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  #11  
Old 01-28-2020, 04:44 PM
greghughespdx's Avatar
greghughespdx greghughespdx is online now
 
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Quote:
Originally Posted by rgmwa View Post
Was the fatigue crack initiated by the weld? How is the new leg different to the old one in that area? How many landings had the training aircraft done in those 1700 hours?
Good questions. It's unknown how many landings were performed in that airplane, but it is used for primary flight training and had accumulated 1700 hours of flight time as an active trainer - so we do know that it had been subjected to a lot of student landings.

The crack occurred in an area of high stress concentration located approximately at the location of the weld (actually just under it). Analysis showed that the weld itself did not cause the crack to form. Rather, repeated significant forces on the gear leg initiated a crack in the high stress concentration zone. That crack then propagated around the circumference of the tube. The weld's heat-affected area in the assembly could potentially contribute to the material cracking, but we did not determine that to be a primary cause. We also made some general changes to the weldment assembly which reduced the focus of any stress concentration.

The new gear leg is significantly different than the original one, in that it is double-walled and incorporates a second tube that is located/sleeved inside the external tube. You can see one of four round "rosette" welds in the first photo posted above. Those welds join the internal tube and external tube at a point well above and below the area of highest stress concentration. The additional tube and total thickness, and other modifications to the assembly, results in the load stresses being spread over a much larger area. in addition, the internal tube is unaffected by welding at that high stress concentration location. It is a substantially strong assembly.
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Building RV-8A since Sept 2014 (N88VX reserved)
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  #12  
Old 01-28-2020, 04:48 PM
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greghughespdx greghughespdx is online now
 
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Quote:
Originally Posted by magiccarpet View Post
Are the VA-268 and VA-269 drill bushings part of the SB-19-08-26 nose leg delivery or to be purchased extra?
The bushings are in a hardware bag that is included in the service bulletin kit.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Building RV-8A since Sept 2014 (N88VX reserved)
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Hillsboro, OR (EAA 105)

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  #13  
Old 01-28-2020, 05:00 PM
rgmwa rgmwa is offline
 
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Great reply Greg, thanks. Much appreciated.
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  #14  
Old 01-28-2020, 05:34 PM
Bob Y Bob Y is offline
 
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Hate to pile on with the questions, Greg, but your description of the upgrades incorporated prompts me to ask the weigh difference between the old and new assemblies.
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  #15  
Old 01-28-2020, 06:28 PM
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greghughespdx greghughespdx is online now
 
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Quote:
Originally Posted by Bob Y View Post
Hate to pile on with the questions, Greg, but your description of the upgrades incorporated prompts me to ask the weigh difference between the old and new assemblies.
No problem, Bob - That's what I'm here for! In return, I'll pile on with some nerd-level detail.

There is no significant/meaningful difference in weight - the new leg assembly weighs 0.65 pounds more than the original design (6.52 lbs new vs 5.87 lbs original). Note that AC 43-13-1B Chapter 10 explains that any weight change of less than one pound is considered negligible (for aircraft in our class). When the second tube was added, there was also material removed from the original-design gear leg (specifically, a welded vertical flange that ran between the two mounting brackets/plates with four lightening holes in it, which was removed as part of the steps taken to reduce stress concentration, and because in our analysis it was found not to be adding structural value).
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Van's web site | Instagram | Facebook
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Building RV-8A since Sept 2014 (N88VX reserved)
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Hillsboro, OR (EAA 105)


Last edited by greghughespdx : 01-28-2020 at 06:42 PM.
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  #16  
Old 01-28-2020, 06:57 PM
NinerBikes NinerBikes is online now
 
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Just curious, Greg, but is this update in any way related to the plane and the flight school that was looking for a new engine mount too, located in MD, that had some hard landings by a student and cracked the engine mount too, needing a new one, as no one else would touch welding up the old one and guaranteeing it, so you scrounged a new engine mount up for them, to get their school plane back in service?

Or is this a separate incident /plane?


Sort of wondering out loud, even with the really long drill bits, how access is going to be from the cockpit side to oil and drill through that new plate down there. I'm not the shortest guy around at 6' 5" or as flexible in the back as I once was, might have to hire a strong, small man to get in there to get 'er done.

Are the E-AB build guys with different engines and motor mounts going to get to have the same fun and games as the E-LSA crowd?

Last edited by NinerBikes : 01-28-2020 at 07:17 PM.
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  #17  
Old 01-28-2020, 07:24 PM
hiline hiline is offline
 
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So to be clear this is the only RV12 that this has happened to,not one more anywhere but a 1700 hr flight school RV12.??
Thanks.
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  #18  
Old 01-28-2020, 07:32 PM
RFSchaller RFSchaller is offline
 
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The leg replacement SB lists applicable serial number as 12080 and previous. Mine is 120402. Is there a typo in the SB? Should it be 120080 or 120800?
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  #19  
Old 01-28-2020, 07:37 PM
RFSchaller RFSchaller is offline
 
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Just reread the SB and realized the SLSA serial number format is different.
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  #20  
Old 01-28-2020, 07:37 PM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by greghughespdx View Post
No, sorry.
Odd that there is no photos available of the failed part. When Sensenich prop hub failed they supplied photos...
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