Ditching a helicopter: (incl pictures)
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Thanks rotortorque for the info. At 3 degrees night and 5 day, little rollover potential is there.
Now heedm, please compare 5 degrees to the picture Lu made of rolling tossing ships in a storm, and understand one reason why I dismiss his argument.
Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".
The real culpret in this roll-over scenario is exactly BACKWARDS from Lu's assertion. The rotor is stuck with the fuselage, so in a rolling motion with a strong wind, the rotor is forced into an angle relative to the wind that creates strong roll-over forces. This can be considered as if the roll of the ship in a 35 knot cross wind causes the rotor to make a lateral quickstop maneuver because the rotor MUST follow the fuselage. The rotor's strong stability relative to the rolling motion is the problem, and Lu is yet again exactly ass-backward!
It does not matter if the rotor is underslung or not, nor does it matter if I am a test pilot or not, these are facts, not opinions. The problem we all have is the democratic principle, where if enough idiots vote that there is a green cheese moon, it must be true. The fact that Lu can email, and that he can spout theories, does not make him correct, nor does it make his discussion worthy. What is most difficult for me to face is that I could post 100 accurate descriptions of the physics and aerodynamics of the situation, and he will squirm out into another corner, squirt some ink of incredible colors, and be off and running!
In short, to avoid roll-over on a tossing deck, stay off wildly tossing ones, keep the rotor level with the horizon (at the peril of the people around the aircraft) and try to avoid situations where the cross wind and the roll are in the same direction.
Also, try not to believe that mysterious rotor dynamic misbehavior is the culpret, because you will be a worse pilot - an ignorant one - and more likely to have an accident. Also, believe nothing someone tells you just because they are a test pilot, or a consultant engineer!
Now heedm, please compare 5 degrees to the picture Lu made of rolling tossing ships in a storm, and understand one reason why I dismiss his argument.
Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".
The real culpret in this roll-over scenario is exactly BACKWARDS from Lu's assertion. The rotor is stuck with the fuselage, so in a rolling motion with a strong wind, the rotor is forced into an angle relative to the wind that creates strong roll-over forces. This can be considered as if the roll of the ship in a 35 knot cross wind causes the rotor to make a lateral quickstop maneuver because the rotor MUST follow the fuselage. The rotor's strong stability relative to the rolling motion is the problem, and Lu is yet again exactly ass-backward!
It does not matter if the rotor is underslung or not, nor does it matter if I am a test pilot or not, these are facts, not opinions. The problem we all have is the democratic principle, where if enough idiots vote that there is a green cheese moon, it must be true. The fact that Lu can email, and that he can spout theories, does not make him correct, nor does it make his discussion worthy. What is most difficult for me to face is that I could post 100 accurate descriptions of the physics and aerodynamics of the situation, and he will squirm out into another corner, squirt some ink of incredible colors, and be off and running!
In short, to avoid roll-over on a tossing deck, stay off wildly tossing ones, keep the rotor level with the horizon (at the peril of the people around the aircraft) and try to avoid situations where the cross wind and the roll are in the same direction.
Also, try not to believe that mysterious rotor dynamic misbehavior is the culpret, because you will be a worse pilot - an ignorant one - and more likely to have an accident. Also, believe nothing someone tells you just because they are a test pilot, or a consultant engineer!
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To: Nick Lappos
“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)”.
On a Coast Guard icebreaker (at least in my experience) the Captain will not accommodate a pilot during the landing of a helicopter when in the icebreaking mode. While in this mode the ship can be rolling +/- 18-degrees (maximum) and at the same time, pitching up and down several degrees. Because of the inherent dangers involved in landing along the centerline of the flight deck (approaching over the stern) the pilots would land athwartship trying very hard not to contact cable stays and a large boom. And they would be flying sideways and forward in order to maintain their position in relation to the moving flight deck. The danger in landing in either direction was that there were no wheel brakes on the helicopter and the parking brakes, which were set upon touchdown, were ineffective. Because of this the ground crew had to attach tie downs and chocks to restrict any further movement. If the helicopter had to be restarted in this position under the stated conditions there would be a severe instability due to the helicopter moving on its’ oleos and the imbalance of the rotor system during start up. It was the same when the helicopter was aligned with the ship centerline but there was less chance of losing the helicopter over the side. Now these are my experience and they differ from the rules and regulations that exist at this time. Most likely they occurred prior to the birth of most of the pilots on this forum.
Another point to consider, is that if during the landing sequence, the icebreaker hit large/thick pack ice and became stalled in its’ forward movement the pilot would crash on the other helicopter on the deck. Or in the case of our ship, also hit a very large fuel tank that we were transporting to the Alert weather station. Perchance we were the pathfinders that would lead to changing the rules to those that presently exist.
“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)”.
