What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

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

Interesting. How many hours are on that bolt? Was a new nose gear leg installed per Vans SB 07-11-09, and if so was the new leg drilled by Langair or by someone else?
 
The plane has a little over 300 hours. There were no modifications made, but I was not the builder and never looked at the bolt prior to the collapse. I did have a pre-inspection done, but this issue was missed.

Thanks!

Jim
 
Last edited:
The good news is........ IT DID NOT FLIP.

The bad news is this aircraft has not been properly inspected IAW the service bulletins from the manufacturer of the kit.

With the stop installed wrong causing excessive stress on the leg bolt when the wheel hit the stop during a turn or induced shimmy, and maybe the bolt not installed according to the plans, there would only be one end of the bolt to hold back the twist of the leg, a failure of the bolt is expected.

Inspect the nose gear off of the ground at each annual. And check here here https://www.vansaircraft.com/public/service-rv7.htm for any updates.
 
Breakout force on nose wheel pivot

Jim,
I just watched a couple of your videos including the nose wheel shimmy video you made a year or so ago.

That video showed the front tire swinging what looked like perpendicular the the runway. That makes me think maybe the breakout force on the nose wheel pivot at that time was not high enough. I know the plans show how much force is recommended, and I know of many people that go much higher on the breakout force to help prevent that type fo thing from happening in the case where a shimmy starts.

I dont know of any negative consequences of having the breakout force higher than the plans indicate, but maybe that is something the factory can shed some light on.
 
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.
 
Jim,
I just watched a couple of your videos including the nose wheel shimmy video you made a year or so ago.

That video showed the front tire swinging what looked like perpendicular the the runway. That makes me think maybe the breakout force on the nose wheel pivot at that time was not high enough. I know the plans show how much force is recommended, and I know of many people that go much higher on the breakout force to help prevent that type fo thing from happening in the case where a shimmy starts.

I dont know of any negative consequences of having the breakout force higher than the plans indicate, but maybe that is something the factory can shed some light on.

Richard - The video you reference is not one that I did. If you have a link to it, i'd like to see it!

Jim
 
I may have missed something in the video but it appears the standard bolt was installed but could not take the abuse of the improperly installed limiting bracket on the nose gear yoke. I wouldn't blame the bolt, in other words.
 
I may have missed something in the video but it appears the standard bolt was installed but could not take the abuse of the improperly installed limiting bracket on the nose gear yoke. I wouldn't blame the bolt, in other words.

The bolt that Van's calls out for can be a little short...... The bolt just fits through the mount with the threads at the edge of the hole. Take a bolt and measure it just past the threads, it is a few thou smaller than the rest of the shank. So that means that only one side (the head side) of the bolt is holding back shear. It will fail much sooner than if both ends were holding shear.

To resolve this issue, go to the next longer bolt and add a washer under the head. Two will be needed under the nut. Do what needs to be done to get full shank contact..... snug fit at each end of the bolt.
 
Last edited:
Pdf

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.

[email protected]

Thanks,
Dave shenk
 
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.
 
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.
 
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.
 
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.
 
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.
 
Back
Top