. My wish that the two intermeshing rotors could provide gyro stability was an attempt to get a free benefit from the rotors without having to add gismos. 
gismo ~ A device that adds weight, complexity and cost.
Dave
I'm actually puzzled why you are so resistant to gyro-aug, when you were arguing for the gyro stability of intermeshers.
gismo ~ A device that adds weight, complexity and cost.
Dave
Joined: Mar 2002
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From: Surrey, UK
This discussion points up, IMHO, the sheer engineering elegance of the Pegasus engine and the genius of Sydney Camm and the Bristol-Siddeley engine team...what is needed is a vectored thrust solution with enough robustness to permit a vertical landing with one engine out...
Joined: Apr 2003
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From: USA
The inexerable loss of power from vectored thrust will be a hurdle for decades to come for them. To vector thrust like a Harrier requires about 1000 times more horsepower to lift a pound of payload. This penalty is fine when you need a military aircraft to bomb the end of its own runway, but it is almost laughable for any vehicle that must earn its way. It is elegant, in its way, but of no practicality in the real commercial world.
Those who don't understand disk loading are doomed to chase the sexiest idea, in spite of its impracticality. Those who think there is an inventor who will break Newton's laws in his garage next year are ripe pickings for the Mollers and Tilt Rotor advocates.
Those who don't understand disk loading are doomed to chase the sexiest idea, in spite of its impracticality. Those who think there is an inventor who will break Newton's laws in his garage next year are ripe pickings for the Mollers and Tilt Rotor advocates.
Joined: Nov 2004
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From: Cambridgeshire, UK
"My wish that the two intermeshing rotors could provide gyro stability was an attempt to get a free benefit from the rotors without having to add gismos."
Believe me i really do understand this. My understanding of the problem is that no helicopter could be designed for hands off hover, unless it became aerodynamically impractical. The various four rotor aero-jeeps of the '60s came closest, but you are only considering two - this always leaves one unstable degree of freedom. An absolutely rigid rotor with seriously impractical cone angle may do the trick, but at a cost of weight and hub complexity (or needs a tip tension ring
).
It is your project, but trust me hover control is the greatest impediment to wider rotorcraft appeal - try it if you don't believe me! The gyro system can be easilly designed into the swash plate of a single rotor design, and i honestly don't understand why it has not become a standard light heli feature - but then neither have rigids/articulated. A twin rotor could either use a common gyro, or one on each hub.
For high speed work, i am convinced that the intermesher config is (theoretically) unbeatable for a given engine power. But this has to be outboard advancing and feathered retreating, ideally with pusher prop to keep constant trim, for serious aerodynamic gains. Less than high speed sees fewer, if any, advantage for intermeshing (especially when comparing gyro-aug machines) - i'm with Nick on that one. If you are serious about IRAT control, i don't understand why a proven gyro stabiliser ups the stakes so much. The control system needs development, so you start with a lower spec intermeshing project...
Mart
Believe me i really do understand this. My understanding of the problem is that no helicopter could be designed for hands off hover, unless it became aerodynamically impractical. The various four rotor aero-jeeps of the '60s came closest, but you are only considering two - this always leaves one unstable degree of freedom. An absolutely rigid rotor with seriously impractical cone angle may do the trick, but at a cost of weight and hub complexity (or needs a tip tension ring
).It is your project, but trust me hover control is the greatest impediment to wider rotorcraft appeal - try it if you don't believe me! The gyro system can be easilly designed into the swash plate of a single rotor design, and i honestly don't understand why it has not become a standard light heli feature - but then neither have rigids/articulated. A twin rotor could either use a common gyro, or one on each hub.
For high speed work, i am convinced that the intermesher config is (theoretically) unbeatable for a given engine power. But this has to be outboard advancing and feathered retreating, ideally with pusher prop to keep constant trim, for serious aerodynamic gains. Less than high speed sees fewer, if any, advantage for intermeshing (especially when comparing gyro-aug machines) - i'm with Nick on that one. If you are serious about IRAT control, i don't understand why a proven gyro stabiliser ups the stakes so much. The control system needs development, so you start with a lower spec intermeshing project...
Mart
Last edited by Graviman; 16th May 2005 at 20:30.
