Author Topic: airplane tie-down knots  (Read 24643 times)

knot4u

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Re: airplane tie-down knots
« Reply #15 on: November 05, 2012, 07:09:47 PM »
When will you guys learn that the Versitackle and/or Truckers hitch are NOT suitable knots to use tying down an aircraft. Large aircraft use nylon straps and tensioning devices because they have fixing points that are strong enough to take tension - these are used by trained aircraft handlers  .  Light aircraft on the other hand are tied down with SHORT lengths of rope which have to be carried  (thus weight is important) and are tied to the aircraft by PILOTS who, apart from the very few, have no interest in learning complicated (to them) knots.  Reading through the reports of failures - I note they are all in the USA and the damage caused seemed to me to be due mainly to ignoring weather forecasts!

You say that pilots are basically uninterested in knots, and so we all should just stoop down to their level.  I'm not sure if your noticed, but this is a forum for knots nerds.  If a pilot wants to tie a knot the right way, then he can come here and learn better tie-downs than a Round Turn and Two Half Hitches, which is what you suggested.  If you want all conversation to stop at that knot, then you're in for a rude awakening.
« Last Edit: November 05, 2012, 09:30:15 PM by knot4u »

knot4u

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Re: airplane tie-down knots
« Reply #16 on: November 05, 2012, 07:20:40 PM »
I am going to the airfield tomorrow so will go along the lines of tied down planes and do a survey of the knots actually used.

Problem, you already admitted the pilots are not particularly interested in the study of knots.  Each pilot is probably just doing what somebody else told the pilot to tie, without thinking about how good the knot really is.  As I've said, I've watched about 20 videos of airplane tie-downs.  Those must be the pilots who ARE interested in knots.  Still, those guys can do a lot better.

Look.  This application is not that complicated.  We're not here discussing what will get the job done.  I'm sure I could get the job done by tying a Gleipnir, but there are better solutions.  So, we're discussing which knots will get the job done in the best and most efficient manner.  Yes, we are getting into the nuances of knot tying.  That's what we do here.

Actually, a Gleipnir doesn't sound like a bad option.  Discuss.  8)
« Last Edit: November 05, 2012, 07:44:28 PM by knot4u »

Sweeney

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Re: airplane tie-down knots
« Reply #17 on: November 05, 2012, 09:57:55 PM »
Actually, a Gleipnir doesn't sound like a bad option.  Discuss.  8)

No doubt it could be made to work but it would use a fair bit of rope and then a couple of half hitches to lock it so not for me I don't think.  I think I'd prefer a fixed loop at one end placed  through the anchor point with the main standing part then reeved through the loop (ie a noose eg a running bowline) then a trucker's hitch at the other end (I've seen one video where the TH was used though the finish was a single slipped half hitch). Once tied down is it really likely that the pilot would revisit the tie down to adjust tension (the argument for a versatackle)? Or would he simply remove the rope and retie it (assuming he did ever check it later)?  I wonder if insurers ever watch these videos?  :'(

Barry

roo

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Re: airplane tie-down knots
« Reply #18 on: November 05, 2012, 10:38:19 PM »
Once tied down is it really likely that the pilot would revisit the tie down to adjust tension (the argument for a versatackle)?
The general argument for the Versatackle does include its continually adjustable nature to equalize things, but it doesn't stop there.  It also takes less effort to get more tension, and doesn't require any real dexterity or expert skill to prevent the loss of your peak heaving tension. 


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kd8eeh

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Re: airplane tie-down knots
« Reply #19 on: November 06, 2012, 03:42:47 AM »
so, firstly i never expected this much imput about airplane tie downs.  you guys are awesome.  secondly, i've been meaning to post the knot i've actually seen pilots use.  so here it is.

knot4u

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Re: airplane tie-down knots
« Reply #20 on: November 06, 2012, 08:02:23 AM »
All due respect to pilots, but wtf is that?

