Intermeshing Helicopters
Dave Jackson Said:
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.
Maybe they have a department that makes pictures of mythical helicopters there. They haven't built it, have they?
-- IFMU
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.
Maybe they have a department that makes pictures of mythical helicopters there. They haven't built it, have they?
-- IFMU
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IFMU,
That's right, they haven't built it (reverse velocity rotor). The problems with speculating on these improvements is that they are improving on a problem that doesn't exist anymore, where symmetry is a perfection that must be chased, like unicorns and rainbow's ends.
Dave seeks a "balanced, symetrical" rotor as solution to handling issues that have been solved years ago without doing mechanical backflips - by installing a fly-by-wire control system. Chasing the ease of handling by adding whole rotors and mythical super-rigid rotors is a way to convert money into piles of scrap experimental helicopters. There is no designer on earth who would seek better handling by adding rotors and blades, not when good, cheap and powerful computers are available to solve that problem.
Following this logic, our cars should never have had anti-lock brakes (a fly-by-wire system) nor should we have had electronic fuel injection (another fly-by-wire system) we should have had mechanical systems with a boot full of critical parts instead.
That's right, they haven't built it (reverse velocity rotor). The problems with speculating on these improvements is that they are improving on a problem that doesn't exist anymore, where symmetry is a perfection that must be chased, like unicorns and rainbow's ends.
Dave seeks a "balanced, symetrical" rotor as solution to handling issues that have been solved years ago without doing mechanical backflips - by installing a fly-by-wire control system. Chasing the ease of handling by adding whole rotors and mythical super-rigid rotors is a way to convert money into piles of scrap experimental helicopters. There is no designer on earth who would seek better handling by adding rotors and blades, not when good, cheap and powerful computers are available to solve that problem.
Following this logic, our cars should never have had anti-lock brakes (a fly-by-wire system) nor should we have had electronic fuel injection (another fly-by-wire system) we should have had mechanical systems with a boot full of critical parts instead.
Last edited by NickLappos; 2nd May 2005 at 06:18.
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"Dave seeks a "balanced, symetrical" rotor as solution to handling issues that have been solved years ago without doing mechanical backflips - by installing a fly-by-wire control system."
Just my two cents worth - feel free to refute (i certainly value the opinion of the ABC T.P. very highly). I see the advantage of intermeshing as primarily being aerodynamic, by avoiding the retreating blade tip stall and reverse flow area. If blade divergence at u>0.5 can be avoided it would be possible to build a helicopter capable of hover, then safe transition into flight up to the limits of either compresibility or at least engine power. The synchropter, if well designed, just has the advantage of reduced drag/power in all flight conditions.
Agreed that fly-by-wire, or even a mechanical gyroscopic derivative cures all the handling quirks on a conventional. Other handling advantages come out of the symmetry, but are not driven by it. As i have freely admitted to Dave, my own interest really comes out my wish to understand the limits of helicopter technology, plus how easily implementable the techniques are in practice. (I tried for a job at Westlands, just as they were about to lay people off
- bad times in the UK)
Mart
Just my two cents worth - feel free to refute (i certainly value the opinion of the ABC T.P. very highly). I see the advantage of intermeshing as primarily being aerodynamic, by avoiding the retreating blade tip stall and reverse flow area. If blade divergence at u>0.5 can be avoided it would be possible to build a helicopter capable of hover, then safe transition into flight up to the limits of either compresibility or at least engine power. The synchropter, if well designed, just has the advantage of reduced drag/power in all flight conditions.
Agreed that fly-by-wire, or even a mechanical gyroscopic derivative cures all the handling quirks on a conventional. Other handling advantages come out of the symmetry, but are not driven by it. As i have freely admitted to Dave, my own interest really comes out my wish to understand the limits of helicopter technology, plus how easily implementable the techniques are in practice. (I tried for a job at Westlands, just as they were about to lay people off
- bad times in the UK)Mart
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Nick,
Thanks for the response and the pleasure of a lively discussion.
You appear to be implying that current helicopters are aerodynamically OK. However, it is common knowledge that governments and commercial interests want higher speeds from VTOL craft.
The computer alone is not going to provide these higher speeds. The increase in speed is an aerodynamic problem.
I think that you will agree that tiltrotors and Boeing's Canard Rotor Wing (with its Absolutely Rigid Rotor
) are not satisfactory solutions; even though both are latterly symmetrical , in forward flight.
