Tail Wires

[Steve W]

Thought I should share what I experienced during my first hour of test flying. Most everything was uneventful. Small oil leak at the HP governor line. More left rudder needed which was expected with the whole vertical fin being off set to specs instead of just the bottom, no heavy wing. Cylinder temps 350 and a high oil temp. Will play with that later. I experienced a problem with one wire end that bolts together at the top of the fin. The end was made per the plans. Female threads, bushing stock flattened, bent and built up as shown. It broke around the 40 minute mark. I heard a thump and the trim went a little funny and the elevator became very stiff. Thought I lost a fairing. I eventually landed with extremely sensitive pitch, I found the right upper wire about 2 feet back of from where it was attached.
I will be ordering some AN665’s and will use them with a bent 1/8” tab. I wanted to relate this to others who probably are like me and not a metallurgist to have the foresight to successfully heat and shape the ends of these forks. I probably made mine way too sharp, thus the fracture. Just in case someone else has walked down the same path with the same limited knowledge, there are other alternatives to these fork end assemblies. Also take note that the plane won’t fall out of the sky with a broken wire!

[Steve W]

My apologizes. I see that the AN 665 were to be used as set out in the plans. I don’t remember right at this moment where I got the idea to make them the way I did. Anyways, if you made them like the plans say, then carry on. If you didn’t and end up with something like I made, I’d strongly urge to make them
like the plans.

[BTAZ]

Did the wire itself break or did the forged end piece break?

The description "about two feet back from where it was attached" isn't clear.

[Steve W]

Forged end piece. If you look at the second picture one end is broken. The wire moved/pivoted on the lower stab bolt about two feet back at the top. I moved it back to it’s position in the first picture.
I see the engineering notice in the 2009 newsletter on how the ends were made on the prototype patrol. I made them with the radius too small.

[Mark Goldberg]

We found on the LSA that this type of end fitting for the tailwires resulted in everything being too rigid which resulted in harmonics/vibration/cracking. The 1/8" tabs with AN665's allow for some movement and do not seem to cause the problems we saw on my LSA. I had one fitting crack kind of like you did. Then I had one tail wire break twice in exactly the same place. I suggest that the 1/8" tabs and AN665's are the best way to go. Mark

[Steve W]

Thanks Mark. The break in the metal is all shiny so it looks like a fresh fracture. I do believe I substantially weakened it with the short radius. I have all four wires covered with streamline tubing so I had hoped to cut down on the harmonic/drag stresses. I have them aligned into the relative air flow but could have something happening with asymmetric thrust acting on one of the wires. Which wire gave you the grief? Mine was upper right side. I did have them very tight also.

[Mark Goldberg]

It was the upper right wire on my LSA. Another factor could be the vibration of the whole tail at certain airspeeds or engine RPM. If you have a camera which you could point aft and keep an eye on your tail - that might be a good idea. For some reason, a few of the Patrols have issues with the tail struts and wires vibrating at times. Mark

[Mark Goldberg]

And congratulations for finishing and flying your plans built Patrol. Quite an accomplishment. Mark

[BTAZ]

Sorry, for some reason your photos aren't showing up for me in your post. I tried both Firefox and Edge but no joy. However, if I logged out then went to your post they would show as a link that wouldn't open until I logged in. Very strange....

[Steve W]

Thanks Mark. 5600 hours and used your rib and spar kit plus some other stuff. Like I mentioned I have the wires covered with RC aluminum streamlined tubing but will have to check their alignment again when I get the ends replaced and flying again. With all that was going on, I do remember thinking I will need the prop balanced and thought the vibration lessened when I felt the wire let go. A camera would be the way to go. Same wire so there is a destructive pattern of airflow around the tail. Some aircraft kits have trouble with similar airflow when horsepower is increased and modify their tail to handle the turbulence. Now that I think of it, maybe the prudent thing to do would be to remove the streamline tubing. Was seeing speeds of 155mph at 2450 square so hate to start adding drag but.......
BTAZ, the photos and placement on the site was done on my iPhone so not sure what’s compatible.
Thanks again for the responses

[Steve W]

Mark, has anyone had a failure with the commercial streamline wires?

[Mark Goldberg]

Just on my LSA. The same upper right wire broke twice. And each of the wires that broke was from a different manufacturer. So it was the plane and not the wires. And replacing those rigid tube end fittings with AN665's and the .125 tabs seemed to have solved the problem.

For the hor stab strut of streamline tubing - there are some glue on things that sail planes use to disturb the airflow a little and keep the harmonic and vibrations from developing. One builder glued on some velcro "dots" which helped. But you are kind of in the dark unless you can see what is happing back there. Maybe you can look back and see all the tail surfaces and wires without a camera. Mark

[Steve W]

Thanks Mark. I'll see if one of my boys or one of their buddies have a go pro. I think the 200 hp has something to do with it too. You never see what's happening back there. I've watched the tails of Cubs on floats taking off and the buffeting is extremely violent to say the least until the airflow starts moving across the surfaces. Hard to believe sometimes that they aren't shedding parts all over the place. I remember having the landing gear strut fairings on my Glastar not correctly lined up with the relative air flow and the wheel assemblies would bounce along in flight. You could feel it in the fuselage. When I painted the plane, I re positioned the fairings and all was well.