Joined: Jul 2003
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From: Port Townsend,WA. USA
graviman,
Consider this. Your interest in a gyro stabilizer may not apply after you learn to hover.
The Hiller rotormatic and the Bell stabilizer system went away. The Hiller FH1100 has some other system and Jet Rangers have no flybar.
It takes more than just the ability to hover to be a pilot and pilots like control more than stability.
A bicycle is hard until learned. No need for stabilizing training wheels after the first lessons.
A little slower reacting rotor wouldn't hurt, but try not to add extra parts. Just my view on the subject.
Consider this. Your interest in a gyro stabilizer may not apply after you learn to hover.
The Hiller rotormatic and the Bell stabilizer system went away. The Hiller FH1100 has some other system and Jet Rangers have no flybar.
It takes more than just the ability to hover to be a pilot and pilots like control more than stability.
A bicycle is hard until learned. No need for stabilizing training wheels after the first lessons.
A little slower reacting rotor wouldn't hurt, but try not to add extra parts. Just my view on the subject.
Joined: Nov 2004
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From: Cambridgeshire, UK
Hi SlowRotor,
"...interest in a gyro stabilizer ... learn to hover."
True, but my point is that a good machine eases the pilot workload. Especially if he/she is preoccupied, possibly in an emergency. It also reduces the likelyhood of accidents.
"The Hiller rotormatic and the Bell stabilizer system went away."
Both systems are fundamentally flawed, the primary reason being that they affect teetering rotors not rigid/articulated rotors (less pitch/roll control). Hiller also relied on aerodynamics, which at the hub are not steady. The Bell system only increases rotor apparent inertia, and does absolutely nothing for heli control.
"It takes more than just the ability to hover to be a pilot and pilots like control more than stability."
True, but i suspect pilots doing the three Ds would be greatful for a machine that "flew itself". If it was purely mechanical, then it could be relied on to a greater extent.
"A little slower reacting rotor ..."
The Lockhheed system has absolutely no effect on rotor response time. It just provides attitude feedback, so that into cyclic controls pitch/roll rate directly (like a fixed wing) - in simple terms: the pilot flys the gyro, the gyro flies the heli. It is the basis of all articulated rotor gyro electro-hydraulic systems (and future FBW systems). It that respect it was widely adopted, but not in it's original mechanical form.
Mart
"...interest in a gyro stabilizer ... learn to hover."
True, but my point is that a good machine eases the pilot workload. Especially if he/she is preoccupied, possibly in an emergency. It also reduces the likelyhood of accidents.
"The Hiller rotormatic and the Bell stabilizer system went away."
Both systems are fundamentally flawed, the primary reason being that they affect teetering rotors not rigid/articulated rotors (less pitch/roll control). Hiller also relied on aerodynamics, which at the hub are not steady. The Bell system only increases rotor apparent inertia, and does absolutely nothing for heli control.
"It takes more than just the ability to hover to be a pilot and pilots like control more than stability."
True, but i suspect pilots doing the three Ds would be greatful for a machine that "flew itself". If it was purely mechanical, then it could be relied on to a greater extent.
"A little slower reacting rotor ..."
The Lockhheed system has absolutely no effect on rotor response time. It just provides attitude feedback, so that into cyclic controls pitch/roll rate directly (like a fixed wing) - in simple terms: the pilot flys the gyro, the gyro flies the heli. It is the basis of all articulated rotor gyro electro-hydraulic systems (and future FBW systems). It that respect it was widely adopted, but not in it's original mechanical form.
Mart
Last edited by Graviman; 16th May 2005 at 20:36.
Thread Starter
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From: Vancouver, BC, Canada
Mart,
I agree with all that you say, except for the use of the word "impractical".
Hopefully, a large fixed coning angle of 4º or 5º will be practical for stability during hover and also for stability during forward flight.
During fast forward flight, an Absolutely Rigid Rotor will not provide any flap-back to give speed stability. This is where the higher than normal coning angle should be an advantage. This large pre-cone angle should assist with speed stability by offsetting the nose down drag, which is caused by the fuselage.
Dave
for hands off hover .... An absolutely rigid rotor with seriously impractical cone angle may do the trick.
