Author Topic: airplane tie-down knots  (Read 24645 times)

kd8eeh

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airplane tie-down knots
« on: November 02, 2012, 03:35:42 AM »
i already know some nice binders that work for this pupose, but my dad uses a chain hitch for this purpose and i don't think it is a very secure way of doing it.  however, he says that he just wants something that may be tied very quickly.  so, i was wondering if anyone out there would like to give a second opinion

roo

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Re: airplane tie-down knots
« Reply #1 on: November 02, 2012, 03:03:56 PM »
i already know some nice binders that work for this pupose, but my dad uses a chain hitch for this purpose and i don't think it is a very secure way of doing it.  however, he says that he just wants something that may be tied very quickly.  so, i was wondering if anyone out there would like to give a second opinion
http://notableknotindex.webs.com/Versatackle.html

Once the loops are spaced correctly for your application, they can be left in place for fast re-application in the future.
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knot4u

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Re: airplane tie-down knots
« Reply #2 on: November 02, 2012, 07:36:57 PM »
Note this other thread talks about not having too much tension in an airplane tie-down. So, don't get overly enthusiastic about cranking down on the tension, whatever knots you tie.  I'd go with a Trucker Hitch in springy cord.  A Trucker Hitch is quickly adjustable and can be left with loose tension, which are characteristics you need.  I don't see the need for a Versatackle, which is not as easy to adjust and is specifically for jobs that require the user to crank down on the tension. 

http://igkt.net/sm/index.php?topic=4044.0
« Last Edit: November 02, 2012, 07:40:49 PM by knot4u »

roo

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Re: airplane tie-down knots
« Reply #3 on: November 02, 2012, 07:40:45 PM »
be left with loose tension, which are characteristics you need. 

I disagree.  You don't want the plane to be able to bounce around and build up kinetic energy. 

If you hold a shotgun loosely when you fire it, you will get a much harder impact than if you had it firmly seated against your shoulder.
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knot4u

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Re: airplane tie-down knots
« Reply #4 on: November 03, 2012, 12:56:16 AM »
be left with loose tension, which are characteristics you need. 

I disagree.  You don't want the plane to be able to bounce around and build up kinetic energy. 

If you hold a shotgun loosely when you fire it, you will get a much harder impact than if you had it firmly seated against your shoulder.

The term "loose tension" is relative of course.  My point is that if I crank down on an airplane's wing by using a Versatackle, I'm confident I could damage the airplane.  An experienced person in the other thread specifically said not to do this.  It's a point worthy of note and not obvious.  Again, for this application, there is no need for a Versatackle and the monster tension enabled thereby.
« Last Edit: November 03, 2012, 02:33:28 AM by knot4u »

roo

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Re: airplane tie-down knots
« Reply #5 on: November 03, 2012, 04:41:23 PM »
The term "loose tension" is relative of course.  My point is that if I crank down on an airplane's wing by using a Versatackle, I'm confident I could damage the airplane.  An experienced person in the other thread specifically said not to do this.  It's a point worthy of note and not obvious.  Again, for this application, there is no need for a Versatackle and the monster tension enabled thereby.
I think you're overestimating your strength and the mechanical advantage of the Versatackle if you think you're going to accidentally rip the wings off a plane with a rope and your arms.   Aircraft wings need to be strong enough to support inverted flight during a barrel roll (accidental or intentional), for example.

A key advantage of using the Versatackle is that you can continually adjust its tension without untying it.  With a trucker's hitch, if you don't have the tension you want after tying off, you have to undo it and try again.
« Last Edit: November 03, 2012, 04:46:27 PM by roo »
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Fairlead

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Re: airplane tie-down knots
« Reply #6 on: November 03, 2012, 06:16:59 PM »
What a lot of 'tripe'  - It is obvious that roo or knot4u have ever tied a light aircraft down or even know what a tiedown is!
The rope used is already secured to a heavy weight or ground spike (if not it is secured to a ground line with a round turn and two half hitches or similar hitch) - the wing end is adequately secured to a ring built into the underside of the wing using a round turn and two half hitches (slipped if you like) NO purchase is required just make sure there is no slack between the two fixings. 

