Martin Wire Revisited

[skip]

The fabric is on the wings, the Ailerons are stitched, and I am ready to put in the Martin wire clips.

Having read all the posts from the last several years about differences in Martin Wire, I figured that I should see what wire is currently available and what the current situation is with the wire.

I have three examples of wire available.


The first is a couple hundred feet of NOS Taylorcraft wire (THANKS drude!!!) that I intend to use for this recover job. The second is the wire of unknown origin from the previous recover in 1991. This wire has held the fabric well for the last 20 years, and I was careful taking it off. I have almost enough to use if needed as a backup. Finally, I ordered one roll of Aircraft Spruce's Martin Wire. I was curious of the reported "worn machine" that their supplier used had really been repaired. The diameters are: NOS .0322", Old .0330", AS .0332". The old wire seems to be stainless while both the NOS and the AS wires seems to be a plain steel.

To see how the wire layed on a rib, I drilled a piece of thin steel with 1/8" holes on 3" centres so that I could get uncluttered pictures. Besides, my ribs are already covered and I don't really want to play with them at this point. I DID mesure the ribs and the holes are 1/8" on 3" centers as closely as I can measure.


The critical dimension of the wire is from the front of the barb that locks into the hole in the rib (The right-hand barb below) up to the square back of the next barb that locks that previous barb in place with no possibility of backing out (The center barb in the picture below). This dimension should be 3" - the 1/8" hole size, or 2 7/8" which is 2.875"


My three wires measure:
NOS: 2.830"
Old: 2.875"
AS: 2.885"

I THINK that my old wire is right on at 2.875 because it was installed in the holes for 20 years. The NOS wire takes a little work to fit in the jig that I made, but the bending of the barb for insertion into the 1/8" hole seems to relax it out to the proper dimension. The AS wire is just a few thousandths long. This isn't enough to require the Z-Bend referenced in other posts, but does make the wire just a bit looser in the holes than the other two wires. So it seems that AS has fixed whatever problem referenced in those earlier posts about wire so loose that it needed a Z-Bend! Good for them.

I put each of the wires into my jig. All three wires layed straight between holes and were tight enough that I could use any of the three. Although they all fit fairly well, the AS wire moves in the hole just a bit making it seem loose. The AS wire could be used, but it seems marginal without a little tightening. The funny thing is that putting the AS wire in the holes, bent its barb enough that its shape is virtually identical to my old wire. However, it is just a bit looser as mentioned above. For those ribs that have had wires ripped out and holes expanded, the AS wire is least desirable. The NOS wire will stay tighter in slightly enlarged holes and the looser AS wire will be even sloppier in such enlarged holes. Fortunately almost all of my ribs have nice clean round holes.

First, the NOS wire:


Next, my old re-usable wire:


Finally, the Aircraft Spruce wire:


So, in summary, I intend to use the NOS wire. It is tighter than the other two. There is one concern with re-using my old wire. It seems that bending and unbending the barbs by installing and then removing, tends to work-harden the wire in the bends. I had two barbs break as I bent them to fit in my jig. Neither of the other two wires showed any tendency to break when bending. If I were to use the AS wire, I would probably spend two or three hours with a long-nosed pliers tightening the angles that make up the barb to more closely match the NOS wire.
However, the Aircraft Spruce wire does seem, at least, usable.

Well Thanks for reading this far. What do you all think of my methodology? How about results? Other recent experience with Martin wire? I intend to start punching the clips them in Monday, so let me know what you think. The collective wisdom of all you folks has helped loads so far!

Skip Egdorf
TF #895
BC12D N34237 SN 7700 Flying soon I hope...

[skip]

Re: Martin Wire Revisited

I'll reply to my own post. Today I put all three wires into the wing just to see how fit and finish work for each.

The first is the NOS Taylorcraft wire. It fits tightly and lays flat. This will be how my wing looks when I am done.



Next I put in one of my old wires from the previous recover. It mostly fit well, but one section has a bow up. I will probably leave this just to have a conversation piece on the underside of my wing.



Finally the Aircraft Spruce wire. Well, I believe that it would be airworthy. No Z-Bends are really needed. That being said, this would have enough bumps in the covering tape that it would look really really poor. I removed this wire and replace it with my NOS wire.

So what do we do when the old hangers full of NOS Taylorcraft wire are gone? I think that If the next rebuild has the choice of Aircraft Spruce wire or rib stitching, I will do the stitching.



As of this evening, the wings have wires installed on the underside. Tomorrow, I should be able to finish the uppers. Then the finish tapes and finally the fill and paint steps. There might be light at the end of the tunnel!

Skip Egdorf
TF #895
BC12D N34237 sn7700

[Pearson]

Re: Martin Wire Revisited

So what do we do when the old hangers full of NOS Taylorcraft wire are gone? I think that If the next rebuild has the choice of Aircraft Spruce wire or rib stitching, I will do the stitching.

Skip,

First of all, my compliments on a very well written post, and backed up by some very nice pictures. Instead of wire I plan to use pop rivets when I recover my wings. I have a copy of a 337 that allows the use of PK screws along with a letter from the FAA saying that pop rivets may be used instead of the screws. I sent a copy in to someone to post on the Taylorcraft website a few years ago. If you don't see it there, let me know if you are interested in a copy.

[M Towsley]

Re: Martin Wire Revisited

Skip,

Though I am not restoring anything I would like to echo Richard's praise. You did a very nice job on reporting on a subject that has popped up now and then over the years. Great work!

[mike lutz]

Re: Martin Wire Revisited

I have used the pop rivets on a AgCat and a Citabria,and was very pleased with the end result.The rivets are all alum. and are the faa approved rivets for the Gruman and Champion series.Very easy to install or remove.I seen a champ wing once that was rib stiched,and half of the stitching was chaffed apart on both wings.It should have had the pk screws or the fabric rivets instead of the laceing cord.There was no provision done to prevent chaffing,and if all the stiching would have failed,most likely would have been a fatality.Heard about a Pitts once that all the stiching failed on a wing due to inproper installation,and was fatal.

[birdlegs]

Re: Martin Wire Revisited

I used this approach as well,, Rich may recall my letters, and the guys that did the work in Montana ( thanks Tyler and Merrill ) whom I asked to try the wire said they couldn't find wire with correct spacing for the hole center's. Merrill does fabric wings for a living, and the I.A. agrees that pop rivets make a much better bond. Wings are done and serviceable, *but a footnote to others the aircraft had been signed into service with screws since 1958,,so just saying.