Strut Tensile Testing

[1938BF50]

FYI....

Later today I will be pulling nearly (40) prepared tensile pull test specimens.

My goal is to give us all a good warm and fuzzy of how varying degrees of corrosion affect the strength of the material. Mike Redpath was kind enough to have sent me several strut ends ranging from severely corroded (holes thru) pre-war stuff to late material with excellent mechanical integrity. I laser-cut (2)ea. specimens from the lower 6 inches of each strut and (1) from the upper 16" or so as a baseline for that particulat strut. A couple others here on the forum have offered to assemble my data in "official" govt. format for presentation to the FAA.

Mike C.

[Ragwing nut]

Re: Strut Tensile Testing

Cool, is the AD still open for comment?

Mike

[1938BF50]

Re: Strut Tensile Testing

I understood the comment period to be open until Oct 12th?

I have been compiling results all day today. I did want to share one small pc. if it let's anyone get a warm and fuzzy that they are not going to fall out of the air if a stool sample or X-Ray shows a flake of rust. My main intent is to give those in the decision making position, FACTUAL data on just what varying degrees of corrosion mean to all of us.

Here is a pic of the WORSTcase strut that I tested. It had corrosion thru the metal in (2) places(easily seen in the pic). I was very surprised to see the test results showing 50% and 52% remaining strength in the samples pulled. This means that this particular strut with VERY HEAVY CORROSION still has a safety factor of half what it originally had. If 10X then it might still support 5X.

Most testing of even moderate corrosion (fairly heavy flaking and pitting) shows remaining strength in the upper 90 percentile BASED ON THE LOW END OF THE RATED TENSILE STRENGTH FOR THE GIVEN MATERIAL.

[Dano"T"]

Re: Strut Tensile Testing

Gotta love an Engineers mind.....nice work Mike.

[VictorBravo]

Re: Strut Tensile Testing

Is it just me, or does everyone else also think we have to get together and buy this guy a case of really good beer?

Thank you, Mike, sincerely on behalf of everyone here. Keep Going !!!

[cpirrmann]

Re: Strut Tensile Testing

Alternatively, we could buy him a taffy pulling kit!

[N74DV]

Re: Strut Tensile Testing

this is a great thread! I'm anxious to see all the data in the end.

THANKS!!!

[1938BF50]

Re: Strut Tensile Testing

Apparently all for naught!

Forwarded my findings to Andy McAnaul (FAA) this morning. Just got off the phone with him and was fairly discouraged to find that what I had presented will have no impact in the furtherance of the Strut AD. For those of you interested, my observation is: even moderate (to heavy) corrosion leaves a substantial safety factor on the remaining strength of the parent material. I understand that much of this data is somewhat intangible by definition but had really thought it might provide a platform to support an extension of the duration of the repetitive inspection.

In support of Andy, he was professional, polite and accommodating in conversation. This was just not data he was willing to use in any supportive function.

Data is attached. Make your own conclusions. Please feel free to either reply or call me if you want to discuss further.

[cpirrmann]

Re: Strut Tensile Testing

So, in short, it appears to prove what we knew all along, that with regular inspection and using our curent struts, we're not in any danger of falling out of the sky. The fickle finger of blame seems to point back down to Texas. Sorry, don't need to fan those flames again. Now... the attach fitting could be another matter.

[AKbrew]

Re: Strut Tensile Testing

Mike, I'm sorry to hear the data you collected will not be considered toward modifying the AD.

Thank you for doing something so meaningful and tangible for the cause. Even though it appears to be "all for naught", we all greatly appreciate the time and effort you put into this project.

If I had a good way to ship you a case of fine Alaskan Amber beer I would do it...of course if you want to come collect in person you are welcome any time!

[whake]

Re: Strut Tensile Testing

It would be neat if some ingenious person with a machine shop could remove the tubeing and salvage the end pieces and come up with remanufactured sealed struts at $1600 a set.

[Hank Jarrett]

Re: Strut Tensile Testing

Would the Feds accept that as a "owner manufactured"? I have a friend who can get the tube and the fixture isn't hard to build (if you know what you are doing). We could even "seal" the end fittings prior to welding them on the tube.
Hank

[Forrest Barber]

Re: Strut Tensile Testing

THANK YOU for all the effort, as mentioned somewhere, I personally ahve flown ships home that we had to destroy the struts, elevators, tube doors
( on a CUB do to corroision. The neutral axis of the strut takes the load and the rear end of the streamline can be virtually missing and still have sufficient strength to fly. We know this, but have to protect many owners who are not as knowledgeable as many of our group, thank you and I have the data.
I am a great one for show me stuff I had each batch of wing wires and tail wires pulled to destruction 1 out of 100..... teleconference is starting NOW! bye

[robbie]

Re: Strut Tensile Testing

Thanks Mike for you efforts was interesting data.
It shows those stuts would need to be in really bad shape and one would be able to see punch thru before the struts would fail.
Thanks again for your time and work.

[DanBrown]

Re: Strut Tensile Testing

Agreed!! This again points up the robustness of CG's design. Mike's great work gives me a warm feeling that as long as I do a good pre-flight, insist on a quality annual inspection and don't abuse my T-Craft she will do right by me.