On a Coast Guard icebreaker (at least in my experience) the Captain will not accommodate a pilot during the landing of a helicopter when in the icebreaking mode. While in this mode the ship can be rolling +/- 18-degrees (maximum) and at the same time, pitching up and down several degrees. Because of the inherent dangers involved in landing along the centerline of the flight deck (approaching over the stern) the pilots would land athwartship trying very hard not to contact cable stays and a large boom. And they would be flying sideways and forward in order to maintain their position in relation to the moving flight deck. The danger in landing in either direction was that there were no wheel brakes on the helicopter and the parking brakes, which were set upon touchdown, were ineffective. Because of this the ground crew had to attach tie downs and chocks to restrict any further movement. If the helicopter had to be restarted in this position under the stated conditions there would be a severe instability due to the helicopter moving on its’ oleos and the imbalance of the rotor system during start up. It was the same when the helicopter was aligned with the ship centerline but there was less chance of losing the helicopter over the side. Now these are my experience and they differ from the rules and regulations that exist at this time. Most likely they occurred prior to the birth of most of the pilots on this forum.
Another point to consider, is that if during the landing sequence, the icebreaker hit large/thick pack ice and became stalled in its’ forward movement the pilot would crash on the other helicopter on the deck. Or in the case of our ship, also hit a very large fuel tank that we were transporting to the Alert weather station. Perchance we were the pathfinders that would lead to changing the rules to those that presently exist.
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Nick said,
Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".
Response,
So when I walk out to the hangar and stand on a step ladder and grab the end of the 206 blade and move it up and down from bump stop to bump stop, I see no change in pitch angle. Please re read my previous posting on this thread and I invite someone to tell me why I'm wrong.
Jiff
Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".
Response,
So when I walk out to the hangar and stand on a step ladder and grab the end of the 206 blade and move it up and down from bump stop to bump stop, I see no change in pitch angle. Please re read my previous posting on this thread and I invite someone to tell me why I'm wrong.
Jiff
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Jiff:
Using your example there will be minimal pitch change at low collective because the pitch horn/pitch link connect point is on or near the teeter axis. If the collective is raised and you teeter the blades there will be some pitch change because the pitch horn/pitch link connection are no longer coincident with each other. This is the same as pitch coupling.
Using your example there will be minimal pitch change at low collective because the pitch horn/pitch link connect point is on or near the teeter axis. If the collective is raised and you teeter the blades there will be some pitch change because the pitch horn/pitch link connection are no longer coincident with each other. This is the same as pitch coupling.
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A point to ponder:
Let’s talk about everybody’s Favorite subject GYROSCOPIC PRECESSION. If you have a gyroscope with three degrees of freedom and you move or rotate the entire gyroscope the rotor will maintain its’ position in relation to the local horizon. If you take one of the degrees of freedom away and rotate the assembly the rotor will nutate or precess 90-degrees after the input of the changing force. The first type of gyro is used in an inertial navigation system or autopilot. The second type is used in a directional gyro. Now, let’s apply the second type of gyro to the rotor system of a helicopter. The rotating disc is the same as the spinning rotor on the gyro. The rotor disc can be commanded through control input to change its’ position relative to the local horizon. If the rotor moves with the helicopter due to the application of a local force the disc, which is maintained in position due to gyroscopic, rigidity will respond to the external force because it also exhibits precession just like the rotor on the gyro. There does not have to be relative movement between the fixed pitch link and the pitch horn to make the rotor move in this manner. As I explained to Jiff above, when the collective is at the low pitch position the pitch horn/pitch link are coincident with the flapping axis and there is no coupling. However, according to the laws of physics the rotor should nutate or precesse 90-degrees after the input of the external force. This may or may not apply to single rotor helicopters.
Propellers on fixed wing aircraft exhibit this gyroscopic turning moment but the movement is in the outer areas of the blade and the major resistant force is the crankcase bearings. On the V-22 when it is in the aircraft mode and the attitude changes the prop rotors respond by precessing as they are mounted in rubber. Any precessional movement of the prop rotor is corrected by the servo system.
Now if Nick sees it any differently let him explain it without mentioning my mental capacity or my age.
[ 16 November 2001: Message edited by: Lu Zuckerman ]
[ 16 November 2001: Message edited by: Lu Zuckerman ]
Let’s talk about everybody’s Favorite subject GYROSCOPIC PRECESSION. If you have a gyroscope with three degrees of freedom and you move or rotate the entire gyroscope the rotor will maintain its’ position in relation to the local horizon. If you take one of the degrees of freedom away and rotate the assembly the rotor will nutate or precess 90-degrees after the input of the changing force. The first type of gyro is used in an inertial navigation system or autopilot. The second type is used in a directional gyro. Now, let’s apply the second type of gyro to the rotor system of a helicopter. The rotating disc is the same as the spinning rotor on the gyro. The rotor disc can be commanded through control input to change its’ position relative to the local horizon. If the rotor moves with the helicopter due to the application of a local force the disc, which is maintained in position due to gyroscopic, rigidity will respond to the external force because it also exhibits precession just like the rotor on the gyro. There does not have to be relative movement between the fixed pitch link and the pitch horn to make the rotor move in this manner. As I explained to Jiff above, when the collective is at the low pitch position the pitch horn/pitch link are coincident with the flapping axis and there is no coupling. However, according to the laws of physics the rotor should nutate or precesse 90-degrees after the input of the external force. This may or may not apply to single rotor helicopters.
