Another Tail Wire Thread

[Archer39J]

Say I don't want to pay ~$800 for streamline tail "wires". The remaining options are to use at 1/4" dia end-threaded rod per the plans or a 5/32 1x19 cable per what other's have said Bob has approved in other threads.

Couple questions:

If I go with the cable what are the options for connecting these at the tail wire links? I've seen mention of a swaged end which requires additional parts and tooling, I've also seen nicopress mentioned which suggests a shackle and thimble setup which seems... draggy.

If I go with the rod where's a good place to get these? I hear tell it's best to have rolled threads rather than cut so that sounds like they need to be sourced correctly.

Either swaged cable or threaded rod requires purchase of 8 additional AN665 ends too, would have been nice to include that in my Wicks order...

[Chris In Milwaukee]

Aircraft Spruce will make wires to whatever length you like, no special tools required:

http://www.aircraftspruce.com/catalo...clickkey=94754

[BTAZ]

For my LSA, I spent a good bit of time researching wires used on certified aircraft and was able to come up with a set(around $225 for all four) that way. Looking through Univair's resources for wire lengths was key.

Unfortunately I think most certified wires are 3/16(10-32 thread) but maybe there are some similar certified four place planes(like Maules or Pacers perhaps) that would use larger wires.

[Archer39J]

Aircraft Spruce will make wires to whatever length you like, no special tools required:

http://www.aircraftspruce.com/catalo...clickkey=94754

Oh nice, thanks I hadn't seen that before.

Also I found the Beartracks where Bob specifies how to fab your own which is appealing to me. He calls for cut threads and says something like 1900 hours on such has worked fine. Have those proven to be troublesome? I'm leaning toward fabbing myself per Bob's design.

[Archer39J]

Hrm, having to turn down the entire piece... Perhaps ACS is best.

[Chris In Milwaukee]

Those wires that I mentioned aren't rigid, though. They're cables with swaged ends on them. It another option beside solid wires. Just in case you didn't notice.

[Bdflies]

Aircraft Spruce will make wires to whatever length you like, no special tools required:

http://www.aircraftspruce.com/catalo...clickkey=94754

Just checked what a pair would cost. Less than $50.00 a piece, for custom cables with rotary swaged stud ends. Seems like a pretty good deal to me!

Bill

[Archer39J]

Those wires that I mentioned aren't rigid, though. They're cables with swaged ends on them. It another option beside solid wires. Just in case you didn't notice.

Yep, braided cables. The option with the most drag is the cheapest, funny how that works. Question is do I get the the swaged fork on one end and use a stud and AN665 on the other, or AN665's for both ends for adjustment? Hmmm.

[Bdflies]

Studs with AN665's both ends. One end left hand threads, other end right hand threads. That allows adjustments without twisting the cable.

Bill

[BTAZ]

My recollection is that the 1/4" rod is turned down to be below the minimum diameter of the cut thread. That would eliminate a stress riser formed by the discontinuity of the last thread where it would transition back to full diameter. Removing that material from the entire wire in between the threads would be for weight reduction.

So if you are turning the rod down close to a 3/16" diameter, I would be inclined to see if there are off the shelf 3/16" wires availible in the correct lengths and then ask Bob if you could use them.

of course, I would guess Bob already explored this.

[Archer39J]

Yeah that makes sense, but probably precludes starting with 3/16" stock.

[BTAZ]

Rolled threads on 3/16" wires aren't relieved as described. They are 3/16" OD full length.

As Bob's process describes, start with a 1/4" OD rod, thread the ends, and then turn the inner section down to at or slightly below the minimum diameter of the thread.

That leaves the cut threads proud of the surface but leaves the center section thinner than 1/4".

[Archer39J]

Ah, missed the full-length rolled thread part. Thanks!

