RV-7a Nose-Gear Collapse Part 3 - Video of the retaining pin

[6ato14a]

Originally Posted by BillL

There was a very good thread with these contributors on this subject a few years ago. I collected the information, references and made a PDF with just the facts.

Contributors (in alphabetical order): Walt Aronow (“Walt” on VAF, RV-7A), Bruce Hill (bruceh, 9A), Bill Palmer (same, 8A in- work), Bill Pendergrass (rzbill, 7A), and Alex Peterson (AlexPeterson, 6A).

Send me a PM via EMAIL and I will send this to you. I tried to get DR to post it to no avail.

Please send me the PDF you referenced.

Klmoexpo@gmail.com

Thanks,
Dave shenk

[nedricher]

Did I miss somthing. The SB calls for replacing the bolt if the stop bracket was installed backwards, was this SB complied with before the failure or after it broke? If it was complied with, was the bolt replaced at the time. Just wondering if this is a problem with aircraft that had the stop bracket installed correctly at first flight.

[Raymo]

Originally Posted by nedricher

Did I miss something. The SB calls for replacing the bolt if the stop bracket was installed backwards, was this SB complied with before the failure or after it broke? If it was complied with, was the bolt replaced at the time. Just wondering if this is a problem with aircraft that had the stop bracket installed correctly at first flight.

You did not. I agree, the problem was not the bolt, per se, but the improperly installed stop bracket. Unfortunately, the buyer/owner/OP was not aware of the potential issue and the pre-buy inspection did not catch it either.

Installation of a longer bolt, IMO, would not have avoided the problem. Though it may have delayed the inevitable.

[rvbuilder2002]

Originally Posted by boandrv7a

Part 3 - I got a bunch of questions about the nose-gear retaining pin. I took a video of the mangled retaining pin (the pieces I could find).

See it here:

https://www.youtube.com/watch?v=6hJx_xsAAFc

Jim

Your reference to galling on the surface of the bolt in your video is no different than what you would likely see if you kept repeatedly hitting the bolt with a hammer over and over while rotating it (basically what has been happening with your bolt since the airplane first flew).

Because the tool you are measuring the bolt diameter with is tampered, it is impossible to measure as you did with any accuracy. If you use a tool that can measure accurately (a caliper or micrometer) you will probably find a diameter difference of only a few thousandths of an inch, but that is more than enough to cause a problem.

The view in your video isn't very clear but it looks like the failed ends are classic of a progressive failure through about 1/2 of the cross section and then evidence of a single event shear failure of the remaining un-failed portion.
Point being is that the bolt had probably been partially cracked for quite a while and then one single high load event (possible a hard pivot turn with one brake locked?) caused it to fail the rest of the way.
It is unfortunate that no one had detected it previously or caught it in the pre-buy inspection. (good evidence for using one of the shops that specialize in working on / inspecting RV's... even if it costs more to get it to them)

BTW, for anyone that finds their way to this thread in the future, the Service Bulletin related to this construction error describes a procedure for check for proper installation of the steering stop without removing the nose wheel fairing so this check can easily be done by anyone that is able to move the airplane with a tow bar. If you own a tri-gear 2 place RV (other than the RV-12) and you don't know whether this check/inspection has even been done, it would be a good idea to do it your self.

[bret]

Remove 4-6 screws to pull a wheel pant nose to not risk a 50,000.00 repair is quite worth the 40 seconds of labor involved! or just take your 10.00 smart phone borescope cord up into the wheel pant.

[rvbuilder2002]

Originally Posted by bret

Remove 4-6 screws to pull a wheel pant nose to not risk a 50,000.00 repair is quite worth the 40 seconds of labor involved! or just take your 10.00 smart phone borescope cord up into the wheel pant.

I would take a bet on it taking you 40 seconds to get the tools and then get it removed.........

Regardless, it can be confirmed a number of different ways so do it how ever you want, but the procedure described in the S.B. will show with absolute certainty if it is installed backwards or not and it can simply be done any time you are already moving the airplane with a tow bar.