Broken Tail Flying Wire

[Nev]

Wanted to add one data point to this thread. I was out flying two days ago and noticed my left side tail flying wire was vibrating quite noticeably. Changes in airspeed had no effect until down to to 70 knots. I discussed with the local engineer and we made a very slight adjustment to the angle of the wire, barely noticeable. Flew again and couldn't observe any vibration so hopefully it's fixed. I'll be keeping a close eye on the wires during preflight.

[Smokybear]

I have no experience building with these airfoil shaped flying wires, but I immediately correlate this to another circumstance that I think is a good visual explanation of what is happening. If you've ever seen an 18-wheeler on the highway with a flatbed truck with cargo strapped down with the 3-4" strap going over the top of the cargo, you'll notice they twist these cargo straps on each side. BUT, every once in a while they forget one and leave it un-twisted. The un-twisted strap will always violently flutter at highway speeds. I attribute this to the strap trying to find the correct angle of attack, but the force of the wind pushes it past the correct angle, and then back the opposite way too far over and over again (hence, violent flutter). Applying this to the flying wire theory, these wires are likely never perfectly positioned as an airfoil. At best they are only perfect at one given airspeed (hopefully at cruise). So the possibility of flutter seems almost inevitable at any tension.

Now given the ideas about the velcro and the am/fm antenna having a twist around a round wire stopping the flutter, that makes a lot of sense.

Correct tension, along with a quality made airfoil shaped wire likely negates all issues of flutter and cracking, but it still seems that round control cable would be the best against preventing any flutter at any angle, given that the twisted steel cable acts in the same manner that the am/fm antenna with a twist would. What's most interesting is that I've never given airfoil shaped flying wires a second thought until reading this post.

Casey

[svyolo]

Certification is psychotically expensive because you have to test and prove bad stuff DOESN'T happen, over lots for hours/cycles.

In the experimental world less/little testing is required.

Vibration/noise/harmonics are signs of impending failure. Doesn't matter if it is a bicycle, car, or airplane. Noise and vibration are always destructive.

[spinningwrench]

For what its worth American Champion uses 3/16" round stainless wire for all their airfoils and don't have any problem with breakage.

[jim.mclaughlin924]

I used 5/32 1x19 ss wire with swaged ends, per Bob. No problem in 150 hrs and no need for any adjustment. Also very cost effective.

[Nev]

I used 5/32 1x19 ss wire with swaged ends, per Bob. No problem in 150 hrs and no need for any adjustment. Also very cost effective.

Thanks Jim and others above for contributions. jim.mclaughlin924 do you have a means of adjustment on the ends ? I'm thinking that it might make a good backup for us here in NZ if someone breaks a wire, while we're waiting on a replacement part.

[Ray Strickland]

Nev,
See my post dated 7/13/2022.
Details and photo.