[Mark Goldberg]

Making your own tail wires out of 4130 bar stock is something I think only Bob has done. Bob turns the body of the piece down below .200. He does this for another reason that BTAZ didn't mention above. Vibration and potentially damaging harmonic with the full mass of the .250 wire. Turning it down, according to Bob, makes it less likely to develop a harmful vibration.

About ordering cables with swagged ends - if you follow Bob's guidance on what is acceptable you can save some $$ at the expense of some drag. One thing about doing that - the male threaded ends supplied do not have a lot of thread. I want to say 1/2" but that is probably wrong. Point is - your measurement of the length you need has to be pretty spot on. I ordered a set for my Patrol and ended up not using them because they were off too much in length from what I ended up needing. So if you go that route - measure carefully and make sure all the tail surfaces are good before measuring. Mark

[BTAZ]

For clarification/summary as I'm getting confused, production round tail wires use a rolled thread and are not reduced in OD.

So a typical 3/16" wire will have about 3" or so of thread on either end and the un-threaded portion will remain 3/16"

A cut thread will leave a stress riser at the end of the thread where it transitions back to the full rod diameter. Bob eliminates this transition by reducing the OD of the unthreaded portion of the rod down to the minor diameter of the thread(.206" for 1/4-28, .187" for 1/4-20, reference here(https://www.engineersedge.com/screw_threads_chart.htm))

I wasn't aware of the vibration concern Mark brought up but makes sense though perhaps hard to quantify. Dropping the diameter would "tune" the wire for a higher resonant frequency at a given tension. But I would bet you could walk up to ten different aircraft and strum the tail wires and get ten different notes..

I do know that round wires have dramatically more drag than streamlined but it is recommended the lower wires be round as they are more resistant to nicks. I believe there is an AD about this for some of the Pipers.

20180105_171508.jpg

[Steve W]

I plan on using aluminum streamline tubing over the 1/4" rod. Not sure what size has enough inside diameter to accommodate the rods but wouldn't weight much. It's used in the RC world. Very cheap too!

[Archer39J]

Making your own tail wires out of 4130 bar stock is something I think only Bob has done. Bob turns the body of the piece down below .200. He does this for another reason that BTAZ didn't mention above. Vibration and potentially damaging harmonic with the full mass of the .250 wire. Turning it down, according to Bob, makes it less likely to develop a harmful vibration.

About ordering cables with swagged ends - if you follow Bob's guidance on what is acceptable you can save some $$ at the expense of some drag. One thing about doing that - the male threaded ends supplied do not have a lot of thread. I want to say 1/2" but that is probably wrong. Point is - your measurement of the length you need has to be pretty spot on. I ordered a set for my Patrol and ended up not using them because they were off too much in length from what I ended up needing. So if you go that route - measure carefully and make sure all the tail surfaces are good before measuring. Mark

Thanks for the warning, I was wondering about getting the lengths just right. Sounds like 2 AN665 per wire would be prudent if I go that route. Waiting to hear back from my local metal shop about some 4130 bar, I still think I like that solution best.

[BTAZ]

Since I was bored.....

Bruntons gives a "Min. strength Spec." for 3/16 wires as 2100lbs for round, 2400 lbs for streamlined. (http://www.steenaero.com/products/flying_wires.cfm)

The common "Breaking Strength" spec for 7x19 5/32 stainless cable is 2400 lbs.(http://www.fairburyfastener.com/cable_specs.htm)

So if one could "tease out" an appropriate length set of 3/16" wires from production aircraft using data available at Univair, it would probably be worth talking it over with Bob.

UPDATE; per Mark G. the cable needs to be 1 x 19. 1x19 5/32" stainless has a higher "breaking point" (2800 to 3300 lbs, https://www.chain-cable.com/wirerope.htm ) so would seem to eliminate off the shelf 3/16" tail wires as a possible option.

[Mark Goldberg]

If you use wire/cable - you have to use a non stretchable cable like 1 x 19. Not normal control cable which is made to have some stretch. I used 1 x 19 cables on my FlyBaby as these wires hold the wings on. Mark