Flight Dynamics: The Swashplate and Phase-angle
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes
on
0 Posts
Chiplight,
".... delta-3 must help reduce flapping over what it would be for a rotor system without such geometry
...."
You are correct. Negative delta3 does reduce flapping (teetering). The interesting part is how it does it.
An example:
If the pilot puts 10-degrees into the swashplate [control plane] this will start the blade climbing toward a 10-degrees flap angle at 90-degrees azimuth later [tip path plane]. At the start of this action, there is no difference between a conventional teetering rotor and a teetering rotor with delta3.
As the blade on the delta3 rotor teeters up, an ever increasing portion of the positive pitch will being pulled out of the blade by the delta3 [no feathering plane]. In other words; in a conventional teetering rotor, the [control plane] tells the [tip path plane] where to go and the [tip path plane] arrives their 90-degrees later. In a delta3 teetering rotor, the [control plane] tells the [tip path plane] where to go, BUT, the [no feathering plane] steps between the two and say '"blade, you're only going as far as I tell you to where go ".
To add a little more to the explanation; the phase angle on a teetering rotor with delta3 is less than 90-degrees because the blade does not flap to the commanded 10-degress. It may only go to perhaps 7-degrees and therefore it arrives their in less than 90-degrees of rotation. The next half revolution will then move the blades another 7/10 of the way toward the originally command 10-degrees. After a number of revolutions, the [tip path plane] eventually arrives at the full 10-degrees.
The delta3 'softens' the cyclic control.
delta3,
This is the reason why I asked the previous question of you.
".... delta-3 must help reduce flapping over what it would be for a rotor system without such geometry
...."
You are correct. Negative delta3 does reduce flapping (teetering). The interesting part is how it does it.
An example:
If the pilot puts 10-degrees into the swashplate [control plane] this will start the blade climbing toward a 10-degrees flap angle at 90-degrees azimuth later [tip path plane]. At the start of this action, there is no difference between a conventional teetering rotor and a teetering rotor with delta3.
As the blade on the delta3 rotor teeters up, an ever increasing portion of the positive pitch will being pulled out of the blade by the delta3 [no feathering plane]. In other words; in a conventional teetering rotor, the [control plane] tells the [tip path plane] where to go and the [tip path plane] arrives their 90-degrees later. In a delta3 teetering rotor, the [control plane] tells the [tip path plane] where to go, BUT, the [no feathering plane] steps between the two and say '"blade, you're only going as far as I tell you to where go ".
To add a little more to the explanation; the phase angle on a teetering rotor with delta3 is less than 90-degrees because the blade does not flap to the commanded 10-degress. It may only go to perhaps 7-degrees and therefore it arrives their in less than 90-degrees of rotation. The next half revolution will then move the blades another 7/10 of the way toward the originally command 10-degrees. After a number of revolutions, the [tip path plane] eventually arrives at the full 10-degrees.
The delta3 'softens' the cyclic control.
delta3,
This is the reason why I asked the previous question of you.
Join Date: Jul 2001
Location: CT, USA
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
Dave_Jackson,
Ok, but the key is that the rotor does not need to move through 10 degrees to catch up to where the stick is all at once. As soon as you start to move the cyclic, the rotor follows, moving just a degree or two per revolution and therefore never far behind the commanded position at any given point. At 530 rpm, thats almost 9 revolutions per second. Even if delta-3 pulls out some pitch as you are adding it, the disc will re-orient to be parallel with the swashplate in fractions of a second. Also, the fact that delta-3 is eliminating some of the wee-wa(cross coupling) effect means that the rotor will track closer to the actual direction of stick movement and this may translate into a crisper feel.
Ok, but the key is that the rotor does not need to move through 10 degrees to catch up to where the stick is all at once. As soon as you start to move the cyclic, the rotor follows, moving just a degree or two per revolution and therefore never far behind the commanded position at any given point. At 530 rpm, thats almost 9 revolutions per second. Even if delta-3 pulls out some pitch as you are adding it, the disc will re-orient to be parallel with the swashplate in fractions of a second. Also, the fact that delta-3 is eliminating some of the wee-wa(cross coupling) effect means that the rotor will track closer to the actual direction of stick movement and this may translate into a crisper feel.
Last edited by Chiplight; 1st Dec 2004 at 06:01.
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes
on
0 Posts
Chiplight,
Agreed. The large angle of 10-degrees was used as an overly simplistic attempt to explain the activity of delta3.
The follow is less simplistic than the previous one and hopefully answers your concern.
Prouty has said that a rotor flies to position within half a revolution.
