Just wondering if spectra lines work well for scale airplanes and what weight of line are you using?

I've only flown GSUMP lines on 1/2-A sport models, but I suspect it'd work great for scale.

Note, though, that the wording for line requirements in the current rules clearly assumes that you'll be using steel lines, and not all that is said makes sense for GSUMP -- given that I wouldn't take GSUMP lines to a contest unless the event director had said it was OK, and I may even want to get that in writing before I potentially wasted a contest weekend on a plane that I couldn't fly.

Note that the whole conversation in stunt circles about lines got so complicated, between material requirements and attachment methods and whatnot, that the rules about lines is now boiled down to -- essentially -- "use whatever, so long as you pass the pull test".

Quote from: Matt Curtis on June 14, 2025, 01:24:26 PM
Just wondering if spectra lines work well for scale airplanes and what weight of line are you using?

     I don't know about the legalities of it, but I think you can let stunt use be your guide. If using a 2.4ghz radio for throttle or any other functions, that should make things easier. I have a profile model of the full scale Dusty Crophopper airplane I have flown in C/L profile Scale with a 2.4 radio for throttle, and also in profile stunt and it would be a good candidate for Spectra lines. Line weight will be a function of model weight. I'll just use 60 ounces as a random number. Going by the AMA stunt rule of thumb that I think most follow, pull test for that airplane at that weight will be 60 ounces time 10 to equal 600 ounces. Divide that by 16 and your pull test is 37,5 pounds. If you round that up to 40, and add 10 to make 50 pounds, that would be a good place to start with line weight. And keep in mind that you will have two lines to share that pull test and flight loads. That is more or less how I have been picking my flying line weight for my stunt models. Read the rule book carefully and slowly, then consult whoever is the Event Director for C/L Scale at the NATS for some guidance.
  Type at you later,
   Dan McEntee

My 2 cents.  I am 2 years into Spectra with no desire to change back.  In the weight range I fly (60-70oz - I know it is heavy) the lines and plane hold up to the pull text.  I am on the other side of the scale so I question if the pull was actually 50lbs (10x) but I have pulled both the 80lb and 100lb sets to 60lbs pre-stretching the lines with no hint of failure.  Your pull test at my weight is 1/2 that so I see no reason not to use Spectra, especially if you are using 2 lines.   On three lines you need to make sure you pre-stretch them till you are tired of stretching, or the family start laughing.  Spectra lines seem to have a very small memory.  Just learn the knots.  Whichever one you use; it has to be a self-tightening knot.  I am more worried about the bellcrank mount that I am the lines.

It is fishing line so what do the fishermen use to catch Marlin and Tuna - 30lb Spectra (but they cheat and use a flexible rod and drag).

Ken

So I flew in 2 contests this year with spectra lines with no objection from anyone. I was able to get higher scores in stunt and I got a lower score in scale as the scale airplane needs more practice by me and better setup as well. I don't notice that much diffrence in feel between steel and spectra? I will be trying spectra again on some other airplanes as well. the planes I am flying are all over the place for weight and how they  fly so this will be a good test for the spectra lines. I hope to continue to use spectra as it is cheaper and easier to make than steel lines and I can buy the line at local stores instead of having to mail order heat shrink tubing cable in 2 sizes and eylets and copper wire.

According to the AMA CL General and CL Scale rules, Spectra lines are not approved for use in Scale competition.

so I assume if I went to tuscson or the nats or Dallas I would not be allowed to use spectra lines at these contests? in other words I just got lucky being able to use them this year.?

Contest Directors have the authority to change rules if safety is not compromised. Deviations from the AMA rules are supposed to be listed ahead of time, and approved by the AMA. I can see how some officials would consider that the approval of spectra lines in an event not allowing them would be a safety issue, and would say "no". Putting the CD on the spot at the contest isn't good form. If you know you need permission to deviate from published rules, best to work it out well in advance.

All that being said, spectra lines are allowed in stunt and combat, because the rules for the specific event rules permit them.

Sounds like someone with a dog in the fight needs to submit a rule change.  Personally I can't see any reason to not allow Spectra except the rule book.  Not specifying a change in the contest flier is totally unfair to anyone that shows up with them and anybody that wanted to use them and didn't.
I will defer to currently active CD's but in my day I would never give a waiver from rule book on anything related to safety.

Ken

I am glad that I went and looked at the current rules for this. I do not have a problem using steel lines for scale as I do not want to cause a problem by trying to ask to use spectra. A cd has enough to do already.  I can see why for carrier as well since they have a high pull test rating for that event and speed as well. Would be hard to try to figure out if spectra would work or be safe enough? I am glad that I am capable of making both types of line sets to handle this when needed as I might want to use steel again for stunt as well if I think it might work better for certain types of stunt models?

I had always thought that Spectra was stronger than steel so I asked my friendly neighborhood AI.

The tensile strength of a 0.018 inch diameter 7 strand steel cable can vary based on the specific material and construction, but it is generally available in the range of 10,000 to 15,000 lbs. This value is based on the typical specifications for 7 strand steel cables, which are commonly used in various applications. For precise values, it is recommended to consult specific manufacturers or engineering resources.

Guess I was wrong.

Ken

Apparently Mr. AI doesn't know the difference between the breaking strength of .018 cable in pounds and the tensile strength of steel in psi. 

