Tie down rope material advice request

[Henning]

Thanks for the terminolgy. Never knew what to call'em.
Why are straps suboptimal? I'm hangared so tiedowns are short term use.

For short term it's fine to use mcycle straps with metal hooks, just snug em up good. For long term tie down it's suboptimal because you can set up an electrolytic loop with your plane as the anode in the right atmospheric conditions. For example, if you used it in Key West or Okrakoke or so, your plane will be giving up a continuous slow trickle of aluminum electrons to ground through the metal hook and moist salty strap.

 

[alfadog]

Thanks for the terminolgy. Never knew what to call'em.
Why are straps suboptimal? I'm hangared so tiedowns are short term use.

One reason to go with rope is that the cheap straps like the ones I use are only rated for 400 lbs or so. I imagine a stiff wind will generate more uplift on the wing of my Arrow than that. However, I do not think the anchors I use (the screw-in doggy types) will stand up to much more than that anyway. Also the 400 lb rating carries a factor of safety of prolly 2x.

edit: I should mention that this is just the setup I used one time at last SnF. On the ramp, I have hefty ropes and secure tie-down rings.

 

[Lawreston]

a local glider pilot has a small dog named "Tailwheel"

During my 27 years as a camera store owner my two cats were "Pentax" and "Iris."

HR

 

[Cap'n Jack]

For short term it's fine to use mcycle straps with metal hooks, just snug em up good. For long term tie down it's suboptimal because you can set up an electrolytic loop with your plane as the anode in the right atmospheric conditions. For example, if you used it in Key West or Okrakoke or so, your plane will be giving up a continuous slow trickle of aluminum electrons to ground through the metal hook and moist salty strap.

That has nothing to do with the strap and everything to do with metal fittings. The same thing would happen if rope with hooks were used. If the hooks and eye were made of same material, nothing would happen. Or just get the coated hooks and check the coating before use.

 

[Henning]

That has nothing to do with the strap and everything to do with metal fittings. The same thing would happen if rope with hooks were used. If the hooks and eye were made of same material, nothing would happen. Or just get the coated hooks and check the coating before use.

As I said, metal hooks are suboptimal, he asked why, I explained the whole loop.

 

[weilke]

One reason to go with rope is that the cheap straps like the ones I use are only rated for 400 lbs or so. I imagine a stiff wind will generate more uplift on the wing of my Arrow than that. However, I do not think the anchors I use (the screw-in doggy types) will stand up to much more than that anyway. Also the 400 lb rating carries a factor of safety of prolly 2x..

Most of those cargo straps have a very low rating (e.g. the 400lbs mentioned) while the ratchet is in motion. When the handle is laid down and both ratchet sears engaged, they can handle a lot more, maybe 2000lbs.

As for the screw-in anchors: After one of the gust-front incidents last year, someone had pictures of planes on their backs with the tail tiedown still in place but the concrete blocks with both wing tiedowns yanked out of the asphalt and deposited right next to the upside down plane. It is a weakest link thing.

 

[ejensen]

For short term it's fine to use mcycle straps with metal hooks, just snug em up good. For long term tie down it's suboptimal because you can set up an electrolytic loop with your plane as the anode in the right atmospheric conditions. For example, if you used it in Key West or Okrakoke or so, your plane will be giving up a continuous slow trickle of aluminum electrons to ground through the metal hook and moist salty strap.

Interesting. I've never been around salt air/water much. I do remember at Mustang Island the chains at the airport lasted only a few months.

BTW, no aluminum in the Jabiru:wink2:

 

[flyer]

I wonder what the reasoning is behind the "no tiedown" rule...

My guess would be they dont the liability of the planes parked on the ramp. The last airport I was at that discouraged tieing down also had a sign on the ramp that said "tie down at your own risk, the airport X is not responsible for loss or damage to aircraft"

There was one airport I landed at in Oklahoma once that didnt allow tie downs period, only overnight hangars.