Propellers on fixed wing aircraft exhibit this gyroscopic turning moment but the movement is in the outer areas of the blade and the major resistant force is the crankcase bearings. On the V-22 when it is in the aircraft mode and the attitude changes the prop rotors respond by precessing as they are mounted in rubber. Any precessional movement of the prop rotor is corrected by the servo system.
Now if Nick sees it any differently let him explain it without mentioning my mental capacity or my age.
[ 16 November 2001: Message edited by: Lu Zuckerman ]
[ 16 November 2001: Message edited by: Lu Zuckerman ]
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Nick, I doubt if this has caused any confusion, but I've always been thinking of a helicopter floating, not one on a ship. I guess it's because the post is titled, "Ditching". It shouldn't matter, though, because all we require is something external to the helicopter that moves the fuselage.
As far as who I believe, I trust in the experience of people like yourself, but I still like to see reasons rather than just trusting expertise.
In my original post on this thread I said, "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."
With all the knowledge and experience in this group, I'm surprised that none of these "experienced helicopter pilots" noticed that the blade pitch actually decreases at 12 o'clock. Thus, the rotor disk flies itself to follow the fuselage's motions.
I didn't put that error in there to prove anything, it was an honest mistake. It turns out to be a good example of why not to blindly trust experience, but rather to demand rational explanation.
I was wrong. I'm sorry if I misled anyone.
Matthew.
As far as who I believe, I trust in the experience of people like yourself, but I still like to see reasons rather than just trusting expertise.
In my original post on this thread I said, "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."
With all the knowledge and experience in this group, I'm surprised that none of these "experienced helicopter pilots" noticed that the blade pitch actually decreases at 12 o'clock. Thus, the rotor disk flies itself to follow the fuselage's motions.
I didn't put that error in there to prove anything, it was an honest mistake. It turns out to be a good example of why not to blindly trust experience, but rather to demand rational explanation.
I was wrong. I'm sorry if I misled anyone.
Matthew.
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So, if the jet ranger rolled, the disk would fly its self back to its original position relative to the fuselage but there would be no precessive forces applied to the fuselage, assuming the collective is at its minimum i.e. zero pitch.
This means that a helicopter with an underslung system would have no added stability or instability effect from the rotor system while it was bobbing about on the sea?
Back to the Lynx on floats, because of the rigid head the fuselage would experience precessive forces as it rolled or pitched?
A quick thought,
Here we are discussing helicopter aerodynamics and forces, just stop and think for a moment what the pioneer's of this industry went through!
Jiff
This means that a helicopter with an underslung system would have no added stability or instability effect from the rotor system while it was bobbing about on the sea?
Back to the Lynx on floats, because of the rigid head the fuselage would experience precessive forces as it rolled or pitched?
A quick thought,
Here we are discussing helicopter aerodynamics and forces, just stop and think for a moment what the pioneer's of this industry went through!
Jiff
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I venture in with trepidation,
heedm: If the helo rotor is at operational RPM and is then rolled to the left by a wave, then I cannot see what would change the blade pitch. The pilot is presumably holding the rotor controls in a neutral position
There will be a tendency for precession to occur and may tilt the airframe in the water accordingly. The size and frequency of the waves in this scenario will affect the outcome.
If the wave came from the fore or aft direction then the airframe may tend to tilt left or right, as well as in the direction of the wave tilt. That would be destabilizing.
In your example, the top of the mast and hub-trunnion are going to be putting the main input force into the rotor. The swashplate will follow but not change its angle relative to the mast.
That would mean there is no aerodynamic input or result. In fact the swashplate will be working to stop the blade pitch changing.
The only stabilizing effect (that I can see) is the gyroscopic rigidity of the rotor (its resistance to angular change) and that may only help if the helo experienced one wave.
If the rotor is slowing to a stop (as would be the case after a successful autorotation)without a rotor brake in a turbulent sea, then the rotor will start flailing about as it loses aerodynamic control and then move independently of the fuselage.
heedm: If the helo rotor is at operational RPM and is then rolled to the left by a wave, then I cannot see what would change the blade pitch. The pilot is presumably holding the rotor controls in a neutral position
There will be a tendency for precession to occur and may tilt the airframe in the water accordingly. The size and frequency of the waves in this scenario will affect the outcome.
