Helicopter Dynamics: Gyroscopic Precession
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I'm starting to comment more on helicopter stuff and less on physics stuff. I feel I understand the helicopter stuff, but I'll still try restrict my comments to areas where I have the appropriate background.
Lu said, "If gyroscopic precession plays no part in the tilting of the disc either as a single entity or as individual blades then please explain this."
I guess it gets down to semantics. As best as I can tell, the definition of gyroscopic precession is limited to rotating bodies whose geometry allows the 90 degree apparent lag. Rotor systems whose axis of rotation does not pass through the flapping hinges are one example of a geometry that won't allow a 90 degree lag. Answering your question, since the definition of gyroscopic precession doesn't really apply, it is fair to say it plays no part.
For a teetering rotor, it seems that gyroscopic precession is a valid description.
Since the "blade flying to position" derivation can be used for a general derivation of gyroscopic precession, I think that in special cases the two theories are the same. One (fly to pos.) requiring more basics, the other (GP) accepting more terminology.
Lu also said, "In the light of the above I ask why the 90-degrees if gyroscopic precession is not involved. Why couldn’t they just put the control inputs anywhere and just let the blades seek their own position."
Read through my previous long post where I talk about the pendulum. The natural frequency of the blade acting as a pendulum is exactly one per revolution when the axis of rotation passes through the flapping hinge. It is less than 90 degrees when the flapping hinge is offset.
helmetfire, I believe that flapping to equality applies only with translational movement of the helicopter. In a zero wind hover, there is no flapping to equality.
Matthew.
[ 10 August 2001: Message edited by: heedm ]
Lu said, "If gyroscopic precession plays no part in the tilting of the disc either as a single entity or as individual blades then please explain this."
I guess it gets down to semantics. As best as I can tell, the definition of gyroscopic precession is limited to rotating bodies whose geometry allows the 90 degree apparent lag. Rotor systems whose axis of rotation does not pass through the flapping hinges are one example of a geometry that won't allow a 90 degree lag. Answering your question, since the definition of gyroscopic precession doesn't really apply, it is fair to say it plays no part.
For a teetering rotor, it seems that gyroscopic precession is a valid description.
Since the "blade flying to position" derivation can be used for a general derivation of gyroscopic precession, I think that in special cases the two theories are the same. One (fly to pos.) requiring more basics, the other (GP) accepting more terminology.
Lu also said, "In the light of the above I ask why the 90-degrees if gyroscopic precession is not involved. Why couldn’t they just put the control inputs anywhere and just let the blades seek their own position."
Read through my previous long post where I talk about the pendulum. The natural frequency of the blade acting as a pendulum is exactly one per revolution when the axis of rotation passes through the flapping hinge. It is less than 90 degrees when the flapping hinge is offset.
helmetfire, I believe that flapping to equality applies only with translational movement of the helicopter. In a zero wind hover, there is no flapping to equality.
Matthew.
[ 10 August 2001: Message edited by: heedm ]
I don't want to pretend to be any kind of expert on this subject, however the aerodynamic principles that are talked about with reference to phase lag and flapping to equality do seem fair enough to me.
Here's a shot at trying to describe what happens, for an anticlockwise when viewed from above rotor:
For a helicopter in the hover in nil wind, the pitch setting on the blades could be said to be the same, and lift equal, all the way round.
Let's say you want to tilt the disc forward to, funnily enough, fly forward.
You move the cyclic forwards. The pitch change system acts to make the pitch of the blades vary around the disc, with the maximum setting occurring on your left, and the minimum on your right. That means that from the rear of the disc, the blades experience less lift than they had in the hover and therefore start to fly down. The minimum pitch setting occurs on your right, so that's where the blades are flying down fastest - but they haven't finished heading downwards.
That doesn't happen until they get to the front of the disc, where they will again be at the original 'equilibrium' pitch setting.
From there, on the left side, they will start to fly up again, so you finish up with the disc tilted forwards like you wanted.
When the aircraft just starts to fly forwards, the left and right sides are producing the same amount of lift, so you are 'wings level'.
As you pick up speed, the advancing side gets more airspeed and the retreating side less, so the aircraft should roll, you'd think.
