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Tiedown Rope Length?

David Paule

Well Known Member
I plan to get some tiedown rope. I've selected the type and size (high-tech core, polyester or Technora cover, double braid and 1/4" diameter) but don't know the length. Any recommendations?

I expect that the wing ropes and tail rope will be different lengths.

Dave
 
Considering the at most tie-downs are set up for airplanes much larger than a -3, I carry enough for a 40-foot spacing. I would have to go dig out the kit, but I think I have 25’ for each wing, and probably a 15 or 20 for the tail. I’ve using 5 or 6 mm climbing rope, so not terribly heavy. A set of lightweight carabiners is also part of the kit.

Paul
 
Thanks, Paul, looks like 70' then.

I'll be getting New England Ropes Endura Braid, 1/4" diameter. Strength isn't an issue at around 4,500 lbs.

Dave
 
Is this for taking with you, for use in transient parking...just in case?
guessing this because if it was for your own fixed location you would know the spacing and how much you need....

70ft of climbing rope makes for quite a big pile of rope....

This is just a thought based on some experience in non-aviation applications.... have you considered using dynema rope (such as Am-steel) for that use? It's very strong so a much smaller diameter can be used...taking up much less space in storage, and probably lighter weight too. Maybe there's something about it that I'm not considering, that makes it not good for the application.... so this is just a thought to consider
 
I had never heard of Dyneema Rope. I looked it up and it is pretty impressive. I saw this - a different brand and pretty cheap if it lives up to the specs. 8500 lbs pulling strength for 1/4" sounds hard to believe. At $20 I may give it a try on my ranch and see how it works. If good, it would be a nice replacement for the bigger rope I have in my plane. https://www.amazon.com/dp/B096LTDR1X/ref=syn_sd_onsite_desktop_0?ie=UTF8&pd_rd_plhdr=t&th=1

This is just a thought based on some experience in non-aviation applications.... have you considered using dynema rope (such as Am-steel) for that use? It's very strong so a much smaller diameter can be used...taking up much less space in storage, and probably lighter weight too. Maybe there's something about it that I'm not considering, that makes it not good for the application.... so this is just a thought to consider
 
More than you probably wanted to know...

Dyneema won't hold knots under sustained load. I have pull-tested it and watched the line slowly slither through the knot, which held shape and tightness. Even a stopper knot doesn't help.

And the full strength is unobtainable with knots, since they reduce the assembly strength by as much as 50%. That said, and within its limitations, it's excellent. It's tough and somewhat resistant to abrasion. The way to obtain 100% of its strength is through a spliced loop. I prefer Brummel splices, or did back when I still had my sailboat, but perhaps there are other suitable splices too. The Brummel splices are fairly easy to make.

If you look up the Endura Braid which I'm planning to get, you'll see that it's got a Dyneema core and a polyester cover. The cover adds the ability to pull the rope and hold a knot, since bare Dyneema is a bit slippery.

I've got like 80' or 100' of 1/8" Dyneema line laying around which I used in a block and tackle to pull my non-RV back into the hangar. It was hard to keep that from tangling. I now have a wonderful tug that does the job so nicely.

The main criteria for tie-down ropes is low-stretch. That takes the right material and a large enough diameter to build EA. E stands for Young's Modulus, a material characteristic, and A for the cross-sectional area. I would buy the 3/16" Endura Braid except that I felt it would be too stretchy.

Dave
 
For conveniently and rapidly shortening the rope after using the carabiners to secure both ends (wing/ground anchor), what would be the preferred buckle or other such device? It seems to me that that would be the weak spot in any tie-down mechanism....(excluding security of the ground anchor, of course).
 
Hook the 'biner on the wing tiedown loop. Tie the rope as tight as you can and knot it with three half-hitches. Repeat on the other wing. Go to the tail tiedown, clip the 'biner to it, and use that rope to pull the plane aft until it's very firmly anchored.

No rope adjustments needed nor desired.

Do not leave slack in any rope. The last thing you want is for the plane to move - in strong winds, that'll lead to rocking or bouncing and the dynamic overload will fail something. And the plane will be lost.

