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  #41  
Old 08-29-2017, 08:44 AM
waterboy2110 waterboy2110 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post

The books are full of AD's that were issued because of just a few high time or heavy use aircraft developed a problem. The books are also full of many that after public comment were converted to periodic inspection and then repair if a problem is found.
That's simply not true. Airworthiness Directives and Service Bulletins are derived from observations and failures in the field. When warranted through objective data, changes are incorporated into these documents. While AD's may be seen as over-reaching in some instances the goal of these documents is to save lives and protect property.

No matter what the design, engineering, modeling, testing or standards to which a part is created, if it is failing in the field, it is failing in application and warrants scrutiny. A perfectly functioning part is not redesigned and / or re-enforced without good reason. That simply doesn't happen.

My point was to simply expose the callous attitude taken WRT these failures. My entire career was based around Quality Assurance and Failure Analysis. It was my job to champion the concerns of our customers. Thus my bias for safety.
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  #42  
Old 08-29-2017, 09:08 AM
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Quote:
Originally Posted by waterboy2110 View Post
No matter what the design, engineering, modeling, testing or standards to which a part is created, if it is failing in the field, it is failing in application and warrants scrutiny.
At what level? Does Michelin revamp their entire tire lineup because one guy has a blowout? You know that doesn't happen - there has to be a certain level of field-failures that can be laid at the feet of the part unequivocally and not on the user before you start a recall/SB/AD procedure. Sticking with the tire example, the Firestone debacle some years ago on Ford vehicles was a good one - the number of failures in the field definitely exceeded "normal wear and tear" limits and we saw the result. Without hard numbers being presented about total units in service, time in service, and failure RATES per thousand hours, there is simply not enough data currently in evidence for anyone to rationally stand up and say there has to be a revision/SB/AD.
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  #43  
Old 08-29-2017, 09:10 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by waterboy2110 View Post
While AD's may be seen as over-reaching in some instances the goal of these documents is to save lives and protect property.
I wasn't debating the goal, just pointing out that there is often times a failure in the system (and that it seems you are implying that any component failure on an aircraft deserves an AD and correction on all aircraft of the same Make/Model...that is simply not true), but this is getting way off track from the original point of the thread.
I have nothing more to add.
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  #44  
Old 08-29-2017, 01:20 PM
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I have a couple photos of two different failures, my photo service won't let me post. EMail me at Dongeneda at rgv.rr.com and I will email one to you.
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  #45  
Old 08-29-2017, 01:36 PM
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Piper J3 Piper J3 is offline
 
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Don - I just sent you my email address. If you send me photos I can post them in this thread.

Photos from Don below...



-



-

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Last edited by Piper J3 : 08-29-2017 at 02:14 PM.
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  #46  
Old 08-29-2017, 05:38 PM
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Steve Melton Steve Melton is offline
 
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Default welded alum cracks are bad

fracture mechanics



FATIGUE CRACK GROWTH ANALYSIS
=============================
DATE: 29-Aug-17 TIME: 21:04:12
NASGRO(R) Version 8.20 (DLL), January 2017
Final Version
Copyright(c) 2017 Southwest Research Institute(R).
All Rights Reserved.


PROBLEM TITLE
-------------
[no title given]
U.S. customary units [in, in/cycle, kips, ksi, ksi sqrt(in)]

Crack Growth Model: Non-Interaction
Ratio of growth increment to current crack size = 0.0050

Mode of Computations: Regular
(Beta factors computed cycle-by-cycle, if the block is such)

Equation/Table: NASGRO Equation

Material Data Source: User-entered


GEOMETRY
--------
MODEL: SC01 -Surface crack (2D) in finite width plate.

Plate Thickness, t = 0.2500
Plate Width, W = 3.0000


INITIAL FLAW SIZE (user specified)
----------------------------------

a (init.) = 0.1000
c (init.) = 0.2500
a/c (init.) = 0.4000


MATERIAL
--------

Material File Name: NASMF.XMLZ
Material File Description: NASA data/NASGRO eqn (single temp)

MATL 1: 1000-9000 SERIES AL
6000 series
Material 1, Data ID: M6ABA1AB1
Alloy Description: 6061-T6,T62 Al

Alloy Cond/HT: Weld (unk); weld/parallel/as welded; LA
; Room temp


Material Properties:

:Matl: UTS : YS : K1e : K1c : Ak : Bk : Thk : Kc : Keac :
: No.: : : : : : : : : :
:----:-------:-------:-------:-------:-------:-------:-------:-------:-------:
: 1 : 26.0: 23.0: 35.0: 26.0: 1.00: 0.75: 0.250: 45.4: :