However, because we have flapping hinges and/or flexible blades, the advancing blade flaps upwards (decreasing it's angle of attack) and the retreating blade downwards (increasing it's angle of attack) until they are back at the original equilibrium between lift and centripetal force (or whatever the force is called that wants to throw them outwards!).
They have therefore 'flapped to equality' of lift, and the machine doesn't roll.
However, to achieve this, as we said, the advancing blade flaps up and the retreating blade down, with the maximum and minimum pitch angles respectively occurring at the left and right sides of the helicopter.
Lift is equal laterally, but the blade is flapping, with the maximum rate of flap at the sides.
As described above, however, the maximum extent of travel isn't reached until 90 degrees later; i.e. the blade would be flapping down fastest on our left, reaching its lowest point at the back, relatively speaking (bearing in mind it's already been pushed forward in the first place).
This is the phenomenon of flapback, meaning we now have to push more forward cyclic than we would have otherwise to keep going forward.
No gyroscopics required! That's not to say no gyroscopic forces are present, but I think aerodynamics explains things easily and adequately.
That's quite enough of a post for now, my brain hurts.
Here's a shot at trying to describe what happens, for an anticlockwise when viewed from above rotor:
For a helicopter in the hover in nil wind, the pitch setting on the blades could be said to be the same, and lift equal, all the way round.
Let's say you want to tilt the disc forward to, funnily enough, fly forward.
You move the cyclic forwards. The pitch change system acts to make the pitch of the blades vary around the disc, with the maximum setting occurring on your left, and the minimum on your right. That means that from the rear of the disc, the blades experience less lift than they had in the hover and therefore start to fly down. The minimum pitch setting occurs on your right, so that's where the blades are flying down fastest - but they haven't finished heading downwards.
That doesn't happen until they get to the front of the disc, where they will again be at the original 'equilibrium' pitch setting.
From there, on the left side, they will start to fly up again, so you finish up with the disc tilted forwards like you wanted.
When the aircraft just starts to fly forwards, the left and right sides are producing the same amount of lift, so you are 'wings level'.
As you pick up speed, the advancing side gets more airspeed and the retreating side less, so the aircraft should roll, you'd think.
However, because we have flapping hinges and/or flexible blades, the advancing blade flaps upwards (decreasing it's angle of attack) and the retreating blade downwards (increasing it's angle of attack) until they are back at the original equilibrium between lift and centripetal force (or whatever the force is called that wants to throw them outwards!).
They have therefore 'flapped to equality' of lift, and the machine doesn't roll.
However, to achieve this, as we said, the advancing blade flaps up and the retreating blade down, with the maximum and minimum pitch angles respectively occurring at the left and right sides of the helicopter.
Lift is equal laterally, but the blade is flapping, with the maximum rate of flap at the sides.
As described above, however, the maximum extent of travel isn't reached until 90 degrees later; i.e. the blade would be flapping down fastest on our left, reaching its lowest point at the back, relatively speaking (bearing in mind it's already been pushed forward in the first place).
This is the phenomenon of flapback, meaning we now have to push more forward cyclic than we would have otherwise to keep going forward.
No gyroscopics required! That's not to say no gyroscopic forces are present, but I think aerodynamics explains things easily and adequately.
That's quite enough of a post for now, my brain hurts.
Iconoclast
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I am constantly being chastised because many of you say I am wrong because I don’t agree with you as individuals or as a group. I keep telling you that I do agree with you because I accept what you are saying as an alternate theory that obviously works for you. I use terms that you do not accept and you use terms that I am not familiar with. Granted it has been a long time since I attended a factory or military school for helicopters and maybe the teaching methods have changed but I never heard of flapping to equality until I started posting on these threads. Try to understand that POF is taught differently in the US as opposed to the POF theory that is taught in the UK, OZ and NZ. Now if RW-1 can keep his nose out of this post I will make the following suggestion. All of the theories I have expounded on relative to gyroscopic precession are contained in the Sikorsky Blue Book and I think you should contact the Factory School at Sikorsky and request a copy of the Blue Book. That is the source of my statements so if you disagree with me then do as I mentioned to Nick Lappos and tell them they are wrong and tell them why they are wrong.