If the wave came from the fore or aft direction then the airframe may tend to tilt left or right, as well as in the direction of the wave tilt. That would be destabilizing.
In your example, the top of the mast and hub-trunnion are going to be putting the main input force into the rotor. The swashplate will follow but not change its angle relative to the mast.
That would mean there is no aerodynamic input or result. In fact the swashplate will be working to stop the blade pitch changing.
The only stabilizing effect (that I can see) is the gyroscopic rigidity of the rotor (its resistance to angular change) and that may only help if the helo experienced one wave.
If the rotor is slowing to a stop (as would be the case after a successful autorotation)without a rotor brake in a turbulent sea, then the rotor will start flailing about as it loses aerodynamic control and then move independently of the fuselage.
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heedm,
Your last post hit the nail on the head. I think we see it the same way now.
Sproket,
Try not to think about gyroscopic precession, its effects are small at the roll and pitch rates we are talking about here. The rotor will automatically fly itself back to the position commanded by the flight controls, even if the aircraft and mast are rolling around due to wave forces (which are the same wether the aircraft is floating or on a ship). The reason is that the swashplate will hold its position relative to the mast, and as the mast is rolled and pitched, it will send the proper control inputs via the pitch links to the rotorhead. In reality, there is no precessional force, and no unusual rotor behavior due to the rolling (as long as the rates are in the few degrees per second range).
The Lu bugaboo about unstable rotor behavior that he pushed in his earlier posts is backwards, as the rotor is actually too stable relative to the airframe, so it develops aerodynamic forces due to the wind that accompanies the waves. It is the combination of the wind and the wave slope that eventually could roll the aircraft, not funny gyro or unstable rotor forces.
Lu, I have NEVER used your age against you, nor will I. I have strong respect for tolerance regarding age, race and sex, and I resent your slur in that vein. Your posts are simply inane, not due to age, due to your inability to realize what you do not know, and your inability to learn. These are not age issues, I think. I have lots of respect for your experience, and your breadth of knowledge. It is you that destroys your own credibility when you venture so far from what you know, and when you keep pressing the same old bull into every post.
I absolutely refuse to answer your posts, I will be glad to discuss issues with any other ppruner.
Your last post hit the nail on the head. I think we see it the same way now.
Sproket,
Try not to think about gyroscopic precession, its effects are small at the roll and pitch rates we are talking about here. The rotor will automatically fly itself back to the position commanded by the flight controls, even if the aircraft and mast are rolling around due to wave forces (which are the same wether the aircraft is floating or on a ship). The reason is that the swashplate will hold its position relative to the mast, and as the mast is rolled and pitched, it will send the proper control inputs via the pitch links to the rotorhead. In reality, there is no precessional force, and no unusual rotor behavior due to the rolling (as long as the rates are in the few degrees per second range).
The Lu bugaboo about unstable rotor behavior that he pushed in his earlier posts is backwards, as the rotor is actually too stable relative to the airframe, so it develops aerodynamic forces due to the wind that accompanies the waves. It is the combination of the wind and the wave slope that eventually could roll the aircraft, not funny gyro or unstable rotor forces.
Lu, I have NEVER used your age against you, nor will I. I have strong respect for tolerance regarding age, race and sex, and I resent your slur in that vein. Your posts are simply inane, not due to age, due to your inability to realize what you do not know, and your inability to learn. These are not age issues, I think. I have lots of respect for your experience, and your breadth of knowledge. It is you that destroys your own credibility when you venture so far from what you know, and when you keep pressing the same old bull into every post.
I absolutely refuse to answer your posts, I will be glad to discuss issues with any other ppruner.
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To: Nick Lappos
OK, but before you withdraw yourself from my "inane" comments please answer my post on Weather and other nasty stuff.
OK, but before you withdraw yourself from my "inane" comments please answer my post on Weather and other nasty stuff.
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For gyroscopic precession to occur, a moment has to be applied to the rotor disk. This does not appreciably happen by moving the fuselage or mast with a teetering rotor, or with other types.
A rigid rotor would have a moment applied by the fuselage rolling and/or pitching, but the amount of rotation added to the rotor disk is so small compared to it's existing roll that the effect would be difficult to observe.
Matthew.
A rigid rotor would have a moment applied by the fuselage rolling and/or pitching, but the amount of rotation added to the rotor disk is so small compared to it's existing roll that the effect would be difficult to observe.
Matthew.
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HeliEng,
I hope you are still sane! I am new to the gang so for the moment I still "enjoy" the fight between the two "masters".
Here some info on floats as far R22, R44, Bell-47īs.
