Steel Braided flying lines - are all brands of equal strength?

[Dennis Toth]

Guys,
A question came up at the field about lines stretching. Seems that although the rules allow ships up to a certain weight to use a certain line diameter some flyer's felt the lighter lines (.012" vs .015") were stretching giving spongy feeling controls. This has been stated by different flyer's some of whom are top 5 level. My question is are all brands of braided cable lines created equal (i.e. Brodak, Sullivan, RMS, etc.)? What brands stretch the least?

Best,       DennisT

[Bill Little]

HI Dennis,

I have never found much (if any) difference in the various company's lines, but I have noticed the difference in using different gauge lines.  If in doubt, I use the next bigger line anyway.  On piped models, regardless of "weight", I feel more comfortable with .018 lines. (just an example)

Bill

[Howard Rush]

I measured some.  Staystrates from PAW are less stretchy than seven-strand stainless cables the same diameter.  Tom Morris's 19-strand stainless cables are only slightly stretchier than seven-strand.  I'll publish this and a bunch of related calculations one of these days.  Meanwhile, I gotta practice me some stunt.. 

[NED-088]

To me the stainless 7 strand lines of different sources were all alike.
I've been using them from 1990 to 2004.
Then I went back to Staystrate, the modern version of Laystrate. Howard already referred to them.
These lines are non-stainless, but tinned. And 3 strand.
I like the more direct feel -less 'springyness'- and the smaller 'back bow', maybe there's less air resistance.
As I'm flying to FAI rules I can use any diameter as long as it passes the pull test.

[Dennis Toth]

Guys,
Is there a US source for the Staystrates lines?

Best,      DennisT

[Larry Cunningham]

I wonder - even if the different brands of steel lines are from different sources - are they really? That is, might they all be pretty much using the same grade and alloy of steel?

Not sure why but my gut was telling me the 3-strand wire would likely be more stretchy that the 7- or 9-wire (my cross sectional area guess?). Anyway, the proof is in the measured stretch, right? (Which blows both of my assumptions.)

L.

"A man who does not plan long ahead will find trouble right at his door." -Confucius

[Howard Rush]

Is there a US source for the Staystrates lines?

I got Staystrates from Eric Clutton, http://www.cafes.net/doctordiesel/ , but I don't see them in his current calalog.  Staystrates are similar to what people in East Europe are selling for F2D.  I got some F2B lines from ViKo, but they are smaller than .015"-- OK for FAI, but not for AMA. 

[Tim Wescott]

I wonder - even if the different brands of steel lines are from different sources - are they really? That is, might they all be pretty much using the same grade and alloy of steel?

I wouldn't count on that.  But different steels have remarkably similar moduli of elasticity -- so different grades of steel should make a difference to how hard you pull before they break, but not how much they'll stretch.

Not sure why but my gut was telling me the 3-strand wire would likely be more stretchy that the 7- or 9-wire (my cross sectional area guess?). Anyway, the proof is in the measured stretch, right? (Which blows both of my assumptions.)

How the strands are laid would have an effect, too -- more turns/inch would mean more stretch for the same starting materials, while those same strands laid dead straight should show less stretch (and smaller diameter, and really crappy handling characteristics).

[Larry Cunningham]

Yeh, I wasn't even thinking in terms of winding, just cross sectional area, and didn't quite know (except for 3-strand) how it might equal diameter strands might be assembled for 7- or 9-strand..

Strength and Materials was never a strong suit for me in college, only thing I found less interesting was Thermo (what with the Steam Tables and all..). I know that's not much of an excuse.

(Ask me about my Wronskians.)

L.

PS - Let me amend that, I found Orbital Mechanics (after college) to be the Least Interesting Subject In The World.

"Early morning cheerfulness can be extremely obnoxious." -William Feather

[Tim Wescott]

Strength and Materials was never a strong suit for me in college, only thing I found less interesting was Thermo (what with the Steam Tables and all..). I know that's not much of an excuse.

I managed to escape the college system with a Master's degree in electrical engineering and no thermodynamics at all.  I felt this lack acutely, until I spent some time working with the Acknowledged Expert in Thermo at the 500-employee company I worked at.  This was an engineering manager with 25 guys under him, who folks still went to for the Last Word in solutions to thermodynamics problem.

And, when push came to shove, Bruce never ever passed on a design until someone had put a lightbulb or power resistor into a box or onto a heat sink, with appropriately-placed thermocouples inside and out, to test and make sure that the math was right.

