Flying & Landing Wires

[JDD]

Hi All,

I am looking into a late 1920's early 1930's Biplane project. One area of concern is the Flying Wires.

The project has a complete original set. The owner tells me that they were painted from the factory. Some of the paint has pealed off and has "rust spots" on them.

Since a complete new set is $10K, I wanted to know how one can determine if the old set is useable or not. I have found an old Budd Davisson article (http://www.airbum.com/articles/Flyingwires.html) on the subject, but it is a little thin on specific's.

If there any more detailed documentation on how to test and determine the condition of flying wires?

The project is a basket case KR-34 although the engine and prop are zero and ready to go. If I have to add $10K to the project...it may tip the scales against it for me.

Anything people may have on flying wires would be a help.

Thanks, JD.

[1600vw]

Just me but on flying wires, any corrosion and I would not use them. Having one break in flight would not be good. If any others are corroded they could all break. Just me but replace them. More then likely this is why they airplane has sat. Corrosion on to many parts to get the bird flying with out spending a fortune.

My two cents.

Tony

[Frank Giger]

Those are rods, so yeah, I'd replace them. I'd look around to see if they can be sourced from stock material and then cut and threaded rather than by pre-cut part number.

[Aaron Novak]

Those are rods, so yeah, I'd replace them. I'd look around to see if they can be sourced from stock material and then cut and threaded rather than by pre-cut part number.

If you can match the exact threadform, material and process that should be just fine. The last time I got slightly involved in making replacement wires, the cost of having the custom progressive dies ground to cut the threads pretty much eliminated the cost benefit of making them vs. buying them. If the threads were rolled, forget it. Its not as easy as ordering up a die and rod from McMaster and going at it on the shop vise unfortunately.

[martymayes]

Anything people may have on flying wires would be a help.

I think I have some old inspection info on flying wires but it might take a while to find it. I believe in your case it will be like anything else. Remove all corrosion products, inspect with a 10x magnifiying glass, if the surface is pitted, might can blend out, might require something else.

[skyfixer8]

The following was issued by WACO folks in 2014. Sounds like good advice to me, referencing the underlined statement. http://www.wacoaircraft.com/assets/P...Inspection.pdf

[JDD]

Thank you for the link. This looks like it was written by their lawyers and not by an engineer. It is a CYA document. If this same standard applied to everything in the aircraft then no airplane would every fly again other than once!

[WGlandry]

IMHO, I would replace them if they are as old as you say. The paint could be hiding other problems besides rust.

[9402sierra]

Thank you for the link. This looks like it was written by their lawyers and not by an engineer. It is a CYA document. If this same standard applied to everything in the aircraft then no airplane would every fly again other than once!

Don't be so quick to shout CYA on this one. Biplanes of that era carry all of the positive g loads on the wings through the flying wires to the aircraft structure. The landing wires carry all of the negative g loads as well as the loads encountered during landing into the aircraft structure. Most aircraft of the barnstorming era have redundant flying and landing wires so that if a wire breaks in flight, the second wire will prevent the wings on that side from moving unless the second, redundant, wire is stressed beyond its limit. More modern designs starting in the late thirties pretension the flying and landing wires so that normal loading conditions relieve the loads on one set while not appreciably increasing the loads on the other. On my Travel Air, there is no pretension, so the load on the flying or landing wire set is directly proportional to the g loading on the airplane. After having reviewed the stress analysis originally submitted for Travel Air certification I can tell you there isn't a huge margin of safety in the flying and landing wires and I suspect it isn't much different for other aircraft of that era.

Nicks concentrate the load at the point of the nick. As an absolute minimum, nicks should be smoothed out to a distance on both sides of the nick of at least ten times the initial nick depth with no scratches visible under 10x magnification in any of the area smoothed. The minimum thickness of the wire at the point of maximum smoothing depth should never be less than 90% of the original dimension of the wire. If the wire has to be thinned more than that to remove the nick, the wire should be scrapped.

Corrosion is worse in that it involves more uncertainty. Depending upon its source and the resulting corrosion products it can change the molecular structure of the wire leading to the development of fault lines in the material eventually leading to cracks. A cracked wire will soon be a broken wire and a broken wire will spoil your entire day.

Carefully strip the wires of paint and inspect their entire length. If they are free of nicks and corrosion measure the wires along their length to assure that they aren't necked down as a result of excess tension or past smoothing of nicks. If they are corrosion free and constant diameter, refinish them, replace all the end fittings with new hardware and reuse them. It's a lot of work, so replacement may be your best option.

Enjoy your project.

A Travel Air Nut.

[Aaron Novak]

Don't be so quick to shout CYA on this one. Biplanes of that era carry all of the positive g loads on the wings through the flying wires to the aircraft structure. The landing wires carry all of the negative g loads as well as the loads encountered during landing into the aircraft structure. Most aircraft of the barnstorming era have redundant flying and landing wires so that if a wire breaks in flight, the second wire will prevent the wings on that side from moving unless the second, redundant, wire is stressed beyond its limit. More modern designs starting in the late thirties pretension the flying and landing wires so that normal loading conditions relieve the loads on one set while not appreciably increasing the loads on the other. On my Travel Air, there is no pretension, so the load on the flying or landing wire set is directly proportional to the g loading on the airplane. After having reviewed the stress analysis originally submitted for Travel Air certification I can tell you there isn't a huge margin of safety in the flying and landing wires and I suspect it isn't much different for other aircraft of that era.

Nicks concentrate the load at the point of the nick. As an absolute minimum, nicks should be smoothed out to a distance on both sides of the nick of at least ten times the initial nick depth with no scratches visible under 10x magnification in any of the area smoothed. The minimum thickness of the wire at the point of maximum smoothing depth should never be less than 90% of the original dimension of the wire. If the wire has to be thinned more than that to remove the nick, the wire should be scrapped.

Corrosion is worse in that it involves more uncertainty. Depending upon its source and the resulting corrosion products it can change the molecular structure of the wire leading to the development of fault lines in the material eventually leading to cracks. A cracked wire will soon be a broken wire and a broken wire will spoil your entire day.

Carefully strip the wires of paint and inspect their entire length. If they are free of nicks and corrosion measure the wires along their length to assure that they aren't necked down as a result of excess tension or past smoothing of nicks. If they are corrosion free and constant diameter, refinish them, replace all the end fittings with new hardware and reuse them. It's a lot of work, so replacement may be your best option.

Enjoy your project.

A Travel Air Nut.

Excellent post, thank you!
-Aaron