Ditching a helicopter: (incl pictures)
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Nick
You contributions to the forum are highly valued, for obvious reasons. And of course it's helpful when you point out theories/statements which are incorrect.
Whether you choose to enter into a discussion justifying your opinions is a matter of choice for you as far as I'm concerned.
Lu
You ask "How about the views of a Senior Reliability Maintainability and Systems Safety Engineering consultant .... How about my experience as a maintenance technician on Bell and Sikorsky Helicopters etc"
Hoverbover has already answered that question far more eloquently than I could.
I enjoy many of your posts, particularly the anecdotes. The problem is that you don't seem able to let your theories drop, and try to squeeze them into unrelated threads. (This one was about floats/ditching!)
You know as well as I do the effect that has had on so many contributors. They get fed up!
This doesn't happen with anybody else, but it constantly happens with you.
Let's try a new approach...
I get the feeling that people have now had enough of the 'problems' of gyroscopic precession and 18 degree rigging theories, and don't want either topic brought into other discussions so often, or at all.
Do you get the same impression?
What about letting them drop?
You contributions to the forum are highly valued, for obvious reasons. And of course it's helpful when you point out theories/statements which are incorrect.
Whether you choose to enter into a discussion justifying your opinions is a matter of choice for you as far as I'm concerned.
Lu
You ask "How about the views of a Senior Reliability Maintainability and Systems Safety Engineering consultant .... How about my experience as a maintenance technician on Bell and Sikorsky Helicopters etc"
Hoverbover has already answered that question far more eloquently than I could.
I enjoy many of your posts, particularly the anecdotes. The problem is that you don't seem able to let your theories drop, and try to squeeze them into unrelated threads. (This one was about floats/ditching!)
You know as well as I do the effect that has had on so many contributors. They get fed up!
This doesn't happen with anybody else, but it constantly happens with you.
Let's try a new approach...
I get the feeling that people have now had enough of the 'problems' of gyroscopic precession and 18 degree rigging theories, and don't want either topic brought into other discussions so often, or at all.
Do you get the same impression?
What about letting them drop?
Iconoclast
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The following was extracted from the article about the rollover of the Super Puma in the North Sea.
The passages are not in the order of their occurrence in the article. I changed their order for journalistic juxtaposition.
“The rotor blades were still turning as the Super Puma helicopter rolled and it is understood one blade struck the co-pilot, breaking his leg”.
“According to a spokesman, the West Navion was pitching and rolling between four and five meters. A westerly wind was blowing at 33knots-gale force seven to eight – and visibility was 4,000m.
"If it was sitting steady on the deck I can only imagine it was pitch and roll that caused the problem."
This may very well be a case of dynamic rollover but is there a possibility that the pitching and rolling effected the stability of the rotor system?
We had a similar situation on an icebreaker with our S-51s. What kept it from rolling over was that it was tied down during start-up and released as the piliot pulled collective. If the movement of the helicopter was violent enough we would release and the pilot would clear the deck by pulling collective.
This will be my last input on this subject.
Of course my fingers are crossed.
The passages are not in the order of their occurrence in the article. I changed their order for journalistic juxtaposition.
“The rotor blades were still turning as the Super Puma helicopter rolled and it is understood one blade struck the co-pilot, breaking his leg”.
“According to a spokesman, the West Navion was pitching and rolling between four and five meters. A westerly wind was blowing at 33knots-gale force seven to eight – and visibility was 4,000m.
"If it was sitting steady on the deck I can only imagine it was pitch and roll that caused the problem."
This may very well be a case of dynamic rollover but is there a possibility that the pitching and rolling effected the stability of the rotor system?
We had a similar situation on an icebreaker with our S-51s. What kept it from rolling over was that it was tied down during start-up and released as the piliot pulled collective. If the movement of the helicopter was violent enough we would release and the pilot would clear the deck by pulling collective.
This will be my last input on this subject.
Of course my fingers are crossed.