[Howard Rush]

...no thermodynamics at all.

Another potential electric car customer.

[Leonard Rennick]

"I got some F2B lines from ViKo, but they are smaller than .015"-- OK for FAI, but not for AMA"

Howard you need to check your measuring stick and the rules, FAI min is .385mm (.01515743) with no minus. I have checked many F2D lines and they are all over .016 with some as large as .017.

Leonard

[Tim Wescott]

Another potential electric car customer.

 

I know the three laws of thermodynamics:

1: You can't win
2: You can't break even
3: You can't get out of the game

Besides, electric cars will Save the World because they are powered by Electricity, which, as every schoolchild knows, comes from the wall.  And if that doesn't work, then it'll come from hydrogen, or solar, or by burning whale oil or some other appropriate biofuel.

[Randy Cuberly]

Quote from Howard Rush.

"I measured some.  Staystrates from PAW are less stretchy than seven-strand stainless cables the same diameter.  Tom Morris's 19-strand stainless cables are only slightly stretchier than seven-strand.  I'll publish this and a bunch of related calculations one of these days.  Meanwhile, I gotta practice me some stunt.. "


Howard,
I think from a pure mechanical point of view there is more stretch with more strands.  This comes from the spring stretch of the individual wires in the cable closing together as force is applied.  This likely accounts for much more stretch in cables than the actual tensil stretch of the material.  This phenomenom doesn't occur with the Laystrait (or to a much lesser degree)  .014 solids stretch about 15% less than typical .018 cables...at least according to testing I did a number of years ago and never published.  I'd do it again but don't have direct access to a manometer anymore.  Retirement does have some downsides.  
Most of the testing was on varius sources of .015 and .018 cables for breaking strength.  Never published that data because it scared me a little.  "Snow storm results"with the cables, and I didn't want to open a can of worms when the practical results of flying seemed to be fine.
Similar testing with solids to verify the test proceedure gave good numbers and considerably higher strengths than the mean numbers of the snow storm...uhhh sorta mean...(numerically weighted center of the snowstorm).

Randy Cuberly

[Brian Hampton]

I've just put my mic over 3 different types of lines. One is Staystrate, the other 2 both come on the red Sig reels but one has a silvery colour and the other is more coppery. The coppery 7 strand measures .37mm (.0146"), the silvery measures .0385mm (.0152") and the Staystrates measure .04mm (.0157"). The Staystrate label indicates a breaking strain of 17Kg (36 pounds). I believe the main difference in material is that the Staystrate is made from carbon steel wire which presumably is why it can be soldered. How that affects strength compared to stainless I don't know but I'd guess is stronger. AFAIK the Staystrate is identical to the old Aeroflyte Laystrate.

[qaz049]

Guys,
A question came up at the field about lines stretching. Seems that although the rules allow ships up to a certain weight to use a certain line diameter some flyer's felt the lighter lines (.012" vs .015") were stretching giving spongy feeling controls. This has been stated by different flyer's some of whom are top 5 level. My question is are all brands of braided cable lines created equal (i.e. Brodak, Sullivan, RMS, etc.)? What brands stretch the least?

Best,       DennisT

Are all braided cables created equal?

Don't know, however comparing Brodak .015" with  Aeroflyte .015" three strand soldered for strength then the Brodak wins by about 15% IIRC!

However the Aeroflyte (like the "Staystraight") is reputably considerably faster. I'd guess it was because there was less metal in the cross section so less drag even though both types have the same measured diameter.

The Load/Extension curves were done last year in a Tensometer. I was interested in comparing the strengths since the 3 strand is said to be faster with team racers and Goodyear racers.

I have the raw data including Gauge Lengths somewhere.

 

The Circle data points plot the Brodak, the crosses the 3-strand Aeroflyte.

[Howard Rush]

"I got some F2B lines from ViKo, but they are smaller than .015"-- OK for FAI, but not for AMA"

Howard you need to check your measuring stick and the rules, FAI min is .385mm (.01515743) with no minus. I have checked many F2D lines and they are all over .016 with some as large as .017.

Leonard

Leonard, you need to check your reading glasses.  F2B, not F2D.

[Tim Wescott]

The Circle data points plot the Brodak, the crosses the 3-strand Aeroflyte.

Did you perhaps start the test with new line, then do progressively stronger pulls, relaxing the line between each pull?

