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  #151  
Old 02-27-2020, 08:46 AM
Jeff Vaughan's Avatar
Jeff Vaughan Jeff Vaughan is offline
 
Join Date: Jan 2005
Location: West Chester, Pa
Posts: 574
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Let Vans know when your annual is. They were very helpful getting my leg to me in time. BTW. Not difficult to replace. Mostly time consuming
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RV 12 N237VW ELSA
RV 7A N561EV Sold
West Chester Pa

2020 donation current
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  #152  
Old 02-29-2020, 08:13 AM
D&M Dan D&M Dan is offline
 
Join Date: Sep 2006
Location: Webster, NY
Posts: 89
Default Parts Delay?

Anyone else get an email this week that parts ordered for the SB maybe delayed until July or August? I sent Van's an email stating my condition inspection is due in May and I believe I have ordered parts in a timely fashion. Would not wish to loose the summer without the aircraft!
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  #153  
Old 02-29-2020, 03:35 PM
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TomVal TomVal is online now
 
Join Date: Dec 2007
Location: SC & CA
Posts: 879
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Quote:
Originally Posted by rvbuilder2002 View Post
If there was a concern about drilling holes in the gear leg for the leg fairing attach screws, they would have never been specified there originally, and/or they would have been deleted when the new nose gear leg was designed, so no FEA on the screw holes is like to happen (see below for reason).

Sorry if that sounds a bit sarcastic.... I don't mean it to be, but it is the reality.

A bit of engineering and physics needs to be applied to understand why these holes are not an issue.

One, would be to understand what the bending loads are along a beam or arm such as the nose gear leg. The bending loads are the highest at each end where the arm attaches to other members (think of the effect that a long lever arm can have to amplify force). The bending loads are the lowest at the very mid point of the arm (that is where the lever arm is the shortest distance to other members where the loads are being applied).

That is why the screw holes are at the very mid point of the leg, vs a pair of holes at the upper end, and a pair at the lower end.

Another factor is the way the loads are distributed through the arm.

In the case of the nose gear leg, when a high upward load (hard landing for example) is applied, and the leg tries to bend, the material along the very top of the tube is being compressed along the length of the leg, and the material along the bottom edge of the tube is being stretched as the tube tries to bend into a curved shape.

The screw holes are purposely located on the sides of the leg, which puts them in the neutral axis of the tube..... the portion of the tube where there is no compression or tension load when the leg is being loaded vertically.

This is an overly simplified explanation.

Go to this reference (or just google "neutral axis") for more details.
https://www.quora.com/What-is-the-ne...axis-of-a-beam
Scott,

Thank you for your detailed explanation. I decided to forego the screws. Today I wrapped 3 bands of weather stripping on the gear leg. The foam from the weather stripping captures the nose gear fairing securely. The protruding nose gear tow hook also captures the fairing in place.

Regards,
Tom
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  #154  
Old 03-17-2020, 07:24 PM
Tacco Tacco is offline
 
Join Date: Jan 2017
Location: White Salmon, WA
Posts: 130
Default Kit Contents

What exactly is in the retrofit kit? E.g. does it include a cotter pin for the nose fork? Just want to know what to add to my order.
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  #155  
Old 03-17-2020, 09:43 PM
Wolfgang Wolfgang is offline
 
Join Date: Dec 2018
Location: salida, co
Posts: 16
Default Nose gear leg replacement delivery date estimate

Vans had advised me that my gear leg was scheduled for a June 2d shipping date. Today they said is now scheduled for late April, so things are speeding up. This will be fine since my annual is due by the end of June.
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  #156  
Old 03-17-2020, 11:18 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,636
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I am doing my annual now (ELSA). I decided to defer nose gear leg replacement to next year. I put a bore scope down the leg to examine it, but the results are not definitive. Maybe a professional NDE guy could draw conclusions, but the geometry of access and lack of a 45 deg mirror to look 90 deg off camera axis made it a fruitless task for me. I have about 950 hrs TTAF.