In addition to this, let's assume that;
1) The pilot is gradually moving the cyclic stick in one direction at a constant speed of 0.01-degree per half revolution of the rotor, also
2) The delta3 is removing 30% of the ongoing difference between the cyclic stick [control plane] and the disk's [tip path plane]
Therefore;
a) In the first half-revolution, the disk will teeter 0.01 x 70% = 0.007-degrees.
b) In the second half-revolution, the disk will teeter another 0.01 x 70% PLUS 0.01 x 70% x 30% = 0.0091-degrees
c) In the third half-revolution, the disk will teeter another 0.01 x 70% PLUS 0.01 x 70% x 30% PLUS 0.01 x 70% x 30% x 21% = 0.009541-degrees.
In other words, the disk is tilting at 70% of the current discrepancy between the [control plane] and the [tip path plane] PLUS the declining residue from the previous half-rotations.
Simply put;
If the rotor has no delta3 the disk will be tilting at a constant rate of 0.01-degrees per half-revolution.
But, since the rotor has delta three, after 7 or 8 half-revolutions, the disk will be tilting at constant rate of 0.00964-degrees per half revolution.
____________________
Edit
I believe that you will find that the We-wa is compensated for by the phase-angle.
The information here may be of some interest.
Agreed. The large angle of 10-degrees was used as an overly simplistic attempt to explain the activity of delta3.
The follow is less simplistic than the previous one and hopefully answers your concern.
Prouty has said that a rotor flies to position within half a revolution.
In addition to this, let's assume that;
1) The pilot is gradually moving the cyclic stick in one direction at a constant speed of 0.01-degree per half revolution of the rotor, also
2) The delta3 is removing 30% of the ongoing difference between the cyclic stick [control plane] and the disk's [tip path plane]
Therefore;
a) In the first half-revolution, the disk will teeter 0.01 x 70% = 0.007-degrees.
b) In the second half-revolution, the disk will teeter another 0.01 x 70% PLUS 0.01 x 70% x 30% = 0.0091-degrees
c) In the third half-revolution, the disk will teeter another 0.01 x 70% PLUS 0.01 x 70% x 30% PLUS 0.01 x 70% x 30% x 21% = 0.009541-degrees.
In other words, the disk is tilting at 70% of the current discrepancy between the [control plane] and the [tip path plane] PLUS the declining residue from the previous half-rotations.
Simply put;
If the rotor has no delta3 the disk will be tilting at a constant rate of 0.01-degrees per half-revolution.
But, since the rotor has delta three, after 7 or 8 half-revolutions, the disk will be tilting at constant rate of 0.00964-degrees per half revolution.
____________________
Edit
I believe that you will find that the We-wa is compensated for by the phase-angle.
The information here may be of some interest.
Last edited by Dave_Jackson; 1st Dec 2004 at 06:28.
Fascinating stuff! I don't have a simulator but have performed this simple test:
Whilst sitting in the left hand seat of the aircraft, with the window open and doing about 70 kts, I placed my hand into the airflow. With my hand flat, thumb side up and fingers pointing into the direction of travel, there was minimal drag force (this could simulate a streamlined fuselage travelling in normal cruise).
I then turned my hand 90 degrees left, allowing the flat palm to face the airflow: rather akin to a sudden 90 degree yaw, perhaps? and found the drag increased markedly!
I came to the conclusion that if I were flying a relatively streamlined helicopter that had a relatively bluff side plan, with a teetering head, and applied maximum yaw pedal in the cruise, there was every chance that the transient change in the thrust drag coupling could result in head to mast contact with the potential for a more significant change in the thrust drag relationship. In fact no thrust, just drag and the able assistance of gravity.
Wildly flapping is what you then do in the cockpit.
This would be the KISS theory but is no doubt wrong!
Whilst sitting in the left hand seat of the aircraft, with the window open and doing about 70 kts, I placed my hand into the airflow. With my hand flat, thumb side up and fingers pointing into the direction of travel, there was minimal drag force (this could simulate a streamlined fuselage travelling in normal cruise).
I then turned my hand 90 degrees left, allowing the flat palm to face the airflow: rather akin to a sudden 90 degree yaw, perhaps? and found the drag increased markedly!
I came to the conclusion that if I were flying a relatively streamlined helicopter that had a relatively bluff side plan, with a teetering head, and applied maximum yaw pedal in the cruise, there was every chance that the transient change in the thrust drag coupling could result in head to mast contact with the potential for a more significant change in the thrust drag relationship. In fact no thrust, just drag and the able assistance of gravity.
Wildly flapping is what you then do in the cockpit.
This would be the KISS theory but is no doubt wrong!
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
Dave and Chiplight,
You analysis of delta 3 is unique, I have not seen it explained that way, but the explanation works. Let me try another way to explain the same thing, a method I have used in the past:
The angle between the pitch horn and the blade flap hinge is the delta 3 angle. It establishes the "new"hinge through which the blade flaps. In the case of the Robinson, the flap axis is no longer tangent to the rotor path (and perfectly aligned with the blade span), it is 17 degrees prior to that tangent. The blade flaps up 17 degrees earlier in rotation, thus it is phased 17 degrees earlier, and needs 17 degrees less lead on its control inputs. Same thing as your explanation, but easier to imagine physically.