Gordon (PPL(A))

knot4u

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Re: airplane tie-down knots
« Reply #7 on: November 03, 2012, 07:38:57 PM »
What a lot of 'tripe'  - It is obvious that roo or knot4u have ever tied a light aircraft down or even know what a tiedown is!
The rope used is already secured to a heavy weight or ground spike (if not it is secured to a ground line with a round turn and two half hitches or similar hitch) - the wing end is adequately secured to a ring built into the underside of the wing using a round turn and two half hitches (slipped if you like) NO purchase is required just make sure there is no slack between the two fixings. 

Gordon (PPL(A))

Weird, I've watched about 20 videos on airplane tie-down knots. Nobody uses a Roundturn & Two Half Hitches. For one thing, it looks like the rope is often too thick to go twice through the ring on the airplane.  You should make a video to school everybody, including this guy...

http://youtu.be/V2AGOMD_kYg
« Last Edit: November 04, 2012, 12:23:59 AM by knot4u »

Dan_Lehman

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Re: airplane tie-down knots
« Reply #8 on: November 04, 2012, 06:33:26 AM »
Trying, with tremendous trepidation, not to trip on the tripe ...   ;D

I find some direct information here:
www.airventure.org/planning/tying_down.html
which states that one should set the tie-down lines so to
allow "1 inch of movement", using rope of 3-4_000 # tensile
strength, preferably nylon or dacron; it also notes that one's
tie-down is no better than one's knot, so use an "anti-slip"
knot such as the bowline & square knot .  That should
set everyone's heart at ease!  --no hint is given how these
two different-class knots could both equally server ... !?
(And we should question the OP about his notion of "some
nice binders that work for this situation."  Binders?!)

And I don't see so much of any "experienced person" in the
earlier thread.  THANKS MUCH for connecting this to that, Knot4U.
(But that thread didn't get us far, did it.)

Now, to the above *official* (FAA, I think) & echoed advice,
one wise to cordage and physics should have some immediate
questions:
1) How does one guage "1 inch of movement"?
2) Is that stricture the same at all tie-in lines (wondering,
because I think that those of the wings are longer than that
on the tail)?
3) Is that stricture independent of the lines used --which
might differ considerably in their elasticity (braided dacron
w/little stretch vs. laid nylon with much)?
4) Is there any special recommendation for expected severe
weather (well, something believed to be survivable, but say
a thunderstorm's punch)?

Now, as for Fairlead's suggestion that experience in tying down
something --even the particular items of focus, here : airplanes--
will deliver sage advice, I offer the incredible (!!) variety of opinions
from supposed airplane pilots & tyers-down from this 2003 thread
about how well/poorly it is observed done (with reports of considerable
variety of nature & condition tie-down materials!):
www.supercub.org/forum/archive/index.php/t-20265.html
(If I'm reading this rightly, "supercub" is a type of small plane.)

Here's one post in that fascinatingly varied thread:
Quote
I thought the goal of tying down was to keep the plane from moving.
My ropes are tight. Not so tight the spars are squeaking, but tight.
Watch a plane in the wind.  If there's slack in the ropes it rocks all over the place.
Every time it hits the end of the rope's travel there's an impact,
right where you don't want it. The impact makes more slack,
the plane rocks worse....bad news.
I have always used non-stretching 1/2" mountain climbing rope
to tie the plane. It hold knots well, and lasts forever.

Of course, even in 2003 there was no such thing as "non-stretching
1/2 mountain climbing rope" --not so thick, and of course stretching.
We'll presume that some kernmantle rope is intended, likely for SAR
or caving.  (Rockclimbers' low-elongation accessory cord is thinner.)
Anyway, that used rope likely doubles the rec'd tensile strength
(and so indeed will be pretty non-stretching!).

