Mike, I am as sure as you that Spectra will not cause us any safety problems. My concern is that the CLPA contest board would have to approve any change. I don't see enough positive comment yet, either here or in Stunt News, to be fairly sure that such a proposal would succeed.
At any rate, here is the original report to the AMA competition committee. It is a little dated, particularly as to the knots. Steve Helmick or other fishermen should speak to the ever changing fashions in tying, as the fishing community is a lot bigger than C/L flying. (Please note that the video clips will not post here. They are available at the AMA website in the C/L General rules.)
Spectra Lines
Here’s the results of some knot and line testing on various brands of spiderwire/stren/cabelas brands of braided super fishline. It is most commonly called Spectra braid, but is all manufactured by Honeywell under license from Dyneema, a Dutch conglamerate. It is sold exclusively under the trade name Spectra in the US. Since Spectra is the name under which it is sold, I will refer to it by that name.
By way of preface, I have some familiarity with the use of cordage for fishing and small boats, but am far from expert in either. It turns out that any knot must be tied so as to generate equal tension among all fibers throughout. This means that when you tie, both the tag end (the leftover end) and the standing part (the line to be used) must be under tension when the knot is pulled down tight. The line should also be lubricated with saliva to get it to tighten evenly. This is not an exact process, so most really proficient fisherman tie at least a few knots for practice before the one for use is tied. For light tackle or tournament use, 10 or 20 practice knots are common.
That said, the first tests were just tensile strength of the line itself. The test rig was made up by wrapping the line around a dowel, 5 or 6 turns, and holding it in place with plywood pads held under a C clamp . The standing end was wrapped around a dowel clamped in a vise, between small plywood pads, and the free end wrapped around another dowel held between pads with a C clamp. A spring scale I use for pull tests was hooked around the free dowel and pulled by hand, and the readings recorded. For reference, it would have been better to have a slider on the scale so the reading at failure could be ‘saved’. As it was, I simply pulled slowly and watched the scale closely until failure occurred.
The lines were Cabelas Ripcord, 25lb test, yellow. This was used for all the knot tests which follow. I also pulled 20lb Stren braid and 30lb Spiderwire. All passed without difficulty, breaking at about 2-4 lbs over rated strength. All of these measured about .007- .009 inch diameter. This is an estimate because the braid does collapse some under the pressure of the caliper or micrometer jaws. I elected to average the readings between when the first contact with the braid could be felt, (about .011 in.) and when under full compression (about .005 in.).
On to the knots themselves, the best website I found is the kite knots page under
http://members.aol.com/goodheavens/knots.html. For curiosity’s sake, see the following websites: Animatedknotsbygrog, realknots and thefishingsite. Here’s the results:
Knot Result Pull CA Remarks
Improved clinch slid 3 lb no
Double larks head slid 4, 12, 15 lb no 3 tests
“ broke 16 lb yes
Albright slid 5 lb no 10 turn
“ broke 16 lb yes 10 turn
“ broke 12 lb yes 7 turn
Double larks head
With Clinch added broke 21 lb yes Hard to tie
Palomar broke 21 lb no
Note that the Albright was tied to a loop of 27 lb Dacron flyline backing, all other were tied to a wire loop simulating a line clip. I expected the cushioning effect of the softer Dacron loop would make the Albright the best choice. Not so, the Palomar is the easiest to use, and gets up to 21/25 or about 81 % of the rated line strength. Not bad for any knot.
I also opted not to test the knot sleeves the kite guys use. They put the spectra through a Dacron sleeve to add cushioning and friction to the knot. I don’t think it’s a good idea because the sleeve will prevent the user/pit boss from seeing a broken or bulged strand in the spectra line. For the same reason, my preference is to avoid the use of CA to prevent knot slippage. If you’d like to try some sleeves, they can be bought ($2.50) from the site at flyingdragonkites under sleeving kit.
