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Some questions on lines

Old 10-10-2007, 02:09 PM
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EF
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Default Some questions on lines

I'd appreciate some help on these issues please:

1) Sullivan offers leadout cable kits, one is refered to as Class A-B and the other is Class C-D. What does this mean? they both are seven strand wires.
2) Line connectors - I saw 25 Lb and 50 Lb tensile strength types. Which suits what model/engine size combos?
3) Sullivan Kevlar lines - how do they compare with normal steel lines?
4) Is there some table that links model size/weight/engine displacement, with recommended line diameter and lengths?
5) If using insulated lines (for electronic control) is there some compensation to the above table due to larger cable diameter?

And another one not related to lines - before I get involved with a 60 powered scale model, thought I'd practice CL flying (been away from it for quite a few years) in general, and throttle (electronic) controlled flight (never done it before) on a small profile fuse model. Question - how small would still be practicle? a 20 powered model of some 36-38" span would be suitable for this?

Thanks!
Old 10-10-2007, 05:37 PM
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Default RE: Some questions on lines

EF,
The A,B,C, and D refer to old designations based on engine size. To the best of my recollection A went up to .15 cubic inch displacement (2.5cc) B went to .29 (5cc) not sure about C but D went to .60 or maybe .65 (10cc)

Go with the 50# line connectors regardless.

I have never used Kevlar.

Regarding line sizes, go to www.modelaircraft.org and look for competition regulations. Then go for control line stunt--precision aerobatics--and there will be information that is very good for sport models. Generally up to .40 engine lines are 0.015 inches diameter and usually 52.5 to 70 feet length. Above .40 stunt generally uses 0.018 diameter. There are also rules for scale models under that category that cover heavier models. It is also broken down to whether you are using 2 or 3 lines. Usually the same line lengths as stunt. The FAI scale class has a maximum of 21.5 meters IIRC which is slightly over 70 feet and a minimum length of 15 meters.

I have a hard copy of old scale rules-the website may be different because we have had a snarled up rules change within the last year. The rules talk about single strand lines, but scale fliers don't use them. Multi-strand, like the Sullivans, call for 0.021" diameter for two line systems for models up to 8 pounds and 0.018 for three line systems. If model is greater than 8#, 0.027" is specified for two line systems.

Our rules are silent on the size of insulated lines, but I think everyone goes by the size of the stainless wire core. I doubt the insulation provides any significant strength. Most of us here use coated fishing leader. The stuff advertised as approximately 120# test is the 0.027" steel cable. I use this with two 15# models and also with a 7# model. There does not seem to be a significant adverse effect on the smaller model. I only use one insulated and one bare line with my electronic systems. Industrial supply houses here, for example www.mcmaster.com sell wire rope that is what many of us use for lines.

Maybe someone else will comment on smallest practical model for electronic control. My smallest two have a .61 or two .30 engines.
Chuck
Old 10-11-2007, 01:21 AM
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Default RE: Some questions on lines

Thank you Chuck!
That is extremely helpful.
Old 10-11-2007, 08:30 AM
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Default RE: Some questions on lines

For a brief period, Kevlar was being used for parachute suspension lines. It was found to not be dimensionally stable and parachutes using it were going out of trim fairly quickly. It was also more subject to degradation from grit and sweat than Spectra or Dacron was and loses its strength faster than others when exposed to sunlight.

I have a set I use occasionally, but the Kevlar lines are very draggy compared to the SS. You wouldn't want to use'em on a plane that tended to be light on the lines to begin with. The extra drag might compensate for a plane that tended to slew to the outside too much that didn't have adjustable leadouts.

They won't get kinked in a weedy field. That's one advantage.
Old 10-11-2007, 09:43 AM
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Default RE: Some questions on lines

EF,

I think most folks who have tried Kevlar lines have relegated them to pull lines for stooges, etc. I have not heard ANY positive comments about flying with them. In all fairness though, I have not tried them...nor will I.

When using the AMA sizes suggested above, bear in mind that these are USA regulations. You might want to search for FAI regs or local regs for line sizes. The AMA site has lots of other good information such as how to wrap the ends of the lines. I think most prefer the non-solder method.