X1

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Re: airplane tie-down knots
« Reply #21 on: November 06, 2012, 11:16:33 AM »
  It is a series of half hitches / nipping loops (1), a safe, secure, simple way of tying up or down anything ( airplanes included).
  I prefer to protect my airplane from the elements, by putting it inside a box... :)
   
  http://storrick.cnc.net/VerticalDevicesPage/Ascender/KnotPages/KnotHitchSeries.html
« Last Edit: November 06, 2012, 11:49:54 AM by X1 »

Sweeney

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Re: airplane tie-down knots
« Reply #22 on: November 06, 2012, 11:51:18 AM »
And it looks like the first half hitch has been reinforced by taking the working end back over the hitch. Seems a clumsy way of doing this even if it does hold.

Quote
The general argument for the Versatackle does include its continually adjustable nature to equalize things, but it doesn't stop there.  It also takes less effort to get more tension, and doesn't require any real dexterity or expert skill to prevent the loss of your peak heaving tension.

I agree - the versatackle is a great system but it seems that pilots are trying to avoid applying tension. The rope in the video I saw using a trucker's hitch was not pulled very taut - the TH was used simply as a way to secure the rope not to apply tension (http://www.youtube.com/watch?v=1qinEa2PN7A). If there should be a degree of tension the versatackle would be an excellent choice.

Barry

X1

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Re: airplane tie-down knots
« Reply #23 on: November 06, 2012, 12:27:35 PM »
the first half hitch has been reinforced by taking the working end back over the hitch.

   I think that this is a very difficult question to answer - and it would be answered someday, one way or the other, only by detailed experiments. Do we really reinforce a half hitch/nipping loop, by taking the working end over/through the hitch/loop another time ? Does a double nipping loop hold better than two single ones ? Or does the internal friction that is "wasted", so to speak, within the two turns, diminishes the nipping power of the half hitch/nipping loop, instead of reinforcing it ? Why one has to spread the friction along a longer segment, making a second turn, if the Amontons second law of friction is valid in this scale ? And is friction coefficient a constant of each material, independent of the geometry of the loading ? (1) It is said that physicists' best kept secret is their deep ignorance about the phenomenon of friction...
 
   1. Static Friction Coefficient Is Not a Material Constant, Phys. Rev. Lett. 106, 254301 (2011)
       O. Ben-David and J. Fineberg,

   
   
« Last Edit: November 06, 2012, 12:32:25 PM by X1 »

TMCD

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Re: airplane tie-down knots
« Reply #24 on: November 06, 2012, 02:12:17 PM »
Kd8eeh's pictures are the way most seem to tie their planes down. I watched a bunch of you tube videos last night and quite a few follow that basic structure and design. There was a guy who used the Trucker's Hitch in one video and quite frankly, that was the best option IMO. The only thing different he did was to keep the Trucker Hitch relatively loose, no cranking down was done. In this form, the TH performs exactly what the plane's pilot wants in the tie down scenario.

One thing I've learned on this forum is that if you ask a knot question, you'll get ten different answers and they're generally correct. There's more than one way to skin the ole cat and knots prove that to the highest degree. Heck, two half hitches and a somewhat loosened taut line at the other end would work perfectly for an airplane tiedown. A loosened Trucker Hitch works, the Versatackle works, Gleipner would work too, lots of options.

kd8eeh

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Re: airplane tie-down knots
« Reply #25 on: November 06, 2012, 03:02:39 PM »
quote knot4u
All due respect to pilots, but wtf is that?

so, i think you can plainly see why i don't like the way pilots tie down their airplanes.  with any luck, i'll be able to actually teach pilots how to tie a trucker's hitch, but i have little faith they will learn it well.  a versitackle, being a few steps more complicated, would be even harder to teach a pilot, as most of them are already incapable of higher knotting.  also, to tie a good trucker hitch, i need a good loop to teach, that is easy to learn and even if they fail miserable tying it, it will still be secure.  any ideas?

kd8eeh

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Re: airplane tie-down knots
« Reply #26 on: November 06, 2012, 04:55:06 PM »
so, i got around to trying to teach my parents (who are pilots) a trucker's hitch.  i have absolutely no idea what it is.  however, they got an in line figure 8 mostly right, and is seems to be pretty secure even when tied horribly wrong.  i will try some other ideas for loops, but they can only learn so many knots so fast.  as far as the other half of this mess, hopefuly i can teach them at least two half hitches.  they seem to really like slipping the final loop.  also, i found that in the past, one of them has been in groups where they tied down their airplanes with a slippery hitch.  so, it'd be really great if someone could figure out something better to teach them.