Avoid imitations
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To All,
It is obvious that the discussion is going nowhere, just as I originally feared it would.
My understanding remains as it always was. I have worked with many pilots of other nationalities, American pilots included and NONE of them has ever been at odds with my understanding.
Rotor blades are controlled by adjusting the aerodynamic forces affecting them. They are FLOWN around the disc by pilot inputs on the cyclic. The result of them being flown around is that forces are fed back to the swashplates which result in the hull of the aircraft experiencing those forces. The way in which the feedback forces act to alter the aircraft's flightpath depends on a number of factors.
Gyroscopic forces do of course exist by definition but they are NOT modified directly in order to control the helicopter (as Lu seems to prefer). An aircraft with lighter blades generally has a more responsive rotor, one with heavier blades less so because of the gyroscopic forces appertaining to each. Gyroscopic precession in the case of helicopter rotors is a result of aerodynamic effects, not the cause of them.
That is why we refer to cyclic PITCH, not cyclic GYROSCOPIC PRECESSION.
Lu's understanding of helicopter rotor dynamics is not the same as mine because he appears to put a different emphasis on the factors involved. I think his understanding is incomplete but I can't see him ever being prepared to accept this.
There is only one set of laws of physics and it doesn't actually matter what colour the cover of the book is.
I will now leave it to those of you willing to slug it out, I'm afraid.
ShyT
It is obvious that the discussion is going nowhere, just as I originally feared it would.
My understanding remains as it always was. I have worked with many pilots of other nationalities, American pilots included and NONE of them has ever been at odds with my understanding.
Rotor blades are controlled by adjusting the aerodynamic forces affecting them. They are FLOWN around the disc by pilot inputs on the cyclic. The result of them being flown around is that forces are fed back to the swashplates which result in the hull of the aircraft experiencing those forces. The way in which the feedback forces act to alter the aircraft's flightpath depends on a number of factors.
Gyroscopic forces do of course exist by definition but they are NOT modified directly in order to control the helicopter (as Lu seems to prefer). An aircraft with lighter blades generally has a more responsive rotor, one with heavier blades less so because of the gyroscopic forces appertaining to each. Gyroscopic precession in the case of helicopter rotors is a result of aerodynamic effects, not the cause of them.
That is why we refer to cyclic PITCH, not cyclic GYROSCOPIC PRECESSION.
Lu's understanding of helicopter rotor dynamics is not the same as mine because he appears to put a different emphasis on the factors involved. I think his understanding is incomplete but I can't see him ever being prepared to accept this.
There is only one set of laws of physics and it doesn't actually matter what colour the cover of the book is.
I will now leave it to those of you willing to slug it out, I'm afraid.
ShyT
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Lu SHOULD READ ShyTorque's last post, which is true in all aspects. And make the small attempt to understand what was said.
That was another windbag windup paragraph that goes in circles ....
What those have stated to you are not ALTERNATE THEORIES to anything. They are FACTS.
FACTS that trash and disprove LZ's FLAWED THEORIES.
Because LZ has no capability to accept that he is wrong. It isn't because of an alternate thery, what rubbish.
Study the two short paragraphs above well, and quit making yet another excuse; the one now where you retreat to another manual that you believe is wrong or has some other non-LZ understood theory or fact.
Again someone said it correctly:
LZ's mantra: "Anytime I appeared to be wrong it was because someone told me to say the wrong thing, or the manual is saying something else, and anytime I am right, it is because I have been around since Christ flew crew changes on the Arc."
The books are ALL FINE, it is your INTERPRETATION that is flawed, and thus leads to flawed output.
And since you wanted to talk about my website, lets remember a key sentance on the page you want to quote so often:
"precession is not a dominant force in rotary-wing aerodynamics"
It ISN'T, and you must STOP treating it as the RULE governing all.
All these threads have gone as predicted by me at the beginning, LZ has no change of ever learning anything here, it is always a rehash of another misinterpretation on his part, restated or reformulated to yet have another useless discussion on the topic.
Just place this by your name and everyone can take a rest:
I am "the" Lu Zuckerman.
I am not a pilot.
I am not an engineer.
I am not involved, nor have experience with
rotor head design/aerodynamics to be making any type of assertions to those who do on this forum.