Here's another intriguing snippet, from one claiming 3 decades' experience:
Quote
I too have been tying down planes in AK for 30+ years and when I came
to the "lower 48" I was shocked. Dog chains wore out clothes line, 3/8 poly
that had been in the sun for years?--to name a few.

Many folks I saw had a couple of half hitches 2 feet down the rope and the tail in a loop?
also Cessnas tyed down by the little ringy thingy that is springloaded into the strut
(held by a 3/16 bolt that is sometimes 40 plus years old unattended?)

I have nearly worn out the fabric reinforcement around the top of my 'AK' cubs
making a couple raps around the strut abouve the tiedown attach point
then tying the first hitch as tight as possible next to the strut,
making the ropes tight enough that the plane can only move with the give in the gear/tires.
...//...
the either 1/2-5/8 braided gold line (stored in a dry place in the cub)
or now more recently a Kevlar reinforced climbing rope!

The upper underlined expression makes me wonder if he's denoting
some intended tie-down anchor, which itself entails shock absorption?
In any case, it seems that he violates the *official* advice NOT to tie
to a strut (sadly this was expressed in a PDF file with one rational being
that the strut lacked adequate strength, but a warning on the image
that pointed to the risk of the attachment point slipping to a weak(er)
part of the strut --which latter risk could be redressed by a friction hitch).

And, goodness, this fellow's gone for even thicker rope, or --egads--
"kevlar-reinforced climbing rope" --no idea what that is, but surely not
rockclimbing rope!!  (His note about "dry place" is fine, but less an issue
for synthetics.)   (Yes, I think that there was such a "goldline" or rather
"gold'n'braid" braided marine rope; the famous rockclimbing line
was derived from a marine line (both laid), IIRC --made w/harder lay
(and 7/16"), and MUCH stretch.)

Here's another site's take on things, with yet further muddying of
these waters --tripe is ripe, but which is it?!
www.eaa.org/lightplaneworld/articles/1105_tiedowns.asp
Quote
Weights Don't Work
In an emergency or in desperation, it's tempting to tie the plane to something heavy.
It doesn't take much math to figure out why this approach often fails. I once made
the foolish mistake of tying my ultralight to a pair of 80-pound concrete blocks on a calm day.
It worked great until a fairly small dust devil happened to pass by and flipped over my plane,
flinging the blocks on the ends of their ropes like they were toys. At Sun 'n' Fun,
it was reported that a destroyed Kitfox was picked up while tied to a pair of 600-pound weights.
That may sound fantastic until you realize how much weight those wings can normally lift
when the wind speed is more than twice the minimum flying speed.

Ropes and knots are generally preferred over ratcheted webbing cargo straps
because they're lighter and easier to pack
, but it's important to use knots
that won't loosen or slip.  Most pilots use some version of the taut-line hitch
which can be seen in this video.  We like it because it's adjustable.  You can go
around the airplane and snug up all your tiedowns.  However, it can loosen
in gusty conditions because it works best when under constant tension.
The anchor hitch or fisherman's bend shown here might be better for extreme conditions.
Be very careful if you use the ratcheted webbing cargo straps.
They're strong enough and easy to fasten, but the ends are usually open 'S' hooks!
If your landing gear deflects and allows the wing to dip
as much as one inch during a storm, it could slip right off.

I was wondering if cargo straps (w/ratchet tightener, yes?) were going
to enter the scene --for those are quite unstretchy, to my awareness.
The only caution given against there here, beyond less convenience
in packing/storage, is that their built-in attachment mechanism
of an "S"-hook could come off if the line's slackened; one could
redress this risk by using some other hardware there.

One more URLink, and this one has a video (which I might last
to see, w/slow dial-up feed) :
www.golfhotelwhiskey.com/how-to-tie-down-an-aircraft-properly/

Quote
... he emphasized that tying down an aircraft is not like stringing a guitar,
as, if there is a windy day or a storm, you don't want the aircraft so tightly tied
down to the ground that it ends up getting damaged
. In other words,
you need to remember to leave some flex in the rope.

