Trying, with tremendous trepidation, not to trip on the tripe ...
I find some direct information here:
www.airventure.org/planning/tying_down.htmlwhich 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:
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:
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.aspWeights 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/... 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
noosesuch 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:
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)!
--dl
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