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Lu,
I don't understand how you call yourself an RMS Engineer when you don't have an Engineering Degree. Are you a member of a professional engineering institute or association?
I should call myself a Helicopterologist.
I don't understand how you call yourself an RMS Engineer when you don't have an Engineering Degree. Are you a member of a professional engineering institute or association?
I should call myself a Helicopterologist.
Iconoclast
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To: sling load
True, I do not have an engineering degree. I majored in Industrial Design with a minor in general science. I did take several courses that were a part of the Engineering curriculum but not enough to be called an engineer. After leaving school my first job was with Sikorsky and after completion of a fourteen-month training program I was given the title of Field Service Engineer. Ever since that time I have been working in various aspects of the engineering field and in every one of those jobs I was considered to be an engineer.
Regarding professional organizations I have belonged to many of them. If I wanted to take the time and expend the effort I could attain professional status as a Reliability Engineer, a Maintainability Engineer, A Safety Engineer or a Quality Assurance Engineer. At my age and experience level the obtaining of professional status does me no good.
Now, I will ask you the same question. Why do they call aircraft mechanics in the UK and most likely in OZ and NZ Engineers when they do not have an engineering degree?
True, I do not have an engineering degree. I majored in Industrial Design with a minor in general science. I did take several courses that were a part of the Engineering curriculum but not enough to be called an engineer. After leaving school my first job was with Sikorsky and after completion of a fourteen-month training program I was given the title of Field Service Engineer. Ever since that time I have been working in various aspects of the engineering field and in every one of those jobs I was considered to be an engineer.
Regarding professional organizations I have belonged to many of them. If I wanted to take the time and expend the effort I could attain professional status as a Reliability Engineer, a Maintainability Engineer, A Safety Engineer or a Quality Assurance Engineer. At my age and experience level the obtaining of professional status does me no good.
Now, I will ask you the same question. Why do they call aircraft mechanics in the UK and most likely in OZ and NZ Engineers when they do not have an engineering degree?
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Lu got me thinking when he mentioned the rotor disk staying in plane but the fuselage rolling and pitching with the waves causing the swash plate to change it's orientation with respect to the rotor disk. I think he's right that it causes disk movement, but I see it increasing stability and rotor clearance rather than generating any problem.
This discussion only requires a response from the rotor due to a change in swashplate orientation. It doesn't require any mention of gyroscopic precession, aerodynamic precession, Newton's Laws, etc.
Consider a Jet Ranger on floats that rolls left. The rotor disk wants to stay in plane but the swashplate at 3 o'clock (from above) rises. This causes blade pitch increase at 12 o'clock which causes the disk to tilt to a new plane with the tips highest at 9 o'clock and lowest at 3 o'clock.
Since the helicopter rolled left, this new disk position would attempt to roll the helicopter back to level.
Seems to me that this generates stability.
Matthew.
This discussion only requires a response from the rotor due to a change in swashplate orientation. It doesn't require any mention of gyroscopic precession, aerodynamic precession, Newton's Laws, etc.
Consider a Jet Ranger on floats that rolls left. The rotor disk wants to stay in plane but the swashplate at 3 o'clock (from above) rises. This causes blade pitch increase at 12 o'clock which causes the disk to tilt to a new plane with the tips highest at 9 o'clock and lowest at 3 o'clock.
Since the helicopter rolled left, this new disk position would attempt to roll the helicopter back to level.
Seems to me that this generates stability.
Matthew.
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Lu,
Yes in Australia and the UK Maintainers are called Engineers, but the term is to do with the Licence they are issued Licensed Aircraft Maintenance Engineer, or LAME, its a carry over of the old ways, like the days when flying boat skippers were piped on and off the "vessel". If you call them mechanics they would probably smack you in the face and turn you into a hand puppet. The term Engineer has stuck instead of saying the full title, only difference is they don't design things, they fix them.