 

[alfadog]

Interesting. I've never been around salt air/water much. I do remember at Mustang Island the chains at the airport lasted only a few months.

BTW, no aluminum in the Jabiru:wink2:

I imagine that was more due to oxidation than electrolysis.

 

[ejensen]

Most of those cargo straps have a very low rating (e.g. the 400lbs mentioned) while the ratchet is in motion. When the handle is laid down and both ratchet sears engaged, they can handle a lot more, maybe 2000lbs.

As for the screw-in anchors: After one of the gust-front incidents last year, someone had pictures of planes on their backs with the tail tiedown still in place but the concrete blocks with both wing tiedowns yanked out of the asphalt and deposited right next to the upside down plane. It is a weakest link thing.

I usually tie the ratchet closed with the excess.

A friend had her Arrow totaled with the tiedown ring failed on one wing in 65 knot winds. As you say the weakest link.

 

[Cap'n Jack]

As I said, metal hooks are suboptimal, he asked why, I explained the whole loop.

Just get the coated ones, and check them for breaks in the coating (insulation) before use, and you break the circuit.

 

[alfadog]

Most of those cargo straps have a very low rating (e.g. the 400lbs mentioned) while the ratchet is in motion. When the handle is laid down and both ratchet sears engaged, they can handle a lot more, maybe 2000lbs.

As for the screw-in anchors: After one of the gust-front incidents last year, someone had pictures of planes on their backs with the tail tiedown still in place but the concrete blocks with both wing tiedowns yanked out of the asphalt and deposited right next to the upside down plane. It is a weakest link thing.

The ones I looked at on Harbor Freight (similar to what I had in me truck and took to SnF) have the strap rated for 400 - 500 lbs. One said the ratchet was rated for 500 lbs.

 

[alfadog]

I usually tie the ratchet closed with the excess.

A friend had her Arrow totaled with the tiedown ring failed on one wing in 65 knot winds. As you say the weakest link.

See, that I don't get. Not about you but just something I was thinking about.

The airplane is tied down with a fairly low AOA on the wing, like a cruise AOA. It takes maybe 120 kt to generate enough lift to fly the airplane at that AOA for the Arrow. You would have to have enough wind to fly the airplane PLUS additional lift to tear out the tiedown ring.

Hurricane, yes. In fact, my Arrow was damaged that way in Hurricane Wilma with the prior owner. Lifted it up and set it down on the strut of the shade hangar, damaging an aileron.

Tornado, of course. See 2011 SnF and many other instances.

65 kt wind? I don't think so. There may have been a small tornado involved? Or is there something I am missing here?

 

[Henning]

Interesting. I've never been around salt air/water much. I do remember at Mustang Island the chains at the airport lasted only a few months.

BTW, no aluminum in the Jabiru:wink2:

Lol, but if it was carbon all the fasters would be sacrificial.

 

[Henning]

See, that I don't get. Not about you but just something I was thinking about.

The airplane is tied down with a fairly low AOA on the wing, like a cruise AOA. It takes maybe 120 kt to generate enough lift to fly the airplane at that AOA for the Arrow. You would have to have enough wind to fly the airplane PLUS additional lift to tear out the tiedown ring.

Hurricane, yes. In fact, my Arrow was damaged that way in Hurricane Wilma with the prior owner. Lifted it up and set it down on the strut of the shade hangar, damaging an aileron.

Tornado, of course. See 2011 SnF and many other instances.

65 kt wind? I don't think so. There may have been a small tornado involved? Or is there something I am missing here?

Bouncing.

 

[Clark1961]

Bouncing.

That was the description from witnesses at the airport. Of course I got that third hand so ya never know...

 

[Cap'n Jack]

Lol, but if it was carbon all the fasters would be sacrificial.

How so?

 

[Henning]

That was the description from witnesses at the airport. Of course I got that third hand so ya never know...

I've seen it during a storm, they vibrate and bounce, then the lines get wet and stretch and they start bouncing more, then you see something snap and then the oscillations get greater and suddenly, destruction and it comes part and flips.