What configuration do you think is the most promising for the future?
Dave
Thanks for the response and the pleasure of a lively discussion.
You appear to be implying that current helicopters are aerodynamically OK. However, it is common knowledge that governments and commercial interests want higher speeds from VTOL craft.
The computer alone is not going to provide these higher speeds. The increase in speed is an aerodynamic problem.
I think that you will agree that tiltrotors and Boeing's Canard Rotor Wing (with its Absolutely Rigid Rotor
) are not satisfactory solutions; even though both are latterly symmetrical , in forward flight.What configuration do you think is the most promising for the future?
Dave
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Flamout Restart...
I would also like to touch on yaw control in this thread, since i see this as the biggest single weakness in intermeshing rotorcraft. Most do it by differential yaw control, either by torque biasing or differential cyclic.
The Unicopter concept has twin rear pusher props, which will allow a very natural and responsive pilot yaw control in all flight conditions. My thoughts on this post are really for the Synchrolite concept, which has just the twin main rotors, since this may suffer reduced yaw response in conditions of slow speed reduced loading (not sure if there was a controlled rudder) - a climbing pushover for instance. Remember that i see the main advantage of the intermesher as being performance (especially if gyro stability augmented).
Apologies Dave, it must really seem that i am joining the "throwing sharp pointy things" brigade!
I am honestly just trying to get to the bottom of what i believe to be a good concept, that just needs a little grounding in engineering common sense. I am just this bad as a professional truck designer - but the product really does benefit.
Mart
The Unicopter concept has twin rear pusher props, which will allow a very natural and responsive pilot yaw control in all flight conditions. My thoughts on this post are really for the Synchrolite concept, which has just the twin main rotors, since this may suffer reduced yaw response in conditions of slow speed reduced loading (not sure if there was a controlled rudder) - a climbing pushover for instance. Remember that i see the main advantage of the intermesher as being performance (especially if gyro stability augmented).
Apologies Dave, it must really seem that i am joining the "throwing sharp pointy things" brigade!
I am honestly just trying to get to the bottom of what i believe to be a good concept, that just needs a little grounding in engineering common sense. I am just this bad as a professional truck designer - but the product really does benefit. Mart
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Mart,
Criticism and concerns are genuinely wanted. It's a lot better to discover the problems on the drafting table then later, on the assembly table.
All helicopters have pros and cons. There are numerous concerns about the intermeshing configuration . IMO, the primary one is rotor-to-rotor vibration and next one is yaw control.
The means of reducing rotor-induced vibration was covered in a previous post in this thread. Here is some additional information on this subject
Yaw control should only be a concern when considering autorotation. This concern is applicable to the intermeshing and the coaxial configurations. Here are a couple of pages on yaw control, as it related to the SynchroLite; DESIGN: SynchroLite ~ Control - Flight - Directional & DESIGN: SynchroLite ~ Rotor - Disk - Opposed (Differential) Lateral Cyclic
______________
When considering the pros and cons of different rotor configurations, you might look into the interleaving. If there is any desire for a discussion about the interleaving configuration, it should probably be done on its own thread.
Dave
Criticism and concerns are genuinely wanted. It's a lot better to discover the problems on the drafting table then later, on the assembly table.
All helicopters have pros and cons. There are numerous concerns about the intermeshing configuration . IMO, the primary one is rotor-to-rotor vibration and next one is yaw control.
The means of reducing rotor-induced vibration was covered in a previous post in this thread. Here is some additional information on this subject
Yaw control should only be a concern when considering autorotation. This concern is applicable to the intermeshing and the coaxial configurations. Here are a couple of pages on yaw control, as it related to the SynchroLite; DESIGN: SynchroLite ~ Control - Flight - Directional & DESIGN: SynchroLite ~ Rotor - Disk - Opposed (Differential) Lateral Cyclic
______________
When considering the pros and cons of different rotor configurations, you might look into the interleaving. If there is any desire for a discussion about the interleaving configuration, it should probably be done on its own thread.
Dave
Last edited by Dave_Jackson; 6th May 2005 at 17:46.
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Hmm, lots of food for thought...
"...discover the problems on the drafting table..."
My thinking exactly. BTW i seriously suggest you invest in a low cost 3D cad system. On my current project we (collectively) moved from 2D to 3D (Ideas NX). You will find it bottoms out your concepts much better, since your 2D drawings are not linked to each other. When you come to drawing, the 3D model is the template, so it is much easier to assemble.
