Making control cables

[Bill Johnson]

I've ordered 1000" of .015 cable, eyelets and getting some copper wire to wrap the ends. My question is about cable stretching. It seems that the cables will tend to stretch a bit and I've seen it on full size aircraft cables. What I was wondering is if there's any advantage to pre-stretching the cable prior to terminating the second end.

For example, for a set of 60' lines, cut initially to 65'. Terminate one end to the AMA standard, hook that end to a post and at the other end, create a false end and apply a load with a spring scale and let it set for an hour. Do both cables like that then measure for finished length.

A waste of time?

[Randy Cuberly]

I think the problem with pre stretching might be measuring the actual amount of "pre stretch" correctly so that it doesn't become "over" stretch and over stress!

The amount of stretch in .015 lines can be easily tolerated, especiall with the use of a hard point handle.  If a cable handle is used the amount of stretch in the cables around the adjustment devices in probably 10 times or more what the cable stretch is.

If you're really concerned about stretching of the lines use .014 solids.  They stretch only about 1/3 as much as .015 cables.

I use solids but typically only fly in Arizona where it's very dry.

Randy Cuberly

[Perry Rose]

It's a waste of time.
 I have two spools of .015 and tie a thimble on the end of each. Hook both ends on a nail and roll out the length of line you want, pull the lines evenly tight and mark each line at the length you want. Cut the lines 6 inches to a foot longer and tie the remaining thimbles at the length mark. At you leisure tie a thimble in the ends of the lines on the roll ready for the next set. With one spool it takes more steps but comes out the same.

[Joseph Patterson]

     As the Rose said, "a waste of time".
        Doug

[john e. holliday]

Perry, that is the way the old DOC does the lines.    Two spools of each with the ends ready to hook to plane.  Roll out length needed and make terminations at handle end.

[Bill Johnson]

Thanks, gentlemen. I'm on a business trip and on weekends, just too much time to over-think stuff.......

[Steve Helmick]

My yard is terraced and driveway short, so I have no place to wrap lines, except down at the flying field. I'd rather fly when I'm at the flying field, so I order my lines from Tom Morris, ready to use. I like to think I'd do better, but they are well done, safe, and are not much more $ than a set of unfinished lines from Brodak, SIG, or Sullivan, plus he'll send them on a spool that might cost me $3 or more. Can't recall the shipping cost, but it's very reasonable and they arrive in my mailbox in a few days!  Steve

[Tim Wescott]

I have a line jig.  Two posts made out of 4" PVC epoxied to a board so that one turn around the posts is five feet (I established the distance between posts the practical engineering way -- I calculated it every twelve ways to Sunday, then found out when I was about to glue things down that it was wrong.  So I just wrapped a tape measure around both posts and adjusted them until they were right).  There's various headless nails along the bottom edge to make up various lengths of line, and I can always drive in more.

The only downside is that it's very easy to make a pair of lines that differ by five feet -- careful turns counting and re-checking before cutting is vital.

[Phil Krankowski]

I run lines down the hallway inside from a bedpost to the kitchen.  My wife complains when she sees me do this, of course, but she is understanding.

Phil

[Allan Perret]

I calculated it every twelve ways to Sunday, then found out when I was about to glue things down that it was wrong.  So I just wrapped a tape measure around both posts and adjusted them until they were right

Distance around an oval is a pretty simple calc., why did it come out wrong ?

[Motorman]

The only downside is that it's very easy to make a pair of lines that differ by five feet

LOL.


MM

[Tim Wescott]

Distance around an oval is a pretty simple calc., why did it come out wrong ?

I don't know.  I think I was using the wrong figure for the radius, because I wasn't off by much (1/4 inch or something).  I would have double-checked all my calculations, but I had the posts there, with the tape around them, and I had clamps and weights and pencils, so it was easy enough to just make the thing measure out to the correct distance, glue it down, and call it done.

[Bill Johnson]

Distance around an oval is a pretty simple calc., why did it come out wrong ?

Just a SWAG, but 4" schedule 40 PVC is not 4" O.D. It's actually 4.5".

[Tim Wescott]

I know -- 4" pipe means that nominally it's 4" ID (but don't try running a 4.000" diameter stainless-steel sphere through it!).  If I recall correctly, I measured the pipe.  Wrong, apparently.

I'm an engineer.  For a good part of my living I do highfalutin' math that 95% of other engineers won't touch.  Knowing when to put the math book aside and grab a tape measure is important.

[Garf]

I take a spool of .015" wire, make an end on the free end, attach 2 line clips to the chain link fence in the front yard, attach the made end to one of the clips, run out about 6" more line than I want, repeat for other line, Measure exact line length plus 3", cut both lines even, make both remaining ends. Attach handle and torture test lines (about 50% over normal pull test). I have had only one line fail since doing this. I would rather they fail now than while flying. I only crimp lines, never wrap. I used to wrap leadouts, but gave up on that long ago.

[Phil Krankowski]

I know -- 4" pipe means that nominally it's 4" ID (but don't try running a 4.000" diameter stainless-steel sphere through it!).  If I recall correctly, I measured the pipe.  Wrong, apparently.

I'm an engineer.  For a good part of my living I do highfalutin' math that 95% of other engineers won't touch.  Knowing when to put the math book aside and grab a tape measure is important.

Sometimes estimating with math, then assembling with a measuring device is really the best way.  I am positive that the guys on the assembly floor do it that way since it is quicker, easier, and gives the correct result.  They generally don't tell the engineers this though.

Phil

[bill bischoff]

I fly carrier, where the 3 line handle is non adjustable. I could tell that new lines would stretch non uniformly, but only small fractions of an inch. Just enough to mess things up. Once I started applying a one-time pull to the lines prior to tying them to length, they stopped changing. It's very easy to do and only takes a few extra seconds when tying lines. Worth the effort in my opinion.

[Ted Fancher]

I have no idea whether a pre-wrap stretch would stay "stretched" and, frankly, never thought about it.  On the other hand, I'll take exception to those who think the idea has no merit.  Cables do, in fact, stretch when loaded and the difference between cables and solid lines is easily felt at the handle...an noted by the judges if you've foolishly changed between rounds because of wet condition.  I speak from experience, unfortunately.  At a Team Trials a hundred or so years ago my solids were sticking due I believed, to excess wear.  I had a set of cables of the same length and opted to go with them for the next round.  First thing I noticed was that during the pull test it took surprisingly more pull to complete the check, i.e what took very little pull away from the tester with the solids required easily twice as much distance.  During flight the airplane felt like "mush" on the end of the lines and the flight and the score sucked.  My commitment to a hard point handle combined with .018 lines (vice the FAI legal .015) whether required by AMA  rules or not quickly followed.

I've no idea whether  pre-stretching of the smaller diameter lines would make a lasting difference but if I were still competing regularly I'd sure as heck give it a try and then fly back to back flights with the stretched and un-stretched lines to see if the sponginess of the stock lines was eliminated.  If so, I would again consider using .015 cables in FAI competition to eliminate the drag of the .018s I found necessary for positive control inputs when used with a hard point handle.

Ted Fancher

[Bill Johnson]

Thanks for everyone's input. What got me thinking about it is I have, right now, only one good handle and one set of .015" lines. I know for a fact that one of the lines stretched permanently because after about 5 flights, one with particularly high line tension, I had to go to a shorter connector on that line. Not a big deal but then trying to get a good set-up on the other 2 planes became somewhat of a PITA.