I am simply a wannabe guru.
I am never wrong.
My heli post's are for entertainment purposes only, and should not be used or considered in actual flight operations/planning.
I keep telling you that I do agree with you because I accept what you are saying as an alternate theory that obviously works for you.
What those have stated to you are not ALTERNATE THEORIES to anything. They are FACTS.
FACTS that trash and disprove LZ's FLAWED THEORIES.
Because LZ has no capability to accept that he is wrong. It isn't because of an alternate thery, what rubbish.
Study the two short paragraphs above well, and quit making yet another excuse; the one now where you retreat to another manual that you believe is wrong or has some other non-LZ understood theory or fact.
Again someone said it correctly:
LZ's mantra: "Anytime I appeared to be wrong it was because someone told me to say the wrong thing, or the manual is saying something else, and anytime I am right, it is because I have been around since Christ flew crew changes on the Arc."
The books are ALL FINE, it is your INTERPRETATION that is flawed, and thus leads to flawed output.
And since you wanted to talk about my website, lets remember a key sentance on the page you want to quote so often:
"precession is not a dominant force in rotary-wing aerodynamics"
It ISN'T, and you must STOP treating it as the RULE governing all.
All these threads have gone as predicted by me at the beginning, LZ has no change of ever learning anything here, it is always a rehash of another misinterpretation on his part, restated or reformulated to yet have another useless discussion on the topic.
Just place this by your name and everyone can take a rest:
I am "the" Lu Zuckerman.
I am not a pilot.
I am not an engineer.
I am not involved, nor have experience with
rotor head design/aerodynamics to be making any type of assertions to those who do on this forum.
I am simply a wannabe guru.
I am never wrong.
My heli post's are for entertainment purposes only, and should not be used or considered in actual flight operations/planning.
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This has nothing to do with the person. But I'll allow that in this case his personality is as flawed as the theory.
It has to do with fundamentals listed above.
If it were you then the names would change, but the reality would remain the same.
It is not about education, not about learning, he will rant and rave giving any possible excuse until someone agrees with the flawed theory put forth, which isn't going to happen for it just doesn't happen, and no amount of preaching will make the facts, nor the physics change to suit that flawed theory.
I don't like bull****, and unfortunately with each new excuse he places to avoid the issue at hand, he reeks of it. Plain and simple.
[ 10 August 2001: Message edited by: RW-1 ]
It has to do with fundamentals listed above.
If it were you then the names would change, but the reality would remain the same.
It is not about education, not about learning, he will rant and rave giving any possible excuse until someone agrees with the flawed theory put forth, which isn't going to happen for it just doesn't happen, and no amount of preaching will make the facts, nor the physics change to suit that flawed theory.
I don't like bull****, and unfortunately with each new excuse he places to avoid the issue at hand, he reeks of it. Plain and simple.
[ 10 August 2001: Message edited by: RW-1 ]
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heedm
Please forgive me for all the things I thought about you.
Looks like you're right.
The amount of rotor tip that will result from the creation of a moment on a teetering rotor disk was done. These calculations were done for aerodynamic 'precession' and for gyroscopic precession. The results are essentially the same. A moment of 50 pounds at 75% of rotor radius gave 0.47" and 0.44" of tipping at the 75% radius, 90 degrees later.
For those that doubt, are really bored, or want to find fault, the attached page is offered; http://www.synchrolite.com/0940.html#Comparison
Lu; please note that the above is for a simple teetering rotor and its 90-degree phase angle. Any delta3 or flapping hinge offset will reduce the phase lag to below 90-degrees.
[ 11 August 2001: Message edited by: Dave Jackson ]
Please forgive me for all the things I thought about you.
Looks like you're right.
The amount of rotor tip that will result from the creation of a moment on a teetering rotor disk was done. These calculations were done for aerodynamic 'precession' and for gyroscopic precession. The results are essentially the same. A moment of 50 pounds at 75% of rotor radius gave 0.47" and 0.44" of tipping at the 75% radius, 90 degrees later.
For those that doubt, are really bored, or want to find fault, the attached page is offered; http://www.synchrolite.com/0940.html#Comparison
Lu; please note that the above is for a simple teetering rotor and its 90-degree phase angle. Any delta3 or flapping hinge offset will reduce the phase lag to below 90-degrees.