Maybe SolidWorks would be well suited to you. Whatever stage you feel the project is at, believe me it will benefit greatly from a move to 3D. For a start it is much quicker and easier than your blue styrofoam mockups...
"... rotor-to-rotor vibration ... yaw control."
Agreed about 3 blade rotors, but 4 blade rotor Unicopter is definately complexity overkill. You would be much better getting into retreating blade feathering (or ABC) by this stage - the ultimate way to avoid downwash interference vibration.
BTW i'm confused on rotor rotation direction of Synchrolite --> Unicopter. If Unicopter is a development of Synchrolite (which is by far the best engineering approach) then i really would settle on one rotation direction - ideally outboard advancing so inboard can (eventually) be feathered. Don't get hung up on roll/yaw coupling, since you will otherwise need to develope 2 stabilty scenarios - bad idea (unecessary development), besides vert stabilisers and aumentation will help. You may even be able to hand over componentry and tooling...
"Yaw control should only be a concern when considering autorotation...."
Hmm, longitudinal differential cyclic: bad idea on helicopter where rotor clearance reduction is an objective - seriously risking an extreme manouvre clash accident. Electric motor idea interesting, but complexity again. Considering differential collective ineffectiveness/reversal in autorotation, i really don't understand why the controls would be reversed as long as rotor loading was >0g - the concern comes when in a reduced g situation, such as pushover.
Are you really against cable operated tip (or even hub) spoilers? The linkage could be arranged so that spoiler only comes in when rudder and differential collectice ineffective (ie large pedal movements required), at the risk of unecessary complexity. Maybe it's my turn to eat crow...
"...look into the interleaving."
No, i'm convinced intermeshing is the best solution (thanks for helping me see this). Too much risk of interleaver shaft failure, and besides you go back to all the retreating blade problems. Ideal rotorcraft is feathered retreating blade synchropter - let Vertol play with SBS tandems...
Mart
PS: check out www.midwestcontrol.co.uk for control linkages.
My thinking exactly. BTW i seriously suggest you invest in a low cost 3D cad system. On my current project we (collectively) moved from 2D to 3D (Ideas NX). You will find it bottoms out your concepts much better, since your 2D drawings are not linked to each other. When you come to drawing, the 3D model is the template, so it is much easier to assemble.
Maybe SolidWorks would be well suited to you. Whatever stage you feel the project is at, believe me it will benefit greatly from a move to 3D. For a start it is much quicker and easier than your blue styrofoam mockups...
"... rotor-to-rotor vibration ... yaw control."
Agreed about 3 blade rotors, but 4 blade rotor Unicopter is definately complexity overkill. You would be much better getting into retreating blade feathering (or ABC) by this stage - the ultimate way to avoid downwash interference vibration.
BTW i'm confused on rotor rotation direction of Synchrolite --> Unicopter. If Unicopter is a development of Synchrolite (which is by far the best engineering approach) then i really would settle on one rotation direction - ideally outboard advancing so inboard can (eventually) be feathered. Don't get hung up on roll/yaw coupling, since you will otherwise need to develope 2 stabilty scenarios - bad idea (unecessary development), besides vert stabilisers and aumentation will help. You may even be able to hand over componentry and tooling...
"Yaw control should only be a concern when considering autorotation...."
Hmm, longitudinal differential cyclic: bad idea on helicopter where rotor clearance reduction is an objective - seriously risking an extreme manouvre clash accident. Electric motor idea interesting, but complexity again. Considering differential collective ineffectiveness/reversal in autorotation, i really don't understand why the controls would be reversed as long as rotor loading was >0g - the concern comes when in a reduced g situation, such as pushover.
Are you really against cable operated tip (or even hub) spoilers? The linkage could be arranged so that spoiler only comes in when rudder and differential collectice ineffective (ie large pedal movements required), at the risk of unecessary complexity. Maybe it's my turn to eat crow...
"...look into the interleaving."
No, i'm convinced intermeshing is the best solution (thanks for helping me see this). Too much risk of interleaver shaft failure, and besides you go back to all the retreating blade problems. Ideal rotorcraft is feathered retreating blade synchropter - let Vertol play with SBS tandems...
Mart
PS: check out www.midwestcontrol.co.uk for control linkages.
Last edited by Graviman; 7th May 2005 at 16:26.
