Intermeshing Helicopters
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After reviewing
Chiplight,
Chuck maybe able to 'upchuck' some of the crow he ate.
The previously mentioned web page http://www.accs.net/users/cefpearson/gyro.htm talks about the Gimballed Gyroscope. I believe, it is saying that a continually applied force is necessary to rotate a gyroscope about its gimbal bearings. This implies that this force is greater then the force that would be required to simply start a stationary mass rotating.
It appears, to me, that the above should also apply to the tipping of two counter gyroscopes, which are located on a common axis.
If this activity was transferred to a helicopter, which had two absolutely rigid rotors, the power-train and fuselage should represent the rim, which is shown in the sketch of the gimballed gyroscope.
If the above is true, then two, counterrotating, absolutely rigid rotors, should experience some amount of damping during pitch and roll. I.e. Dynamic stability.
Dave
Any thoughts?
Chuck maybe able to 'upchuck' some of the crow he ate.
The previously mentioned web page http://www.accs.net/users/cefpearson/gyro.htm talks about the Gimballed Gyroscope. I believe, it is saying that a continually applied force is necessary to rotate a gyroscope about its gimbal bearings. This implies that this force is greater then the force that would be required to simply start a stationary mass rotating.
It appears, to me, that the above should also apply to the tipping of two counter gyroscopes, which are located on a common axis.
If this activity was transferred to a helicopter, which had two absolutely rigid rotors, the power-train and fuselage should represent the rim, which is shown in the sketch of the gimballed gyroscope.
If the above is true, then two, counterrotating, absolutely rigid rotors, should experience some amount of damping during pitch and roll. I.e. Dynamic stability.
Dave
Any thoughts?
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Dave,
My primitive thoughts on the matter are this:
If the two spinning masses are on one shaft, then they cannot both be tilting in different directions. That's the point, really. Sure it takes force to tilt one gyroscope, but if if a second gyroscope acts to prevent that motion and there is therefore no total tilting motion, then no work has been done to change the orbit of either gyroscope.
If you do tilt the object as a whole, whatever resistance is offered by one gyro is always nullified by the other and only the static mass properties remain.
To take this to an extreme, think of billions of gyroscopes assembled into one structure. The spin of each gyro is random, so the total angular momentum is zero.
That pretty much describes ordinary matter, which is made of atoms, each of which is a little gyroscope.
By your reasoning, all matter should resist being moved about any axis because all the gyro forces of all the atoms somehow add together.
Chuck's experiment with a drill and some odds and ends confirmed it very nicely. Only then did he dine on crow...
My primitive thoughts on the matter are this:
If the two spinning masses are on one shaft, then they cannot both be tilting in different directions. That's the point, really. Sure it takes force to tilt one gyroscope, but if if a second gyroscope acts to prevent that motion and there is therefore no total tilting motion, then no work has been done to change the orbit of either gyroscope.
If you do tilt the object as a whole, whatever resistance is offered by one gyro is always nullified by the other and only the static mass properties remain.
To take this to an extreme, think of billions of gyroscopes assembled into one structure. The spin of each gyro is random, so the total angular momentum is zero.
That pretty much describes ordinary matter, which is made of atoms, each of which is a little gyroscope.
By your reasoning, all matter should resist being moved about any axis because all the gyro forces of all the atoms somehow add together.
Chuck's experiment with a drill and some odds and ends confirmed it very nicely. Only then did he dine on crow...
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"If the above is true, then two, counterrotating, absolutely rigid rotors, should experience some amount of damping during pitch and roll. I.e. Dynamic stability."
Nope, sorry Dave it really doesn't work that way!
"If the two spinning masses are on one shaft, then they cannot both be tilting in different directions."
Yup, that's about the size of it!
Don't be too disheartened Dave, i really do think the Unicopter offers a number of major advantaged over the conventional - but additional hover stability ain't one of 'em. On the other hand, so what - with some repackaging of the gearbox you can fit in a simple Lockheed gyro stability system, and really get the most from your Absolutely Rigid Rotors.
I have the greatest admiration of the pioneering work of Eric Laithwaite in mag-lev technology. He really was just totally wrong about gyro-levitation (but i sympathise with the intention). The best explanation i ever heard was from a pal of mine who had retired from Rolls-Royce:
A gyroscope can be thought of as a series of point masses spinning about the axis. If the disk is additionally rotated about an axis on the plane, when seen along this new axis, each point is either travelling toward or away from the new rotation centre. By rotating about new axis, each point is subject to the good old coriolis force (frequently the subject of chopper discussions). When you think about the position of each point around the disk, and the direction of it's coriolis force, you realise that the torque along the orthogonal axis is inevitable.
That really is al there is to it! Gyroscopic precession is just a convenient engineering way of reversing the problem, so that the torque becomes the input and rotational velocity becomes the output. In actual fact the gyro will wobble/fidget on application of input torque until a new equibrium between torque and movement is established. There really is no mystery when you see it like this, and besides it makes understanding the teetering rotor 90 degree lead angle make so much more sense.
Anyhow, you never commented on blade tip flaps to force an elliptical lift distribution. The idea is that the swash plate thus only affects the blade root - assuming blade is torsionally soft (and not flutter divergent). I seriously believe this will reduce tip losses significantly in all flight conditions. This reduces bladeslap (handy for uncoordinated pilots
) - and besides I was quite astonished at the poorness of the R22 autorotation "glide slope".