[ 11 August 2001: Message edited by: Dave Jackson ]
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What exactly did you think about me, Dave?
Interesting information on the unicopter site. I had a similiar discussion to this one with Doug Marker a year or two ago. Back then I knew even less about rotors than I do now. It's talking like this that brings the point home.
I wouldn't say it proves I'm right, but it does support what I've said. It may be fluke that that one set of data worked out so closely.
You going to Abbotsford this weekend?
Matthew.
Interesting information on the unicopter site. I had a similiar discussion to this one with Doug Marker a year or two ago. Back then I knew even less about rotors than I do now. It's talking like this that brings the point home.
I wouldn't say it proves I'm right, but it does support what I've said. It may be fluke that that one set of data worked out so closely.
You going to Abbotsford this weekend?
Matthew.
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I'm sure that someone will sort this out for me. More years ago than I care to remember I displayed the British Army Lynx for a year. From memory whenever I pitched from a steep climb, (aiming at 90 nose up, but probably more like 80 on a good day) to 90 nose down, the aircraft had a tendency to roll(right I think but I can't be sure). I always thought that this was some from of gyroscopic reaction, thoughts ?
Iconoclast
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To: Dave Jackson
“Lu; please note that the above is for a simple teetering rotor and its 90-degree phase angle. Any delta3 or flapping hinge offset will reduce the phase lag to below 90-degrees”.
This may be true relative to the calculation being applied to a simple teetering rotorhead. Although there is no offset hinge on the teetering rotorhead there is a delta 3 pitch coupling that occurs when the blade teeters. This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor. Again referring to your statement about an offset hinge reducing the phase angle to a level below 90-degrees. This to may be true but in the design of almost all rotor systems the designers assume a 90-degree phase angle and they design the control system to accommodate that 90-degree phase angle. If the rotor system does no respond to direct control input and flies as if the phase angle is 88 or 92 –degrees the pilot will simply adjust his cyclic input to result in forward flight as opposed to flying slightly to the left or right.
The certification of rotorcraft stipulates that it is acceptable to have a few degrees of coupling but the direction of flight must be in the same sense of control input.
“Lu; please note that the above is for a simple teetering rotor and its 90-degree phase angle. Any delta3 or flapping hinge offset will reduce the phase lag to below 90-degrees”.
This may be true relative to the calculation being applied to a simple teetering rotorhead. Although there is no offset hinge on the teetering rotorhead there is a delta 3 pitch coupling that occurs when the blade teeters. This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor. Again referring to your statement about an offset hinge reducing the phase angle to a level below 90-degrees. This to may be true but in the design of almost all rotor systems the designers assume a 90-degree phase angle and they design the control system to accommodate that 90-degree phase angle. If the rotor system does no respond to direct control input and flies as if the phase angle is 88 or 92 –degrees the pilot will simply adjust his cyclic input to result in forward flight as opposed to flying slightly to the left or right.
The certification of rotorcraft stipulates that it is acceptable to have a few degrees of coupling but the direction of flight must be in the same sense of control input.
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heedm
What exactly did you think about me, Dave?
Only good things. You postings portray a person who can give and take a joke.
Interesting information on the unicopter site.
Thanks. The UniCopter concept may not work. But, until some person or calculation shows that won't, it is being pursued.
You going to Abbotsford this weekend?
No. Too busy thinking up postings, and also, Nick didn't say that the Comanche was going to be there. Are you going?
______________________
Lu;
I agree with what you say and have reiterated it in different words
The basic Bell rotorheads have a 90-degree teetering, without delta3.
The Robinson and the Kaman rotorheads have teetering with delta3, but their types of delta3 differ from each other.
In tail rotors, the delta3 is 45-degrees, therefore every degree of teeter is 'removed' by an identical number of degrees of opposing pitch.
The only area of disagreement is the small point below and it is probably only the terminology;
This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor.
This [teetering] coupling (ie. delta3) removes pitch from the blade that is teetering up and adds pitch to the blade that is teetering down.