Because while the curve leveling off is consistent with the strands tightening up against one another, I have a hard time believing that as you pulled harder the line actually shrank.  I think that perhaps instead you have inadvertently proved that a new rope is stretchier than one that's been stretched a few times until it settles in.  (There's got to be a term for that).

[Howard Rush]

Ray, that's interesting. I only checked a few points and assumed that slope applied to the range we operate over.

[dirty dan]

A real-world example might help even if I am interested in seeing Howard's data.

It was several years ago when Derek Moran and I were at the NW Regionals. I had my second Wimpact with me and after testing 7-strand .012s, 7-strand .015s and Staystrate .012s had settled on the latter as being best for this particular application.

While Derek's Wimpact was not yet completed he did have his 20FP-powered Skyray 35 with him and on Friday we were testing. Derek's model had a consistent "bounce" when exiting hard corners, especially in the squares. He was using 7-strand .012s (this despite the fact I had cautioned him to at least use .015s).

As it happened, prior to the NWR I had the bulk of Derek's Staystrate line material in my shop and cut a set to the exact length as the lines he was then using. Amazingly enough I cut them to "Ted Standards" which resulted in no changes needed to neutral setting at the handle.

The point is we did not change anything at all other than the line material.

The annoying bumps at corner exits were immediately gone. And gone completely.

His 7-strand .012s were stretching too much for accurate flying. While his Staystrates were surely stretching as well, not enough to give him fits. It was not a subtle change, okay?!

Yes, I know there are other ways to get the same result, some always work, some work in a few instances. But it is my view that far too few of us recognize the possibilities and then do the appropriate testing.

As to drag of these lines, during my testing with the Wimpact the 7-strand .015s of course showed more "belly" in the lines during flight which is what one would expect. What I did not expect was a perception the .012 Staystrates seemed to exhibit less drag than the same size lines in 7-strand configuration as shown by less belly in lines when flying.

To my untrained eye the Staystrates would seem to be more draggy; and they might be but we probably need some input from Howard on this.

Dan

[Tim Wescott]

To my untrained eye the Staystrates would seem to be more draggy; and they might be but we probably need some input from Howard on this.

Maybe it's the dimple-on-a-golfball effect?  Certainly the Reynold's number of an 0.012" diameter wire traveling at below 30m/s is way slower than almost anything we're used to thinking about, so there's not much intuition that would apply.

[NED-088]

To my untrained eye the Staystrates would seem to be more draggy; and they might be but we probably need some input from Howard on this.

If you check my postings on this, you'll see that I wrote:

I like the more direct feel -less 'springyness'- and the smaller 'back bow', maybe there's less air resistance.

They have less back bow.

[Howard Rush]

That's what I have heard.  I couldn't find any experimental data on these shapes, and the aero guys to whom I talked didn't have a theoretical explanation. 

[Lauri Malila]

If you check my postings on this, you'll see that I wrote: They have less back bow.

 Well, the Staystrate lines have only 3 strands. This means that even though measured diameter is same as with 7- or 19-strand lines, the average frontal area is less. That makes air drag smaller.
 But, they have less metal per cross area. Anyway, the elognation under tension is less than with stainless steel lines because of stronger piano wire material.
 Another but, they are clearly heavier than stainless .015's, the weight comes from the tin solder. That also contributes to the flexy feeling.
 I used Staystrates for a while but stopped because they needed too much attention, especially when flying alone.
 In the beginning I used to polish the new lines with ScotchBrite or similar, that made them a lot smoother, but because it partially broke the tin coating, the steel started to corrode and they were not so smooth anymore.
 The manufacturer recommended to wipe the lines first with an oily rag (WD40) and then polish with dry cloth. That'sperhaps OK for combat & team racing.
 Some of the russian carbon steel lines are very good, but beware, there are several types. The best has 4-strands and rather coarse coil.

 Just random thoughts.. L

[qaz049]

Did you perhaps start the test with new line, then do progressively stronger pulls, relaxing the line between each pull?

Because while the curve leveling off is consistent with the strands tightening up against one another, I have a hard time believing that as you pulled harder the line actually shrank.  I think that perhaps instead you have inadvertently proved that a new rope is stretchier than one that's been stretched a few times until it settles in.  (There's got to be a term for that).

You obviously don't understand what a Tensometer is! While the data points in each curve fall in a straight line the wire is stretching elastically.