I figure you should be aiming for a minimum lift/drag of at least 10:1 at best cruise speed. This is why i am also keen on feathering retreating blade, to follow local airstream - avoids "bi-plane" effect. It is realistically the only way forwards for choppers.
Would it offend anyone if i discussed blade hub mount dynamics in this forum? I have been bouncing ideas around for a while and would like some thoughts. Dave favours something called CVJ+HS, while i favour lead/lag unimpeded rigid roots, with damping (and possibly corriolis correction for blade flex - i notice Sikorsky/Boeing have gone this route with the Comanche). Westlands are playing with servo-electric HHC (their name H.E.A.T. - can't remember the abreiviation), and i wonder if they are wearilly treading this path too...
Mart
Nope, sorry Dave it really doesn't work that way!
"If the two spinning masses are on one shaft, then they cannot both be tilting in different directions."
Yup, that's about the size of it!
Don't be too disheartened Dave, i really do think the Unicopter offers a number of major advantaged over the conventional - but additional hover stability ain't one of 'em. On the other hand, so what - with some repackaging of the gearbox you can fit in a simple Lockheed gyro stability system, and really get the most from your Absolutely Rigid Rotors.
I have the greatest admiration of the pioneering work of Eric Laithwaite in mag-lev technology. He really was just totally wrong about gyro-levitation (but i sympathise with the intention). The best explanation i ever heard was from a pal of mine who had retired from Rolls-Royce:
A gyroscope can be thought of as a series of point masses spinning about the axis. If the disk is additionally rotated about an axis on the plane, when seen along this new axis, each point is either travelling toward or away from the new rotation centre. By rotating about new axis, each point is subject to the good old coriolis force (frequently the subject of chopper discussions). When you think about the position of each point around the disk, and the direction of it's coriolis force, you realise that the torque along the orthogonal axis is inevitable.
That really is al there is to it! Gyroscopic precession is just a convenient engineering way of reversing the problem, so that the torque becomes the input and rotational velocity becomes the output. In actual fact the gyro will wobble/fidget on application of input torque until a new equibrium between torque and movement is established. There really is no mystery when you see it like this, and besides it makes understanding the teetering rotor 90 degree lead angle make so much more sense.
Anyhow, you never commented on blade tip flaps to force an elliptical lift distribution. The idea is that the swash plate thus only affects the blade root - assuming blade is torsionally soft (and not flutter divergent). I seriously believe this will reduce tip losses significantly in all flight conditions. This reduces bladeslap (handy for uncoordinated pilots
) - and besides I was quite astonished at the poorness of the R22 autorotation "glide slope".I figure you should be aiming for a minimum lift/drag of at least 10:1 at best cruise speed. This is why i am also keen on feathering retreating blade, to follow local airstream - avoids "bi-plane" effect. It is realistically the only way forwards for choppers.
Would it offend anyone if i discussed blade hub mount dynamics in this forum? I have been bouncing ideas around for a while and would like some thoughts. Dave favours something called CVJ+HS, while i favour lead/lag unimpeded rigid roots, with damping (and possibly corriolis correction for blade flex - i notice Sikorsky/Boeing have gone this route with the Comanche). Westlands are playing with servo-electric HHC (their name H.E.A.T. - can't remember the abreiviation), and i wonder if they are wearilly treading this path too...
Mart
Last edited by Graviman; 29th Apr 2005 at 14:32.
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OK, who is giving who the spin?
Mart,
Agreed. It is better to keep different subjects on different threads. Plus, a thread does not cost much.
Go for it.
Chiplight & Mart,
I understand and agree 100% with your basic argument that the gyroscopic precession of one gyroscope will be canceled by the opposing gyroscopic precession of the other. This is why "He [Laithwaite] also had big problems with the shafts breaking."
However, the gyroscope does not appear to be that simple. It appears that "only the static mass properties remain" ain't quite true. If only the static mass properties remain then any TEMPORARY moment applied to the static mass will start it rotating and this rotation will continue. It can only be dampened by bearing friction, or aerodynamically in the case of a helicopter.
Again, please note that the web page http://www.accs.net/users/cefpearson/gyro.htm talks about the Gimballed Gyroscope. It says; " Gyroscopes, when gimbaled, only resist a tilting change in their axis. The axis does move a certain amount with a given force." These two statements imply the application of a CONSTANT force.
Reading the section "A more detailed explanation of how a gimbaled gyro functions" appears to logically support the necessity of a CONSTANT moment, if the rotation is to be maintained. This means that a (possibly small) dampening is constantly taking place.
Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros.
Chuck was probably unable to detect this constant damping. Reference the Questions and Answers near the end of this page.
Dave.
Agreed. It is better to keep different subjects on different threads. Plus, a thread does not cost much.
Go for it.Chiplight & Mart,
I understand and agree 100% with your basic argument that the gyroscopic precession of one gyroscope will be canceled by the opposing gyroscopic precession of the other. This is why "He [Laithwaite] also had big problems with the shafts breaking."
However, the gyroscope does not appear to be that simple. It appears that "only the static mass properties remain" ain't quite true. If only the static mass properties remain then any TEMPORARY moment applied to the static mass will start it rotating and this rotation will continue. It can only be dampened by bearing friction, or aerodynamically in the case of a helicopter.
Again, please note that the web page http://www.accs.net/users/cefpearson/gyro.htm talks about the Gimballed Gyroscope. It says; " Gyroscopes, when gimbaled, only resist a tilting change in their axis. The axis does move a certain amount with a given force." These two statements imply the application of a CONSTANT force.
