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Tiedown Technique

David Paule

Well Known Member
I'm repeating this here for broader distribution. Initially, I wrote it for someone's trip write-up.

For tiedown knots, ditch those "tent" knots that you're using, they won't hold up to a real blow. They'll slide up the rope and things will get sloppy and loose and the plane will start rocking and eventually something will break. Instead, use three half-hitches right at the tiedown rings after pulling the ropes just as tight as you can get them -- don't use chocks while doing this. I tie one main, then the other one, cranking down on it, and then the tail, pulling the plane back as I do for more tightness.

When the length of the ropes permit, I double-up the rope. The idea is to gain more stiffness. Anything to keep the plane from moving around. It's the dynamic movement of the plane which breaks things.

Also, if you have an idea where the winds will come from, it's best to orient the plane so that the wind comes from a front quarter. Directly nose into the wind seems to increase the loads on the ropes and rings, while aft winds can damage the control surfaces. Directly sideways is acceptable.

Of course you'll use your control locks.

I learned this after some 100+ mph winds at the Boulder Airport in 1981 or 1982. We lost about a dozen airplanes. I walked among the wreckage examining what failed, and among the survivors, examining what worked.

Dave
 
A picture is worth a thousand words.

I once printed off a diagram from the Alaskan Bush Pilots guide on the knot they recommend. I think it's close to what you are describing. In the end I just use extra long nylon cargo straps and I tie the lose end with the bush knot.
 
Google "Aircraft tie down knot" and there are a million. Don't know what it's called, but this is what I use. Easy and works well ...

noEMOd50OJCYN4FJJoyu3igkR0qTz55WbD3icoDu3A9yHwGVoqKufuVlcBx5EPzkY5mDlrmJWt7df7SzgXJybCrjmlmHtCi185pmGIsRy75upBQ5ahDkeg4_d1vw5scEujqGV9rXjP4lItEphzeiH0jvcyWfzyJqSvkcnomb2OEhPQxIJR2gQ0KjNaTlQauYdFqvpvie4cZEECior_7q4DLtKvR3XTfrTxIHYCrmCYypSL4VcB270z3EqhN12nhoMGdmY1jdFK7oXhw-wsdZkt4e4yudZCEIB3DSu4VxDPWiZ0mqT2zZaiD5dxuyP4cXN5QGkPXPQETxpr8sG6jMhLQg-PhnkQ0A3auUa6Ixahz6gNrhsdfBRHU4K-XPmR0pC_QNaFvwFSW4UKKMIhOvzbA6_suJ7Gj3dGljBp6AIOCO9KBwbLDlqWFp6y1u6UVh8lykq5UiFOOYEI_FDLPe-E1ml_DZ2uealB9_KmeYzD-lzpN447D2vfnkp2ARyDpmQfpHBUK_BDfTlbejTdyvxmioemo0tmP3wQzaSNeYU7dhGreajS8IxaZhieefwdBkiDf-Dwj1BazJ-dTz8hjGfO6kmjvswZDd9RJTe5dQNoUlkLPCJZP5tn7VFyoJ3724UhY7XB-X7zflXU16V9Hu338pwZMV4R2aC_Ifi3o=w296-h866-no
 
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Whatever knot you use, make darn certain that it can't slip. The best way to do that is to snug it up against the ring, with a thoroughly tight rope.

This is the knot that will slip:

knot7.jpg


It lets you add a bit of tension to the rope and that's good. But when things get nasty the rope jerks and it comes undone or slips and then the plane is lost. I've seen it.

Caveat, I haven't seen any instances of this snugged tight against a tiedown ring. It might work there, especially if the free end has a couple of half-hitches. But I won't use it anywhere.

Dave
 
I've always used the taught line hitch shown in az_ gila's post. I once saw a Blanik get flipped by a small tornado. The taught line hitch held fine, it pulled the permanent ground anchor out of the ground!
 
You only need to tie it down correctly if the wind's really going to blow. In gentle breezes, say under 40 or 50 kts, especially if steady, it doesn't matter so much.

Dave
 
Another sound piece of advice...don't take for granted your passenger(co-pilot) did a good job with the tie downs. I learned that the hard way and found my plane lying on its back on the Tarmac. The only rope that held was the one I tied. Still my fault and a sad day it was.
 