________________
We are talking about a number of different 'devices' such as delta3 (wonder what happened to delta1 and delta2), flapping hinge offset, phase angle and gyroscopic precession. Each one has its own sub-divisions and complexities, even before addressing the complexities of tying them together.
To separate the subjects; I would like to start a separate new thread [Helicopter Dynamics: Phase Angle].
Maybe we can jointly learn some more about this subject as well.
[ 11 August 2001: Message edited by: Dave Jackson ]
What exactly did you think about me, Dave?
Only good things. You postings portray a person who can give and take a joke.
Interesting information on the unicopter site.
Thanks. The UniCopter concept may not work. But, until some person or calculation shows that won't, it is being pursued.
You going to Abbotsford this weekend?
No. Too busy thinking up postings, and also, Nick didn't say that the Comanche was going to be there. Are you going?
______________________
Lu;
I agree with what you say and have reiterated it in different words
The basic Bell rotorheads have a 90-degree teetering, without delta3.
The Robinson and the Kaman rotorheads have teetering with delta3, but their types of delta3 differ from each other.
In tail rotors, the delta3 is 45-degrees, therefore every degree of teeter is 'removed' by an identical number of degrees of opposing pitch.
The only area of disagreement is the small point below and it is probably only the terminology;
This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor.
This [teetering] coupling (ie. delta3) removes pitch from the blade that is teetering up and adds pitch to the blade that is teetering down.
________________
We are talking about a number of different 'devices' such as delta3 (wonder what happened to delta1 and delta2), flapping hinge offset, phase angle and gyroscopic precession. Each one has its own sub-divisions and complexities, even before addressing the complexities of tying them together.
To separate the subjects; I would like to start a separate new thread [Helicopter Dynamics: Phase Angle].
Maybe we can jointly learn some more about this subject as well.
[ 11 August 2001: Message edited by: Dave Jackson ]
Iconoclast
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To: Dave Jackson
“This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor”.
This [teetering] coupling (i.e. delta3) removes pitch from the blade that is teetering up and adds pitch to the blade that is teetering down.
We are both saying the same thing. The blade moving forward has pitch added to it by the pitch coupling and the blade going back has pitch subtracted from it.
My comparison to the tail rotor was incorrect, as it is the opposite of the main rotor. The advancing blade because of the oncoming air loads, will flap out, and in the process will have pitch taken out of it. The retreating blade, which is moving with the relative wind and is mechanically connected to the other blade, will flap in and the delta hinge will add pitch to it, which equalizes the lift across the tail rotor disc.
“This coupling tends to restore the pitch in the blade moving forward and takes pitch out of the blade moving backwards very much like a tail rotor”.
This [teetering] coupling (i.e. delta3) removes pitch from the blade that is teetering up and adds pitch to the blade that is teetering down.
We are both saying the same thing. The blade moving forward has pitch added to it by the pitch coupling and the blade going back has pitch subtracted from it.
My comparison to the tail rotor was incorrect, as it is the opposite of the main rotor. The advancing blade because of the oncoming air loads, will flap out, and in the process will have pitch taken out of it. The retreating blade, which is moving with the relative wind and is mechanically connected to the other blade, will flap in and the delta hinge will add pitch to it, which equalizes the lift across the tail rotor disc.
Lu, you said:
>>We are both saying the same thing. The blade moving forward has pitch added to it by the pitch coupling and the blade going back has pitch subtracted from it.<<
I believe you are starting to understand cyclic feathering and flapping to equality. I note that Arm out the window posted an excellent description for you above, which raised no comment from you: are we beginning to help your understanding?
>>We are both saying the same thing. The blade moving forward has pitch added to it by the pitch coupling and the blade going back has pitch subtracted from it.<<
I believe you are starting to understand cyclic feathering and flapping to equality. I note that Arm out the window posted an excellent description for you above, which raised no comment from you: are we beginning to help your understanding?
Iconoclast
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To: Helmet Fire
“I believe you are starting to understand cyclic feathering and flapping to equality. I note that Arm out the window posted an excellent description for you above, which raised no comment from you: are we beginning to help your understanding?
Please understand that I did not have a light bulb go off over my head as a result of any of the above posting. I have been aware of cyclic feathering and pitch coupling ever since 1949 when I was first introduced to helicopter maintenance. What I did not know was the term flapping to equality.