In addition the the AMA site, you might want to check Goran Olsson's site (Sweden?) at: http://www.go-cl.se/cl.html


George
Old 10-11-2007, 11:49 AM
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Default RE: Some questions on lines

I also fly with electronic controls and use the American Fishing brand of wire called SURFLON. For my smaller models I use the 30 lb test, for carrier I use the 60 lbs test and for larger models I use the 80 or 140 lbs test wire depending on how big the model is. When I reference the size of the wire I use the measured wire diameter and ignore the acutal overall diameter.
Old 10-11-2007, 06:57 PM
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Default RE: Some questions on lines

EF,

The smaller size model is a good idea to get the system setup and 'feel' of flying it. The biggest consideration is the weight and bulk of the electronics. From the world of RC today, we can find a lot of small, light gizmos to use. There are people here, in the USA, who have done great work in electronic auxiliary controls - Fred Cronenwett among them.

I feel it is still best to use mechanical control of the elevator - the loads may be considerably heavier than on throttle, or in driving a servo for other functions. I also prefer the physical feel of elevator response...

As to small size, your estimated span sounds about right for modern .20-.25 engines. The modern engines are quite powerful for their size, too, so that's some help with carrying installation weight.

As mentioned, the USA's National Model Aviation Club: AMA, has a website where you can read (our domestic) competition rules for line diameter and type (i.e., solid or braided cable.) The CLPA (Stunt) rules on lines and pull standards are used generally for non-competition models which don't have specifications, and for sport flying that may not be to any specific event performance standards. For CL Scale events, AMA has pull test standards related to weight of the model. I don't have a set of the FAI rules handy, but they may differ from the AMA specs.

I believe that the metal core in an insulated line is what is measured, not the outside of the insulation. That makes sense. Also, and I think the FAI applies this, too, the coder/decoder pulse train is what is conducted down the lines to the model. NO radio frequency transmission!
Old 10-11-2007, 11:50 PM
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EF
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Default RE: Some questions on lines

Thank you Lou, I definitely will keep the elevator control conventional, only intend to control the throttle electronically.

It is obvious to me that the wire core of an insulated line is what is referred to and I see I probably did not phrase my question well however, what I was referring to was that given the wire core, and considering that the insulation adds weight and drag to the lines, should I shorten the length of an insulated line vs. the non-insulated same line I would otherwise be using, or does the insulation have a negligible effect?
Old 10-12-2007, 11:46 AM
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Default RE: Some questions on lines

The insulated lines are definatey heavier and have more drag, but in some cases I shorten my lines a foot or so if the power and model weight does not keep adequate line tension. at the end of the day the actual wire diameter is very important to keep in mind. for that reason the only models I fly with 30lb test are the smaller 3 lb models, the faster 4 lb carrier models that have higher line tension requires 60lb test. My big camera plane (7' span, OS 90 four stroke) gets the heavy line due it weight (12 lbs without camera)

You will probably have to buy the insulated flying line Online, I can't find any stores locally that have the 300 foot rolls on hand or even willing to order the stuff.
Old 10-12-2007, 02:32 PM
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Default RE: Some questions on lines

EF-
I have one model that I had to shorten the lines. It is set up with two insulated lines. Originally they were 60' and I cut them down by about 3'. Just a guess, nothing scientific. That was my first model with electronic control. On subsequent models I only used one insulated line because there is a lot of friction when the insulated lines rub together and I found control to be insensitive. The insulated line does have more drag and will cause the elevator control to go off center. I use the insulated line on the "up" line and set my handle so I have about 1/8th inch down elevator when the handle is neutral.

The FAI scale rules are silent on the issue of line diameter. Anything that will pass the 5 g pull test is OK.
Chuck
Old 10-15-2007, 02:12 PM
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EF
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Default RE: Some questions on lines

I haven't flown CL for many years but do remember seeing the lines during flight, and they did not touch each other, so where does the friction come from? or are you referring to the situation after a loop for example when they twist around each other?

Anyway I'll probably go for a simple no-throttle profile fuselage trainer first, just to get back into this, then build something a little more elaborate with throttle control.
Old 10-18-2007, 02:21 AM
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Default RE: Some questions on lines

EF,

Profile is a good way to start. You can build the bellcrank through the fuselage, and later convert that mounting plate to a mechanical 3-line system, or an on-board electronic system. The lines will be outside the wing, however. That's a relatively slight disadvantage, considering the obvious advantages for converting it to whatever throttle or other functions you want to try.

And, yes, as others have mentioned, the added drag of a third line - particularly an insulated 3d line - is often simply offset by shortening the radius by 5% or 10%. If YOU can handle the changed lap-time, where's the problem?

Luck!


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