Yes in Australia and the UK Maintainers are called Engineers, but the term is to do with the Licence they are issued Licensed Aircraft Maintenance Engineer, or LAME, its a carry over of the old ways, like the days when flying boat skippers were piped on and off the "vessel". If you call them mechanics they would probably smack you in the face and turn you into a hand puppet. The term Engineer has stuck instead of saying the full title, only difference is they don't design things, they fix them.
Iconoclast
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To: heedm
What you say may be true but you have taken a snapshot in time. The helicopter does not just roll in one direction. As the trough of the wave passes the helicopter will roll in the opposite direction and if the helicopter is at an angle to the trough the helicopter will also pitch as well as roll. Once it rolls and pitches in one direction it will move in the opposite direction. This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage. This is not stability.
What you say may be true but you have taken a snapshot in time. The helicopter does not just roll in one direction. As the trough of the wave passes the helicopter will roll in the opposite direction and if the helicopter is at an angle to the trough the helicopter will also pitch as well as roll. Once it rolls and pitches in one direction it will move in the opposite direction. This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage. This is not stability.
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heedm,
Lu is all wet yet again!
The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick.
The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate.
Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense.
Please, please, please watch yourself with Lu, it is almost like talking to one of those shopping cart fellows down town, the ones who think Nixon came back as Socks the Cat.
Lu is all wet yet again!
The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick.
The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate.
Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense.
Please, please, please watch yourself with Lu, it is almost like talking to one of those shopping cart fellows down town, the ones who think Nixon came back as Socks the Cat.
Iconoclast
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To: Nick Lappos
“The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick”.
Response:
Once again Nick you have let your alligator mouth overload your hummingbird ass. Nowhere did I ever say that the rotor developed feedback forces sufficient to overcome the forces developed by the servos. In fact it is because the servos hold the swashplate in the last commanded position that creates a resistance that when the blade moves in relation to the swashplate that resistance causes the blade to move against the pitch rod. Do the sticks move during pitch flap coupling? The answer is no. It is the same thing here if the rolling motion causes the disc to try and maintain its’ position due to gyroscopic rigidity and the disc moves in relation to the fixed control system then there will be a resultant pitch input.
Get you head out of your ass, not everybody flies a helicopter with a rotorhead that is six feet across with a very high moment of inertia and a high level of offset interlock nor, do they operate off an LHA or an aircraft carrier. There are smaller helicopters and there are smaller ships that have a very rapid roll rate. If you have ever been on a ship passing through the Davis Straits you would know. In that area the water flows from three different directions and on a ship that does not have bilge keels the roll and pitch rate are fantastic. So much so, we almost lost both of our helicopters over the side. One other point is that some helicopters operate on floats and are subject to unrestrained wave action. In the case of ships with rapid roll rates and helicopters operating on floats there can be large changes in the disc position. Everybody knows what you do and your level of expertise and because of that they have a great deal of respect for you. Hell for that matter I have a lot of respect for you but when you tell me and everybody else that my experiences operating off the back end of an icebreaker are false and the words of an ignoramus then I take offence. I keep telling you don’t get so personal.
“The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate”.
“Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense”.
Response:
Read my response above especially the part about alligators and hummingbirds. Coming from a person of your stature people will begin to believe what you say about me. But as I stated before your opinions don’t effect me.
PS READ THE LAST FEW POSTS ON THE NORTH SEA CRASH THREAD.
[ 15 November 2001: Message edited by: Lu Zuckerman ]
[ 15 November 2001: Message edited by: Lu Zuckerman ]
“The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick”.
Response:
Once again Nick you have let your alligator mouth overload your hummingbird ass. Nowhere did I ever say that the rotor developed feedback forces sufficient to overcome the forces developed by the servos. In fact it is because the servos hold the swashplate in the last commanded position that creates a resistance that when the blade moves in relation to the swashplate that resistance causes the blade to move against the pitch rod. Do the sticks move during pitch flap coupling? The answer is no. It is the same thing here if the rolling motion causes the disc to try and maintain its’ position due to gyroscopic rigidity and the disc moves in relation to the fixed control system then there will be a resultant pitch input.