As to my knowledge flapping to equality is not used as an explanation for the phenomenon in the United States and that is the root of the entire argument, which is how, POF is taught in different parts of the world.
[ 12 August 2001: Message edited by: Lu Zuckerman ]
“I believe you are starting to understand cyclic feathering and flapping to equality. I note that Arm out the window posted an excellent description for you above, which raised no comment from you: are we beginning to help your understanding?
Please understand that I did not have a light bulb go off over my head as a result of any of the above posting. I have been aware of cyclic feathering and pitch coupling ever since 1949 when I was first introduced to helicopter maintenance. What I did not know was the term flapping to equality.
As to my knowledge flapping to equality is not used as an explanation for the phenomenon in the United States and that is the root of the entire argument, which is how, POF is taught in different parts of the world.
[ 12 August 2001: Message edited by: Lu Zuckerman ]
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Heedm said; ~ I wouldn't say it proves I'm right, but it does support what I've said. It may be fluke that that one set of data worked out so closely.
It might be interesting to put the algorithms for calculation by gyroscopic precession and those for calculation by aerodynamics side by side. Then look at the sources of the data for each. This will show what inputs they have in common and what inputs are unique to each.
Another thought is to change the rotor's mass and see if it is possible to get the results from both methods to show a greater discrepancy.
Something for a very very rainy day.
Also, I just found a reference to gyroscopic precession in 'Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling', 1999, by Gareth D. Padfield.
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It's appearing that there may not be a definitive answer.
Lu ~ Your use of gyroscopic precession may well be totally acceptable.
It might be interesting to put the algorithms for calculation by gyroscopic precession and those for calculation by aerodynamics side by side. Then look at the sources of the data for each. This will show what inputs they have in common and what inputs are unique to each.
Another thought is to change the rotor's mass and see if it is possible to get the results from both methods to show a greater discrepancy.
Something for a very very rainy day.
Also, I just found a reference to gyroscopic precession in 'Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling', 1999, by Gareth D. Padfield.
_______________
It's appearing that there may not be a definitive answer.
Lu ~ Your use of gyroscopic precession may well be totally acceptable.
JTC,
Interesting point about the Lynx.
Confirm it has an anticlockwise when viewed from above rotor?
I'm just thinking out loud here, but there could be a couple of effects at play when you pitch forward -
Firstly, there should be a reduced inflow at the front of the disc and increased at the rear due to your pitching action which would tend to increase the angle of attack at the front and reduce it at the rear.
That should produce a rolling moment to the right, I think.
Secondly, if gyroscopic forces are significant, you would be providing a 'downward force on the front of the gyro' which should manifest itself as a roll to the left.
So I guess in balance, the aerodynamic force appears to be the winner (!)
Anyone else got ideas about it? There are probably a bunch of other things influencing the motion, even assuming that you kept all the controls relatively still once the pitching was initiated.
Interesting point about the Lynx.
Confirm it has an anticlockwise when viewed from above rotor?
I'm just thinking out loud here, but there could be a couple of effects at play when you pitch forward -
Firstly, there should be a reduced inflow at the front of the disc and increased at the rear due to your pitching action which would tend to increase the angle of attack at the front and reduce it at the rear.
That should produce a rolling moment to the right, I think.
Secondly, if gyroscopic forces are significant, you would be providing a 'downward force on the front of the gyro' which should manifest itself as a roll to the left.
So I guess in balance, the aerodynamic force appears to be the winner (!)
Anyone else got ideas about it? There are probably a bunch of other things influencing the motion, even assuming that you kept all the controls relatively still once the pitching was initiated.
I remember a thread some time ago, can't remember if it was here or on Mil Pilots, about this particular Lynx flying quality.
If the search is working, might be worth a gander.
P.S. - if it was a "gyroscopic" type reaction, in a push-over, would the expected result not be a roll to the left ?
[ 13 August 2001: Message edited by: The Nr Fairy ]
If the search is working, might be worth a gander.
P.S. - if it was a "gyroscopic" type reaction, in a push-over, would the expected result not be a roll to the left ?
[ 13 August 2001: Message edited by: The Nr Fairy ]