Dave
 
I got the WROUGH Synthetic Winch Rope 1/4 x 50 Winch Line Cable Rope Breaking Strength for 8500lb today and tried to pull my truck with my tractor across the snow covered mushy grass. It worked fine. Im not sure how much it stretched. I will try and figure out how to test it. Maybe just pulling my truck in park with the tractor and marking a 4- section and see how far it stretches before it breaks. The pull test gave me confidence in its strength.

I will let you know how the test goes. So far, for $20 I will get more to use around the ranch. I like it.
 
For my current high wing airplane I purchased 15' long double braided nylon dock lines. They have been plenty long for all tie downs that are anywhere near the wings & tail.

What I like about a dock line is that it has a braided in loop or eyelet at one end. Normally that would go over a cleat on a boat, but I see it as one less knot I have to tie. Just feed the loop in through the tie down on the ground and then feed the other end of the rope through the loop and pull tight.

I also wish I would have bought bright yellow, orange or red lines instead of the dark color I have now. I think that would be safer for those walking around the plane.
 

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Runners can be useful

Runners are loops of webbing, with strength enough for climbing or tie downs, yet add almost no weight to your bag. ( available at REI etc.)

I have found the carabiners will not fit ( or easily fit) around the large tie down anchors found at many airports. The runners make it easy to connect, as you just slide it through and the clip the ‘biner through the doubled loop.
 
How tiny is a RV3? I've never measured, but I find it hard to believe that most GA tie down pads would require you to have 70' of rope.

A 172 has a 36' wingspan and is about 25' long. The mental picture I have of one setting in the tie downs makes me think that most pad eyes are about 20' apart.

Combine that with the fact that RV's are low wings and it seems like 10'-12' per rope wing would be plenty, but thats just my mental impression, I guess I could be wildly off in my guesstimate.
 
Do not leave slack in any rope. The last thing you want is for the plane to move - in strong winds, that'll lead to rocking or bouncing and the dynamic overload will fail something. And the plane will be lost.

Dave


Juan Brown was talking about this relative to the latest snow storms out where he lives (4 feet of snow). He noted planes tied down at his local airport collecting enough snow on the wings and tail to exceed their negative G limits, made worse by how tight the wing tie-downs were...pushing down the tail from snow weight put even bigger lever loads on the wings that were tightly tied down. He predicts several of those planes will have been over-G'd from the snow load. Granted, not a consideration for most of us, but interesting to think about.

Knotting the tiedowns in the venerable old half-hitch manner is problematic with the Dyneema rope, for example, which wants to untie itself under load (not to mention less convenient). I'm looking around for ratcheting rope hooks like the NiteIze CamJam, but something stronger. In the meantime, I've been using some cam lock tie down straps and carry some soft loops for those occasional problematic recessed concrete anchors.
 
For my current high wing airplane I purchased 15' long double braided nylon dock lines....What I like about a dock line is that it has a braided in loop or eyelet at one end.....

Nylon is probably one of the worst materials to use for tiedowns because the material is relatively stretchy. You'd need a large heavy diameter to make that satisfactory.

You can splice a loop into most ropes, by the way. Some splices are kind of fun.

Dave
 
Juan Brown was talking about this relative to the latest snow storms out where he lives (4 feet of snow). He noted planes tied down at his local airport collecting enough snow on the wings and tail to exceed their negative G limits, made worse by how tight the wing tie-downs were...pushing down the tail from snow weight put even bigger lever loads on the wings that were tightly tied down. He predicts several of those planes will have been over-G'd from the snow load. Granted, not a consideration for most of us, but interesting to think about.

Knotting the tiedowns in the venerable old half-hitch manner is problematic with the Dyneema rope, for example, which wants to untie itself under load (not to mention less convenient). I'm looking around for ratcheting rope hooks like the NiteIze CamJam, but something stronger. In the meantime, I've been using some cam lock tie down straps and carry some soft loops for those occasional problematic recessed concrete anchors.

