Cracks found on Challengers

[Tiger Tim]

Just in case anyone here flies a Challenger and wasn’t aware of this:

https://copanational.org/en/2019/04/11/tsb-finds-fatigue-cracking-on-many-challengers/?utm_source=wysija&utm_medium=email&utm_campaign=Newsletter-20190412

 

[BJC]

That's scary - glad that they found it.


BJC

 

[BoKu]

Wow, the way the center part of that bracket is loaded in bending appears to be a thoroughly mediocre piece of design. I'm a bit surprised that anybody is surprised that it fatigued and broke.

 

[pictsidhe]

Ewww!

 

[D Hillberg]

A "U" strap of steel 'doubler' would fix it.

 

[blane.c]

Stuff like that is just the "IQ test" before the "Darwinism" award.

 

[radfordc]

This problem was identified in Challengers 10-15 years ago and the factory did provide a "U strap" fix, and also specified using steel brackets instead of aluminum.

 

[pwood66889]

Thanks for the tip. I'll examine that WeedHopper I'm assisting on.
It always looks good on paper when all the forces go through the same point - no "moments" and other pesky things...

 

[Mike W]

About 10 to 15 years ago I carried out a stress analysis on the Challenger for the then PFA, now LAA in the UK and flagged up likely failure of this bracket. We fitted a 1/4 in spreader plate on the UK aircraft as shown in the photo and also rotated the bracket 90 deg so that the lift strut could flex vertically without applying additional loading to the bracket and its attachment fittings. Also the 1/4 boom attachment bolt looked iffy in fatigue and was increased to 5/16. This was sent to the interested parties in the USA.

I saw the above Canadian report and passed it onto our LAA who contacted the Canadian authorities with details of all my findings. So far I have had no feedback on it.

 

[David Lewis]

The struts subtend a shallow angle with the wing because the fuselage isn't that deep. The tension load on those struts has got to be enormous.

 

[pictsidhe]

About 10 to 15 years ago I carried out a stress analysis on the Challenger for the then PFA, now LAA in the UK and flagged up likely failure of this bracket. We fitted a 1/4 in spreader plate on the UK aircraft as shown in the photo and also rotated the bracket 90 deg so that the lift strut could flex vertically without applying additional loading to the bracket and its attachment fittings. Also the 1/4 boom attachment bolt looked iffy in fatigue and was increased to 5/16. This was sent to the interested parties in the USA.

I saw the above Canadian report and passed it onto our LAA who contacted the Canadian authorities with details of all my findings. So far I have had no feedback on it.

If the 'interested parties' included the manufacturer, this reflects badly on them.

 

[Victor Bravo]

I agree with D Hillberg and others, a strap doubler around the longeron would resolve many of the problems. It would also provide an alternate load path than just the one bolt in tension.

Now if a backyard bozo model builder like me can see this easily, how did this design get past the factory engineer?

Well, it's not like that bracket holds the wings on the airplane or anything.

Oh, wait...

 

[Hephaestus]

I'll attach a pic from FB... I just get this impression that the factory doesn't see it as a problem.

"One failure in 37 years" ... Um that's actually 1 detected and proven failures - can we reopen all those not investigated crashes?

The two "low hour" ronys that were found with damage now are also claimed to be damaged by misinstallation or overloading.

I keep eyeballing the Challenger, I want one but some of this stuff I have a really hard time swallowing.

 

[Mike W]

My findings on the Challenger were sent to Quad City and we received a strongly worded and insulting letter back from Dave Goulet refuting all my findings and threatening both me and the PFA with litigation.

 

[Hephaestus]

There have been enough pictures of brackets and bolts the 2 fb groups, that I can't help but think - all is not well. Their answer is always overloaded, damaged by mis-installation, that landing surely was a crash etc etc etc.

Sure doesn't give me warm fuzzies. Since they're still refusing to really address the issue, beyond "we're working on a solution". I really do wonder how seriously they're taking it.

 

[pictsidhe]

My findings on the Challenger were sent to Quad City and we received a strongly worded and insulting letter back from Dave Goulet refuting all my findings and threatening both me and the PFA with litigation.

Have you sent a copy of that to Canada?
If they decide it does need alteration, they are opening themselves up to litigation for other accidents after they were told the bracket had a design flaw.

 

[BoKu]

Metal fatigue is a thing.

 

[BBerson]

A thick bar under the bolt head would prevent fatigue bending.

 

[Victor Bravo]

A thick bar used to beat the designer would be beneficial as well.

 

[BJC]

There have been enough pictures of brackets and bolts the 2 fb groups, that I can't help but think - all is not well. Their answer is always overloaded, damaged by mis-installation, that landing surely was a crash etc etc etc.

Sure doesn't give me warm fuzzies. Since they're still refusing to really address the issue, beyond "we're working on a solution". I really do wonder how seriously they're taking it.

View attachment 86304

Are those bolts as indicated in post #3? Which ones?


BJC