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Chiplight
You mention "near zero". Can you shed anymore light on this? I did the Beaty two counter-rotating bicycle wheel thing and the gyroscopic precession was gone. However, there did seem to be a little more resistance to movement when the wheels were rotating, as compared to when they were non-rotating. Maybe it was just wishfull thinking. I'll try to get the wheels to rotate faster and see if that changes anything (besides busting the axle 
)
"If you mount two gyroscopes with their axles at right angles to one another on a platform, and place the platform inside a set of gimbals, the platform will remain completely rigid as the gimbals rotate in any way they please. This is this basis of inertial navigation systems (INS)."
This statement, from the Internet, may mean that the two counterrotating rotors would slightly contribute to the stability of a rigid intermeshing configuration. This is because the masts on the intermeshing UniCopter are at 18º to each other. Do you have any thoughts?
Graviman,
The rotors on the SynchroLite turn inside forward (breaststroke). This appears to be typical of all previous intermeshing rotorcraft. Either Flettner or Kaman tried the opposite direction and then went back to breaststroke.
The rotors on the Unicopter turn outside forward. this was done to take advantage of the 'wanted' lateral dissymitry of lift. Stepniewski's concept is also outside forward.
There is an earlier thread that discusses this. Basically, in powered flight the rotors are driving the air where as in autorotation the air is driving the rotors.
Dave
"Counter rotating disks(such as coaxial props on a single shaft) nullify gyroscopic precession effects. You might expect twice the resistance to movement out of plane, but in fact it is near zero."
)"If you mount two gyroscopes with their axles at right angles to one another on a platform, and place the platform inside a set of gimbals, the platform will remain completely rigid as the gimbals rotate in any way they please. This is this basis of inertial navigation systems (INS)."
This statement, from the Internet, may mean that the two counterrotating rotors would slightly contribute to the stability of a rigid intermeshing configuration. This is because the masts on the intermeshing UniCopter are at 18º to each other. Do you have any thoughts?
Graviman,
"BTW i'm confused on rotor rotation direction of Synchrolite --> Unicopter. If Unicopter is a development of Synchrolite (which is by far the best engineering approach) then i really would settle on one rotation direction - ideally outboard advancing so inboard can (eventually) be feathered."
The rotors on the Unicopter turn outside forward. this was done to take advantage of the 'wanted' lateral dissymitry of lift. Stepniewski's concept is also outside forward.
"Considering differential collective ineffectiveness/reversal in autorotation, i really don't understand why the controls would be reversed as long as rotor loading was >0g"
Dave
Last edited by Dave_Jackson; 9th May 2005 at 07:02.
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"...counter-rotating bicycle ... gyroscopic precession was gone... little more resistance ... when the wheels were rotating..."
Hmm, well the physics is pretty well established. I imagine that the wheels were not counter-rotating at the same speed...
"... masts on the intermeshing UniCopter are at 18º to each other."
The vertical axis components will cancel, but yes there will be some residual horizontal component. This would give some roll/yaw stability, and accounts for the Flettner direction of rotation - breaststroke is thus equivalent to single gyro going top forwards, bottom backwards. In sideslip the vertical tailplane would input yaw torque, to cause gyro precession roll as if dihedral. Same sideslip causes downwind rotor to produce more lift, so precession causes yaw towards sideslip (like a tailplane). Don't forget sideslip "dihedral" is being countered, to some extent, by incorrect lift balance of rotors. There is also the yaw effect caused by torque imbalance of downwind rotor seeing more lift, breaststroke rotation causing yaw into wind.
However, non of this will really reduce pilot workload in hover, however , unless you have accounts of F282 hovering hands-off - this has to be one aim of your project...
"...Unicopter turn outside forward ... 'wanted' lateral dissymitry of lift."
I do see this, but my concern is that you will not be using synchrolite to learn how to stabilise an intermeshing heli with rotors turning the "wrong way" (ie outside forwards). To my mind the whole point of intermeshing is to improve aerodynamic efficiency, otherwise just fit the lockheed gyro system to an R22 - far simpler. Basically i believe that a large tailplane, above heli centroid, would overcome the adverse stability of the effective gyro going top rearwards - and the resulting T-tail is perfect for high speed flight without downwash affecting trim. Alternately fit a gyro running top forwards (engine flywheel?) to counter rotor precession . Either way, you have to admit, Synchrolite is the perfect test bed...