The snow weight will off-load the tiedown rope's tension due to landing gear deflection.

The tendency of Dyneema not to hold a knot is why I prefer the covered ropes like Endura Braid, which do hold knots.

Dave
 
How tiny is a RV3? I've never measured, but I find it hard to believe that most GA tie down pads would require you to have 70' of rope.

A 172 has a 36' wingspan and is about 25' long. The mental picture I have of one setting in the tie downs makes me think that most pad eyes are about 20' apart.

Combine that with the fact that RV's are low wings and it seems like 10'-12' per rope wing would be plenty, but thats just my mental impression, I guess I could be wildly off in my guesstimate.

Tiny, Terry! :)

Truth is that out here in the real west, tie-downs can be few and far apart. If you find them spaced twenty feet, you’ve found an airport with great funding and a manager with an attention to detail. More often, we will find very widely spaced spots filled with sand, and oftentimes, they are unusable, so you have to tie to the next one over. And the tail tie-down can be a long ways away….

I don’t carry that much rope all the time, but if I am traveling, its in teh bag (and not very heavy at small diameters…)

Paul
 
Wow, I guess I'm lucky here in the midwest...Then again, we do have frequent 30 knot days and the occasional flying cow during tornado season, so tie downs have to be plentiful and robust.
 
What is wrong with nylon stretchy rope? I would rather have the rope stretch when a wind gust loads the airplane to absorb the shock, than the shock transferring to the airplane (like a chain). The only thing I don't like about nylon is that it absorbs water. I don't understand the reasoning to not use a stretchy rope. Please explain.
 
Stretchy ropes lead to the airplane rocking or lifting and dropping. Of course this only happens in violent wind, but that's when good tiedown performance is critical. When that sort of movement occurs, the dynamic loads tend to be higher than what a static loads analysis would suggest, and the higher dynamic load sometimes leads to failure.

Back in '81 or '82 I had an airplane tied down at the Boulder Airport in January. There was a windstorm. I went out to see how my plane was doing, and saw about a dozen wrecks scattered around. When I got there the wind was decreasing below 100 mph, and yes, standing or walking was difficult. They'd had various sorts of tiedown failures - ropes that slipped their knots, tiedown rings broken, loose ropes long enough that the plane could be pushed into another airplane, you name it.

I was an aerospace structural analyst and it was professionally fascinating to see all this and figure out what happened. I even saw some airplanes bouncing around like crazy, but surviving.

Here's another tip.... if you can tie a rope from a tiedown anchor to the landing gear, that will prevent the plane from crow-hopping sideways.

Bottom line - do anything you can to prevent rope stretch. I often double-up on my tiedown lines for less stretch, for example.

Dave
 
Thank You David Paule for the "stretchy rope" explanation. It seems to me that all these airport tie downs are designed around a tailwheel airplane. There should be a tie down point for the nose wheel on a tricycle airplane. If one looks at the position of the wing tie down points and the gear as a pivot point on many tricycle airplanes, the angle of attack of the wings can change relatively easy is a strong wind. I think we would lose far fewer airplanes to winds if a complete redesign of tie down locations on airplanes and airports be considered. (Not going to happen-I know) ....
 
Another tip that only works if you know the wind direction in advance and the direction stays constant, which is often the case here, is to position the place so the wind doesn't hit it head-on but at an angle. You don't want the wind to come from the rear at all, though. The idea here is to reduce the lift on the wings.

And double-rope the upwind wing.

Dave
 
10% vs 1% stretch at 20% of breaking load

That is roughly what stretch is for 3 strand nylon vs a high performance line like dyneema. (And roughly 30% stretch for nylon at breaking point)

Add that to difficulty in getting larger nylon line tight,….and planes can start bouncing around.

Flip side is that if you fail to get a high performance line tight,…. There will be a real “jerk” (loading spike) when it is pulled tight with movement
 
Chocks

Even very lightweight chocks, low enough for wheelpants, are just as key as rope and knots and control locks to weather a storm.
 
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