PHOENIX "rescue" No thanks!
Gray - if the stretcher wants to spin and you have friction in the swivel to slow it, that torque will be transmitted to the cable and could easily start to unwind it causing all sorts of problems - once you 'birdcage' a hoist cable it is pretty much unusable.
reading comprehension Crab, reading comprehension.
there is a value in the middle that I am looking at.
how much force to freely spin a basket, how much force to unwrap a cable designed to not unwrap.
these are two very distinct and different values. and likely very repeatable if you measured them.
8 N to spin you, 100N to unrwap a cable as a hypothetical example. I have no idea of the actual values, but if there is a specific spread you determine a friction that falls between and it does whats intended. which is stop the basket from spinning, and stop the cable from unwinding.
think of your collective friction and its designed purpose.
there is a value in the middle that I am looking at.
how much force to freely spin a basket, how much force to unwrap a cable designed to not unwrap.
these are two very distinct and different values. and likely very repeatable if you measured them.
8 N to spin you, 100N to unrwap a cable as a hypothetical example. I have no idea of the actual values, but if there is a specific spread you determine a friction that falls between and it does whats intended. which is stop the basket from spinning, and stop the cable from unwinding.
think of your collective friction and its designed purpose.
I have no idea of the actual values,
Perhaps if it was such a simple solution as you suggest, someone might have already invented it - stretchers have been spinning for many years under helicopters and you are the only one to come up with the solution - all hail!
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Having kept my mouth shut whilst listening to all the arm chair experts, it is about time somebody put some realistic comment into this:
Stretchers spin, especially if there is not a winchman to assist by manoevering it to change the airflow over it.
A Tag Line (Hi Line) will stop the spin if it is rigged correctly and if it does not snap.
There is no such thing as an anti-spin cable, the layers of the cable are wound in opposite directions to resist spin, but the winch hook has a bearing to allow the hook to spin and stop the cable winding up and birdcaging.
From the video, it looks like there were better options to sort out a problem that had developed, the reasons that the problem developed are pure conjecture at this stage.
Trial by Internet video will not give the reasons, the real problem or the solution because the people involved have already been tried and found guilty by social media. Would you want to try to justify or lay open your mistakes to a bunch of people who have never been in that situation and therefore can not really understand what has happened.
I would not pass judgement on the situation without having discussed it in the bar with the crew, I have seen numerous situations that turn out to be very different from that shown on video.
What do I know, only 30 years of SAR winch operating so that does not give me much street cred compared to some posters on here.
Heads Down, Look out for the Flak
Stretchers spin, especially if there is not a winchman to assist by manoevering it to change the airflow over it.
A Tag Line (Hi Line) will stop the spin if it is rigged correctly and if it does not snap.
There is no such thing as an anti-spin cable, the layers of the cable are wound in opposite directions to resist spin, but the winch hook has a bearing to allow the hook to spin and stop the cable winding up and birdcaging.
From the video, it looks like there were better options to sort out a problem that had developed, the reasons that the problem developed are pure conjecture at this stage.
Trial by Internet video will not give the reasons, the real problem or the solution because the people involved have already been tried and found guilty by social media. Would you want to try to justify or lay open your mistakes to a bunch of people who have never been in that situation and therefore can not really understand what has happened.
I would not pass judgement on the situation without having discussed it in the bar with the crew, I have seen numerous situations that turn out to be very different from that shown on video.
What do I know, only 30 years of SAR winch operating so that does not give me much street cred compared to some posters on here.
Heads Down, Look out for the Flak
Originally Posted by [email protected]
but you feel content to criticise my reading comprehension - just consider the force required to make a stretcher spin like that in the video and then the counter force required to restrict that - you are content that won't have any effect on the cable windings despite having no idea of the actual forces involved - genius!
Perhaps if it was such a simple solution as you suggest, someone might have already invented it - stretchers have been spinning for many years under helicopters and you are the only one to come up with the solution - all hail!
Perhaps if it was such a simple solution as you suggest, someone might have already invented it - stretchers have been spinning for many years under helicopters and you are the only one to come up with the solution - all hail!
I suppose I can flip your comments right back at you because you offer nothing as well.
I'll try my best to continue to speak my point, totally accepting you'll jump onto my back and pummel me with the idiot comments. I have thick skin and am not deterred.
The spinning force starts off at a low value. you can comprehend that right? as soon as the stretcher lifts and the tag line is lost for whatever reason, the rotor wash imparts its forces and voila, stretcher starts to turn. basic physics. Its not immediately going at 300rpm and 5g's force right? takes more force to get them spinning, but once they are spinning, the forces tend to take over and you'll spin easier and faster, and faster yet. this lady experienced that acceleration and we watched in horror.
