Grounded again

[seastar]

CHECK YOUR STRUT ATTACHMENTS BEFORE EVERY FLIGHT!!!

Happy New Year!
Bill

[Joseph206]

Hi Seastar,
What year is your plane???

[Springloaded]

[QUOTE=seastar;14488]Well it's happened again!

I am begining to believe that the Carbon Cub is very fragile and designed with parts that are much too weak to be reliable.
That part is aluminum and should be stainless steel or some other stronger material




Morning Bill
I had one break on my 2009 sport cub. I too was upset more because I couldn't go flying than anything else. CubCrafters sent me new ones with larger studs. I put another 400hrs on it with no problems.They are made of stainless steel,the collar or nut might be aluminum but that's not what broke looking at the picture. I have put well over a 1000 hrs on my airplanes S2 and carbon cubs in some very unfriendly places ,to say they are fragile in any way or not reliable I don't believe is a fair statement. It's unfortunate that yours has had problems,with anything Mechinacal things break doesn't matter what it is. CubCrafters has always stood by there product with good customer support thats why I bought another one. I'm sure if you call them they will help you get back flying as soon as possible. In my opinion the only real problems are when nobody's willing to help with it and I just don't believe that will be a issue with CubCrafters from my experience with them.
Good luck
Chuck

[seastar]

1234

[Dan L]

I had that same part break on my EX. The problem though was the little plastic bushing hadn't been installed. That was my fault. The bushing absorbs vibrations and without it the part will break.

[stede52]

Well it's happened again!
A part that holds my Carbon Cub together has broken. 235 TT.
I found this before a flight on Christmas Eve.
g

Thats the attachment assembly that connects the jury strut and brace to the front lift strut.
Those broke early on in the history of this airplane. As well as several other more serious parts.
They were all replaced with more substantial parts and now one of them has broken.
I am begining to believe that the Carbon Cub is very fragile and designed with parts that are much too weak to be reliable.
That part is aluminum and should be stainless steel or some other stronger material.
A bracket made of aluminum with an AN bolt through the lift strut would be easy to design.
The aluminum thread sheared at the attachment point just as I would expect in hindsight.

CHECK YOUR STRUT ATTACHMENTS BEFORE EVERY FLIGHT!!!

Happy New Year!
Bill

Bill, I have heard that fitting is prone to breakage if that fastener is not properly torqued. If that particular fastener is torqued to 40lbs like the top jury strut fastener it will do just as yours did. This lower fitting has that plastic bushing in the mount which is used to absorb the vibration from the movement of the lift strut. If this fastener is torqued too tight (should be about 28lbs) it gets squashed in the fitting and can't absorb the vibration and will eventually fatigue and break. When pre-flighting this fitting I always make sure I feel a very slight amount of movement in the jury strut at that fastener which insures me that the plastic bushing is doing its job. If someone other then yourself does the annuals and happens to tighten that fastener because there was some movement at that fitting, that would be a bad thing. If the fastener was torqued properly, well then there was a problem with the fitting itself. Sorry to hear that happened, I too hate fixing airplanes.

[seastar]

I just received the replacement parts from Jeff at the factory.
That's vey good service.
i can fix it tomorrow and maybe fly the airplane then.
Bill

[stede52]

It was torqued correctly when originally installed because I did the reaming of the through hole and the installation.
It had not occurred to me that some dumb a$$ mechanic might have "adjusted" it.
The nylon bushing was in perfect condition when I removed the broken part.
Ill ask the mechanic if he messed with the bottom strut bushing because the thread on the eye bolt broke.
Bill

If the plastic insert is crushed, it was over tightened by someone.

[turbopilot]

Question? What is the purpose of the jury strut? Is it structural or way to dampen vibration in the main strut? Combination of both? Based on all of my tries to get video around the strut structure on the CC there sure seems to be a lot of vibration in the strut system with some harmonic frequencies associated with prop RPM that seems to increase vibration significantly.

[seastar]

Not sure, but in a positive G condition the lift strut is in tension and the jury strut does nothing but damp vibration.
In a negative G condition the lift strut is under compression and might tend to bend if not restrained by the jury strut.
Under compression the jury strut cuts the "beam length" about in half which, if I remember my mechanics correctly, greatly increases the lift Struts ability to resist bending.
Additionally the combination of the jury struts and the wing ribs along with the brace between the front and rear lift struts forms a strong "box section"at the center of the wings.
I think you could fly the airplane without jury struts if you resisted the temptation to do negative G maneuvers and took great care in landing and avoided rough air. LOL!

But then what do I know?
Bill