I can't believe any of you former Boy Scouts don't recognize Tom's knot

It is a bowline knot. It is very strong, but it does not tighten the slack like a taught line hitch does. So, if you use a bowline knot, it will not come loose, but there will be a little slack in the line. Also, it will be more difficult to untie than a taught line hitch, or the one my instructor taught me a million years ago, the rolling half hitch (the one shown by David Paule).
 
I flunked out of the Boy Scouts ;)

What is wrong with a couple of half-hitches, with the knot hard against the tiedown ring?
 
Bowline is a Sailor's Knot

advantages of a bowline are reliability, high strength and ability to easily untie it, even when it's wet. I typically use a bowline at the ground anchor and a double half hitch at the rings. The double half helps take out slack. Using a single half hitch is little better than leaving the plane untied.
Terry, CFI
RV9A N323TP
 
I use a Midshipman's Hitch from the wing tie down. You can slide the knot on the standing line to take slack out, but it will not slide under load as the knot torques over on itself and just gets tighter and tighter. I have a permanent loop tied on one end for ease, but if it looks like it is going to be nasty, I tie an anchor knot on the ground ring.
Same benefits as above. You can loosen it easily even when highly torqued and/or wet.
I usually put in two of these per line but not sure it buys anything except it looks cool ;)
I used to carry a similar sketch as this with my tie down kit, but over the years have committed it to memory.
Also, if you tie this knot wrong, go over the first hitch, not under, the knot just kind of falls apart. You know immediately that it isn't tied right. I am still a fan of ropes and don't like the nylon straps. Not sure why.

2uo4bpx.jpg
 
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Whatever, the most important thing is leave no slack in the line. And ensure that there's absolutely no possibility of the knot sliding - for that, place the knot securely against the ring.

The cause of many of the failures was that the plane started rocking and moving around, and that basically jerked the tiedown ropes or chains. It was that dynamic load event which broke them, not a static load.

DanH had it right; I prefer 2 or 3 half-hitches and have never had any problem untieing them.

It's been said: "One half-hitch will hold a mule. Two half-hitches will hold anything. Three half-hitches will hold the devil himself." So use 3.

Dave
 
Whatever, the most important thing is leave no slack in the line. And ensure that there's absolutely no possibility of the knot sliding - for that, place the knot securely against the ring.

The cause of many of the failures was that the plane started rocking and moving around, and that basically jerked the tiedown ropes or chains. It was that dynamic load event which broke them, not a static load.

DanH had it right; I prefer 2 or 3 half-hitches and have never had any problem untieing them.

It's been said: "One half-hitch will hold a mule. Two half-hitches will hold anything. Three half-hitches will hold the devil himself." So use 3.

Dave

How do you hold a tight rope and get your first hitch in? I struggle. Once the hitch is in, you can't tighten the standing line. I would like to know your technique.

Taking a knot out of modern core and braided shell rope isn't hard. I think that is a hold over from the days of hemp.
 
How do you hold a tight rope and get your first hitch in? I struggle. Once the hitch is in, you can't tighten the standing line. I would like to know your technique...

If a picture is worth a thousand words, a demonstration must be worth a million... Anyway, I'll give it a shot: Being right handed, I insert the free end of the rope through the right side of the the ring and pull it taught with my left hand on the free end as close as possible to the ring. While holding tension with my left hand, I use my right hand to loop the free end of the rope around the taught side and back through the resulting loop. I then pull up the free end with my right hand, holding tension with the left until the knot gets to my fingers, then tighten it all the way to the ring. Repeat to your heart's content.

I've never had two half hitches come untied or get loose, and they are a piece of cake to untie. Even when my 170 was run over by a stray Cherokee, the one tiedown rope that wasn't broken and/or cut was tight as a banjo string, but still managed to keep what was left of my airplane out of the one parked only a few feet away.
 
Miles points out something else to consider: how the planes near yours are tied down.

If they're not tied down properly yours is at risk when theirs goes over.

Dave
 
Truckers Hitch

The Truckers hitch works great for tying down aircraft, I have used it for many years. It is very easy to get the lines nice and tight. Also works for tying a canoe on top of your car or external load on your floats.
knottruck_zpssa1cllyt.gif
[/URL][/IMG]
 
Same old debate?