If you still dont follow me, go back to when you were 12 oiling your bike chain upside down in the driveway. dad on the porch swilling beers cuz the old lady is nagging at him. pedal a bike wheel in top gear at first and you see what forces i mean. Hard to turn at first, but gets easier as the wheel increases speed. and much easier to stop at the beginning. just grab it with your hand. PSA: dont stick your fingers in the spokes once it gets going though. try a stick.
hard to stop a wildly spinning stretcher once they get going too just like that ol' bike wheel. For sure the wire cable will bird cage if you allow the rotation to get to that point. just like you'll strip out bike spokes if you wait to long to put that stick in there.
what if you counteract that force early enough? no indication I want to stop it completely, only a desire to keep it under resistance to keep it from increasing at a high rate without hitting the value to damage the wire. Thats exactly what a tag line does. its simple and effective, but thats all if its lost. A resistive swivel would be a very good secondary tool to back you up if the tag line failed, but you're still going to have that secondary plan. the time you gain keeping that basket slow and getting the stretcher back on the ground might prevent further injury.
and if you do birdcage a wire, few grand to replace a cable is a cheap cost VS potentially allowing big injuries by spinning wildly out of control.
Perhaps though, someone has tested this. perhaps not. I'll gladly eat a hat if someone can offer this has been looked at. You however will likely just continue you're bullying ways because thats what you do on here. Have a nice day.
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Whether a cable birdcages surely depends on the total number of turns applied to it, rather than how quickly turns are applied.
Bird caging the cable is a very bad thing because it may jam the winch. If the cable is cut, that's the end of winching for the day. Especially bad if there is more than one person to be brought up on the wire. Hence the swivel and 'tag' line method.
Bird caging the cable is a very bad thing because it may jam the winch. If the cable is cut, that's the end of winching for the day. Especially bad if there is more than one person to be brought up on the wire. Hence the swivel and 'tag' line method.
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Dear Mr GreyHorizonheli,
you are arguing from an academic point of view. It you are such an expert, please justify your standing.
Having flown own more hours than I care to remember with Crab, he is talking more sense than has been espoused on this topic than many.
You may be a mathematical genius, but you appear to have have no practical experience of Winch Operating environment.
This topic has been hijacked by yet another bunch of social media experts who appear to run their lives via PlayStation. If I am in error, I appologise, What makes you such an expert?
you are arguing from an academic point of view. It you are such an expert, please justify your standing.
Having flown own more hours than I care to remember with Crab, he is talking more sense than has been espoused on this topic than many.
You may be a mathematical genius, but you appear to have have no practical experience of Winch Operating environment.
This topic has been hijacked by yet another bunch of social media experts who appear to run their lives via PlayStation. If I am in error, I appologise, What makes you such an expert?
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Whether a cable birdcages surely depends on the total number of turns applied to it, rather than how quickly turns are applied.
Bird caging the cable is a very bad thing because it may jam the winch. If the cable is cut, that's the end of winching for the day. Especially bad if there is more than one person to be brought up on the wire. Hence the swivel and 'tag' line method.
Bird caging the cable is a very bad thing because it may jam the winch. If the cable is cut, that's the end of winching for the day. Especially bad if there is more than one person to be brought up on the wire. Hence the swivel and 'tag' line method.
A quick experiment using some ~0.1" twisted cable as a model suggests quite a few twists.
By the time the torques match the stretcher will have accumulated significant angular momentum so will continue to spin for a while before eventually stopping, at which time the counter torque from cable would be higher than downwash induced toque so the stretcher would start spinning in the opposite direction for a while.
Reminds me of a child's toy using twisted strings to spin a large button in the middle, once going wind/unwind to other limit, rinse and repeat.
So basically you might change a bad ride into a truly bad ride, I suspect high constant G is likely better than continuously changing G.
Engineering 101 "you cant push a string" probably applies here. (Unless it is wet and frozen)
BTW: My use of 'torque' in above may/may not be pedantically correct but I believe it is understandable.
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Murphy,
The cable has a bearing so that you-will get minimal twist to the cable.
Will someone who knows what they are talking about please reply to this thread
Heads down. look out for the Flak
The cable has a bearing so that you-will get minimal twist to the cable.
Will someone who knows what they are talking about please reply to this thread
Heads down. look out for the Flak
Last edited by Cabe LeCutter; 13th Jun 2019 at 00:38. Reason: spilling
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My apologies if not clear, I was replying to GrayHorizonsHeli suggestion that a friction clutch in the swivel bearing would be helpful, which as others have also pointed out would be a "bad idea".
Gray - I love your home-spun, back porch analogy (you must have had an interesting childhood if those are memories you are drawing on for inspiration.) but you miss the obvious.