As expected with anything new, you ask the wrong question at first. From all of the pulling and tugging, it feels like line stretch will be the problem, not line strength. I could feel it stretch as each test was made. For comparison purposes, a conventional set of 7 strand stainless steel lines, .015 inch diameter, 60 feet long, stretches about 3.5 inches under a pull test tension of 30 lbs. Steel lines return to their original length when the tension is released. The test rig is simplicity itself. Fix the airplane ends of the lines to an anchor point. Lay a ruler on the ground, pull up the lines to get about zero tension, set the zero end of the ruler directly under the edge of the handle. Sight across the edge of the handle to the ruler when you pull the lines to tension.
I made up a set of 61’1” foot lines from 100 lb test Cabelas spectra to stretch test against the steel benchmark. The 61’1” length was the initial length, measured before any tension had been applied to the lines. All measurements of overall length were measured against a 2 lb pull to draw the slack out. Results are:
Tension Stretch under tension Overall length
10 lbs 3 in
20 lbs 7 in
30 lbs 10.75 in
After a prestretch of 25 lbs, held for 1 minute:
30 lbs 7 in 61’5”
After a prestretch of 40 lb applied for 1 minute:
30lbs 7.5 in 61’5.5”
So the difficulty isn’t the knot strength at all. The lines have to be much stronger than the required pull test (3 times as much for this test set) in order to control the stretch. After the prestretch, this 100 lb spectra appeared to stretch just twice as much as steel. A couple of anecdotal stories: Phil Cartier let me fly a 75MPH combat ship on Spectra this spring. It turned about as well as one would turn on steel lines. The big difference in feel is that the lighter line weight is very noticeable. There is less roll in turns, and it felt like the tip weight was much less than that needed for steel. So changing the lines will require retrimming, at least to take out tip weight, and probably changing the line rake as well. Second, Larry Scarinzi had a lot of flight time on .010 solid music wire lines in the 1950’s. He feels they were more responsive but had to give up on them when K&B greenheads got to towing his combat ships over 100 MPH. At those speeds, the thin lines stretched in turns, and the turns widened uncontrollably. So the diameters went up to
.015 7 strand stainless. Safety? Not a care in the world! My, my, times do change. Anyhow, that’s what there is so far.
The above was a post on the Stunthangar forum on August 22, 2007. Since then the Spectra lines have changed little, but the fishing community has gained considerable additional experience in how to use them. There are several knots which pull to 100% of the strand strength. I looked at the Bimini Twist and San Diego Special but rejected them because they are quite slow and hard to tie. The one I settled on is the 5 Turn Uniknot. A very good clip explaining it is at :
My testing of it tied with Spectra Braid 30lb test from Cabelas gave failures at 38-40 lb., when tied on a bight, or double strand. These tests all exceeded the initial tests of the same line with the same scale, which measured 32 lbs on the strand alone, without a knot. It failed at 30 lbs., 100%, when tied on a single strand. It is fairly easy to tie with two hands and no other vise or assistant. It seems that this should be the knot to use in the termination section of the CL General rules.
There are some other areas of concern that have come up over the last few years of using Spectra. It is available in a high visibility yellow color. This is a good step above either camoflage colored Spectra line or the brown tinted 7 strand stainless. The bright yellow is very easy to see against grass or blacktop.
Spectra is also nonconductive to electricity at 5 volts. Flying with it to date has not given any of the static discharges which are common with steel on bright sunny days. It looks as if the static discharges come from sweeping a long connector across whatever electric fields occur in nature. It should be noted that this WILL NOT result in any protection at all if a flyer uses Spectra in a lightning storm or near a high voltage transmission line. Apparently that discharge comes from ionizing the air molecules along the path to ground, so the conductivity of the line is not a governing factor.
The performance of the model is very favorably affected by the use of Spectra, because it weighs about one fifth as much as steel. A set of .011 x 60 Spectra (50 lb test Spiderwire) comes in at 4.8 gr, and a similar set of .015 x 60 stainless 7 strand at 28.2 gr. In flight, the difference in feel is dramatic. The lines follow the airplane, and have much less momentum which causes the airplane to lag control inputs while the lines are pulled in a new direction. The Spectra does require that the airplane be retrimmed with much less tip weight, and a little less line rake as well.
