spectra lines

[sleepy gomez]

With Spectra lines being or soon to be legal in combat what about the uses of Spectra lines in stunt?  Okay. not (yet) legal for stunt but has anyone used them for sport flying on full sized ships?  Speculate on the possibility that Spectra lines will be legal in stunt.  What diameter and/or test would be used? 

[john e. holliday]

Will they stand the pull of a 69 ounce plane doing 5.2 laps on 65 feet of line?

[sleepy gomez]

Supposedly so, but that is why I'm asking.  The competition kite people say it will.  I have heard that line diameter for line diameter the Spectra is the equal or better of braided steel with almost zero stretch.  Has anyone pull tested Spectra?  You are supposed to use only a palomar knot for terminations.  I'm looking for more information and not negative attitudes.

[Russell Shaffer]

The back part of the new AMA magazine has the details on what Spectra is legal. See page 152. To answer Doc's question, "yes".  Over 64 ounces of airplane needs 100# test which measures .018, same as steel.  I've been flying 65# test and it breaks at the knot at 38 pounds of pull.  I pull test the individual lines to 25 pounds every so often just to be sure they haven't deteriorated with use.  I think it stretches less than steel cable, it doesn't have that rubberband feel that you get from a stainless cable.  The one and only problem I have encountered is that Spectra is very flexible, floppy, whatever, just like any string.  If the lines get loose in a high maneuver, they can easily fall into a coil and catch on any small bump on the handle.  If the down line loops around the up connector it causes a problem.  Over all I like the stuff.  It doesn't kink and is readily available and easy to work with.  One more possible problem, it is string and it cuts very easily but only with sharp objects that aren't normally found on my flying fields. 

[sleepy gomez]

Thank Russell, That's the kind of information I wanted.  I do still have a question though.  If the 65# breaks at the knot at 38# what kind of knot and if any kind of adhesive was used?  Could I then expect the 100# Spectra to fail at around 65#, still plenty strong though? 

[Michael Massey]

I have used spectra a lot in fishing for big tuna.  I use spectra in the 130 to 200 lb range.  You can get spectra in varying "strengths" from any larger fishing tackle suppliers.  Some considerations:  Spectra is "slippery" and can pull a knot easier than you would like.  It does not stretch and if the "line" is moving, it will cut whatever it is moving across, much like a very very sharp razor.  (The message here, definitely do not grab your lines if you lose tension.  You could lose a lot more that the plane.)  Most fishing knots rely on some "cement" to help hold the knot from slipping, but as pointed out, this can be a weak area in the attachment. 

With fishing, I used hollow spectra which acts like the old toy "Chinese hand cuffs" where you placed your fingers in a hollow tube, one finger in each end, pull and the tube closed up as you pulled, locking your fingers in place.  The hollow spectra does the same thing.  To make a loop, simply insert the "tag" end of the spectra into the hollow spectra, pushing it into the hollow area a foot or more, forming a loop where the tag end entered the spectra.  Great you say, you don't need any cement to hold you say...well that's the theory.  I never tested to see if any slippage occurred each time the joint was tested.  There may, or may not be any slippage.  If there is any at all, you would be constantly changing your handle adjustments. 

I have never flown an airplane with spectra, and don't plan to.   Considering the safety issue with the "sharp" material and the knotting issue I just cannot see a clear advantage over the lines we currently use.

[Ward Van Duzer]

As an old time tournament fisherman there are 3 things I didnd't like about this stuff.

Knots slip! Already discussed. You can prevent this by tying the right knots, and adding a drop of CA. But remember, fisherman often retie 3 or more times a day!

The line does fray! Relates to the CA creating a weak spot at the glue joint. Again, fishermen retie frequently!

It's also very light, and has the tendancy to fly away.

I've used it on .09 powered ships in the past, but would prefer the agony of .008's

[bob branch]

There was a comment made that spectra does not stretch. That I'm affraid is incorrect. It stretches a lot more than steel does. I have been a little baffled with any desire to use it where line tension is an issue. To date there are none of the synthetic ropes that stretch less than steel. That does not mean they cannot be used in place of steel. Weight and size are considerations. I have used high tech synthetic lines in sailboats for decades up to and including the rigging that holds the mast up. Loads are very high and the need for exact settings to remain constant are critical. Oversizing is the solution that gets used. But if you compare line sizes for planes in the .015 and larger ranges with steel ... and that should be easily available... I am afraid spectra will come out the looser in stretch. As to the knots, they will weaken the line. Pull test everything and often.

bob branch

[Jim Kraft]

The greatest advantage I can see for the Spectra over stainless is the weight of the lines. They will not whip around like the heavier steel. Probably need less tip weight. If the knot thing can be worked out, and they do not stretch anymore than steel, I would think they would be better. Time will tell. My friend is flying .008" Spectra on 1/2A's, and thinks they are great.

[Chucky]

Check the later part of this month's AMA mag.  Apparently the AMA has come to a decision concerning use of these lines for combat.  The knot must be a five-turn uni-knot tied on a bight (doubled line), which I presume doesn't slip or they wouldn't mandate it.  No mention is made of the palomar knot, a favorite of mine for fishing.  Although the last two columns of the line size table in the article appear to be mislabeled, it's pretty clear that relatively heavy line is required -- looks like about double the breaking strain of steel per engine size range.  This is probably so due to the significant loss in line strength that knotting imparts.  For its rated strength, however, spectra line is quite thin, so this may or may not negate the apparent weight advantage over steel.  From what I can find on the internet, the primary reason why the combat flyers like this stuff is because it doesn't kink up when lines get tangled and is thus a lot easier to deal with.  It seems to be significantly more pricey than steel and would most certainly abrade if dragged across pavement, neither of which are likely to be issues for combat.  Given the durability and low cost of steel, spectra lines make little sense for most of the Saturday sport/stunt flying that I do.

[bob branch]

I did some research on Spectra. Stretch is 2 to 3% at max load. Stainless steel cable is about 1.2%. The issue I ran into in using it to replace the stainless steel cables holding up masts was a property called creep as well. Creep is an initial stretching that the material undergoes under load. It is about 10% with Spectra and its derivatives. This is a permanent stretch that it undergoes when initially placed under load and it does not return from it. The problem I ran into with one boat (a 30plus mph trimaran) was that each time we sailed in heavier wind... ie more load but well short of failure loading) we ran into more creep. This was with a braided line. The final solution was to not use turnbuckles as is the norm as the terminal adjustment because they just could not accommodate the amount we ran into. We returned to an ancient method called a bollard which let us adjust the line what ever the amount of creep was.  This particular boat I sailed for 3 years and was continually adjusting for change of shroud length each time I got into heavier winds. The last sail was in 50 mph winds and we still encountered more. 

This is just something to be aware of. In stunt where we adjust our lines so precisely and rely on them staying exactly the same flight after flight as part of our trimming procedures, I am just not sure this would be a positive thing, especially on larger planes that generate some serious line tension. Even if you got it to stabilize, think about a runaway lean run.... the additional line tension would possibly result in a change in line lengths and require retiring. I'm not so sure this is any kind of an issue on half A and small planes as there essentially is not any serious line tension.

Also, if you are going to work with it be aware it is very difficult to cut, especially without fraying it. Knifes and blades do a very poor job. A sharp scissors or nail trimmer seems to work the best.

I have also used spectra medically in surgery. Believe me, you don't want to do much of that. Glad those methods have passed by.

bob branch