212Man,
Your "experiment" is valid, and describes a factor I left off of my discussion of the effects of sideslip on trim. Let me describe it:
With no sideslip at forward speed, the cyclic position is a combination of the longitudinal control necessary to flap the rotor nose down, so that the thrust it provides cancels out the drag of the fuselage. The roll cyclic cancels out the dysymetry-of-lift effects due to lift differences between the upsweeping and downsweeping blades. This precise balance is established by the pilot, who mearly seeks the "right" place to place the stick. Now you jam in some pedal to spin the aircraft around the mast by 10 degrees of yaw to the right. The cyclic is in the wrong place. The longitudinal is now actually inducing some roll away from the sideslip (because the nose is pointed to the right, and the nose down cyclic is actually making some right roll.) There is too little cyclic in the direction of the relative wind, so the aircraft rolls further right. The drag on the fuselage is greater, so if the pilot wants to hold constant speed in the sideslip, he need much more left stick to push the disk down in the direction of the wind (this is where 212Man's concept is shown). That extra drag actually makes the maneuver more violent that a simple rotation of the rotor disk alone.
You analysis of delta 3 is unique, I have not seen it explained that way, but the explanation works. Let me try another way to explain the same thing, a method I have used in the past:
The angle between the pitch horn and the blade flap hinge is the delta 3 angle. It establishes the "new"hinge through which the blade flaps. In the case of the Robinson, the flap axis is no longer tangent to the rotor path (and perfectly aligned with the blade span), it is 17 degrees prior to that tangent. The blade flaps up 17 degrees earlier in rotation, thus it is phased 17 degrees earlier, and needs 17 degrees less lead on its control inputs. Same thing as your explanation, but easier to imagine physically.
212Man,
Your "experiment" is valid, and describes a factor I left off of my discussion of the effects of sideslip on trim. Let me describe it:
With no sideslip at forward speed, the cyclic position is a combination of the longitudinal control necessary to flap the rotor nose down, so that the thrust it provides cancels out the drag of the fuselage. The roll cyclic cancels out the dysymetry-of-lift effects due to lift differences between the upsweeping and downsweeping blades. This precise balance is established by the pilot, who mearly seeks the "right" place to place the stick. Now you jam in some pedal to spin the aircraft around the mast by 10 degrees of yaw to the right. The cyclic is in the wrong place. The longitudinal is now actually inducing some roll away from the sideslip (because the nose is pointed to the right, and the nose down cyclic is actually making some right roll.) There is too little cyclic in the direction of the relative wind, so the aircraft rolls further right. The drag on the fuselage is greater, so if the pilot wants to hold constant speed in the sideslip, he need much more left stick to push the disk down in the direction of the wind (this is where 212Man's concept is shown). That extra drag actually makes the maneuver more violent that a simple rotation of the rotor disk alone.
Thanks Nick, my post was slightly tongue in cheek as the post seemed to be getting too complex for what is not really that complicated a concept.
I once had a co-pilot (handling) let his foot slip on the wet floor of a 212 and hit the right pedal hard . As the a/c had a SFENA SCAS the pedals had micro-switches to release the trim (rather than the combined trim release on cyclic like the basic SCAS). This meant his foot carried on going to full pedal deflection, at 100 kts.
I wasn't monitoring where exactly the cyclic was, but I do know my sandwich ended up in the chin bubble as I grabbed for the controls!
The empirical evidence was enough for me: no need to read the theory.
I once had a co-pilot (handling) let his foot slip on the wet floor of a 212 and hit the right pedal hard . As the a/c had a SFENA SCAS the pedals had micro-switches to release the trim (rather than the combined trim release on cyclic like the basic SCAS). This meant his foot carried on going to full pedal deflection, at 100 kts.
I wasn't monitoring where exactly the cyclic was, but I do know my sandwich ended up in the chin bubble as I grabbed for the controls!
The empirical evidence was enough for me: no need to read the theory.
Join Date: Jul 2001
Location: CT, USA
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
dave's paradox
Dave_Jackson,
I think you should look up Zeno's Paradox.
The runner always covers half the remaining distance with each stride and it seems that he can never get there since you can always cut the remaining distance in half.
In your delta-3 description, you make it seem as if any remaining error is taken out in the next half revolution. I think it is more likely that small errors are taken out in smaller sweeps of the rotor, so that essentially the rotor aligns with the swashplate exttremely fast, akin to a servo mechanism with a high error gain.
I tend to like Nick's method of thinking in terms of a 17 degree lead.
The flap frequency is increased over that of the rotor natural frequency and its like adding two sine waves of slightly different frequencies in electronics. You get a single wave with a phase shift.
I think you should look up Zeno's Paradox.
The runner always covers half the remaining distance with each stride and it seems that he can never get there since you can always cut the remaining distance in half.