I have to look it up in the manual for the R22, but the R44 float-equipment(permanent+pop outīs) are to be used for emergency use only, although the floats are very tough (even the pop outs, which look like the permanent ones but are thinner). That of course includes training. However if you have to land on water because there is no where else to land on permanent basis, the Robinson is not for you. The R22 is okay to land in water, even close to max gross w. But it is quite interesting - donīt try this in heavy seas (preferably in fresh water only!!).
For tuna-checkouts I take students for full touch downs in the R44, however with 2persons on board only and half fuel. The R44 sits awfully deep in the water (which is good when the engine went, bad for training)
As they are to be used for emergency only, this is okay as it gives the helicopter lots of stability once in the water, although with a full load mostlikely you will have water in the cabin. However you probably will float for ever without rolling.
Not so good for training as the R44 airfilter sits very low and even when it is sealed with tape, you better watch out that you do not get any water in there(bad news for the engine!!).
R22 will roll sooner or later except in calm sea. However most pilots make successful emergency-autorotations.Just for the record:
As far as I know the reason on ALL of this e-autos was lousy maintenance......
Other than that, in a Robinson you really do not need Floats, they are the most reliable machines I know (I have about 6000 hrs total, of that about 4000 in R., in all kinds of "interesting" terrain...),they just slow you down (except the pop-outs).
According to the manual of the R44 you can take off again, even on the pop outs, repeatetly.
Last: most helicopters (tuna ops) that go in the sea undamaged, get light to heavy damage on recovery to the tunaboat, due to the movements of the boat and the available recovery gear.
Probably this does not answer all your questions, but it gives you some idea about floats on light helicopters at sea.
To Lu Z.:
What about the Hughes (MD)-500 models, are they fully articulated? They had loads of them in the tuna spotting business on floats, as far as I know no trouble with ground resonance (Although they are out of business now as they can not match the R44 with the easy of maintenance and economy of operation and endurance...). Contrary the few Schweizer 300īs that where tried out where terrible (3 blades...).
Fly safe,
3top
null
I hope you are still sane! I am new to the gang so for the moment I still "enjoy" the fight between the two "masters".
Here some info on floats as far R22, R44, Bell-47īs.
I have to look it up in the manual for the R22, but the R44 float-equipment(permanent+pop outīs) are to be used for emergency use only, although the floats are very tough (even the pop outs, which look like the permanent ones but are thinner). That of course includes training. However if you have to land on water because there is no where else to land on permanent basis, the Robinson is not for you. The R22 is okay to land in water, even close to max gross w. But it is quite interesting - donīt try this in heavy seas (preferably in fresh water only!!).
For tuna-checkouts I take students for full touch downs in the R44, however with 2persons on board only and half fuel. The R44 sits awfully deep in the water (which is good when the engine went, bad for training)
As they are to be used for emergency only, this is okay as it gives the helicopter lots of stability once in the water, although with a full load mostlikely you will have water in the cabin. However you probably will float for ever without rolling.
Not so good for training as the R44 airfilter sits very low and even when it is sealed with tape, you better watch out that you do not get any water in there(bad news for the engine!!).
R22 will roll sooner or later except in calm sea. However most pilots make successful emergency-autorotations.Just for the record:
As far as I know the reason on ALL of this e-autos was lousy maintenance......
Other than that, in a Robinson you really do not need Floats, they are the most reliable machines I know (I have about 6000 hrs total, of that about 4000 in R., in all kinds of "interesting" terrain...),they just slow you down (except the pop-outs).
According to the manual of the R44 you can take off again, even on the pop outs, repeatetly.
Last: most helicopters (tuna ops) that go in the sea undamaged, get light to heavy damage on recovery to the tunaboat, due to the movements of the boat and the available recovery gear.
Probably this does not answer all your questions, but it gives you some idea about floats on light helicopters at sea.
To Lu Z.:
What about the Hughes (MD)-500 models, are they fully articulated? They had loads of them in the tuna spotting business on floats, as far as I know no trouble with ground resonance (Although they are out of business now as they can not match the R44 with the easy of maintenance and economy of operation and endurance...). Contrary the few Schweizer 300īs that where tried out where terrible (3 blades...).
Fly safe,
3top
null
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3 top,
You hit on the principal difference between floats for everyday use, and emergency floats - the amount of flotation. For Sikorsky, we have a rule that the floats must allow safe water entry, they must keep the cabin fully dry, and they must allow full egress for all occupants. The aircraft can settle down where no self respecting pilot would lift it back off again, for instance.
You may find that the R-44 floats will allow takeoff at reduced weight and CG, and would be a problem for lift-off at full weight, mostly because of the amount of bouyancy.
[ 18 November 2001: Message edited by: Nick Lappos ]
You hit on the principal difference between floats for everyday use, and emergency floats - the amount of flotation. For Sikorsky, we have a rule that the floats must allow safe water entry, they must keep the cabin fully dry, and they must allow full egress for all occupants. The aircraft can settle down where no self respecting pilot would lift it back off again, for instance.