Reading the section "A more detailed explanation of how a gimbaled gyro functions" appears to logically support the necessity of a CONSTANT moment, if the rotation is to be maintained. This means that a (possibly small) dampening is constantly taking place.
Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros.
Chuck was probably unable to detect this constant damping. Reference the Questions and Answers near the end of this page.
Dave.
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I sit amused by this thread, which is like those classical arguments about how many angels could sit on a pinhead.
The helo that Dave imagines is only that, imaginary. If someone knows how to build a successful rotor that is incredibly rigid (Dave says "Absolutely" which is also incredible), he is hiding that secret from the rest of the planet.
Dave can you defin "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be?
Dave, you pull this chestnut out about every 60 days! How about building the thing, already?
The helo that Dave imagines is only that, imaginary. If someone knows how to build a successful rotor that is incredibly rigid (Dave says "Absolutely" which is also incredible), he is hiding that secret from the rest of the planet.
Dave can you defin "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be?
Dave, you pull this chestnut out about every 60 days! How about building the thing, already?
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Cheyenne gyro control
To: Graviman
The gyro control on the Cheyenne was mounted above the main rotor and was connected to the swashplate via control rods that ran through the hollow main rotor shaft. The swashplat, springs and the power control unit (servo) were mounted underneath the gearbox. The springs you mentioned were there to provide a force proportional to the movement of the servo piston rods.
Although the pilot would cause the gyro to displace inputting a control force to the respective rotor blades the pilot would return the cyclic stick to the neutral position and the gyro due to rigidity would maintain the position commanded by the pilot. The springs would return to their static position and the nutating force to the gyro would return to “0” This is similar to the control input to that of a fixed wing aircraft.
The original design of the Cheyenne incorporated a 90-degree lead angle on the position of the servo in relation to the swashplate. However this caused problems when the rotor blades were redesigned to compensate for a significant weight increase in the airframe. The Cheyenne had a serious problem with rotor blade divergence resulting in the fatal crash of one Cheyenne and another that flew apart in a wind tunnel.
Parker Bertea the designers of the Cheyenne hydraulic system were charged with finding a solution to the problem of divergence. It took well over a year and they came up with a system of push pull rods and electrical sensors running from the rotorhead down to the servo. The mechanical linkage would sense a divergence and signal the servo to modify the pilots input. (**) The system worked beautifully and provided a vibration free ride. However, there were so many single point failure modes that would cause loss of control and by that time the program was cancelled.
(**) The Lynx has a similar system but it is electronic. If this system were turned off in flight the helicopter would fly to the left with forward cyclic. Did someone say 18-degree offset. The Lynx has a 15-degree offset during the rigging procedure.
The gyro was mounted to the rotorhead using a constant velocity joint. This eliminated leading and lagging of the gyro arms.
The gyro control on the Cheyenne was mounted above the main rotor and was connected to the swashplate via control rods that ran through the hollow main rotor shaft. The swashplat, springs and the power control unit (servo) were mounted underneath the gearbox. The springs you mentioned were there to provide a force proportional to the movement of the servo piston rods.
Although the pilot would cause the gyro to displace inputting a control force to the respective rotor blades the pilot would return the cyclic stick to the neutral position and the gyro due to rigidity would maintain the position commanded by the pilot. The springs would return to their static position and the nutating force to the gyro would return to “0” This is similar to the control input to that of a fixed wing aircraft.
The original design of the Cheyenne incorporated a 90-degree lead angle on the position of the servo in relation to the swashplate. However this caused problems when the rotor blades were redesigned to compensate for a significant weight increase in the airframe. The Cheyenne had a serious problem with rotor blade divergence resulting in the fatal crash of one Cheyenne and another that flew apart in a wind tunnel.
Parker Bertea the designers of the Cheyenne hydraulic system were charged with finding a solution to the problem of divergence. It took well over a year and they came up with a system of push pull rods and electrical sensors running from the rotorhead down to the servo. The mechanical linkage would sense a divergence and signal the servo to modify the pilots input. (**) The system worked beautifully and provided a vibration free ride. However, there were so many single point failure modes that would cause loss of control and by that time the program was cancelled.
(**) The Lynx has a similar system but it is electronic. If this system were turned off in flight the helicopter would fly to the left with forward cyclic. Did someone say 18-degree offset. The Lynx has a 15-degree offset during the rigging procedure.
The gyro was mounted to the rotorhead using a constant velocity joint. This eliminated leading and lagging of the gyro arms.
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Awe Nick, you're changing the subject from Gyroscope to Next Generation Helicopter. 
I use (and have defined) the expression "Absolutely Rigid Rotor" in the context that 'absolute' is the optimal, albeit impossible, objective. When Sikorsky misused the expression 'Rigid Rotor' to describe a blade with the consistency of a wet noodle, it left very little wiggle room.
Since you asked; the blade for an Absolutely Rigid Rotor WITH Active Blade Twist is the current project; when not enjoying the pleasures of posting on PPRuNe.
Having left Sikorsky, you now have the ability to look objectively at ALL rotorcraft proposals. Please explain how in hell the proposed Sikorsky Reverse Velocity Rotorcraft will be able to make a non-fatal transition into autorotation after a loss of power in forward flight.
I say it can't, and, have provided the supporting explaination.
Dave
I use (and have defined) the expression "Absolutely Rigid Rotor" in the context that 'absolute' is the optimal, albeit impossible, objective. When Sikorsky misused the expression 'Rigid Rotor' to describe a blade with the consistency of a wet noodle, it left very little wiggle room.
