Tie Down Length?

[Kyle Wolfe]

I did several searches but can't find any reference to length of tie down ropes, size or tensile strength. I recall 3/8s but what's best, braided, nylon, etc..? And how long have you guys made them? All 3 same length or shorter on the tail? I need to get rid of the old tiestrap tiedowns and wanted your thougts.

Thanks.

[GAHorn]

If you go to marine-supply stores, you can usually find an "anchor rode" package that will be less expensive and perfect for tie-downs. WalMart, Academy, etc., frequently have such. Anchor rodes are usually sold in 50-foot lengths, which will provide three approximately 17-foot-long ropes. Melt the ends with a hot iron or torch/match etc to prevent fraying.

Anyway... a 1/2-inch twisted nylon rope is good tie-down rope for several reasons.

1: It has a breaking strength of about 1200 lbs. (It makes little sense to have tie downs that will not in combination, be equal to the gross weight of the aircraft. Imagine a 2200 lb aircraft that by design ... is capable of generating that much lift.... being "tied down" with restraints that can't match the lifting capability of that wing. The wing tie-downs counter-act the lifting capability of the wing. Two 1/2" nylon ropes are designed to hold up to 2400 lbs, and the tail tie-down merely keeps the airplane's tail constrained.)

2: Nylon is resistant to mold, bacteria, and rot. (A wet rope may remain wet for some time and in fact, may also be stored in that condition for some time. It makes little sense to use ropes of material that cannot withstand such abuse.

3: Ordinary twisted-cord nylon rope is inexpensive and stronger than woven or "braided" ropes, which frequently have been "filled" with loose fibers that contribute nothing to strength. It frequently retails for about 55-cents per foot.

4: Nylon will not shrink when wet, and will allow a certain amount of "stretch" to accomodate gusting winds without unduly stressing the aircraft structure.

Finally, I used my Boy Scout training skills to make eye-splices in one end and end-splices in the "bitter end". By having an eye-splice in one end, it's a simple matter to stick the loop thru the anchor-eye in the concrete or in the eye of the tie down stakes I use (made out of trailer-house anchors with the spiral cut off) and that way no knot is required to attach it at the lower end in the ground, because the bitter end is stuck back thru the eye-splice.... therefore only one set of knots are required after passing thru the strut tie-down eyebolt. (Knots weaken a ropes holding capacity, while splices do not.)

Avoid polyester and polypropylene rope because they do not withstand exposure to sunlight without becoming brittle and weak. Avoid "straps" and such with open "hooks" and "cinching clasps" and such trick hardware, because they typically do not have the same strength as ordinary twisted rope. Straps are too easily damaged at their edges after contact with hardware, and then the integrity of the entire system is compromised. Avoid open hooks at the ends because once any slack develops in the system, a wind might allow an airplane to "rock" at it's moorings, which will then allow the hooks to disengage. In general, avoid anything other than simple, reliable, twisted-cord rope made of durable nylon. 15-20 foot lengths are probably all you'll need.

[Abe]

Kyle,
This is an area that I have a bit of experience as I produce aviation tie down kits...now I'm not advertising George...only going to try and answer the posted question. ..I've found that 14' ropes work well for the majority of wing tie downs and 8' for tying tail sections down...There are some folks who prefer more and a few less, but taking the weight factor in, 14' & 8' will work 98% percent of the time...We use an 8mm (5/16") nylon type rope with a breaking strength of 3650 lbs for each of the three tie down points....I use my tie down ropes for on and off airport use all over the Pacific NW with 04D and have never had a problem with length or strength....I've designed a simple pull testing apparatus that I take in 04D on occasion to test our kits or other pilots tie downs at the various locations (to test in the various soil types) and never have I seen one of our ropes fail....Hope this helps...

[blueldr]

Abe,
You must mean 8mm or 5/16" rather than 3/16" rope.

[GAHorn]

"Working" loads versus "breaking" load ratings of rope are different matters as the terms imply.