"... in powered flight the rotors are driving the air where as in autorotation the air is driving the rotors. "
Not completely with you, since in either case increasing blade pitch will result in opposition torque!?! I can see that there would be loss of this torque strength with autorotation, becoming noticeable below powered descent (approx zero pitch). The real danger comes from reduced g manouvreing, where there will be pedal ineffectiveness. I'm willing to eat crow, but have thought this through
. Maybe this is not worth dwelling on, since the Unicopter twin pusher arrangement solves the problem...
BTW do you still prefer unducted over ducted pusher props? Bearing in mind various pros/cons.
Mart
Hmm, well the physics is pretty well established. I imagine that the wheels were not counter-rotating at the same speed...
"... masts on the intermeshing UniCopter are at 18º to each other."
The vertical axis components will cancel, but yes there will be some residual horizontal component. This would give some roll/yaw stability, and accounts for the Flettner direction of rotation - breaststroke is thus equivalent to single gyro going top forwards, bottom backwards. In sideslip the vertical tailplane would input yaw torque, to cause gyro precession roll as if dihedral. Same sideslip causes downwind rotor to produce more lift, so precession causes yaw towards sideslip (like a tailplane). Don't forget sideslip "dihedral" is being countered, to some extent, by incorrect lift balance of rotors. There is also the yaw effect caused by torque imbalance of downwind rotor seeing more lift, breaststroke rotation causing yaw into wind.
However, non of this will really reduce pilot workload in hover, however , unless you have accounts of F282 hovering hands-off - this has to be one aim of your project...
"...Unicopter turn outside forward ... 'wanted' lateral dissymitry of lift."
I do see this, but my concern is that you will not be using synchrolite to learn how to stabilise an intermeshing heli with rotors turning the "wrong way" (ie outside forwards). To my mind the whole point of intermeshing is to improve aerodynamic efficiency, otherwise just fit the lockheed gyro system to an R22 - far simpler. Basically i believe that a large tailplane, above heli centroid, would overcome the adverse stability of the effective gyro going top rearwards - and the resulting T-tail is perfect for high speed flight without downwash affecting trim. Alternately fit a gyro running top forwards (engine flywheel?) to counter rotor precession
. Either way, you have to admit, Synchrolite is the perfect test bed..."... in powered flight the rotors are driving the air where as in autorotation the air is driving the rotors. "
Not completely with you, since in either case increasing blade pitch will result in opposition torque!?! I can see that there would be loss of this torque strength with autorotation, becoming noticeable below powered descent (approx zero pitch). The real danger comes from reduced g manouvreing, where there will be pedal ineffectiveness. I'm willing to eat crow, but have thought this through
. Maybe this is not worth dwelling on, since the Unicopter twin pusher arrangement solves the problem...BTW do you still prefer unducted over ducted pusher props? Bearing in mind various pros/cons.
Mart
Last edited by Graviman; 10th May 2005 at 11:42.
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OK This ain't fun any more.
Who's the mole?
I was playing with the following two-rotor, 90-degree gyro device outside my place today.
A guy on a bike stops and gives me his business card. It says that he is drywall contractor and his name is George Zachystal. He starts to talk about his gyro inventions. He then says that he had to get out of it. The people around him were being killed by government personnel, because he was onto gyro propulsion. On the back of the card he says go to Yahoo.com and type in ZACHYSTAL and the US patent number 4884465. The conversation was a little difficult because of his heavy accent, so we finished talking and he biked off.
He was obviously a fruit-cake but for the heck of it I punched his name and patent number into Yahoo. Holy ****! There is a patent in his name.
Now I'm really scared. This is more than a coincidence.
I was playing with the following two-rotor, 90-degree gyro device outside my place today.
A guy on a bike stops and gives me his business card. It says that he is drywall contractor and his name is George Zachystal. He starts to talk about his gyro inventions. He then says that he had to get out of it. The people around him were being killed by government personnel, because he was onto gyro propulsion. On the back of the card he says go to Yahoo.com and type in ZACHYSTAL and the US patent number 4884465. The conversation was a little difficult because of his heavy accent, so we finished talking and he biked off.
He was obviously a fruit-cake but for the heck of it I punched his name and patent number into Yahoo. Holy ****! There is a patent in his name.
Now I'm really scared. This is more than a coincidence.
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Dubious...
He probably did have a mad gyro-levitation idea (lots of loons have), and saw you playing with gyros and helis. If anything it just proves how pathetic the Patent service now is, in that it will grant almost anything without investigating the claims or even requiring proof! I take it he had seen area 51...
Mart
Mart