Since you asked; the blade for an Absolutely Rigid Rotor WITH Active Blade Twist is the current project; when not enjoying the pleasures of posting on PPRuNe.
Having left Sikorsky, you now have the ability to look objectively at ALL rotorcraft proposals. Please explain how in hell the proposed Sikorsky Reverse Velocity Rotorcraft will be able to make a non-fatal transition into autorotation after a loss of power in forward flight.
I say it can't, and, have provided the supporting explaination.
Dave
Last edited by Dave_Jackson; 30th Apr 2005 at 14:13.
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Hey hey, this thread is getting pretty interesting...
"Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros."
Well ok using your CVJ+HS hub system, the compliance will allow some seperate gimballing. Hence there will be an initial increase in apparent rotational inertia in pitch or roll, until the hub spring reached equilibrium. Not sure whether the spring limited compliance would really damp the pitch/roll or just limit inertia increase to an initial resistance. For the sort of pitch/roll damping you are talking about you would normally design a damper into the gimble (ie torque/rot_velocity), so that gyro only providided part of restorative force required to resist input.
Don't forget this is all at the cost of reduced clearance between contra-rotating rotors, hence risking rotor clash - pilots are (rightly so) a hard bunch to convince about the safety of a machine. You really do need to build a test rig to understand this interaction properly, before moving on. At any rate this all provides resistance to gust loading, but does not adress my primary concern about pilot controlability - ideally cyclic position would directly control pitch/roll rate.
"If someone knows how to build a successful rotor that is incredibly rigid ... he is hiding that secret from the rest of the planet."
Agreed, and is why i suggest either coriolis correction or damped lead/lag movement. Prouty makes the point very strongly that even a "rigid" blade can be given an effective offset hinge dimension. Dave's proposed CVJ+HS is a half way house design, which aims to keep hub rigidity below rotor without altering pitch horn lead angle. I don't suppose the design will stop with that, but it is a good start - certainly until the dynamics are understood better.
"How about building the thing, already?"
Must admit some practical ground test rigs would be nice. As an engineer i appreciate how much time (and money) this sort of engineering endeavour costs, this is why i have offered any cad/FEA help i can. It is all too easy to start on the wrong path, and run out of cash...
Lu, thanks for the fascinating insight into the Cheyenne system - i have been an admirer for some time. You would be suprised how much of a headache the hydraulics can cause on even a prototype articulated mining truck! Would you say that the Lynx system is the way to go for a private helicopter? I have been thinking along the lines of cost and reliability, hence the idea of a fully mechanical system over an electronically controlled servo-hydraulic system - the CL475 (once the three bladed rotor was fitted) seemed to prove this point. Westland are considering elec-servo to replace the hydraulics, which is a good route but one that must be safety proven (as it has already been in fixed wing) - I would be concerned about development costs.
"The springs would return to their static position ... This is similar to the control input to that of a fixed wing aircraft."
This is very much my reasoning behind incorperating it into the Unicopter development program. Must admit i still find flying the R22 in a turn an interesting experience compared to (say) a K8 glider - admitedly my pedal reflexes are still a little incorrect. I think a complete avinitio would really struggle though.
Dave, I appreciate that the full helicopter design is still to soon. I have admired your packaging bucks, and would like to suggest that maybe it is time for a dynamic test rig. I'm not proposing anything too fancy, but it strikes me that there is a lot of debate speculating about the interaction of the twin rotor hubs, the fuselage, and the control system. Even a simple gyro mass test bed is a good start, and would allow a natual progression to the blade development. Do you prefer to discuss technical issues in detail on this forum, or is there another venue? I'm keen not to outstay my welcome on this forum...
Is there a development grant in Canada that would help you get started? I think you could put forward a good case.
Mart
"Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros."
Well ok using your CVJ+HS hub system, the compliance will allow some seperate gimballing. Hence there will be an initial increase in apparent rotational inertia in pitch or roll, until the hub spring reached equilibrium. Not sure whether the spring limited compliance would really damp the pitch/roll or just limit inertia increase to an initial resistance. For the sort of pitch/roll damping you are talking about you would normally design a damper into the gimble (ie torque/rot_velocity), so that gyro only providided part of restorative force required to resist input.
Don't forget this is all at the cost of reduced clearance between contra-rotating rotors, hence risking rotor clash - pilots are (rightly so) a hard bunch to convince about the safety of a machine. You really do need to build a test rig to understand this interaction properly, before moving on. At any rate this all provides resistance to gust loading, but does not adress my primary concern about pilot controlability - ideally cyclic position would directly control pitch/roll rate.
"If someone knows how to build a successful rotor that is incredibly rigid ... he is hiding that secret from the rest of the planet."
Agreed, and is why i suggest either coriolis correction or damped lead/lag movement. Prouty makes the point very strongly that even a "rigid" blade can be given an effective offset hinge dimension. Dave's proposed CVJ+HS is a half way house design, which aims to keep hub rigidity below rotor without altering pitch horn lead angle. I don't suppose the design will stop with that, but it is a good start - certainly until the dynamics are understood better.
"How about building the thing, already?"
Must admit some practical ground test rigs would be nice. As an engineer i appreciate how much time (and money) this sort of engineering endeavour costs, this is why i have offered any cad/FEA help i can. It is all too easy to start on the wrong path, and run out of cash...