So, here's one for the not-so-tight side.  But I'm unclear on how
"some flex in the rope" prevents damage : what is it that happens
on tightness (where that tension is not itself damaging,
but only become so with wind)?  Is it that if one has anticipated
wing lift by tightening it down, then force will be resisted entirely
by the lines (as they are already working against the wing),
whereas were the lines not tight, the initial resistance comes
from the plane and then is assisted by the lines?  I'm still
chary about effects of momentum, and seeing "1 inch" guideline
a dubious quantity.

HOLY SMOKES : I've seen the video enough to see that all he
ties is --get this (sitting down?)-- two overhands around
the SPart, well distant from the anchor !!! ?  Huh, how
can one DO this and *live*?!  We're talking about a noose
such as one might use for snagging a bear, or stray dog!
INcredible. (Sadly, the video didn't play for me long enough
to hear his rationale for leaving slack --could be another whopper.)

I left this comment, pending moderation:
Quote
Dan Lehman November 4, 2012 at 05:02
{{Your comment is awaiting moderation.}}

I'm dumbfounded : you've tied off your plane >>WITH A NOOSE<<,
set to slip maybe 20 inches???!! Holy hazard, Batman, that's incredible!
(And is that old cotton solid-braid rope, or nylon?)

)-:

Well, Gordon, seen enough from the field of tyers-down?!
--no doubt, there's more (but this really takes the cake)!    :o



--dl
====
« Last Edit: November 06, 2012, 03:54:48 AM by Dan_Lehman »

Sweeney

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Re: airplane tie-down knots
« Reply #9 on: November 04, 2012, 06:14:21 PM »
(Sadly, the video didn't play for me long enough
to hear his rationale for leaving slack --could be another whopper.)

It doesn't get any better if you watch all of it! Certainly looks like cotton rope (and one commenter also mentions this). An FAA circular in 1983 recommended a bowline and square (reef) knot - why the latter is anybody's guess! http://www.flyleadingedge.co.uk/download/securing_your_aircraft.pdf offers advice in the UK where strong winds are common but not hurricanes.  The knot descriptions look OK and the doc warns against the square knot. Leaving slack may be to allow a small wind induced movement (I have no idea how much lift a strong wind generates) rather than risk fatigue from vibration caused by having the line taut. If the wind is very strong the aircraft would still be prevented from flipping over.

Barry

Dan_Lehman

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Re: airplane tie-down knots
« Reply #10 on: November 04, 2012, 07:15:16 PM »
Thanks, Barry.  It's worth remarking at how much of various
Net-available information is echoed --same images, et cetera.

Oh, re the square knot recommendation : I guess that's in case
someone makes a closed-loop sling attachment through rings
at both ends of the anchorage?!  (Though I see also the sheet bend
given in this UK pdf, which isn't even as easy as the squaREef in
getting moderately tight in such a situation.)  --a guess ... .

Pertinent to a main issue here, from this latest source, comes:
Quote
When tying ropes, draw them tight (not stretched) and then back them off a
few centimetres. Too much slack allows the aircraft to jerk against the ropes,
while a rope that is too tight can put inverted-flight stresses on the aircraft,
which may not be designed to absorb such loads.

I wonder at this advice, still.  Won't there be a chance of
having the same effect --as "too tight" tie-down-- if wind
moves the airplane such that the tie-down lines become
more highly tensioned?

(Again, I should emphasize as Roo did that we're not suggesting
that some significant MA-got tightening be done, but only that
the tie-down should be starting in light tension, doing some
support from the start, so not allowing a wing, say, to get
any movement into a slack rope.  Given the contrary specifications
of, instead, providing about 1"/"few centimeters" of slack, it seems
that we're splitting hairs, really --and begs the question as to how
much such a slight difference can matter (and if so, how can one
ignore the tie-down material with regard to its elasticity or not!?
--or, for that matter, the particular angle & length of line, which
both affect the force & stretch of the rope)
?!)