Not trying to discount David's experiences, but the FAA still advises to face directly into the wind and not have the ropes or chains super tight.



Before I had a hangar, one of my well intentioned RV buddies would go "tighten the ****" out of the chains for me when I didn't ask him to. I really found that irritating.
 
I don't think David is relying on his experience, but rather, his knowledge as a very good structural engineer.
 
The Truckers hitch works great for tying down aircraft, I have used it for many years. It is very easy to get the lines nice and tight. Also works for tying a canoe on top of your car or external load on your floats.
knottruck_zpssa1cllyt.gif
[/URL][/IMG]

Thanks!! I have been using this knot for 5 decades for trailer and truck load tie down - motorcycles etc and one had never some loose. But . . . I did not (knot) know it had a name!! I don't even remember where I learned it. Maybe, I invented it? Maybe it is a natural knot borne out of frustration.

Anyway, Thanks!

Edit: Animated= https://www.animatedknots.com/truckers/index.php
 
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Dumb question - any reason not to use ratchet straps ? - I've got three that are rated for 1500 lbs each that don't weigh all that much in my travel bag. While there is a slight weight penalty - seems much easier than ropes unless I am missing something
 
Knots

I had the pleasure of going to Osh this year arrived on Saturday and knew that weather would be coming through so I brought double tie downs with me .
I have been at fly-ins camping out and risk my life to try and save others planes that were no were around that tied down with dog tie downs learned a lot from that experience .It don't matter what kind of knot you tie at a fly-in if your not tied to a ground apparatus that will hold.Not trying to be unkind here but its scary to walk around major fly-ins and look at the tie downs that pilots bring to tie down something they spent many years building and many tens of thousands of dollars. Osh has very good ground for a good tie down apparatus on the other hand Sun and Fun does not and if your going there you need to give it some extra thought.
Bob
 
Truckers Hitch

I also have used the truckers hitch due to the fact it is easy to get tight. One thing I have done to modify it is use an alpine butterfly for the loop, it is easily untied no matter how much it has been loaded up. It seems a bit complicated but once you learn it, it is a breeze to tie. Unfortunately I am not a techno wiz so no picture attached but I am sure a quick google search will turn up instructions.

I agree that some plane tie downs are hideous and I feel there should be more policing of tie downs at events such as Oshkosh. I witnessed many tie downs situation that I would consider "less than favourable"
 
Dumb question - any reason not to use ratchet straps ? - I've got three that are rated for 1500 lbs each that don't weigh all that much in my travel bag. While there is a slight weight penalty - seems much easier than ropes unless I am missing something

Jason, you beat me to it. I also use heavy-strength ratchet straps. In addition, instead of taking all the slack out of the strap before cranking it down, I allow about 6-9 inches of slack in the strap before cranking it down. Reason: This ensures tight strap locks the underlying loops in place, preventing slippage.

So, like Jason, I'd like to know if there are any reasons not to use ratchet straps.
 
Other than the recommendation being 3000-lb capacity at each tie down point, ratchet straps seem ok.

Scroll, whatever you used appeared to hold up just fine during the Saturday night thunderstorms at Osh!
 
There is a thread on here that discusses straps vs. ropes; the concern seem to be how stretchable the straps may be. But there was someone on here a few years back selling ratcheting tiedowns using 3/8" rope. I can't find the posts so I don't know if they are still being sold but I found similar things on the web sold for other purposes. The ratcheting pulley and one end of the rope have carabiners, and you simply attach to a ground ring and the aircraft and then pull the rope tight. I bought a set of three for my -6A and loved them. I just added 'Remove Before Flight' ribbons at the pulleys, and have another brand new set in a box for the RV-10. The only problems I have ever had were that the carabiners will not always fit those fancy set-in-concrete tie downs at some airports but if there is no chain there, then a set of very short pieces of chain kept with the ropes will wrap around those flush tie down points and allow me to attach my carabiners.
 
Agreed!!!

Jason, you beat me to it. I also use heavy-strength ratchet straps. In addition, instead of taking all the slack out of the strap before cranking it down, I allow about 6-9 inches of slack in the strap before cranking it down. Reason: This ensures tight strap locks the underlying loops in place, preventing slippage.

So, like Jason, I'd like to know if there are any reasons not to use ratchet straps.