Yes, the stretcher spins slowly at first because the downwash is limited at a distance below the helicopter.
If you have understood what happened on the video, you will realise that the closer the stretcher gets to the helicopter, the stronger the downwash effect and the larger the torque force applied to the cable - it is not a constant, small force that can be easily overcome with a friction device.
Yes, the stretcher spins slowly at first because the downwash is limited at a distance below the helicopter.
If you have understood what happened on the video, you will realise that the closer the stretcher gets to the helicopter, the stronger the downwash effect and the larger the torque force applied to the cable - it is not a constant, small force that can be easily overcome with a friction device.
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Nope, thanks. Your noble effort to enlighten the unwashed is noted, but the Dunning-Kruger effect is clear from certain responses. I could sink a pint with you though. Cheers
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If the cable "birdcages" it will probably not be possible to rewind it back onto the winch drum and depending on the circumstances might have to be physically cut by the winch op. Winches have a cable cutting guillotine device to allow this to be done in an emergency situation.
Nope, thanks. Your noble effort to enlighten the unwashed is noted, but the Dunning-Kruger effect is clear from certain responses. I could sink a pint with you though. Cheers
Must remember the Dunning-Kruger effect next time I am tempted to postulate a theory supported by no empirical evidence
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I have been made aware of a few things here and taken note of them. Maybe I have not said "cleared to hoist enough". I myself filter .... especially those who critize.
**** happens
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No-one mentioned the cable "catastrophically failing".
If the cable "birdcages" it will probably not be possible to rewind it back onto the winch drum and depending on the circumstances might have to be physically cut by the winch op. Winches have a cable cutting guillotine device to allow this to be done in an emergency situation.
If the cable "birdcages" it will probably not be possible to rewind it back onto the winch drum and depending on the circumstances might have to be physically cut by the winch op. Winches have a cable cutting guillotine device to allow this to be done in an emergency situation.
In any case no matter which way you look at it not having a bearing could lead to a number problems, my thought on cable torsional spring wind up/release interactions being just one of them.
Another question for those who do know.
Have there been any cases of having to use the cable cutting guillotine while hoisting a person?
That would be the ultimate hard decision to have to make. Gives me a queasy feeling just thinking of it.
Last edited by MurphyWasRight; 13th Jun 2019 at 14:04. Reason: duplicated word
Agree that "catastrophically failing" is not the best term, "permanently damaged" or "rendered unusable" would be better.
In any case no matter which way you look at it not having a bearing could lead to a number problems, my thought on cable torsional spring wind up/release interactions being just one of them.
Another question for those who do know.
Have there been any cases of having to use the cable cutting guillotine while hoisting a person?
That would be the ultimate hard decision to have to make. Gives me a queasy feeling just thinking of it.
In any case no matter which way you look at it not having a bearing could lead to a number problems, my thought on cable torsional spring wind up/release interactions being just one of them.
Another question for those who do know.
Have there been any cases of having to use the cable cutting guillotine while hoisting a person?
That would be the ultimate hard decision to have to make. Gives me a queasy feeling just thinking of it.
There have also been situations during engine failures or emergencies (both twin and single engine helo’s) resulting a swift winch out and cut the cable rather than the patient/rescue crewman becoming a sand anchor.
I don’t have time to trawl through reports, it’s not common but cutting the cable does happen.
Most operations also have a quick splice hook on board, so if you need to cut the cable due it it being fouled you can continue using quick splice.
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yes. When the cable gets fouled and cannot be un-fouled.
There have also been situations during engine failures or emergencies (both twin and single engine helo’s) resulting a swift winch out and cut the cable rather than the patient/rescue crewman becoming a sand anchor.
I don’t have time to trawl through reports, it’s not common but cutting the cable does happen.
Most operations also have a quick splice hook on board, so if you need to cut the cable due it it being fouled you can continue using quick splice.
Back in the days of Wessex SAR in UK, a brand new, just out of the long SAR course, winch Op had to cut the cable on his very first rescue.
They were winching to a yacht in poor weather and deployed the winchman - unfortunately, the pilot lost sight of the yacht and started to drift towards the bow.
The winchman hit the mast and was being dragged up it towards the spreader for the stays and would have been sliced to bits had the winch Op not cut the cable.
I wasn't involved but worked at the SAR Taining unit next door so we had just finished training the winch Op.
They were winching to a yacht in poor weather and deployed the winchman - unfortunately, the pilot lost sight of the yacht and started to drift towards the bow.
The winchman hit the mast and was being dragged up it towards the spreader for the stays and would have been sliced to bits had the winch Op not cut the cable.
I wasn't involved but worked at the SAR Taining unit next door so we had just finished training the winch Op.