--dl*
====
« Last Edit: November 04, 2012, 07:49:36 PM by Dan_Lehman »

knot4u

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Re: airplane tie-down knots
« Reply #11 on: November 04, 2012, 09:36:56 PM »
The term "loose tension" is relative of course.  My point is that if I crank down on an airplane's wing by using a Versatackle, I'm confident I could damage the airplane.  An experienced person in the other thread specifically said not to do this.  It's a point worthy of note and not obvious.  Again, for this application, there is no need for a Versatackle and the monster tension enabled thereby.
I think you're overestimating your strength and the mechanical advantage of the Versatackle if you think you're going to accidentally rip the wings off a plane with a rope and your arms.   Aircraft wings need to be strong enough to support inverted flight during a barrel roll (accidental or intentional), for example.

A key advantage of using the Versatackle is that you can continually adjust its tension without untying it.  With a trucker's hitch, if you don't have the tension you want after tying off, you have to undo it and try again.

If I tied a Versatackle in this situation, I'd definitely finish it with a Half Hitch or two.  I'm not leaving the security of the airplane dependent on the little nipping action of the Versatackle.  Nobody should, given there may be slack in the line either initially or in the future.  I'm basically finishing the Versatackle in the same manner I finish a Trucker.  So, the quick adjustment feature of the Versatackle would be non-existent.  Further, a Verstackle is less convenient to loosen than a Trucker.

One caveat, the Versatackle may be more desirable if the initial anchor is on the ground.  In this situation, a basic Trucker would involve the user pulling the working end upward to generate tension.  In contrast, a Versatackle would enable the user to pull downward to generate tension.
« Last Edit: November 04, 2012, 09:46:49 PM by knot4u »

roo

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Re: airplane tie-down knots
« Reply #12 on: November 04, 2012, 11:37:30 PM »
Quote
A key advantage of using the Versatackle is that you can continually adjust its tension without untying it.  With a trucker's hitch, if you don't have the tension you want after tying off, you have to undo it and try again.

If I tied a Versatackle in this situation, I'd definitely finish it with a Half Hitch or two.  I'm not leaving the security of the airplane dependent on the little nipping action of the Versatackle.  [...]  I'm basically finishing the Versatackle in the same manner I finish a Trucker.  So, the quick adjustment feature of the Versatackle would be non-existent. 
I don't care how you deal with the excess rope of the Versatackle after everything is done.  The fact remains that you can continually ratchet up the tension of the Versatackle again and again.  This simply is not an option with a Trucker's Hitch where you heave and then fumble to tie off just to preserve some of the peak tension depending on the level of your dexterity.  If the adjustment of other anchor points changes the restraint dynamic, the only option that allows measured, incremental tensioning to compensate is the Versatackle.

After countless uses, I've yet to have any difficulty undoing the Versatackle.
« Last Edit: November 04, 2012, 11:38:45 PM by roo »
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Fairlead

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Re: airplane tie-down knots
« Reply #13 on: November 05, 2012, 11:55:47 AM »
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!
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.

Gordon

roo

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Re: airplane tie-down knots
« Reply #14 on: November 05, 2012, 04:12:45 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  .
I don't think you realize that by leaving things free to move before hitting restraint, you actually increase the load on tie down points when a hard wind hits and allows kinetic energy to combine with otherwise static tension.  Impact loads are harder on rope, hardware, and knots.

Quote
Light aircraft on the other hand are tied down with SHORT lengths of rope which have to be carried  (thus weight is important)
A couple extra feet of rope is hardly a make or break issue, especially if it allows leaving metallic hardware behind.

Quote
and are tied to the aircraft by PILOTS who, apart from the very few, have no interest in learning complicated (to them) knots. 
Tensioners need not be complicated.  The hardest part about a Versatackle is learning a loop of your choice.
Quote
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.
Enjoy.

« Last Edit: November 05, 2012, 04:14:13 PM by roo »
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