In your delta-3 description, you make it seem as if any remaining error is taken out in the next half revolution. I think it is more likely that small errors are taken out in smaller sweeps of the rotor, so that essentially the rotor aligns with the swashplate exttremely fast, akin to a servo mechanism with a high error gain.
I tend to like Nick's method of thinking in terms of a 17 degree lead.
The flap frequency is increased over that of the rotor natural frequency and its like adding two sine waves of slightly different frequencies in electronics. You get a single wave with a phase shift.
Last edited by Chiplight; 1st Dec 2004 at 15:27.
Iconoclast
Join Date: Sep 2000
Location: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Posts: 2,132
Likes: 0
Received 0 Likes
on
0 Posts
Who is right?
To: chiplight
I know that the report was never finished because the FAA cut the funding. Whether the report was complete and all avenues investigated the FAA took action and issued the Priority letter AD dated: 13 Jan 95
The lead paragraph on that AD stated the following: Until the FAA completes its’ research into the conditions and aircraft characteristics that lead to main rotor blade/fuselage contact accidents, and corrective design changes and operating limitations are identified, pilots are strongly urged to become familiar with the following information and comply with these recommended procedures.
It went on to address main rotor stall and the consequences therein. It continued addressing mast bumping and the causes. One of the causes was excessive sideslip
It addressed five flight regimes that must be followed in order to minimize the possibility of mast bumping and or rotor incursion. The 4th recommendation was to avoid sideslip and maintain in trim flight at all times.
The information on the AD was titled Normal Procedures Section and it was entered into the POH in section 4 however it was never entered into the Log of pages approved by the FAA and as such it was never officially made a part of the POH. As such it had no weight other than to give Robinson a “cover you ass” page that could be used to establish pilot error in the event of a loss of control accident.
Even though the Georgia Tech report was never finished and as you indicated it was not complete within itself the FAA took that information and issued the AD. If you check into it you will most likely find that all testing ceased relative to determining the exact causes of loss of control. I believe this applies to both Robinson and the FAA. The SFAR was promulgated and Robinson initiated the safety-training course. Supposedly this would have solved the problem but there were seven or more loss of control accidents some of which involved very high time pilots since the initiation of the SFAR and the safety-course.
Whether the Georgia Tech report was never completed (for whatever reason) it was the basis for the FAA AD and that is why I reference it in my posts.
Do these situations result in excessive flapping? Some of you say no and others have reserved judgement. In either case the evidence points to excessive flapping as the cause of loss of control.
I once again pose the question. Who is right?
It says there, starting on page 23, that the report was never finished due to funds running out. Also, it was a computer simulation that was never fully validated. It only proved accurate within narrow parameters. Further, they don't seem to have done much in the way of sideslip simulations, because the model wasn't fully developed.
The lead paragraph on that AD stated the following: Until the FAA completes its’ research into the conditions and aircraft characteristics that lead to main rotor blade/fuselage contact accidents, and corrective design changes and operating limitations are identified, pilots are strongly urged to become familiar with the following information and comply with these recommended procedures.
It went on to address main rotor stall and the consequences therein. It continued addressing mast bumping and the causes. One of the causes was excessive sideslip
It addressed five flight regimes that must be followed in order to minimize the possibility of mast bumping and or rotor incursion. The 4th recommendation was to avoid sideslip and maintain in trim flight at all times.
The information on the AD was titled Normal Procedures Section and it was entered into the POH in section 4 however it was never entered into the Log of pages approved by the FAA and as such it was never officially made a part of the POH. As such it had no weight other than to give Robinson a “cover you ass” page that could be used to establish pilot error in the event of a loss of control accident.
Even though the Georgia Tech report was never finished and as you indicated it was not complete within itself the FAA took that information and issued the AD. If you check into it you will most likely find that all testing ceased relative to determining the exact causes of loss of control. I believe this applies to both Robinson and the FAA. The SFAR was promulgated and Robinson initiated the safety-training course. Supposedly this would have solved the problem but there were seven or more loss of control accidents some of which involved very high time pilots since the initiation of the SFAR and the safety-course.
Whether the Georgia Tech report was never completed (for whatever reason) it was the basis for the FAA AD and that is why I reference it in my posts.
Do these situations result in excessive flapping? Some of you say no and others have reserved judgement. In either case the evidence points to excessive flapping as the cause of loss of control.
I once again pose the question. Who is right?
Join Date: Jul 2001
Location: CT, USA
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
Lu,
I did not fully understand the reasons why excessive flapping might occur in a sideslip and I was asking questions. I guess that makes me wrong and you right in your book.
Nick and others took the time to help me out. You, on the other hand, could not even provide a link to the georgia tech study and I had to hunt around for it myself, only to find that it was not quite what you had portrayed it to be.
I hope you got as much out of the posts in this thread as I did.
I did not fully understand the reasons why excessive flapping might occur in a sideslip and I was asking questions. I guess that makes me wrong and you right in your book.