Get you head out of your ass, not everybody flies a helicopter with a rotorhead that is six feet across with a very high moment of inertia and a high level of offset interlock nor, do they operate off an LHA or an aircraft carrier. There are smaller helicopters and there are smaller ships that have a very rapid roll rate. If you have ever been on a ship passing through the Davis Straits you would know. In that area the water flows from three different directions and on a ship that does not have bilge keels the roll and pitch rate are fantastic. So much so, we almost lost both of our helicopters over the side. One other point is that some helicopters operate on floats and are subject to unrestrained wave action. In the case of ships with rapid roll rates and helicopters operating on floats there can be large changes in the disc position. Everybody knows what you do and your level of expertise and because of that they have a great deal of respect for you. Hell for that matter I have a lot of respect for you but when you tell me and everybody else that my experiences operating off the back end of an icebreaker are false and the words of an ignoramus then I take offence. I keep telling you don’t get so personal.
“The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate”.
“Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense”.
Response:
Read my response above especially the part about alligators and hummingbirds. Coming from a person of your stature people will begin to believe what you say about me. But as I stated before your opinions don’t effect me.
PS READ THE LAST FEW POSTS ON THE NORTH SEA CRASH THREAD.
[ 15 November 2001: Message edited by: Lu Zuckerman ]
[ 15 November 2001: Message edited by: Lu Zuckerman ]
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Lu, when you first posted to this thread, you asserted that the helicopter's response to wave action caused a rotor response that is 90 degrees out and generates instability. I showed you that it is 180 degrees out and serves to reduce the motion caused by the waves. You then responded to me by suggesting I was only looking at a snapshot in time. Not so.
I isolated one movement but just as easily could have generalized to any deviation of the helicopter's vertical axis. Combining pitching with the rolling may confuse you, but to the helicopter it is still just a movement away from the vertical axis. As Nick mentioned, the roll rates that the helicopter can generate are much greater than those experienced due to wave action. The rotor won't lag in it's "correcting" position, it will respond to each and every deviation of the helicopter's vertical axis.
Stability is when a system that is disturbed tends to return to it's state prior to the disturbance. What I have described IS stability.
I don't doubt that what you have told us about the icebreakers and some earlier floats is true. I just don't think you've found an appropriate explanation for it. Everything you've said wrt the icebreaker sounds like the natural rebounding frequency of the float was resonant with either the helicopter's vibrations or with the deck motion (I assume the former).
As far as floats vs hulls, the vertical c of g you mentioned is a small part of the story. What's important is how the center of buoyancy moves when the helicopter pitches and/or rolls.
Nick, I think you misunderstood Lu's initial assertion, which I believe is valid. The swashplate's orientation doesn't change with respect to the servos or the fuselage. It does change with respect to the earth, as the fuselage moves. The rotor disk does not want to move when the fuselage rolls or pitches due to it's angular momentum (make this easy and consider either a teetering or a fully articulated rotor). Thus the rotor disk and the swash plate change their orientation with respect to each other....same effect as putting in a control input, but without any change in the orientation of the flight controls with respect to the pilot.
Thanks for the warnings wrt Lu, but you will find I tend to stick to the discussion rather than getting personal.
Matthew.
I isolated one movement but just as easily could have generalized to any deviation of the helicopter's vertical axis. Combining pitching with the rolling may confuse you, but to the helicopter it is still just a movement away from the vertical axis. As Nick mentioned, the roll rates that the helicopter can generate are much greater than those experienced due to wave action. The rotor won't lag in it's "correcting" position, it will respond to each and every deviation of the helicopter's vertical axis.
Stability is when a system that is disturbed tends to return to it's state prior to the disturbance. What I have described IS stability.