Sweeney

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Re: airplane tie-down knots
« Reply #27 on: November 06, 2012, 05:30:06 PM »
Taking into account that you are looking for the simplest rather than necessarily the best solution I would try a simple overhand knot noose  - this should be easy to undo as the tension is not great. Using a more permanent loop is fine except that the rope will always rub against the same part of the loop potentially damaging it over time. There are better solutions but I would avoid eg the bellringer's knot (single or double) simply because of the lack of tension. If you're going to use a slipped half hitch then use a normal half hitch first and slip a second one. This video which I referred to in an earlier post is at least better than most - http://www.youtube.com/watch?v=1qinEa2PN7A - and shows how to tie an overhand noose.

Barry

Luca

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Re: airplane tie-down knots
« Reply #28 on: November 06, 2012, 06:41:12 PM »
Hi  Sweeney and X1,

And it looks like the first half hitch has been reinforced by taking the working end back over the hitch. Seems a clumsy way of doing this even if it does hold.

Do we really reinforce a half hitch/nipping loop, by taking the working end over/through the hitch/loop another time ? Does a double nipping loop hold better than two single ones ?


 
My own opinion is that,during the making of the solution shown by kd8eeh, the"doubling"of the first Half hitch in this way makes effectively sense, since its use prevents,while the tail is tensioned to make the second Half hitch, the risk of the capsizing of the first, having it to support he alone all the load that is applied at that time.I think that the way to achieve the Bowline shown here, is helpful to understand how easily this can happen during the construction of the tie-down solution in question: 

http://daveroot.netau.net/Knots/Knots_SingleLoops.htm#Bowline (Method #2)

In this thread linked above by knot4u, there is shown a similar doubling of the Half hitch (later identified by dfred as Abok #1854(perhaps one of the worst drawings by Ashley)):

http://igkt.net/sm/index.php?topic=4044.msg24177#msg24177

                                                                                                           Bye!

P.S.Hey X1, beautiful your airplane!Maybe I too,can afford this,I'll do a little thought ..and I think I can afford to buy even the box where to keep it, it would be a shame to leave it at the mercy of the elements! :D
« Last Edit: February 03, 2013, 01:45:28 AM by Luca »

X1

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Re: airplane tie-down knots
« Reply #29 on: November 06, 2012, 08:03:03 PM »
...the "doubling" of the first Half hitch in this way makes ... sense,
   since its use prevents the risk of the capsizing of the first Half hitch,
   while the tail is tensioned to make the second Half hitch

   In a "series of Half hitches", only the last one is a genuine, proper half hitch. All the others are nipping loops, because both their legs are loaded - just as the nipping loop of the common bowline, the Water bowline, the ABoK#160-161, and the Sheepshank. Of course, if one insists to "see" a half hitch in the bowline, he can baptize every nipping loop a "half hitch", he will discover a relation between the bowline and the Sheet bend, and he will keep repeating the mistake of Ashley during the next millenium.
   Now, my point is that "two Half hitches" ( i.e., one nipping loop and one half hitch ) are better than a doubled one - and four "Half hitches" ( i.e., three nipping loops and one half hitch ) are better than two doubled ones ( i.e., one double nipping loop and one doubled half hitch, like the one shown in the picture of kd8eeh )
   One may ask : Why then we use double nipping loops, and doubled half hitches ? I believe that this has to do with other things - we do not use them because they nip the penetrating segment more forcefully, but because they form a longer "tube', so this penetrating segment is aligned better - and being aligned better, it is nipped by the next nipping loop / half hitch better ( as in the ABoK#1854-1857 you are referring to.)
   There may also be some other reasons : In the Gleipnir, for example, it is beneficial to use a double, or even a triple nipping loop, so the "tube" formed by the multiple coils will be sufficiently long to encircle two twisted penetrating segments/tails - two segments/tails that make half a turn around each other, in the form of a double helix. This enhances the friction in between those two segments, not between each one of those two segments and the coils of the nipping loop...
   Of course, this is only a theory, that was initiated by the shock of the Gleipnir : the unexpected effectiveness of the nipping loop, without the help of any collar. I hope that somebody will someday test the gripping power of the single, double and triple nipping loops, and settle this issue once for all.