You may find that the R-44 floats will allow takeoff at reduced weight and CG, and would be a problem for lift-off at full weight, mostly because of the amount of bouyancy.
[ 18 November 2001: Message edited by: Nick Lappos ]
Any of you learned fellows know at which RPM gyroscopic procession starts to become an issue? I'm thinking about blade sailing on startup/shutdown and where the moment applied by the wind will have its affect.
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Just about sane!
The topic has wandered somewhat, and many of the issues discussed have gone totally over my head
I was speaking to a colleague, who recommended that I add an addition to my initial post. What purpose do the floats on an S-61 serve? The aircraft is designed to amphibious anyhow, so why have the floats in addition?
(Try not to argue over this one guys!)
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The topic has wandered somewhat, and many of the issues discussed have gone totally over my head
I was speaking to a colleague, who recommended that I add an addition to my initial post. What purpose do the floats on an S-61 serve? The aircraft is designed to amphibious anyhow, so why have the floats in addition?
(Try not to argue over this one guys!)
"Answers on a postcard to......."
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You're likely to start an argument just by mentioning gyroscopic precession. For the record, GP is an effect observed on a rotating body whose geometry has constraints. Some rotors fit in those constraints, others don't. The phenomenon that causes the GP effect is the conservation of angular momentum. That applies to anything that spins, no matter at what speed it spins.
When you apply a force to a blade, it causes the blade to rotate about it's flapping axis. If the blade is already rotating about a vertical axis, then the resultant spinning is a sum of the two.
When the rotors are up to speed and only relatively small forces are imparted to the blade, the result is predictable: gyroscopic precession (or something close).
When the rotors are not up to speed and you have something that imparts a relatively large force on the blade, all the spinning motions are conserved but it may not appear to be like gyroscopic precession.
Consider the rotor just started moving and a gust of wind hits the helicopter causing the forward moving blade at 3 o'clock to rise. The immediate result of the two spins is that the blade will want to spin in a disk that is almost vertical but with the top of the disk leaning slightly forward. The forward leaning is due to the very slow rotor speed. If the blade was allowed to spin 360 degrees in this disk, the maximum displacement would be at the 12 o'clock position, where the tilted disk is highest. This is the result that you expect from the GP explanation. With the rotor stopped, the immediate result of the gust would be for it to spin in a vertical disk.
Notice I mentioned only the sum of the two spins. In helicopters with elastomeric bearings, control geometries that respond to blade position, etc. other forces are imparted on the blades, which may cause yet another spin to occur, which can change the "gamma" to something other than 90 degrees. This doesn't contradict the angular momentum argument, but it gives much more to talk about. It does contradict the gyroscopic precession argument, but only because the rotor doesn't fit within the constraints of what defines a gyroscope anymore.
If you accept gyroscopic precession as a reasonable explanation as to why rotors behave the way they do, then gyroscopic precession occurs at all rotor speeds. Since the blades are normally mechanically restricted on the flapping axis, the immediate result of blade movement doesn't appear to be due to gyroscopic precession.
If you don't accept GP as a reasonable explanation, it doesn't matter. The blade behaves the same way no matter what words you apply to the physics. If you talk about rotational dynamics instead, you would be much more accurate, but very few people would understand you.
For those that want a straight answer.
The faster the rotor is moving, you'll see the maximum displacement of the blade further forward in the rotor's direction of spin.
Matthew.
When you apply a force to a blade, it causes the blade to rotate about it's flapping axis. If the blade is already rotating about a vertical axis, then the resultant spinning is a sum of the two.
When the rotors are up to speed and only relatively small forces are imparted to the blade, the result is predictable: gyroscopic precession (or something close).
When the rotors are not up to speed and you have something that imparts a relatively large force on the blade, all the spinning motions are conserved but it may not appear to be like gyroscopic precession.
Consider the rotor just started moving and a gust of wind hits the helicopter causing the forward moving blade at 3 o'clock to rise. The immediate result of the two spins is that the blade will want to spin in a disk that is almost vertical but with the top of the disk leaning slightly forward. The forward leaning is due to the very slow rotor speed. If the blade was allowed to spin 360 degrees in this disk, the maximum displacement would be at the 12 o'clock position, where the tilted disk is highest. This is the result that you expect from the GP explanation. With the rotor stopped, the immediate result of the gust would be for it to spin in a vertical disk.
Notice I mentioned only the sum of the two spins. In helicopters with elastomeric bearings, control geometries that respond to blade position, etc. other forces are imparted on the blades, which may cause yet another spin to occur, which can change the "gamma" to something other than 90 degrees. This doesn't contradict the angular momentum argument, but it gives much more to talk about. It does contradict the gyroscopic precession argument, but only because the rotor doesn't fit within the constraints of what defines a gyroscope anymore.