Nick and others took the time to help me out. You, on the other hand, could not even provide a link to the georgia tech study and I had to hunt around for it myself, only to find that it was not quite what you had portrayed it to be.
I hope you got as much out of the posts in this thread as I did.
Last edited by Chiplight; 1st Dec 2004 at 17:53.
Iconoclast
Join Date: Sep 2000
Location: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Posts: 2,132
Likes: 0
Received 0 Likes
on
0 Posts
In my own defence.
To: Chiplight
Does it make me a bad person for not being able to provide a link to the Georgia Tech report? I contacted the PhD that supervised the report and he promised me a copy. He for whatever reason did not follow up on his promise.
I could have told you that a copy of the report or at least a part of the report was attached to the NTSB report on the Loss of Control accidents but then you would have asked for a link to that report.
As far as me being able to tell you what causes the flapping I could not do that. My only reference is what the FAA says are the reasons for excessive flapping and what must be done to avoid this condition and this is what I referenced in all of my posts.
Was the Georgia Tech study valid and, was the FAAs response to the report valid. These are questions that must be answered.
Also if there was insufficient technical data in the Georgia Tech report then why did the FAA respond to a report that was both incomplete and not technically accurate?
These are the questions that should be raised on this forum and not a lot of postulating by individuals that want to prove how much they know.
As Nick stated I do not have an engineering degree and my only claim to fame is a heavy maintenance background. It is this plus my 36 years as a reliability, maintainability, and systems safety engineer. I ask questions and I do not always accept the obvious answers to be the truth.
Lets’ see how Nick responds to my last statement.
You, on the other hand, could not even provide a link to the georgia tech study and I had to hunt around for it myself, only to find that it was not quite what you had portrayed it to be.
Does it make me a bad person for not being able to provide a link to the Georgia Tech report? I contacted the PhD that supervised the report and he promised me a copy. He for whatever reason did not follow up on his promise.
I could have told you that a copy of the report or at least a part of the report was attached to the NTSB report on the Loss of Control accidents but then you would have asked for a link to that report.
As far as me being able to tell you what causes the flapping I could not do that. My only reference is what the FAA says are the reasons for excessive flapping and what must be done to avoid this condition and this is what I referenced in all of my posts.
Was the Georgia Tech study valid and, was the FAAs response to the report valid. These are questions that must be answered.
Also if there was insufficient technical data in the Georgia Tech report then why did the FAA respond to a report that was both incomplete and not technically accurate?
These are the questions that should be raised on this forum and not a lot of postulating by individuals that want to prove how much they know.
As Nick stated I do not have an engineering degree and my only claim to fame is a heavy maintenance background. It is this plus my 36 years as a reliability, maintainability, and systems safety engineer. I ask questions and I do not always accept the obvious answers to be the truth.
Lets’ see how Nick responds to my last statement.
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes
on
0 Posts
Chiplight,
There is no argument with Zeno's Paradox, but cut me a little slack. I did take it to 6 decimal places
. In reality, long before the equation gets to the infinite iteration, the pilot has put a new movement into the cyclic.
You are also correct in referencing the sine wave, whereas I used a simpler linear example.
Nick,
As always, I appreciate learning from your knowledge and your challenging of the neurons.
The following is in the context of a healthy challenge;----
I am going to use the word 'teeters' instead of the word 'flaps'. Flapping conjures up the relationship between an articulated rotor and phase-lag. In the current situation, we are discussing the quite different subject of a delta3 teetering rotor and phase-lag.
In the first case, phase-lag is reduced from 90-degrees simply because it is working with a rotor that flaps to position in less than 90-degrees. The second case is much more complex and Frank Robinson has stated this complexity in his previous post on PPRuNe.
You say; "The blade flaps up 17 degrees earlier in rotation, thus it is phased 17 degrees earlier, and needs 17 degrees less lead on its control inputs."
IMHO, this is not quite the case. The sequence of the events in your statement implies that the flapping precedes the control input. This would be true if the flapping was due to an external perturbation. However, in the case of an external perturbation there is no reason why the delta3 teetering rotor will(*) start teetering any sooner than the basic teetering rotor starts.
___________
My previous two posts to Chiplight only covered the activity of delta3. Phase-lag is a separate but associated subject.
Assuming we are considering a pilot induced cyclic change, the phase-lag is reduced from 90-degrees on a delta3 teetering rotor because the blade is not called apon to (initially) teeter the full distance. In other words, a delta3 teetering rotor and a basic teetering rotor will start teetering at the same rate but the delta3 rotor does not (initially) have so far to go. This is very different from the articulated rotor where the phase-lag is reduced from 90-degrees because the blade flaps faster.
(*) Edited to change 'should' to 'will', for clarification.
There is no argument with Zeno's Paradox, but cut me a little slack. I did take it to 6 decimal places
. In reality, long before the equation gets to the infinite iteration, the pilot has put a new movement into the cyclic.You are also correct in referencing the sine wave, whereas I used a simpler linear example.
