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  #1  
Old 08-14-2016, 04:06 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,063
Default Tiedown Technique

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
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  #2  
Old 08-14-2016, 04:30 PM
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f1rocket f1rocket is offline
 
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Location: Martinsville, IN
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Talking

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.
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  #3  
Old 08-14-2016, 05:34 PM
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tomkk tomkk is offline
 
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Location: Port Orange, Fl
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Default

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 ...

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Last edited by tomkk : 07-07-2017 at 08:29 PM.
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  #4  
Old 08-14-2016, 05:37 PM
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az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
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Question

Would it be this taut line hitch?

http://www.blueskyflight.com/doc/tautline.htm

Link with pics...
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  #5  
Old 08-14-2016, 05:55 PM
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tomkk tomkk is offline
 
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Default

I don't think so but that's a good one too.
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  #6  
Old 08-14-2016, 06:44 PM
David Paule David Paule is offline
 
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Location: Boulder, CO
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Default

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:



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
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  #7  
Old 08-14-2016, 06:46 PM
brad walton brad walton is offline
 
Join Date: Jul 2007
Location: Cypress, TX
Posts: 533
Default

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!
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  #8  
Old 08-14-2016, 06:46 PM
David Paule David Paule is offline
 
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Location: Boulder, CO
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Default

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
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  #9  
Old 08-14-2016, 07:22 PM
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Infidel Infidel is offline
 
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Location: WV22
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Default

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.
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  #10  
Old 08-15-2016, 09:55 AM
smiller smiller is offline
 
Join Date: Feb 2008
Location: Hillsboro, Oregon
Posts: 103
Default The FAA's thoughts

AC 20-35C
https://www.faa.gov/regulations_poli...cumentID/22573

I haven't look at this in a long time, and can't right now, but I recall being surprised that they don't mention the knot that most pilots actually use.
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