Hopefully, a large fixed coning angle of 4º or 5º will be practical for stability during hover and also for stability during forward flight.
During fast forward flight, an Absolutely Rigid Rotor will not provide any flap-back to give speed stability. This is where the higher than normal coning angle should be an advantage. This large pre-cone angle should assist with speed stability by offsetting the nose down drag, which is caused by the fuselage.
Dave
Last edited by Dave_Jackson; 16th May 2005 at 21:42.
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From: Cambridgeshire, UK
Hmmm - this took some thinking about..
OK. Maybe it's my turn to eat crow then. 
By balancing the stiffness of the tri-teetering hub and cone angle, it should be possible to have horizontal velocity in any direction cause corresponding dihedral (longitudinal and/or lateral) response of heli without any cross coupling - by tuning lead angle to coning/advancing rotor flap response. This means that heli left to it's own devices should want to hover right side up. This definately needs proving out on a ground-rig though, my main concern being how well the total system is damped (ideally critically at all speeds including hover) - worse case the system could hover/fly in a stable circle
.
The Lockheed system is a lot to live up to - i gave it some thought today. In this case the gyro provided both longitudinal/lateral damping and stability. The dihedral was affected by the blade flap being able to affect gyro reference position (so heli pitched/rolled to oppose motion) - it was actually too much feedback that caused the blade strike when disk load was pushed up on the original system. Attitude was still corrected by gyro, which had so much control power that the correction time constant was pushed well below the dihedral time constant. The effect was that the gyro damped the system.
I am still not entirely certain as to whether the low speed intermesher offers advantages over a conventional, from the aerodynamics standpoint, once you you move away from hover. The advantage of no tail rotor losses may well become offset by two hubs operating at an angle to inflow - as Nick suggests. I do appreciate that the inflow velocity flapping, with anything other than an absolute rigid rotor, will require intermeshing to avoid effective dihedral precession. For high speed, where retreating tip stall reigns, intermeshing (with pushers) is definately the way forwards - ideally outboard advancing, with large vert stabiliser. A low speed (non-pusher) intermesher as a step towards this makes sense, but i couldn't say for sure that it would improve fuel consumption over a conventional.
Again, don't feel i'm poking your project for the sake of it, Dave. I'm just trying to provide engineering feedback...
Mart
[Edited, since i felt my original post too critical of intermeshers
]
By balancing the stiffness of the tri-teetering hub and cone angle, it should be possible to have horizontal velocity in any direction cause corresponding dihedral (longitudinal and/or lateral) response of heli without any cross coupling - by tuning lead angle to coning/advancing rotor flap response. This means that heli left to it's own devices should want to hover right side up. This definately needs proving out on a ground-rig though, my main concern being how well the total system is damped (ideally critically at all speeds including hover) - worse case the system could hover/fly in a stable circle
.The Lockheed system is a lot to live up to - i gave it some thought today. In this case the gyro provided both longitudinal/lateral damping and stability. The dihedral was affected by the blade flap being able to affect gyro reference position (so heli pitched/rolled to oppose motion) - it was actually too much feedback that caused the blade strike when disk load was pushed up on the original system. Attitude was still corrected by gyro, which had so much control power that the correction time constant was pushed well below the dihedral time constant. The effect was that the gyro damped the system.
I am still not entirely certain as to whether the low speed intermesher offers advantages over a conventional, from the aerodynamics standpoint, once you you move away from hover. The advantage of no tail rotor losses may well become offset by two hubs operating at an angle to inflow - as Nick suggests. I do appreciate that the inflow velocity flapping, with anything other than an absolute rigid rotor, will require intermeshing to avoid effective dihedral precession. For high speed, where retreating tip stall reigns, intermeshing (with pushers) is definately the way forwards - ideally outboard advancing, with large vert stabiliser. A low speed (non-pusher) intermesher as a step towards this makes sense, but i couldn't say for sure that it would improve fuel consumption over a conventional.
Again, don't feel i'm poking your project for the sake of it, Dave. I'm just trying to provide engineering feedback...
Mart
[Edited, since i felt my original post too critical of intermeshers
]
Last edited by Graviman; 21st May 2005 at 14:12.