If you remove the stretching force they will return to their original length. You normally don't want to come anywhere near this point with c/l wire where this ceases to be true.

The curve in the data points indicates that the metal is behaving plasticity, ie permanently stretching and failing.

The graph shows that in the final stages before ultimate failure it takes less and less force to continue stretching.

Note that both the wires fail at about the same Force even though the Brodak is much stronger where it matters.

[Brett Buck]

Are all braided cables created equal?

Don't know, however comparing Brodak .015" with  Aeroflyte .015" three strand soldered for strength then the Brodak wins by about 15% IIRC!

However the Aeroflyte (like the "Staystraight") is reputably considerably faster. I'd guess it was because there was less metal in the cross section so less drag even though both types have the same measured diameter.

The Load/Extension curves were done last year in a Tensometer.

   The "less metal" theory could explain the increased spring constant as well. This result surprises me, because it seems at variance with what people feel in flight.

    I have some ideas about other tests that could be done, mine have been pretty crude. One thing I definitely feel at the handle is that old stranded lines seem to have significantly better feel than brand-new.I assume that is because the strands compress into a tighter bundle after maybe 100 flight and 20 pull tests.

   Could you tell me either the unsupported length of the test peice, or the percent elongation.

    Brett

[Tim Wescott]

You obviously don't understand what a Tensometer is! While the data points in each curve fall in a straight line the wire is stretching elastically.

I failed to look at the labels on the axes.  Had I done so, I would have understood.

[Howard Rush]

Could you tell me either the unsupported length of the test peice, or the percent elongation.

And the actual measured diameter, please.

[qaz049]

And the actual measured diameter, please.

The Gauge Length was 100 mm.

The diameters weren't measured apart from both packets claiming a nominal .015" dia.

I wasn't concerned about converting to a Stress/Strain curve partly because of the difficulty of measuring the actual strand diameters, and hence the actual CSA.

The motivation was to check the wire safety with a 100 mph B Class Team Racer during the instant when an engine cutoff was activated on the down line.

During such an event all the Centripetal Force is concentrated on one line.

For the Brodak line with a Limit of Proportionality at about 170 N, and a 24 ounce (0.68 Kg) racer circulating at 100 mph (2.57 S/lap) on 60' (18.3M) lines,

the load would have been about 75 N as the cutout activated. According to my calculations the model would have to do more than 153 mph under the same conditions before the Limit of Proportionality was exceeded.

I also concluded that the pull test loads for the event in our Australian Rules were well founded, and that .015" line was up to the job. I did have some doubts.

[Brett Buck]

The Gauge Length was 100 mm.

The diameters weren't measured apart from both packets claiming a nominal .015" dia.

   So, let's see, I see about 1.5 mm elongation a ~90 newton (20 lbs, the load on an individual line during a 40 lb pull test, 10Gs on a 64 oz model), which is 1.5%. On 64 foot lines (768") that's 11.5" of stretch! In-flight on a typical stunt plane, it's about 3".

    Interesting. That's not far off what I got, certainly within a factor of twoand even if you cut it in half, it's still impressive.

     I see little that looks like a non-linearity or free play in the test setup so aside from a calibration error, it seems like a correct result.

   Brett

[Howard Rush]

Here's what I saw.  Staystrates are the ones below the curve, .0156" diameter. 

[ash]

A slight aside - the mechanism for line failure in combat

I have personal experience of and have heard anecdotal evidence that braided stainless lines are somewhat fragile under combat conditions, especially when in a line tangle with tinned or braided steel lines. The strength figures illustrated above lend some credence to my theory that the failure mechanism in the steel versus stainless tangle situation is the coarse texture of the steel line snagging and notching the individual fine stainless braids one at a time until the overall strength is sufficiently compromised as to cause total failure.

There's no experimental evidence to back this up yet (other than my two fly-aways under after such an encounter), it's just an idea to work with. Does anyone else have ideas, thoughts or experiences in relation to stainless braid in combat?

Obviously in stunt you're not going to get line tangles so this may not be of great concern to most, but it shows that static line test results aren't telling the whole story for other events. The team race shut-off moment might also be more fraught than expected if snap or jerk or impulse is a factor.

[qaz049]

Here's a pic of the Braided Brodak wire just into the failure mode with many strands damaged and the overall shape showing some necking. The process seems quite gradual c/w the other stuff which is much more like a brittle failure.

[qaz049]

This should be a pic of the Aeroflyte .015" wire after failure.