I have a small Craftsman tool bag that is my "tie down kit." It includes 18" spikes. One with a tube welded on the other with a large washer welded on, times 3. When pounded in they for an X. 3 sets of 3000lb ratchet straps, plus a spare. And, a 3lb sledge.

The biggest hassle with this set up is getting the spikes out. Especially, after more than a few days!!! I think there is much more chance of the tie down source coming out than the rope or ratchet breaking.

I respect those who can tie knots but I've failed:) Ratchet straps make it so much easier.
 
I remember that product Patrick. It was very cool. I searched a few years ago and couldn't find them.
I have a good friend who manufactures ratchet straps. He was a plumber and got tired of tying pipe on top of his truck with standard ratchet straps and/or rope so he invented and patented a ratxhet that bolts or is welded to the truck rack and the strap ties back into itself. His company, Rack Strap, is the main supplier to the top rack and trailer manufacturers in the construction industry. If you see a truck rack with a bolted on or welded ratchet, it is probably his gear.
I have a few questions emailed to him about ropes vs ratchet straps. We will see what he says.
 
Truckers hitch

The Truckers hitch works great for tying down aircraft, I have used it for many years. It is very easy to get the lines nice and tight. Also works for tying a canoe on top of your car or external load on your floats.
knottruck_zpssa1cllyt.gif
[/URL][/IMG]

Not flying but been using the "truckers hitch" for years. Easy to tighten and holds. Easy to release. The slip knot can be a bear after hauling a heavy load.
 
With ratcheting straps, you don't want to damage the plane by pulling them too tight.

Many of them have open hooks, and that's bad. Don't use any open hooks no matter what, as they can pop out of the tiedown ring when it gets nasty.

The remaining issue is that if the strap itself is nylon or polypropylene, it's somewhat more stretchy than polyester. Since all ropes are springs to a structural engineer, and springiness is what we want to avoid, let's discuss that for a moment.

The equation for the spinginess of a rope can be described by this equation:

K = E * A / L

where
K is the spring constant, and bigger is better. In U.S. units it is typically pounds per inch;
E is a material property, with units of psi;
A is the cross-sectional area, with units of square inches;
And L is the length of the rope, from the ring to the ground anchor, measured in inches.

So to make K bigger and the ropes therefore less stretchable, we can choose good materials, use a thick rope and keep it short.

Back when I was playing with sailboats I kept a list of different ropes and their manufacturer's data. From that, very roughly, rope and strap materials seem to be have a value for E of about -

Nylon or polypropylene, 60,000 to 80,000 psi,

Polyester, 100,000 to 250,000 psi,

And for the fancy high-tech cored ropes, anything from 350,000 to more than 5 million psi. With these, of course, make sure that they are designed to hold knots as some don't.

Getting back to ratcheting straps, if the cross-sectional area is sufficient, it'll make up for the flexible material.

On my Cessna 180, I use 5/16" polyester rope. I chose New England's Regatta Braid for ease of handling, and I double-up the line to increase the effective cross-sectional area. From the ground anchor, I run it to the tiedown ring, pull down on it and knot it there, and then back to the ground and knot it again.

Dave
 
Not trying to discount David's experiences, but the FAA still advises to face directly into the wind and not have the ropes or chains super tight....

Yes, they do.

They're wrong.

If the plane points into the wind, it will develop lift based upon its design, the angle of attack it's at and the strength of the wind. These can be large forces.

Off the wind there are a couple of things that reduce the effect of the wind. First is the obvious: the fuselage will act sort of as a spoiler for the down-wind wing, or at least part of it.

Second is that the lift-curve slope, or how fast a wing picks up lift with angle of attack, is dependent upon the wing sweep. That's why highly-swept wings like military fighters land at such high nose angles. More sweep, shallower curve and less lift for a given angle of attack. So if the wind is coming partly from the side, the wings are less effective and the forces are lower.

When I was walking around those damaged airplanes, that was one of the things I picked up on.

Also, the FAA isn't considering the dynamic impact loads when a loose rope bottoms out and gets tight abruptly. It's this extra load that is more likely to cause damage than a steady-state load event.