I don't doubt that what you have told us about the icebreakers and some earlier floats is true. I just don't think you've found an appropriate explanation for it. Everything you've said wrt the icebreaker sounds like the natural rebounding frequency of the float was resonant with either the helicopter's vibrations or with the deck motion (I assume the former).
As far as floats vs hulls, the vertical c of g you mentioned is a small part of the story. What's important is how the center of buoyancy moves when the helicopter pitches and/or rolls.
Nick, I think you misunderstood Lu's initial assertion, which I believe is valid. The swashplate's orientation doesn't change with respect to the servos or the fuselage. It does change with respect to the earth, as the fuselage moves. The rotor disk does not want to move when the fuselage rolls or pitches due to it's angular momentum (make this easy and consider either a teetering or a fully articulated rotor). Thus the rotor disk and the swash plate change their orientation with respect to each other....same effect as putting in a control input, but without any change in the orientation of the flight controls with respect to the pilot.
Thanks for the warnings wrt Lu, but you will find I tend to stick to the discussion rather than getting personal.
Matthew.
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Heedm,
I do not misunderstand Lu, unfortunately. Even though he now denies what he posted, his drivel of 14 November said, "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage."
That clearly describes a non-commanded rotor motion, does it not? That is the heart of Lu's drivel, that the rotor has a mind of its own, and the precession causes rotor motions that possibly roll over the Puma.
I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind. No strange forces from Jupiter, and Nixon is still dead. Talking dynamics with Lu is like calling the Psychic Hotline for advice.
I do not misunderstand Lu, unfortunately. Even though he now denies what he posted, his drivel of 14 November said, "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage."
That clearly describes a non-commanded rotor motion, does it not? That is the heart of Lu's drivel, that the rotor has a mind of its own, and the precession causes rotor motions that possibly roll over the Puma.
I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind. No strange forces from Jupiter, and Nixon is still dead. Talking dynamics with Lu is like calling the Psychic Hotline for advice.
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Gee, missed this thread somehow as I was busy.
I am so loving this ....
It leaves no room for error in my past predictions of LZ.
Whatever the topic.
Back to what I was doing ...
I am so loving this ....
It leaves no room for error in my past predictions of LZ.
Whatever the topic.
Back to what I was doing ...
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Nick, I believe a small uncommanded rotor motion occurs. It doesn't create any problems, instead it makes the helicopter more stable in the water with rotors turning than without.
Ignore what was said about gyroscopic precession. Just consider the swash plate moves with the fuselage and the rotor disk will tend to maintain the plane it is spinning in.
This puts a different relative orientation between swashplate and rotor disk.
This is not psychic, it's physics.
"I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind."
Check my posts, I'm not saying this uncommanded rotor movement is causing problems. I say it's small and it slightly helps matters.
Matthew.
Ignore what was said about gyroscopic precession. Just consider the swash plate moves with the fuselage and the rotor disk will tend to maintain the plane it is spinning in.
This puts a different relative orientation between swashplate and rotor disk.
This is not psychic, it's physics.
"I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind."
Check my posts, I'm not saying this uncommanded rotor movement is causing problems. I say it's small and it slightly helps matters.
Matthew.
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Nick,
Imagine this scenario, the Helicopter in question has an underslung rotor system, is on floats and is pitching back and forth and rolling left and right. Doesn't an underslung system allow the fuselage to behave like a pendulum?, which means Lu's statement "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage." is correct. Although the rotor system is moving in relation to the fuselage the rotor system is effectively not moving but maintaining its position in space and the fuselage is the item that is moving.
Now what about a helicopter with a rigid head?, Lynx for example (no I haven't seen one on floats either), I think because of the rigidity between the rotor system and the fuselage if a wave tried to roll the helicopter then we would see an excellent demonstration of precession i.e. it would either pitch forward or backwards respectively.
And while were at it can we stop the personal attacks / insults?