Lu, thanks for the fascinating insight into the Cheyenne system - i have been an admirer for some time. You would be suprised how much of a headache the hydraulics can cause on even a prototype articulated mining truck! Would you say that the Lynx system is the way to go for a private helicopter? I have been thinking along the lines of cost and reliability, hence the idea of a fully mechanical system over an electronically controlled servo-hydraulic system - the CL475 (once the three bladed rotor was fitted) seemed to prove this point. Westland are considering elec-servo to replace the hydraulics, which is a good route but one that must be safety proven (as it has already been in fixed wing) - I would be concerned about development costs.
"The springs would return to their static position ... This is similar to the control input to that of a fixed wing aircraft."
This is very much my reasoning behind incorperating it into the Unicopter development program. Must admit i still find flying the R22 in a turn an interesting experience compared to (say) a K8 glider - admitedly my pedal reflexes are still a little incorrect. I think a complete avinitio would really struggle though.
Dave, I appreciate that the full helicopter design is still to soon. I have admired your packaging bucks, and would like to suggest that maybe it is time for a dynamic test rig. I'm not proposing anything too fancy, but it strikes me that there is a lot of debate speculating about the interaction of the twin rotor hubs, the fuselage, and the control system. Even a simple gyro mass test bed is a good start, and would allow a natual progression to the blade development. Do you prefer to discuss technical issues in detail on this forum, or is there another venue? I'm keen not to outstay my welcome on this forum...
Is there a development grant in Canada that would help you get started? I think you could put forward a good case.
Mart
Last edited by Graviman; 30th Apr 2005 at 17:14.
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Your right ~ I'm wrong. 
A few years ago, it was stated that counterrotating gyros are used in space to hold orientation. I erred by assumed that the gyros were physically holding the orientation, and were not simply the sensors.
Thanks guys.
Tonight's entree is looking a lot like crow.
A few years ago, it was stated that counterrotating gyros are used in space to hold orientation. I erred by assumed that the gyros were physically holding the orientation, and were not simply the sensors.
Thanks guys.
Tonight's entree is looking a lot like crow.
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Eating Crow
Isn't it delicious? :
Seriously, Dave, your humility is appreciated. If only Lu could be so open to suggestion regarding phase offset we could eliminate about a gigabyte of discussion on this forum.
Seriously, Dave, your humility is appreciated. If only Lu could be so open to suggestion regarding phase offset we could eliminate about a gigabyte of discussion on this forum.
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"Tonight's entree is looking a lot like crow."
Aw shuks, no need to get to disheartened about it. As i read through Prouty, i frequently thought about the various aerodynamic arguements put forward for Unicopter. It is still a very viable concept, but like ANY engineering concept will need some development - Synchrolite is the perfect stepping stone.
The Lockheed stability system is seriously worth considering, especially as it has inherent mechanical reliability. For a start if you could guarantee hands off stability, clouds suddenly look less daunting. Basically the chopper has to remain at a fixed attitude when flying hands off, which the stability system ensures, any lateral velocity caused by non-level flight then has to stabilise heli attitude by conventional aerodynamic means - longitudinal and lateral dihedral. You need both for it to work.
This would then open up new markets in temperate zones, where weather put-downs are often a fact of life (like Britain
). As an example, this allows emergency services to consider cheaper helis for more roles - never a bad thing. Other markets in the private sector will also open up....
"A few years ago, it was stated that counterrotating gyros are used in space to hold orientation."
I'm not up on latest techniques, but i imagine laser gyros monitor attitude in 3D, while flywheels are used to adjust attitude trim (conservation of angular momentum). I know that ion plasma drives offer the best (existing) way to reduce propelant mass usage - always the main driver for space stuff.
I think the next thing to consider is definately the hub/blade dynamics for a rigid intermesher. Nick Lappos has a very good point about practically attainable rigidity levels. The trick is going to be allowing the best reduced-g controlability, without introducing unecessary vibration. I favour lead/lag compliance, you favour the CVJ+HS - so there is plenty to evaluate. Retreating blade root feathering, and tip feathering, (or IRAT if you like) is still another avenue of development.
Mart
Aw shuks, no need to get to disheartened about it.
As i read through Prouty, i frequently thought about the various aerodynamic arguements put forward for Unicopter. It is still a very viable concept, but like ANY engineering concept will need some development - Synchrolite is the perfect stepping stone.The Lockheed stability system is seriously worth considering, especially as it has inherent mechanical reliability. For a start if you could guarantee hands off stability, clouds suddenly look less daunting. Basically the chopper has to remain at a fixed attitude when flying hands off, which the stability system ensures, any lateral velocity caused by non-level flight then has to stabilise heli attitude by conventional aerodynamic means - longitudinal and lateral dihedral. You need both for it to work.
This would then open up new markets in temperate zones, where weather put-downs are often a fact of life (like Britain
). As an example, this allows emergency services to consider cheaper helis for more roles - never a bad thing. Other markets in the private sector will also open up...."A few years ago, it was stated that counterrotating gyros are used in space to hold orientation."
I'm not up on latest techniques, but i imagine laser gyros monitor attitude in 3D, while flywheels are used to adjust attitude trim (conservation of angular momentum). I know that ion plasma drives offer the best (existing) way to reduce propelant mass usage - always the main driver for space stuff.
I think the next thing to consider is definately the hub/blade dynamics for a rigid intermesher. Nick Lappos has a very good point about practically attainable rigidity levels. The trick is going to be allowing the best reduced-g controlability, without introducing unecessary vibration. I favour lead/lag compliance, you favour the CVJ+HS - so there is plenty to evaluate. Retreating blade root feathering, and tip feathering, (or IRAT if you like) is still another avenue of development.