Nick,
As always, I appreciate learning from your knowledge and your challenging of the neurons.
The following is in the context of a healthy challenge;----I am going to use the word 'teeters' instead of the word 'flaps'. Flapping conjures up the relationship between an articulated rotor and phase-lag. In the current situation, we are discussing the quite different subject of a delta3 teetering rotor and phase-lag.
In the first case, phase-lag is reduced from 90-degrees simply because it is working with a rotor that flaps to position in less than 90-degrees. The second case is much more complex and Frank Robinson has stated this complexity in his previous post on PPRuNe.
You say; "The blade flaps up 17 degrees earlier in rotation, thus it is phased 17 degrees earlier, and needs 17 degrees less lead on its control inputs."
IMHO, this is not quite the case. The sequence of the events in your statement implies that the flapping precedes the control input. This would be true if the flapping was due to an external perturbation. However, in the case of an external perturbation there is no reason why the delta3 teetering rotor will(*) start teetering any sooner than the basic teetering rotor starts.
___________
My previous two posts to Chiplight only covered the activity of delta3. Phase-lag is a separate but associated subject.
Assuming we are considering a pilot induced cyclic change, the phase-lag is reduced from 90-degrees on a delta3 teetering rotor because the blade is not called apon to (initially) teeter the full distance. In other words, a delta3 teetering rotor and a basic teetering rotor will start teetering at the same rate but the delta3 rotor does not (initially) have so far to go. This is very different from the articulated rotor where the phase-lag is reduced from 90-degrees because the blade flaps faster.
(*) Edited to change 'should' to 'will', for clarification.
Last edited by Dave_Jackson; 1st Dec 2004 at 20:08.
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
Lu says:
"I ask questions and I do not always accept the obvious answers to be the truth."
Not true, Lu. You tell people that serious flaws exist in helicopters that you barely know, using poor logic and inappropriate sources. You fail to learn from others who do for a living what you made mistakes talking about, you make longer and longer answers that blur the original mistakes you make, and then it all implodes in a mess.
You are a very experienced helicopter mechanic with much to offer pprune, but with two grevious faults:
1) you do not know what you do not know
2) you don't mind slurring the hard work of others whose shoes you are not fit to wear.
"I ask questions and I do not always accept the obvious answers to be the truth."
Not true, Lu. You tell people that serious flaws exist in helicopters that you barely know, using poor logic and inappropriate sources. You fail to learn from others who do for a living what you made mistakes talking about, you make longer and longer answers that blur the original mistakes you make, and then it all implodes in a mess.
You are a very experienced helicopter mechanic with much to offer pprune, but with two grevious faults:
1) you do not know what you do not know
2) you don't mind slurring the hard work of others whose shoes you are not fit to wear.
Iconoclast
Join Date: Sep 2000
Location: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Posts: 2,132
Likes: 0
Received 0 Likes
on
0 Posts
With your eyes wide shut.
To: NickLappos
My my, I see you are back on your pedestal preaching to the masses telling any and all that I don’t know what I am talking about. You say that there are people that earn their living doing what I am talking about. That might be correct in certain areas but not about the R-22 flight control and dynamics systems. I have had a very strong interest in this helicopter and by definition the R-44.
What I don’t know I can refer to the POHs for both helicopters and the maintenance manual for the R-22. Or, I can call Robinson or different operators. I will state it again, the rigging procedure sucks and the instructions are ambiguous and can get a mechanic and by extension the pilot in trouble. The flight control system is not in compliance with the FARs yet it was certificated.
Before you make any more sarcastic comments about my knowledge base I suggest you familiarize yourself with the rigging procedures and the 17-degree lead on the blade (R-44) and 18-degree lead on the R-22. I have been involved with this problem (loss of control) since 1994)
According to you, the R-22 has a 72-degree phase angle. Now this may well be true but I would like to know how a rotorhead can be designed and a helicopter built around it and the designer created a blade with a 72-degree phase angle to exactly match the rotorhead. Do you have that capability?
Now that I have posed this question why don’t you respond to my other questions? Is it that you want the safety of making accusation and not want to come out of your retreat and respond to the questions that I posed.
I’ll raise this point one more time for the benefit of the others on this forum relative to your comments about the 17-degree lead. I believe in your illustration the advancing blade flaps (over the right lateral axis) up. Are you addressing flapback or are you saying the helicopter is flying backwards?
One other point that the masses may not understand is when the helicopter is rigged for forward cyclic the blade is advanced 18-degrees ahead of the right lateral axis. The blade must be in this position in order to achieve maximum down flap over the nose. At this point aerodynamic and gyroscopic precession go out the window and with maximum decreased pitch in this position the blade will flap down 72-degrees later (Delta 3 are you listening?)
Your turn.
