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  #1  
Old 04-01-2012, 07:50 AM
Danny King's Avatar
Danny King Danny King is offline
 
Join Date: Dec 2004
Location: Southlake, Texas
Posts: 632
Default Found during condition inspection. Gear leg bolt n Nut



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Bob Dean found one of his gear bolts hanging down when he pulled the cover plate for gear bolt torque check.

Here are the fact given to me by Bob.

1) Time on aircraft: 617 hours.

2) The torque on these bolts are checked once a year at my annual inspection.

3) I have never notice a problem, perhaps one of the bolts needed a little tightening over the years.

4) I had marked both bolts on both sides with Torque-seal to help detect movement.

5) The first picture with the bolt protruding is just the way I found it when I removed the inspection plate.

6) Inside the gear tower, the nut was totally off of the bolt. I cannot remember if the washer was still on the bolt or not. The bolt was sticking up through the gear tower; it seems like at least 3/16 of an inch, perhaps 1/4 inch.

7) I was using the the proper low profile metal lock nut. The threads were stripped, and you could see little metal filings.

8) The washer was the one that came with the kit. I am assuming that it is an AN960-616. As you mentioned they have replaced it with a 062 25783054.

9) The washer was bent. Hopefully, you can see it from the second picture.

10) The other bolt on this gear leg was loose. It took about a full turn of the bolt to get it properly torqued.

11) I have not properly check the other gear leg yet, but I do not see any problems from the visual inspection.

I am going to replace all four bolts with new bolts, new hardened washers and a new nuts.
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  #2  
Old 04-01-2012, 08:04 AM
bird's Avatar
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Default wow

I recieved my fuselage kit in June 2001. I am going to check to see which washers I have. This is a concern for sure. I wonder what caused this. Maybe they need to be inspected more often.

bird
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  #3  
Old 04-01-2012, 08:05 AM
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RickWoodall RickWoodall is offline
 
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Default Good catch

Good job doing a complete high quality annual. Seems some people skim through it with cursory looks etc. Taking the time and really going through each item start to finish and putting a wrench on things is the key.

Glad you found this and are fixing it properly. Hope your post gets others to dig deep and check.

Blue skies.
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Flew to Osh 11,12,15,17,19. SNF 2013. West to Cali /Washington/Vancouver/crossed the Rockies north to Red Deer east to Moosonee and over to maritimes. South to Jekyll Isl, cedar key, and Key West etc. 7 trips and 17 islands of the Bahamas. Flown turtles and dogs for Pilots n Paws too. Love our Rv's
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  #4  
Old 04-01-2012, 09:25 AM
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Ron Lee Ron Lee is offline
 
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Default

If this is a bolt that holds the landing gear to the airframe, I know of one RV-8 that had a gear collapse during early take-off roll due to an APPARENT bolt(s) failure.

Airframe rebuild. Engine rebuild. New CS prop.
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  #5  
Old 04-01-2012, 09:58 AM
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az_gila az_gila is offline
 
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Question

I was using the the proper low profile metal lock nut. The threads were stripped, and you could see little metal filings.

Doesn't this imply incorrect initial assembly? A cross thread or over-torque?

Stripping threads is an unusual failure mode for a correct bolt joint isn't it?

If the nut is actually overloaded in an axial direction, then perhaps it should be a normal high profile nut and not a low profile one....
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  #6  
Old 04-01-2012, 10:50 AM
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Bob Kuykendall Bob Kuykendall is offline
 
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Default

A couple of years ago, Steve Smith and I ran a series of tensile tests on the various types of nuts applicable to the RV-8 landing gear. The results are discussed in this thread:

http://www.vansairforce.com/communit...d.php?p=320444

Edit Add: Here's the money shot:



Thanks, Bob K.
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Last edited by Bob Kuykendall : 03-01-2019 at 12:41 PM.
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  #7  
Old 04-01-2012, 11:17 AM
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az_gila az_gila is offline
 
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Thumbs up

Quote:
Originally Posted by Bob Kuykendall View Post
A couple of years ago, Steve Smith and I ran a series of tensile tests on the various types of nuts applicable to the RV-8 landing gear. The results are discussed in this thread:

http://www.vansairforce.com/communit...d.php?p=320444

Edit Add: Here's the money shot:

<pic snip>

Thanks, Bob K.
Thanks Bob,

This post's failure fits right in with the above linked post and puts your tests right into perspective.
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  #8  
Old 04-01-2012, 01:02 PM
sf3543 sf3543 is offline
 
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Location: San Antonio, TX
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Default one more point

There is one essential item that hasn't been discussed in this scenario. Bob and I discussed the failure and one point mentioned was that the washer was bent. In this case, the washer was ground down on the side so it would fit inside the radius of the longeron angle, as is often the case. Somewhere along the line, probably at initial installation, the washer got turned and was sitting at a slight angle when the bolt got torqued. I'm guessing that over time, the washer began to bend more to make itself fit into the radius of the angle, thus slightly loosening the nut and allowing it to work and wear. It doesn't take much to make this happen. At any rate, regardless of retorquing the nut every year, if the washer allowed even the tiniest gap, in my opinion, that would cause the failure of the nut over time
As a point of interest, Lycoming calls out that no paint is allowed beneath the cylinder nuts when torquing down cylinders since the failure of the paint over time could destroy the proper torque of the nut and actually cause the cylinder to come off the engine. (It has happened!)
At any rate, this discussion is a good lesson in why we need to do thorough condition inspections at regular intervals. You just never know what will happen next.
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  #9  
Old 04-01-2012, 09:51 PM
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Default

Tom Brink @ GAHco has (or had) the required one size longer bolts if you want to use the easily obtained MS21045-6 nuts.

....and if I may....good call Smith and Kuykendall!
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Last edited by DanH : 06-13-2012 at 08:23 AM.
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  #10  
Old 04-01-2012, 11:23 PM
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GAHco GAHco is offline
 
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Default Thanks for the refferals!

Quote:
Originally Posted by DanH View Post
Tom Brink @ GAHco has (or had) the required one size longer bolts if you want to use the easily obtained MS21045-6 nuts.

....and if I may....good call Steve Smith!
We also have the NAS1804 series of 12 point nuts.

http://www.gen-aircraft-hardware.com...f/Locknuts.pdf
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