Mart
Last edited by Graviman; 1st May 2005 at 19:52.
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At risk of opening old wounds....
To: Chiplight
I have been told so many times by so many people that I am wrong about my premise regarding the 18-degree offset that I almost believe it. Having said that I ask you the following question: How much of an aerodynamic genius would it take to design a rotorhead that was entirely different from all other rotorheads in that it had flapping hinges but no capability of leading and lagging. This rotorhead was married to a flight control system similar to that of a Bell and because of this disparity the rotor had to be offset 18-degrees in order to rig the helicopter.
Then this aerodynamic genius had to design a rotorblade that had a 72-degree phase angle.
The Lynx has a 15-degree offset during the rigging process and when forward cyclic is introduced the helicopter would fly to the left. Why couldn’t Westland design a blade that had a 75-degree phase angle so that it would fly like the Robinson which has an 18-degree offset and which according to what I have been told flies straight ahead with the introduction of forward cyclic.
If only Lu could be so open to suggestion regarding phase offset we could eliminate about a gigabyte of discussion on this forum.
Then this aerodynamic genius had to design a rotorblade that had a 72-degree phase angle.
The Lynx has a 15-degree offset during the rigging process and when forward cyclic is introduced the helicopter would fly to the left. Why couldn’t Westland design a blade that had a 75-degree phase angle so that it would fly like the Robinson which has an 18-degree offset and which according to what I have been told flies straight ahead with the introduction of forward cyclic.
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Dave,
I love the way you propose mythical helicopers, and use past mythical helicopters as rationale.
For the record, this isn't a debate, and I continue to have objectivity before, during and after my tenure at Sikorsky. You continue to base your speculations on myths and not on engineering. And you confuse the objections I raise as opinion, when all I ask is that you use some facts!
I love the way you propose mythical helicopers, and use past mythical helicopters as rationale.
For the record, this isn't a debate, and I continue to have objectivity before, during and after my tenure at Sikorsky. You continue to base your speculations on myths and not on engineering. And you confuse the objections I raise as opinion, when all I ask is that you use some facts!
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Dave,
As a follow on to Nicks comment about past failures (real or mythical).
In the book "Whirlibirds" by Jay P. Spenser, is a photo of the Hiller X-2-235s that had "super-rigid rotors" (coaxial configuration). The photo shows two people standing on the blades, at the tips, with little deflection. I don't know if the machine ever flew, there is mention of vibration problems. Of course, we know that Hiller went with single rotor after his experiments with coaxial. And that seems to be the case with countless pioneers. (such as Sikorsky)
The book is quite interesting for a helo designer.
As a follow on to Nicks comment about past failures (real or mythical).
In the book "Whirlibirds" by Jay P. Spenser, is a photo of the Hiller X-2-235s that had "super-rigid rotors" (coaxial configuration). The photo shows two people standing on the blades, at the tips, with little deflection. I don't know if the machine ever flew, there is mention of vibration problems. Of course, we know that Hiller went with single rotor after his experiments with coaxial. And that seems to be the case with countless pioneers. (such as Sikorsky)
The book is quite interesting for a helo designer.
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Lu,
this is a thread about intermeshing helicopters, so I'll promise to make this my only reply on the topic of R22 swashplate phasing.
You always compare a bell system to a Robinson and state that the bell is rigged so that forward cyclic causes forward swashplate tilt, but not so on the R22/44.
I could turn the tables and ask you to again look at both systems,
but this time, watch what happens when you manually raise a blade to simulate flapping.
On the bell rotor, the flapping has no affect on blade pitch, but on the R22/44, it will cause a pitch change.
Now, keeping this in mind, doesn't it make sense that the two rotor systems are rigged with different phase offset ?
Both helicopters will fly forward with forward stick, as has been attested to by many pilots.
When a forward stick input is made on the R22, this affects a cyclic pitch change, which in turn causes rotor flapping, which in turn pulls out pitch...
--an interaction that must be compensated for in the swashplate phasing in the R22, but not in the Bell.
this is a thread about intermeshing helicopters, so I'll promise to make this my only reply on the topic of R22 swashplate phasing.
You always compare a bell system to a Robinson and state that the bell is rigged so that forward cyclic causes forward swashplate tilt, but not so on the R22/44.
I could turn the tables and ask you to again look at both systems,
but this time, watch what happens when you manually raise a blade to simulate flapping.
On the bell rotor, the flapping has no affect on blade pitch, but on the R22/44, it will cause a pitch change.
Now, keeping this in mind, doesn't it make sense that the two rotor systems are rigged with different phase offset ?
Both helicopters will fly forward with forward stick, as has been attested to by many pilots.
When a forward stick input is made on the R22, this affects a cyclic pitch change, which in turn causes rotor flapping, which in turn pulls out pitch...
--an interaction that must be compensated for in the swashplate phasing in the R22, but not in the Bell.
Last edited by Chiplight; 1st May 2005 at 20:20.
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Here we go again...
To: Chiplight
The Bell swashplate tips forward with forward cyclic. Since the Bell has a 90-degree lead on the pitch horn the blades are laterally disposed when rigging for forward cyclic. Conversely the blades are aligned with the longitudinal axis when rigging for lateral cyclic.