Not true, Lu. You tell people that serious flaws exist in helicopters that you barely know, using poor logic and inappropriate sources. You fail to learn from others who do for a living what you made mistakes talking about, you make longer and longer answers that blur the original mistakes you make, and then it all implodes in a mess.
What I don’t know I can refer to the POHs for both helicopters and the maintenance manual for the R-22. Or, I can call Robinson or different operators. I will state it again, the rigging procedure sucks and the instructions are ambiguous and can get a mechanic and by extension the pilot in trouble. The flight control system is not in compliance with the FARs yet it was certificated.
Before you make any more sarcastic comments about my knowledge base I suggest you familiarize yourself with the rigging procedures and the 17-degree lead on the blade (R-44) and 18-degree lead on the R-22. I have been involved with this problem (loss of control) since 1994)
According to you, the R-22 has a 72-degree phase angle. Now this may well be true but I would like to know how a rotorhead can be designed and a helicopter built around it and the designer created a blade with a 72-degree phase angle to exactly match the rotorhead. Do you have that capability?
Now that I have posed this question why don’t you respond to my other questions? Is it that you want the safety of making accusation and not want to come out of your retreat and respond to the questions that I posed.
I’ll raise this point one more time for the benefit of the others on this forum relative to your comments about the 17-degree lead. I believe in your illustration the advancing blade flaps (over the right lateral axis) up. Are you addressing flapback or are you saying the helicopter is flying backwards?
One other point that the masses may not understand is when the helicopter is rigged for forward cyclic the blade is advanced 18-degrees ahead of the right lateral axis. The blade must be in this position in order to achieve maximum down flap over the nose. At this point aerodynamic and gyroscopic precession go out the window and with maximum decreased pitch in this position the blade will flap down 72-degrees later (Delta 3 are you listening?)
Your turn.
Join Date: Mar 2000
Location: UK
Posts: 5,197
Likes: 0
Received 0 Likes
on
0 Posts
Lu
"My my, I see you are back on your pedestal preaching to the masses"
Nick doesn't put himself on a pedestal - he's put there by others who recognise his expertise and experience, and acknowledge that he's one of the leading helicopter experts in the world.
Your 'preaching to the masses' comment is unjustified. There have been numerous comments in this forum over the years about the time Nick devotes to answering questions - not only from high hours professionals but also from low hours PPLs.
Just occasionally, he shows signs of frustration. People can decide for themselves whether that's unreasonable or understandable in the circumstances.
We all have the same opportunity to learn from Nick - whether we take it is up to us.
Heliport
________________
'Certification of the R22 (incl post by Frank Robinson)': Click here
'The 18 degree offset - fact or fiction?': Click here
'Helicopter Dynamics: Gyroscopic Precession', click here
'RBS, precession & LZ', click here
'The myth of Gyroscopic Precession', click here
'Gyroscopic Precession - Revisited', click: here
"My my, I see you are back on your pedestal preaching to the masses"
Nick doesn't put himself on a pedestal - he's put there by others who recognise his expertise and experience, and acknowledge that he's one of the leading helicopter experts in the world.
Your 'preaching to the masses' comment is unjustified. There have been numerous comments in this forum over the years about the time Nick devotes to answering questions - not only from high hours professionals but also from low hours PPLs.
Just occasionally, he shows signs of frustration. People can decide for themselves whether that's unreasonable or understandable in the circumstances.
We all have the same opportunity to learn from Nick - whether we take it is up to us.
Heliport
________________
'Certification of the R22 (incl post by Frank Robinson)': Click here
'The 18 degree offset - fact or fiction?': Click here
'Helicopter Dynamics: Gyroscopic Precession', click here
'RBS, precession & LZ', click here
'The myth of Gyroscopic Precession', click here
'Gyroscopic Precession - Revisited', click: here
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
Thank you, heliport! Here is a quote from a 2001 thread (RBS, precession & LZ):
"To those who read Lu's seemingly curious questions and claimed facts:
He is mostly wrong in his facts, and very mostly wrong in his explanations. If you wish to learn something about helos, try to simply ignore his poor math and poorer explanations.
......
Sorry for the venting, but please take what I say to heart. I know Lu is only trying to help, but the only ray of light I can see is that Lu has not offered any advice on brain surgery, as this is a quicker way to get hurt than following his aviation advice."
"To those who read Lu's seemingly curious questions and claimed facts:
He is mostly wrong in his facts, and very mostly wrong in his explanations. If you wish to learn something about helos, try to simply ignore his poor math and poorer explanations.
......
Sorry for the venting, but please take what I say to heart. I know Lu is only trying to help, but the only ray of light I can see is that Lu has not offered any advice on brain surgery, as this is a quicker way to get hurt than following his aviation advice."
Flight Dynamics: The Swashplate and Phase-angle
Join Date: Mar 2002
Location: Blackpool, UK
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
More things change,
the more they stay the same.