My plan is to section the area of interest when I replace it and PT it to see if anything bad was developing, so Iíll post agin on the thread next March.
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  #157  
Old 03-18-2020, 10:00 AM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 448
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Nose gear, new wheel pant, and nose fork arrived, March 7th. Drill bits and a few other parts still on back order. If the stuff arrives in time, it gets installed before the annual, otherwise, there's next years annual.

E-LSA, 229 hrs.

Our Annual is due by March 31st, so Van's is trying hard to keep the annual guys in business with timeliness.

Last edited by NinerBikes : 03-18-2020 at 10:15 PM.
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  #158  
Old 03-18-2020, 12:40 PM
greghughespdx's Avatar
greghughespdx greghughespdx is offline
 
Join Date: Nov 2011
Location: Aurora, OR
Posts: 725
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Quote:
Originally Posted by RFSchaller View Post
I put a bore scope down the leg to examine it, but the results are not definitive. Maybe a professional NDE guy could draw conclusions, but the geometry of access and lack of a 45 deg mirror to look 90 deg off camera axis made it a fruitless task for me.
Just to make sure people are aware: Performing a borescope analysis of the inside of the tube is not considered by Van's to be an acceptable method of determining whether or not the material has yielded and/or the part has been compromised. If it was a valid means, we certainly would have recommended it rather than going through the process of changing and manufacturing the new parts. I'll explain.

The primary/initially affected area is not examinable, so if you saw something inside the tube, that actually would not be an indicator of initial-stage material yield/failure. Rather, it would indicate the part was already significantly compromised and had already progressed beyond the initial problem stage. Even a perfect-appearing tube inner surface does not indicate whether the part is ok or not. The initial material yield/failure/subsequent crack occurs on the outer surface/diameter of the tube, in the area on that outer tube surface that is unfortunately obscured by the adjoining parts and associated welds. In other words, the lack of a visible crack on the inside of the tube does not guarantee a healthy, unaffected part. It is possible to have a compromised part that does not yet show signs of cracking on that inner diameter surface.

In fact, on the subject airplane that was the focus of the investigation that led to this service bulletin, the material failure occurred in a way where there was never a visible crack on the inner surface of the tube. The crack had progressed partially through the tube thickness at that location but not all the way, but had progressed significantly circumferentially around the outer surface of the tube. The entire area of cracked material was located under the obscured area already noted above.

While a borescope analysis certainly is interesting, and can potentially show if a failure has progressed significantly and the tube is already very badly compromised, Van's must make sure we are clear on this point: Do not perform a borescope analysis of the tube as an alternate means of compliance - It simply is not an acceptable means.

Sorry to feel the need to be blunt/direct, but in the interest of clarity and ultimately safety, we must make sure everyone knows exactly what is considered acceptable per the engineers that have very carefully examined and analyzed the parts. While a borescope might be able to tell you if the part is already badly damaged and failure is probably already imminent, you cannot examine the part to determine with any reliability whether or not it is compromised.
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Last edited by greghughespdx : 03-18-2020 at 02:19 PM.
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  #159  
Old 03-18-2020, 09:11 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 153
Default Service Bulletins

Greg,

We all appreciate your honesty and detailed explanations on this forum. This thread has raised questions about Safety Directives and Alerts, Service Bulletins, and Notifications and Letters.

Will you explain the reason or cause for issuing a Safety Directive vs. a Service Bulletin vs. a Notification or Letter?

Thanks.

John
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Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 240 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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  #160  
Old 03-18-2020, 09:32 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,636
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Thanks, Greg. I was just posting a data point. In the end each EAB and ELSA owner has the responsibility for making decisions regarding these issues. I just decided this was best for me and wanted to let others making the decision aware of what I found. I agree any visible defect indicates failure, and I would not fly with it. My decision to operate another year is what is right for me not necessarily the right thing for anyone else.

Rich
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