Here's a chart of "working" loads, which are the recommended ordinary maximums the ropes should be regularly expected to experience. "Breaking" loads are the maximum loads the ropes can withstand if the ropes are NEW, NOT tied in KNOTS, and not otherwise compromised.

http://www.lehighgroup.com/workingload.htm

Abe, not disputing your specifications, but I'm curious about what kind and how a 3/16" nylon rope can be rated at 3650 lbs/breaking. Lehigh is a reputable rope vendor and mfr.r and their 3/16" nylon rope is only rated at 90 lbs. 3/16" Galvanized steel aircraft cable is only rated at 840 lbs. working.

[Abe]

Thanks for the catch BL, it is 5/16...That would be some real stout 3/16....

[DaveF]

An amusing disclaimer at the bottom of the Lehigh rope page:

Never use rope to secure large flat surfaces or object which could “airplane” or dislodge through buildup of air pressure.

[GAHorn]

Thanks for the catch BL, it is 5/16...That would be some real stout 3/16....

Abe, I still am curious about this matter because 5/16" nylon rope is only rated at 192 lbs. (5/16 is still not as robust as 1/2" which is rated at 1200 breaking.)

[lowNslow]

George, try this stuff. They don't have a 5/16" but they do have a 1/4' rated at 1490 lbs and a 3/8" thats rated at 3340 lbs.
http://secure.cartsvr.net/catalogs/cata ... id=1976842

[Kyle Wolfe]

Thanks for the info guys. Just what I was hoping for - various choices, pros/cons, length, etc.

Abe, you've been a long time contributor to the Assn with donations of your tiedown kits. I just need to bid high enough in Duluth to get that one bought!

Thanks again - can you tell I'm thinking spring and more flying - FINALLY!

[Abe]

Abe, I still am curious about this matter because 5/16" nylon rope is only rated at 192 lbs. (5/16 is still not as robust as 1/2" which is rated at 1200 breaking.)

I know how we all enjoy our airplanes so we've went a bit further and use mountain climbing rope in our kits and hence the higher breaking strength...I figure that if those folks put their lives on the ends of these ropes, I feel safe putting our planes on the end of one too....A bit more in cost, but I'm not one to take short-cuts....

Kyle, I understand about the flying bug you're getting...it was nice today and pifsonic and his family and I took our roundtails out of the snow country and into Hell's Canyon today....It was gorgeous down there...Good weather is coming your way...





ENJOY....

[GAHorn]

...I know how we all enjoy our airplanes so we've went a bit further and use mountain climbing rope in our kits and hence the higher breaking strength...

Aha! THAT makes good sense.

I like the references too, lowNslow. Those are both better ropes than the common hardware store stuff. Thanks.

[W.J.Langholz]

Abe

How the horses doing in Hells Canyon?

W.

[GAHorn]

Waaait-a-minute...lowNslow... I missed the point I made myself earlier... Those charts in that link use BREAKING loads, not working loads, so those ropes are the same as I was previously discussing. (Working loads are generally restricted to about 15% - 25% of the breaking loads of a rope.)

I also made two errors in my first msg. 1/2 nylon rope is much stronger than 1200 lbs breaking. It's breaking strength is more than 5,000 lbs according to the various charts referenced here. And the other error was the size I used for my own airplane. The anchor rode I purchased is 3/8" nylon, rated at about 3,000 lbs tensile strength. (Tensile, maximum, and breaking are the analagous terms used by most rope suppliers.) The 1200 lbs I mentioned in the first post would be closer to a working load for 1/2" nylon.

Another excellent description of the various fibers used for ropes, and an easier chart to read that provides a useful comparison can be found at: http://www.gpjrope.com/ropespecs.htm

There are specialized ropes that provide higher strength, however, and probably that is what Abe utilizes.

[Abe]

WJ,
I'm out of town and just got on a computer....the horses are doing fine, but like allot of us can't wait for spring to get here...and in their cases, can't wait for the grass to get growing....