The tensile strength of Spectra is very close to that of music wire. (Marks Handbook, Wikipedia) Music wire is hard, high carbon steel. Stainless is about 25-30% less strong, but has been in use for 50 years, because of its superior corrosion and fatigue resistance. Spectra is not subject to either uv damage, corrosion or fatigue. My experience in handling Spectra has shown that it is much more able to handle mistreatment by kinking, abrasion, and the like. Although we all try to avoid it, lines do get stepped on and Spectra pretty much makes that type of accident a non-event. It cannot be damaged by kinking, and is much easier to handle on and off the spool.
The table below shows relative tensile strengths between stainless lines and Spectra:
Stainless 7 strand Spectra
Dia. Breaking strength Dia Breaking/Rated strength
.008 11lbs .009 20lbs
.012 24lbs .011 30lbs
.013 40lbs
.015 33lbs .014 50 lbs
.016 60lbs
.018 50lbs .017 80lbs
.018 100lbs
The data for stainless came from the McMaster-Carr website, checked with actual test results obtained by pulling samples to destruction. A few samples failed at one pound below the rating. The data for Spectra is for Cabela's Spectra Braid house brand and Spiderwire, with confirmation by pulling to destruction that the Spectra will withstand tension at the rating shown on the package. No samples were encountered which failed to meet the rating on the package, and some exceeded it by 20-25 %.
At this juncture, the Combat CLCB has voted in favor of using Spectra lines because of their superior abrasion resistance. But the General CL rules do not contain any specifications for the use of Spectra, or termination. The following are my own thoughts as to a first draft amendment to the General CL Rules:
In Para. 2, General, Replace 'Steel wire lines or metal lines of equivalent strength' with 'Steel or Spectra lines'. (Line2)
In para.5, Size, Construction and Measurement of Control Lines. Section 5.3.5, amend the second sentence From: Any system of using knots is specifically considered 'not as strong as' those systems shown as required in 5.3. To: Any system of using knots in steel or stainless steel lines is specifically considered 'not as strong as' those systems shown as required in 5.3.
Add new section 5.3.5.1 Spectra Lines.
Lines made of Spectra fiber, made of gel spun ultra high molecular weight polyethylene are permitted for sport flying and demonstration purposes. Spectra lines are not permitted in competition unless the specific rules for the event flown expressly permit such use. The use of high visibility yellow lines is recommended, but not required. For sport and demonstration flying with two lines, Spectra lines shall have the following strengths:
Aircraft weight AND Engine displacement or Electric less than
not over less than (cu.in) (Watts)
Rated Spectra strength:
24 oz .09 300 20 lbs .010 dia
40 oz .25 450 40 lbs .013 dia
64 oz .40 600 60 lbs .016 dia
75 oz .75 750 100 lbs. .018 dia
All lines shall be pull tested to 10 times the model weight. An aircraft must meet both the weight and power standards to qualify for the stated line size. Exceeding either standard places the aircraft in the next larger line size bracket. Aircraft shall be weighed with either a full fuel tank or battery on board.
Terminations shall be constructed using a 5 turn uniknot, tied on a bight, or two strands of line looped back from the free end. An instruction film of the knot can be found at
. The drawings below show a single strand for clarity, but should be tied on a bight. The knot is tied as follows:
1) Run at least six inches of line through the eye of the clip, and fold to make two parallel lines. Bring the tag end of the line back in a circle toward the clip.
2) Make six turns with the tag end around the double line and through the circle.
3) Hold the double line at the point where it passes through the eye, and pull the tag end to snug up the turns.
4) To create a loop connection: Adjust the loop size by sliding the knot up or down the standing line. Then pull the tag end with pliers to maximize tightness.
5) To create a snug knot: Pull the standing line to slide the knot up against the eye. Then continue pulling until the knot is tight. Trim the tag end flush with the closest coil on the knot.
(End of draft rule amendment)
Please note that the strengths specified and confirmed for the Spectra are approximately twice that of the equivalent diameter stainless steel. This means that the stainless strands are stressed to about half of their breaking strength during the pull test, while the Spectra is stressed to about 30-35% of its breaking strength during the pull test.
I hope this submission is helpful. Please do not hesitate to contact me if I can assist in any way.
Respectfully Submitted
Tom Hampshire
AMA 31919
Topic: High visibility spectra (Read 3755 times)