Jiff
Imagine this scenario, the Helicopter in question has an underslung rotor system, is on floats and is pitching back and forth and rolling left and right. Doesn't an underslung system allow the fuselage to behave like a pendulum?, which means Lu's statement "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage." is correct. Although the rotor system is moving in relation to the fuselage the rotor system is effectively not moving but maintaining its position in space and the fuselage is the item that is moving.
Now what about a helicopter with a rigid head?, Lynx for example (no I haven't seen one on floats either), I think because of the rigidity between the rotor system and the fuselage if a wave tried to roll the helicopter then we would see an excellent demonstration of precession i.e. it would either pitch forward or backwards respectively.
And while were at it can we stop the personal attacks / insults?
Jiff
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Jiff
I understand your last comment - but only up to a point.
But I have much more sympathy for Nick Lappos.
It must be a pain in the butt (as our American cousins might say) for a Test Pilot who voluntarily gives his time to contribute to the forum to be constantly contradicted by the ramblings of a geriatric engineer (mechanic) who's isn't and never even has been a pilot.
I know Lu calls himself "a consultant", but the guy who just sold me a new kitchen also told me he was a "consultant". (I always thought they were called salemen, but you learn something every day).
Anyone can call himself a "consultant" - it means the square root of you know what!
I understand your last comment - but only up to a point.
But I have much more sympathy for Nick Lappos.
It must be a pain in the butt (as our American cousins might say) for a Test Pilot who voluntarily gives his time to contribute to the forum to be constantly contradicted by the ramblings of a geriatric engineer (mechanic) who's isn't and never even has been a pilot.
I know Lu calls himself "a consultant", but the guy who just sold me a new kitchen also told me he was a "consultant". (I always thought they were called salemen, but you learn something every day).
Anyone can call himself a "consultant" - it means the square root of you know what!
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for the group-
The difficulty I have with Lu is mine, and I will wrestle with it. His posts are so misleading, and he is so unwilling to either think or understand that I am completely exasperated!
Imagine the ship is tossing like those movies Lu evokes, with vast pitch and roll motions like a bucking bronko. OK now forget that, it is wrong. Any pilot who lands on that deck without haul-down is nuts, and will be unemployed shortly.
The typical deck landing in commercial service never involves deck angles beyond about 8 degrees (commercial guys, please post the operating limits for deck landings from your ops manuals.) The typical period of motion for a large rig boat is several seconds, usually about 10 seconds or so. For a rig, it is often 20 seconds or so. This makes the deck motion actually very slow in roll or pitch rate, and the contribution of the dynamic motions very small.
The rotor will not wave around or depart from its commanded path due to these motions, no matter what Lu thinks. Even if underslung, the rotor is not free to wave around independant of the aircraft without a swashplate input, unless the angular motions are very fast.
Having investigated the roll-over of several aircraft, I can assure you the results are disappointingly static in nature, a combination of wind velocity (which will move the rotor) deck slope and where the pilot left the stick. For a broad sided helicopter in a cross wind of 35 knots with gusts that are higher, and with a deck roll that compounds the aircraft lean, all it takes is an unattentive pilot to allow a roll-over. The problem with Lu's assertion is that he believes the rotor does its own thing, and that wanders around. He has it backwards! As the aircraft rolls, the rotor follows the aircraft. With a cross wind, the rotor produces strong roll moments that add to the roll tendency that the deck is producing. A pilot would try to put roll cyclic in to keep the rotor disk parallel to the horizon, at the peril of those on the deck under the disk. The pilot is stuck - try to keep the aircraft glued to the deck, but hurt someone around the machine, or risk a roll-over. That is why most operators don't allow large deck angles.
A cure is to ask the ship to turn into the wind, so the roll angle is not aligned with the crosswind, but pilots are reluctant to impose on the ship operations (unless they are in the Navy, where the air boss helps the ship captain decide).
OK, that above is the kind of answer I expect from LU, something based on a blend of experience and common sense, not mumbo-jumbo. Should any pilots with experience want to disagree with what I said, I would (and have) listened, and I always admit when I am mistaken. I want to learn from this forum, too, and I always do. That is what I expect from the posters that I respect - good honest intellectual discussion.