The Robinson swashplate operates identical to that of a Bell in that with forward cyclic the swashplate tips the same way. However the Robinson pitch horn leads the blade by 72-degrees so that in order to rig for forward or aft cyclic the advancing blade is offset 18-degrees in order to place the pitch horn directly over the forward tilted swashplate. The same offset would apply to the lateral setting.
When the Bell blades are static and the blade is moved it will not change pitch because in the static condition the pitch horn is aligned with the teeter hinge so there is no pitch flap coupling.
On the Robinson blade there is pitch flap coupling when the blade is moved about the teeter hinge because the pitch horn is not aligned with the teeter hinge resulting in a Delta hinge effect.
The is no pitch flap coupling if in the static position the blade is moved about the cone hinge. However with the input of collective pitch the two points are no longer in alignment and pitch flap coupling will occur.
However if you read the POH and the maintenance manual there is a warning not to try to move the blades when they are at rest.
You always compare a bell system to a Robinson and state that the bell is rigged so that forward cyclic causes forward swashplate tilt, but not so on the R22/44.
The Robinson swashplate operates identical to that of a Bell in that with forward cyclic the swashplate tips the same way. However the Robinson pitch horn leads the blade by 72-degrees so that in order to rig for forward or aft cyclic the advancing blade is offset 18-degrees in order to place the pitch horn directly over the forward tilted swashplate. The same offset would apply to the lateral setting.
On the bell rotor, the flapping has no affect on blade pitch, but on the R22/44, it will cause a pitch change.
On the Robinson blade there is pitch flap coupling when the blade is moved about the teeter hinge because the pitch horn is not aligned with the teeter hinge resulting in a Delta hinge effect.
The is no pitch flap coupling if in the static position the blade is moved about the cone hinge. However with the input of collective pitch the two points are no longer in alignment and pitch flap coupling will occur.
However if you read the POH and the maintenance manual there is a warning not to try to move the blades when they are at rest.
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Gosh, i'm gonna stand back and let Lu and Chiplight sort this one out for themselves! Remember folks, this thread is intended to be an engineering discusion, so don't get too personal
"...the book "Whirlibirds" by Jay P. Spenser ... is quite interesting for a helo designer."
Gonna have a look, once i've finished reading up on engin' design.
Regarding Nick's comment:
"And you confuse the objections I raise as opinion, when all I ask is that you use some facts!"
I suspect that a ground test rig (a budget whirl tower if you like), with carefully recorded data, would go a long long way towards satisfying his concerns - you'd be suprised how cheap good instrumentation can be. A static rig would get the inertia dynamics right, and i really liked your pick-up rig idea for the aerodynamics...
Mart
Remember folks, this thread is intended to be an engineering discusion, so don't get too personal "...the book "Whirlibirds" by Jay P. Spenser ... is quite interesting for a helo designer."
Gonna have a look, once i've finished reading up on engin' design.
Regarding Nick's comment:
"And you confuse the objections I raise as opinion, when all I ask is that you use some facts!"
I suspect that a ground test rig (a budget whirl tower if you like), with carefully recorded data, would go a long long way towards satisfying his concerns - you'd be suprised how cheap good instrumentation can be. A static rig would get the inertia dynamics right, and i really liked your pick-up rig idea for the aerodynamics...
Mart
Last edited by Graviman; 1st May 2005 at 20:15.
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Hope that this thread doesn't fracture into tooo many subjects.
Mart,
The Constant Velocity Joint + Hub Spring rotor is a theoretically viable concept and it may be of interest to other developers of very-light rotorcraft. However, in my mind, it is only a progressive step in the movement toward an 'absolutely rigid rotor'.
Since there is no desire nor need for government funding or outside investors, I am afforded the liberty of striving for the whole enchilada. The risks are greater but the challenge is more exciting.
____________________________
Nick
Your postings and critiques are truly appreciated. However, your last one is disturbing.
The Flettner Fl-282, the Focke Fw-61 , the Kellett ~ XR-8, XR-10 , and the Sikorsky ABC were not "past mythical helicopters". The only mythical helicopter is the Stepniewski (concept) and you have said in the past that Stepniewski was the aerodynamicist who you admired the most.
I defined Absolutely Rigid Rotor for you. In regard to 'stress' and 'vibration', there is limited time available to deeply consider lower level details, at this stage of development. New concepts come from a top-down approach. A bottom-up approach can do no more than 'tweak' the existing.
While we are talking about mythical helicopters and facts; I have stated and provided a supporting argument on a valid concern about Sikorsky's latest concept, on my web page Sikorsky's Reverse Velocity Rotorcraft Proposal. Your "factual" response will certainly add to the knowledge of the participants on this thread.
_______________________
slowrotor,
A few years ago Nick mentioned that the extremely high vibration of the Hiller X-2-235 had even done damage to a wind tunnel.
The question then becomes; Why?
The answer is the 2/rev lateral dysimitry of lift during forward flight.
This craft has two blades per rotor, which ain't no big deal. However, these rotors are 'absolutly' rigid, and this is a big deal. The blades will be crossing each other at azimuths of 45º, 135º, 225º and 315º. In addition, because the blades are rigid they will be producing more thrust at the back of the craft then at the front. At one moment, two blades are providing high thrust in the left-rear quadrant, then a fraction of a second later two blades are providing high thrust in the right-rear quadrant. = 2/rev lateral shake rattle and roll
Please note that if the blades cross at azimuths of 0º, 90º, 180º and 270º the vibration will be longitudinal instead of lateral.