 

[Capt. Geoffrey Thorpe]

We took the standard open hook design, cut them off and sewed on locking carabiners for "daily use". Not for overnight long term use. Need someone that has the equipment to stitch canvas or parachute harness, seatbelts, etc.

You couldn't bend the hook and slip it off without cutting the strap?

FWIW - Whatever brand of ratchet strap my brother tried to use for some runups when he first assembled his Pitts was not as strong as the engine...

 

[fgcason]

then the lines get wet and stretch and they start bouncing more

+1

Then someone sees it's loose and tightens the wet straps which shrink and tighten a lot when it dries.

 

[ejensen]

See, that I don't get. Not about you but just something I was thinking about.

The airplane is tied down with a fairly low AOA on the wing, like a cruise AOA. It takes maybe 120 kt to generate enough lift to fly the airplane at that AOA for the Arrow. You would have to have enough wind to fly the airplane PLUS additional lift to tear out the tiedown ring.

Hurricane, yes. In fact, my Arrow was damaged that way in Hurricane Wilma with the prior owner. Lifted it up and set it down on the strut of the shade hangar, damaging an aileron.

Tornado, of course. See 2011 SnF and many other instances.

65 kt wind? I don't think so. There may have been a small tornado involved? Or is there something I am missing here?

Maybe you haven't lived in an area prone to chinook (foehn) winds.

Her plane was at Denver Metro (BJC) and this happened several years ago. Don't know if there was anything wrong with the tiedown ring but it pulled loose and the plane flipped on the remaining two. Here's the first example I could find. The Front Range see event like this several times a year. 65 is on the high side but not rare.

Boulder Daily Camera: "Winds as high as 93 mph fueled fires, prompted evacuations, snapped electric poles and flipped over semis as mayhem blew through Boulder County on Wednesday.
The National Center for Atmospheric Research recorded a peak wind gust of 88 mph at noon in Boulder and a 93 mph gust at 3 p.m. in Lyons."

I've seen pictures of a 152 flying on its ropes.

 

[Henning]

Also remember, down bursts can seriously raise the pressure at their core of impact, the form of the pressure wave serves to effectively increase the AOA gaining you greater lift than the windspeed would indicate.

 

[John Baker]

I bought one of these kits. It comes with a small cloth sack to store it in. I keep it with all my other junk for assorted missions I might have.

http://www.sportys.com/PilotShop/product/9623

But all you really need is some rope that has a little bit of a stretch to it, like mountaineering rope or some such similar thing. The stretching factor makes it easier on the plane.

John

 

[alfadog]

Maybe you haven't lived in an area prone to chinook (foehn) winds.

Her plane was at Denver Metro (BJC) and this happened several years ago. Don't know if there was anything wrong with the tiedown ring but it pulled loose and the plane flipped on the remaining two. Here's the first example I could find. The Front Range see event like this several times a year. 65 is on the high side but not rare.

Boulder Daily Camera: "Winds as high as 93 mph fueled fires, prompted evacuations, snapped electric poles and flipped over semis as mayhem blew through Boulder County on Wednesday.
The National Center for Atmospheric Research recorded a peak wind gust of 88 mph at noon in Boulder and a 93 mph gust at 3 p.m. in Lyons."

I've seen pictures of a 152 flying on its ropes.

Thanks

Yes, I can absolutely see a 152 flying on its ropes in 65 kt winds. And yes, I guess that oscillation and shock loading plays a part in breaking the rope and/or the ring.

 

[alfadog]

I bought one of these kits. It comes with a small cloth sack to store it in. I keep it with all my other junk for assorted missions I might have.

http://www.sportys.com/PilotShop/product/9623

But all you really need is some rope that has a little bit of a stretch to it, like mountaineering rope or some such similar thing. The stretching factor makes it easier on the plane.

John

Those look nice and the price is not too bad considering decent rope is a buck a foot and these have the hooks and clamps.