The difficulty I have with Lu is mine, and I will wrestle with it. His posts are so misleading, and he is so unwilling to either think or understand that I am completely exasperated!
Imagine the ship is tossing like those movies Lu evokes, with vast pitch and roll motions like a bucking bronko. OK now forget that, it is wrong. Any pilot who lands on that deck without haul-down is nuts, and will be unemployed shortly.
The typical deck landing in commercial service never involves deck angles beyond about 8 degrees (commercial guys, please post the operating limits for deck landings from your ops manuals.) The typical period of motion for a large rig boat is several seconds, usually about 10 seconds or so. For a rig, it is often 20 seconds or so. This makes the deck motion actually very slow in roll or pitch rate, and the contribution of the dynamic motions very small.
The rotor will not wave around or depart from its commanded path due to these motions, no matter what Lu thinks. Even if underslung, the rotor is not free to wave around independant of the aircraft without a swashplate input, unless the angular motions are very fast.
Having investigated the roll-over of several aircraft, I can assure you the results are disappointingly static in nature, a combination of wind velocity (which will move the rotor) deck slope and where the pilot left the stick. For a broad sided helicopter in a cross wind of 35 knots with gusts that are higher, and with a deck roll that compounds the aircraft lean, all it takes is an unattentive pilot to allow a roll-over. The problem with Lu's assertion is that he believes the rotor does its own thing, and that wanders around. He has it backwards! As the aircraft rolls, the rotor follows the aircraft. With a cross wind, the rotor produces strong roll moments that add to the roll tendency that the deck is producing. A pilot would try to put roll cyclic in to keep the rotor disk parallel to the horizon, at the peril of those on the deck under the disk. The pilot is stuck - try to keep the aircraft glued to the deck, but hurt someone around the machine, or risk a roll-over. That is why most operators don't allow large deck angles.
A cure is to ask the ship to turn into the wind, so the roll angle is not aligned with the crosswind, but pilots are reluctant to impose on the ship operations (unless they are in the Navy, where the air boss helps the ship captain decide).
OK, that above is the kind of answer I expect from LU, something based on a blend of experience and common sense, not mumbo-jumbo. Should any pilots with experience want to disagree with what I said, I would (and have) listened, and I always admit when I am mistaken. I want to learn from this forum, too, and I always do. That is what I expect from the posters that I respect - good honest intellectual discussion.
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Nick, your argument seems to be of the order, "I'm a test pilot and have lots of experience so listen to what I say." If your argument is cogent, it doesn't matter what your resume reads.
Please tell us how the underslung rotor keeps it's rigidity in space with the fuselage rolling and there is no change in orientation of the swashplate with respect to the rotor disk.
Matthew.
(experienced helicopter pilot)
Edited to indicate I am a pilot with experience.
[ 16 November 2001: Message edited by: heedm ]
Please tell us how the underslung rotor keeps it's rigidity in space with the fuselage rolling and there is no change in orientation of the swashplate with respect to the rotor disk.
Matthew.
(experienced helicopter pilot)
Edited to indicate I am a pilot with experience.
[ 16 November 2001: Message edited by: heedm ]
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Currently operating BK117, marine pilot transfers in OZ
We have a limit of 3 degrees at night and 5 degrees during the day. Concidering all the information at hand - wind, swell etc, we can stretch the day limit a bit, but we do not budge on the 3 degrees at night - not so much because of aerodynamics, its more to do with visual cues on approach etc. We turn the ships onto a different course to reduce the rolling if needs be.
We have a limit of 3 degrees at night and 5 degrees during the day. Concidering all the information at hand - wind, swell etc, we can stretch the day limit a bit, but we do not budge on the 3 degrees at night - not so much because of aerodynamics, its more to do with visual cues on approach etc. We turn the ships onto a different course to reduce the rolling if needs be.