If you accept gyroscopic precession as a reasonable explanation as to why rotors behave the way they do, then gyroscopic precession occurs at all rotor speeds. Since the blades are normally mechanically restricted on the flapping axis, the immediate result of blade movement doesn't appear to be due to gyroscopic precession.
If you don't accept GP as a reasonable explanation, it doesn't matter. The blade behaves the same way no matter what words you apply to the physics. If you talk about rotational dynamics instead, you would be much more accurate, but very few people would understand you.
For those that want a straight answer.
The faster the rotor is moving, you'll see the maximum displacement of the blade further forward in the rotor's direction of spin.
Matthew.
The pop-out floats on the S61 were installed to improve the lateral stability of the aircraft in the event of a ditching. As you note, the S61 is designed and approved for amphibious operations.
Due to the high C of G on the helicopter they are prone to capsizing in anything above a moderate sea state (Rotor shut-down in 3 foot seas has been demonstrated). These floats were initially designed for use with the small sponsons installed on the SH-3 (military S61) series utilised by the US Navy.
S-61 floats were mandated by the CAA in the late 70's/early 80's and were retrofitted to all commercial S61's along with some other very practical modifications learnt from previous accidents/incidents.
If you look here you will see a very interesting image of a ditched S61. Unfortunately, in the picture you cannot see that the top of the cockpit is missing, following a blade strike on landing that significantly altered the cockpit arrangement!
The aircraft was flown off the rig and ditched in the water, where, unable to shut it down (no throttles, power, etc.) it was abandoned and cruised around the rig uncommanded, for some quite considerable time before running out of fuel. Fortunately it never contacted anything else out there!
Hence you have the very unusual image of an S61 running on the sea, in what would have to be described as a pretty reasonable swell.
After it ran out of fuel, it sank!
Due to the high C of G on the helicopter they are prone to capsizing in anything above a moderate sea state (Rotor shut-down in 3 foot seas has been demonstrated). These floats were initially designed for use with the small sponsons installed on the SH-3 (military S61) series utilised by the US Navy.
S-61 floats were mandated by the CAA in the late 70's/early 80's and were retrofitted to all commercial S61's along with some other very practical modifications learnt from previous accidents/incidents.
If you look here you will see a very interesting image of a ditched S61. Unfortunately, in the picture you cannot see that the top of the cockpit is missing, following a blade strike on landing that significantly altered the cockpit arrangement!
The aircraft was flown off the rig and ditched in the water, where, unable to shut it down (no throttles, power, etc.) it was abandoned and cruised around the rig uncommanded, for some quite considerable time before running out of fuel. Fortunately it never contacted anything else out there!
Hence you have the very unusual image of an S61 running on the sea, in what would have to be described as a pretty reasonable swell.
After it ran out of fuel, it sank!
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To: Bladestrike
“Any of you learned fellows know at which RPM gyroscopic procession starts to become an issue? I'm thinking about blade sailing on startup/shutdown and where the moment applied by the wind will have its affect”.
Most helicopters, other than the Robinson, that have the capability to flap or for the blade to move in relation to the rotorhead have some type of centrifugally operated locking device that will not unlock until the blade has achieved sufficient rotational velocity and centrifugal forces to sustain the input of cyclic pitch with the resultant movement of the blade. Sikorsky helicopters at least those that I am familiar with have similarly operated locks to restrict flapping and drooping. Some Hughes helicopters do not have locks that restrict flapping but they do have a device that restricts drooping movement. This device supports the static weight of the rotor blades and distributes that weight of the blades evenly. If one blade flaps and stalls out or aerodynamically, is forced to droop, the kinetic energy is translated to the ring support and is absorbed by the resistance of the other three or four blades to move upward. This device is not normally in use once the blades cone up. If in the process of maneuvering one blade hits this stop it will simply shift the ring position in relation to the mast centerline.
I would suspect that those helicopters that are equipped with the centrifugally operated devices are capable of cyclic input and be susceptible to gyroscopic precession once the devices are activated. It is not to say that at speeds lower than the speed necessary to release the locking devices the gyroscopic precession is not present however, the blades are not capable to sustain lift and they could stall out contacting personnel or the fuselage.
On our B-47 (HTL-1) we had no such devices and unless the blades were restrained they would be free to move all over the place both from wind passing over the flight deck or, because of the ship pitching and rolling. This led to a one-time experience. The ship was rolling in heavy seas and the blades were moving all over the place. Prior to our going aboard the icebreaker we removed the springs from the centrifugal clutch. This meant that just as soon as the engine started the blades were moving at engine speed (via the transmission). This was the first time we started the helicopter since coming aboard. The blades were dipped down relative to the local horizon and when the engine started the blades immediately aligned with the local horizon. The forces were so great that the helicopter almost flipped over. Following that experience I would hold the blade tip in the neutral flap position and when the engine started I would pull my hand back. I also learned something from that experience and that was to move my hand back a bit faster as I got hit with the following blade. This model of Bell had restraining cables (Sprague Cables) in the rotorhead which limited the amount of teeter both in the non driven condition and the flight condition.