Dave
 
Yep, ropes are indeed springs! Back in my water skiing days, we used Kevlar tow ropes. The cheap nylon ones stretched so much in a tight slalom turn they wanted to jerk you right off your ski when they recoiled coming out of the turn when the rope was unloaded!
 
Not flying but been using the "truckers hitch" for years. Easy to tighten and holds. Easy to release. The slip knot can be a bear after hauling a heavy load.

You can replace the slip knot portion with a Bowline (with a loop), which is easy to untie. The rest of the "truckers hitch" remains unchanged. In both cases, you can get it as tight as a guitar string if you like -- choose your note. ;-)
 
I have been at fly-ins camping out and risk my life to try and save others planes that were no were around that tied down with dog tie downs learned a lot from that experience .

Not all "dog tie downs" are created equal. Mine are made from titanium, are longer than typical dog stakes, and are screwed in at an angle with a titanium bar. I defy you to pull them out. They work great in most situations except real sandy soil and in those conditions, it takes concrete to hold an airplane in place.
 
Knots

I agree in my case it was Wal-Mart type.
Sandy soil like SNF is a problem.
And all that only cost you an airplane ride if we both make it to Petit Jean.
Bob
 
Not all "dog tie downs" are created equal. Mine are made from titanium, are longer than typical dog stakes, and are screwed in at an angle with a titanium bar. I defy you to pull them out. They work great in most situations except real sandy soil and in those conditions, it takes concrete to hold an airplane in place.

I've got a set of the titanium tie-downs, too. I almost hate to use them, afraid I will leave them somewhere....they are a collector item now.
 
I've got a set of the titanium tie-downs, too. I almost hate to use them, afraid I will leave them somewhere....they are a collector item now.

Yes, you are right. I sold my first pair with my Rocket and needed a set to go with my new lightweight LSA. Fortunately, a friend had a set that he sold to me at a reasonable price.
 
I've got a set of the titanium tie-downs, too. I almost hate to use them, afraid I will leave them somewhere....they are a collector item now.

Yes, you are right. I sold my first pair with my Rocket and needed a set to go with my new lightweight LSA. Fortunately, a friend had a set that he sold to me at a reasonable price.

We are starting to show our age and how long we have been flying Van's RV aircraft. We all purchased the same item from Randy Simpson's Airtime when they first came available. Unfortunately we made the demand for them so great that there are no more new ones to be had. Toward the end of production, delays were very common and buyers were very disappointed.
 
My Randy Simpson Ti-downs have spent the last decade holding down a 10'x20' easy up for two weeks of everything Oshkosh can throw at it. I'm not sure how much lift that thing can develop in the right conditions but it is considerable.

So, here are a couple of photos of 2016's "worst tie down at Oshkosh" award. Maybe some of the rope experts here can comment on these knots... not to mention the plastic tent stake or the cheap carabiner.

69fc932c17409695b4c3e7770e82e1f5.jpg


Note that on the tail, at least he doubled up the ropes a couple of times. That ought to hold it.

B922FB89-2DD3-4754-94B0-9EA7160B192E.jpg


This plane sat in this condition in Homebuilt Camping through Saturday morning. I spoke to the owner as he was leaving- he was a little embarrassed when I gave him "the lecture" but that sort of misses the point. Other airplanes spent the week tied down right next to him- did any of his neighbors take this up with him? There is only so much that EAA or any fly-in organizer can do- but peer pressure can go a long way. So be polite but proactive when you see this at a fly-in.
 
Knots

The first photo of a knot is a "Bowline" ( the one on the right) As an old sailor who has tied 1000s it is the best overall knot.
 
When planning an Alvord Desert trip (think wind) a few years ago, I followed David Paule's advice:
http://www.vansairforce.com/community/showpost.php?p=529604&postcount=8
making titanium tiedowns from McMaster-Carr 3/8" rod cut to 18" pieces, and using Dyneema rope, stirred gently with the EAA tiedown design: http://www.eaa.org/~/media/files/eaa/homebuilders/5aircraft tiedowns.pdf

Threading titanium rod is not fun. Pounding 18" titanium stakes into a dry lakebed was a lot of work. I discovered you can beat the cr*p out of titanium and it sloughs it off. Which may be related to the comment about being difficult to thread.

I used half hitches, ropes pulled tight, but winds never got past 30 mph or so. Thus not exactly a great test.
 
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