Even the three blade 'fairly absolutely rigid rotors' on the Sikorsky ABC created an unacceptable lateral vibration around 225 knots. IMHO, a four blade rotor should eliminate this lateral vibration.
Dave
The Constant Velocity Joint + Hub Spring rotor is a theoretically viable concept and it may be of interest to other developers of very-light rotorcraft. However, in my mind, it is only a progressive step in the movement toward an 'absolutely rigid rotor'.
Since there is no desire nor need for government funding or outside investors, I am afforded the liberty of striving for the whole enchilada. The risks are greater but the challenge is more exciting.
____________________________
Nick
Your postings and critiques are truly appreciated. However, your last one is disturbing.
I love the way you ....use past mythical helicopters as rationale.
And you confuse the objections I raise as opinion, when all I ask is that you use some facts!
Dave can you define "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be?
Dave can you define "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be?
While we are talking about mythical helicopters and facts; I have stated and provided a supporting argument on a valid concern about Sikorsky's latest concept, on my web page Sikorsky's Reverse Velocity Rotorcraft Proposal. Your "factual" response will certainly add to the knowledge of the participants on this thread.
_______________________
slowrotor,
A few years ago Nick mentioned that the extremely high vibration of the Hiller X-2-235 had even done damage to a wind tunnel.
The question then becomes; Why?
The answer is the 2/rev lateral dysimitry of lift during forward flight.
This craft has two blades per rotor, which ain't no big deal. However, these rotors are 'absolutly' rigid, and this is a big deal. The blades will be crossing each other at azimuths of 45º, 135º, 225º and 315º. In addition, because the blades are rigid they will be producing more thrust at the back of the craft then at the front. At one moment, two blades are providing high thrust in the left-rear quadrant, then a fraction of a second later two blades are providing high thrust in the right-rear quadrant. = 2/rev lateral shake rattle and roll
Please note that if the blades cross at azimuths of 0º, 90º, 180º and 270º the vibration will be longitudinal instead of lateral.
Even the three blade 'fairly absolutely rigid rotors'
on the Sikorsky ABC created an unacceptable lateral vibration around 225 knots. IMHO, a four blade rotor should eliminate this lateral vibration. Dave
Last edited by Dave_Jackson; 1st May 2005 at 21:55.
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OK folks, just another gentle reminder to everyone involved in this thread: This is an engineering discussion, the pupose of which is to tease out the best design of intermeshing helicopter. I would really hate for it to all fall apart due to differences of opinion/experience. I appreciate that experts are always passionate about their beliefs, but have been in enough projects to understand that it is critical that all agree to some level of compromise.
--------------------------------------------------------------------------------
Dave,
"The Constant Velocity Joint + Hub Spring rotor ... is only a progressive step ... toward an 'absolutely rigid rotor'. "
Agreed. Your rationale makes complete sense, and i accept that my interest in lead/lag compliance is only one possible long term solution - it may not even be the right one! I have eaten plenty of crow myself over the years...
"...no desire nor need for government funding or outside investors..."
Wow, i wish i was in that position!
"The risks are greater but the challenge is more exciting."
Remember there are those of us who are willing to help you share the workload (if not cost 
).
Mart
--------------------------------------------------------------------------------
Dave,
"The Constant Velocity Joint + Hub Spring rotor ... is only a progressive step ... toward an 'absolutely rigid rotor'. "
Agreed. Your rationale makes complete sense, and i accept that my interest in lead/lag compliance is only one possible long term solution - it may not even be the right one! I have eaten plenty of crow myself over the years...
"...no desire nor need for government funding or outside investors..."
Wow, i wish i was in that position!
"The risks are greater but the challenge is more exciting."
Remember there are those of us who are willing to help you share the workload
(if not cost ). Mart
Last edited by Graviman; 1st May 2005 at 23:31.
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For those who are not bored to death.
Out of respect for Nick's question about vibration, the following is added
Nick,
If your concern is about the vibration within an absolutely rigid rotor blade, then I would suggest that the attempted solutions should be addressed at a lower level in the development hierarchy. If your concern has to do with the craft, as a whole, then it is an uppermost concern.
Regarding the second; The Prewitt evaluation of the Flettner Fl-282 was extremely flattering, however, it did express a concern about the high level of vibration. It appears that this vibration is mainly the result of a rotor to rotor aerodynamic interaction.
The following are the approaches that are been taken to minimize this problem;
Whew!
Dave
Nick,
If your concern is about the vibration within an absolutely rigid rotor blade, then I would suggest that the attempted solutions should be addressed at a lower level in the development hierarchy. If your concern has to do with the craft, as a whole, then it is an uppermost concern.
Regarding the second; The Prewitt evaluation of the Flettner Fl-282 was extremely flattering, however, it did express a concern about the high level of vibration. It appears that this vibration is mainly the result of a rotor to rotor aerodynamic interaction.
The following are the approaches that are been taken to minimize this problem;
- The blade count has been increased from 4 to 6. This increases the blade-to-blade passages per revolution from 4 to 9. This in turn, reduces the amplitude of the vibration and takes its frequency above that which is uncomfortable for occupants.
- The craft is to have a pusher propeller and one of the advantages of this is a reduction in the thrust of the rotors during forward flight.
- Independent Root and Pitch Control plus 2P Higher Harmonic Control on the root will provide a better distribution of thrust.
- Future improvements to rotor induced vibration should be more meaningful to the intermeshing and the interleaving configurations than the single rotor configuration.
Whew!
Dave