Now I will take cover.
[ 18 November 2001: Message edited by: Lu Zuckerman ]
“Any of you learned fellows know at which RPM gyroscopic procession starts to become an issue? I'm thinking about blade sailing on startup/shutdown and where the moment applied by the wind will have its affect”.
Most helicopters, other than the Robinson, that have the capability to flap or for the blade to move in relation to the rotorhead have some type of centrifugally operated locking device that will not unlock until the blade has achieved sufficient rotational velocity and centrifugal forces to sustain the input of cyclic pitch with the resultant movement of the blade. Sikorsky helicopters at least those that I am familiar with have similarly operated locks to restrict flapping and drooping. Some Hughes helicopters do not have locks that restrict flapping but they do have a device that restricts drooping movement. This device supports the static weight of the rotor blades and distributes that weight of the blades evenly. If one blade flaps and stalls out or aerodynamically, is forced to droop, the kinetic energy is translated to the ring support and is absorbed by the resistance of the other three or four blades to move upward. This device is not normally in use once the blades cone up. If in the process of maneuvering one blade hits this stop it will simply shift the ring position in relation to the mast centerline.
I would suspect that those helicopters that are equipped with the centrifugally operated devices are capable of cyclic input and be susceptible to gyroscopic precession once the devices are activated. It is not to say that at speeds lower than the speed necessary to release the locking devices the gyroscopic precession is not present however, the blades are not capable to sustain lift and they could stall out contacting personnel or the fuselage.
On our B-47 (HTL-1) we had no such devices and unless the blades were restrained they would be free to move all over the place both from wind passing over the flight deck or, because of the ship pitching and rolling. This led to a one-time experience. The ship was rolling in heavy seas and the blades were moving all over the place. Prior to our going aboard the icebreaker we removed the springs from the centrifugal clutch. This meant that just as soon as the engine started the blades were moving at engine speed (via the transmission). This was the first time we started the helicopter since coming aboard. The blades were dipped down relative to the local horizon and when the engine started the blades immediately aligned with the local horizon. The forces were so great that the helicopter almost flipped over. Following that experience I would hold the blade tip in the neutral flap position and when the engine started I would pull my hand back. I also learned something from that experience and that was to move my hand back a bit faster as I got hit with the following blade. This model of Bell had restraining cables (Sprague Cables) in the rotorhead which limited the amount of teeter both in the non driven condition and the flight condition.
Now I will take cover.
[ 18 November 2001: Message edited by: Lu Zuckerman ]
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To The Cat:
Lu, how did you get the Bell 47 started in the first place, when the clutch springs where out? I have been flying Bell 47īs on tuna boats and when it happened that the clutch pads would get sticky overnight I had trouble to start at all as the starter would have a hard time to pull all that mass through up to a speed where the engine would fire. I donīt say it is not possible, but I wonder you did that on purpose. I burned more than one starter like that.
3top
Lu, how did you get the Bell 47 started in the first place, when the clutch springs where out? I have been flying Bell 47īs on tuna boats and when it happened that the clutch pads would get sticky overnight I had trouble to start at all as the starter would have a hard time to pull all that mass through up to a speed where the engine would fire. I donīt say it is not possible, but I wonder you did that on purpose. I burned more than one starter like that.
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To HeliEng:
GP, you will always have GP as soon as you try to move the spinning axis of ANYTHING rotating (ever wondered what kind of forces you put on your cars hubs once you do 55 or 120 or so? Spinning wheels and you constantly try to tilt them by moving forward. how about something faster like a Formula 1 or CART race car......)
GP is kind of hard to UNDERSTAND, we all know the effects, but did you ever grasp the "WHY"? (When I look it up I think I get it, but.......)
There is good explanation in an old "flighttraining"-mag and a different one in an as old ArmedForces flight instruction book.
If you want I can find out details about the publications.....
3top
GP, you will always have GP as soon as you try to move the spinning axis of ANYTHING rotating (ever wondered what kind of forces you put on your cars hubs once you do 55 or 120 or so? Spinning wheels and you constantly try to tilt them by moving forward. how about something faster like a Formula 1 or CART race car......)
GP is kind of hard to UNDERSTAND, we all know the effects, but did you ever grasp the "WHY"? (When I look it up I think I get it, but.......)
There is good explanation in an old "flighttraining"-mag and a different one in an as old ArmedForces flight instruction book.
If you want I can find out details about the publications.....
3top