I've been away from the forum for a few years (an ankle-biter and work got in the way).
Back then Lu was swimming against the tide.
Its nice to know he's still keeping fit today.
This is an admirable quality in itself, but its a fine line between tenacious and stubborn.
Its all about trust I suppose.
Sorry Lu, I don't doubt you believe what you say. Your arguments to those of us who are not as knowledgeable are very convincing.
But for me, I trust Nick.
I know his background, I've even seen him on the discovery channel ! I trust his experience as a pilot, and therefore value his opinion.
I can't say that your wrong Lou, but Nick seems to think so.
I accept I'm a no-one in the great scheme of things. Just a ppl who likes to fly - preferably forwards and not sidewards mind you. But like others I lurk on here to learn from all those who would teach.
I listen to all the arguments, and sometimes rely on others to distill the information down to a level I can grasp.
But for me, when it comes down to it, if Nick says its A not B, then A it is.
To all you Robbo drivers out there, just fly safe. Stay within your limits, and keep the tail rotor behind you!!
I'll shut up now.
I've been away from the forum for a few years (an ankle-biter and work got in the way).
Back then Lu was swimming against the tide.
Its nice to know he's still keeping fit today.
This is an admirable quality in itself, but its a fine line between tenacious and stubborn.
Its all about trust I suppose.
Sorry Lu, I don't doubt you believe what you say. Your arguments to those of us who are not as knowledgeable are very convincing.
But for me, I trust Nick.
I know his background, I've even seen him on the discovery channel ! I trust his experience as a pilot, and therefore value his opinion.
I can't say that your wrong Lou, but Nick seems to think so.
I accept I'm a no-one in the great scheme of things. Just a ppl who likes to fly - preferably forwards and not sidewards mind you. But like others I lurk on here to learn from all those who would teach.
I listen to all the arguments, and sometimes rely on others to distill the information down to a level I can grasp.
But for me, when it comes down to it, if Nick says its A not B, then A it is.
To all you Robbo drivers out there, just fly safe. Stay within your limits, and keep the tail rotor behind you!!
I'll shut up now.
Join Date: Nov 2001
Location: Alderney or Lancashire UK
Posts: 570
Likes: 0
Received 0 Likes
on
0 Posts
Rotorhorn,
Welcome back. I wondered where you had gone.
Here are a few things I have learned from PPrune over the years, by listening to intelligent people and arguing with Lu.
1) Theres nothing wrong with the R22 rotor head as a design for a teetering head. It works as designed in spite of Lu's blinkered protestations. An articulated head is better though.
2) The combination of a teetering head and low inertia rotor system and a carburettor engine is possibly not the best combination for a low hour or student pilot. Frank says it was not designed for this market - he is right. Frank talks of killing off the R22. I wonder if this is part of the reason.
3) There may possibly be a problem with R22 MR blades. That makes me more nervous of the R22 than the above.
4) Lu is beyond reason.
5) We are fortunate to have the wisdom of Nick and a few others on PPrune to answer serious questions.
6) I like my articulated rotor head, high inertia, fuel injected helicopter. If you fancy a fly in an Enstrom PM me.
G
Welcome back. I wondered where you had gone.
Here are a few things I have learned from PPrune over the years, by listening to intelligent people and arguing with Lu.
1) Theres nothing wrong with the R22 rotor head as a design for a teetering head. It works as designed in spite of Lu's blinkered protestations. An articulated head is better though.
2) The combination of a teetering head and low inertia rotor system and a carburettor engine is possibly not the best combination for a low hour or student pilot. Frank says it was not designed for this market - he is right. Frank talks of killing off the R22. I wonder if this is part of the reason.
3) There may possibly be a problem with R22 MR blades. That makes me more nervous of the R22 than the above.
4) Lu is beyond reason.
5) We are fortunate to have the wisdom of Nick and a few others on PPrune to answer serious questions.
6) I like my articulated rotor head, high inertia, fuel injected helicopter. If you fancy a fly in an Enstrom PM me.
G
Last edited by Gaseous; 6th Dec 2004 at 02:05.
Join Date: May 2001
Location: perth
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
I havnt contributed much to the forum for a while, but it is interesting to see the discussion on this. I studied Aero Eng at Uni for 2 years but im no engineer, just a pilot.
What i see about the R22 and R44 is that they are widely used helicopter with a lot of low time pilots flying them. Frank Robinson may be right, it was not designed as a trainer.
If you look at how many hours they do with the activity they are mostly engaged in, is it unreasonable to assume there wouldnt be accidents?
Personally, ill take the word of a test pilot over a maintainer any day.
What i see about the R22 and R44 is that they are widely used helicopter with a lot of low time pilots flying them. Frank Robinson may be right, it was not designed as a trainer.
If you look at how many hours they do with the activity they are mostly engaged in, is it unreasonable to assume there wouldnt be accidents?
Personally, ill take the word of a test pilot over a maintainer any day.