In carrier, spectra would be undesirable because of the extra drag of spectra vs wire would slow the model down. Same for racing. Spectra should be OK in scale, where lighter weight lines would be more beneficial than lower drag lines. But first, someone needs to submit a rule change proposal. It won't happen by itself.

so for stunt lines that have more drag would not be good? spectra is lighter but is the drag a problem? It might be a problem with level flight with electric models which might make it harder to fly level especially in windy conditions? i assume the top level nats fliers in stunt do not use spectra lines whether they fly electric or not?

I will NOT use spectra lines on the larger heavy models that have higher than average line tension, not worth the risk.

Fred Cronenwett

Quote from: Fred C on December 28, 2025, 06:59:18 AM
I will NOT use spectra lines on the larger heavy models that have higher than average line tension, not worth the risk.

Fred Cronenwett

Fred, I felt the same way before making the switch.  It was the conditioning process that finally put my fears to rest.  Just to get the stretch out of a set of 100# requires you to pull for an extended period at a value that would break a lot of steel lines.  Once you learn the knots, the lines are stronger.  If the drag, whip and colors are someting you can live with they are better, much better.  Having said that, if I were a top 5 flier using the same metal lines for years I would not bother.  They are not that much better at that level to be worth it but still stronger.

Just my opinion - Ken

Quote from: bill bischoff on December 11, 2025, 01:58:21 PM
Apparently Mr. AI doesn't know the difference between the breaking strength of .018 cable in pounds and the tensile strength of steel in psi. 

In carrier, spectra would be undesirable because of the extra drag of spectra vs wire would slow the model down. Same for racing. Spectra should be OK in scale, where lighter weight lines would be more beneficial than lower drag lines. But first, someone needs to submit a rule change proposal. It won't happen by itself.

Events such as Speed, Carrier, Racing and Combat need to define a very specific line size and material so that line manipulation does not become a point of competition.

Stunt has openly welcomed the use of line size, material and length to the arena. 

In Scale the pull test is minimal and the line choice is wide open.  Since there is no competitive advantage to skinny lines, I play it safe and use stronger lines than required.

I consider scale to be my "fun" event, and I have more than enough steel line to last the rest of my lifetime (there's gonna be some very puzzled people at my estate sale, except for the deep-see fishermen and the control-line pilots -- they'll be happy).

So I don't care.  I can make up steel lines any time I want, for anything bigger than 1/2-A.

But if I did care, I'd either submit a rules proposal, or I'd figure out who's in charge of scale for my district and talk to them.

Spoiler alert, I have completely committed to Spectra for my Stunt, Combat & Sport CL models.  I am only a spectator for Scale. Thus my shaded opinions follow:

Generically, Spectra offers high strength vs size, light weight (about 1/5 the weight of SS Cables) low friction and higher durability (its kink-proof). How does that translate into flying a CL Scale model?

*In the bad old days when some CL Scale models used to use 6 (or more?) lines to control multiple features, Spectra would have been great because of how slippery & light it is.  Now with scale features being driven by RC, the remaining advantages for a 2-line system are durability and weight.

*Of course, if you are using a 3-line system AND if your flight schedule includes loops that twist the lines, the low friction of Spectra would still be your friend!

*Awhile back I made up a set of Spectra lines for someone who had been using .008" SS Cable for their 1/2A Scale models.  The Spectra is also .008" and the line rated at 45' break strength - do not know the rated strength of .008" SS cable but it is far less than 45'!  It is also incredibly fragile.  For this app, Spectra holds the prohibitive advantage for strength, weight, & durability.  In my opinion, it should be mandated for that class of CL model regardless of event!

*Gotta believe that for something like the big 4 engine bombers & transports some folks fly Spectra would hardly matter - the remaining advantages are durability and weight versus the very large size (& weight) of the SS cables that would be used.  Maybe not a big thing, but should be easier to hold the light weight lines up off the ground for maneuvers like taxi.


Of course all is moot until the CL Scale rules are rewritten to allow Spectra usage.


FWIW, I designed an Electric Conversion package (#BH-2030) for Profile Scale models and used the Brodak "Speed Six" for the test build.  Thus I can honestly say I have a CL Scale model started!  If I was flying CL Scale I would at least like to have the option of using Spectra.


BTW there is a thread in the Open Forum titled "ADVENTURES IN SPECTRA" where several of us have been sharing our experiences.  Its a bit longish (7 pages!) but its full of info.

Control Line Scale allows the biggest, heaviest and most powerful models that fly on lines.  While not the fastest, they have most surface area and thus the most downwind force when flown in high winds.

The Rule Book allows pull test values that are a joke compared to other CL events. 

Quote from: Paul Smith on February 01, 2026, 11:41:56 AM
Control Line Scale allows the biggest, heaviest and most powerful models that fly on lines.  While not the fastest, they have most surface area and thus the most downwind force when flown in high winds.

The Rule Book allows pull test values that are a joke compared to other CL events. 

And bans lines considerably stronger.  Every discipline has it's sacred cows.

Ken

A ten-pound model with over one cubic inch of gas or electric power is not the least bit affected by line drag.  All the scale models I fly are on 7-strand steel lines, at least one size above the legal minimum.

If the competition wants to go cheap on lines, I won't complain.

The only reason why Spectra lines are not permitted in Scale is that NOBODY BOTHERED TO SUBMIT A RULE CHANGE TO ALLOW FOR SPECTRA.

So go ahead and make a submittal - it will pass no problem.

I will keep flying my larger models that weigh more than 10 lbs on steel lines. The 14 lb B-29 flies on .024 diameter lines for a reason, It pulls like a tank!

Fred