: Matl :------- Crack Growth Equation Constants -------:
: No. : C : n : p : q : Alpha: Smax/:
: : : : : : : Flow :
:-------:-----------:-------:------:------:------:------:
: 1 : 0.110D-07 : 3.500 : 0.50 : 1.00 : 1.50 : 0.30 :

:Materi-:---------- Threshold & Small-Crack Constants ---------:
: al No.: DK1 : Cth+ : Cth- : Alpha: Smax/: Small Crk Constts :
: : : : : : Flow : a0 : DKth(s)/:
: : : : : : : : DKth(l) :
:-------:------:------:------:------:------:---------:---------:
: 1 : 1.28: 2.20 : 0.10 : 2.00 : 0.30 : 0.0015 : 0.20 :
da/dN multiplicative factor for matl No. 1: 1.0000

Cth+ = 0, Cth- = 0 are used throughout


FATIGUE SPECTRUM
----------------
[schedule title]

[Note: Stress = Input Value * Scale Factor]

Stress Scale Factors for Block Case: 1

Scale Factor for Stress S0: 1.0000
Scale Factor for Stress S1: 0.0000

Schedule info. was input manually

Total No. of Blocks in Schedule = 1

Block Number and Case Correspondences:
Block Number Block Case No.
From - To
1 - 1 1

Stresses: Remote tension, bending or pin load


FATIGUE SCHEDULE BLOCK INPUT TABLE
----------------------------------
[schedule title]

SINGLE DISTINCT BLOCK


S : M: NUMBER : S0 : S1 :
T : A: OF : : :
E : T: FATIGUE : : :
P : L: CYCLES : (t1) : (t2) : (t1) : (t2) :
----:--:-------------:---------:---------:---------:---------:
1: 1: 10000.00 : 0.00: 20.00: 0.00: 0.00:

Environmental Crack Growth Check for Sustained Stresses (Kmax < Keac) Is NOT Enabled.

FATIGUE SCHEDULE BLOCK STRESS TABLE
-----------------------------------
[schedule title]

SINGLE DISTINCT BLOCK


S : M: NUMBER : S0 : S1 :
T : A: OF : : :
E : T: FATIGUE : (ksi) : (ksi) :
P : L: CYCLES : (t1) : (t2) : (t1) : (t2) :
----:--:-------------:---------:---------:---------:---------:
1: 1: 10000.00 : 0.00: 20.00: 0.00: 0.00:

Environmental Crack Growth Check for Sustained Stresses (Kmax < Keac) Is NOT Enabled.


ANALYSIS RESULTS
----------------

Cycles Crack a Crack c F0(a) F0(c) F1(a) F1(c)

0 0.1000000E+00 0.2500000E+00

# ADVISORY: Net-section stress > Yield and failure is imminent
# (Unless (a) UTS > 2 YS, or
# (b) KIc/YS > 0.5 sqrt. in.(2.5 sqrt. mm.) and bending dominates.)
# at Cycle No. 180
# of Load Step No. 1
# of Block No. 1
# of Schedule No. 1
# Crack Sizes: a = 0.102270 , c = 0.250469 , a/c = 0.4083
# Total Cycles = 180

1.2966945E+03 0.1199672E+00 0.2549738E+00 0.100145E+01 0.826871E+00 0.420013E+00 0.693875E+00
2.3530976E+03 0.1400266E+00 0.2623188E+00 0.964617E+00 0.874795E+00 0.304297E+00 0.701604E+00
3.2677681E+03 0.1602117E+00 0.2728431E+00 0.932899E+00 0.919647E+00 0.192276E+00 0.699955E+00
3.4360837E+03 0.1642572E+00 0.2753987E+00 0.927587E+00 0.928584E+00 0.170470E+00 0.698955E+00

# FINAL RESULTS:
# Net-section stress (Sn) exceeds flow stress.
# Flow stress = 0.5*(yield+ultimate).
# Sn by fatigue load = 24.51, Sn by limit stress = 0.00. Flow stress = 24.50.
# at Cycle No. 3436
# of Load Step No. 1
# of Block No. 1
# of Schedule No. 1
# Crack Sizes: a = 0.164257 , c = 0.275399 , a/c = 0.5964
# Total Cycles = 3436


Execution time (hh:mm:ss): 00:00:00.0
Note: this is elapsed wall-clock time, not CPU time!
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Last edited by Steve Melton : 08-29-2017 at 07:06 PM.
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  #47  
Old 08-29-2017, 05:42 PM
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Crafting N112DR Crafting N112DR is offline
 
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This is the old style nose fork? But if I'm correct the NLG leg has not been modified in any version?
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Last edited by Crafting N112DR : 08-29-2017 at 05:43 PM. Reason: typo
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  #48  
Old 08-29-2017, 05:58 PM
rockwoodrv9 rockwoodrv9 is offline
 
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Is that a picture of the nose fork? It is a pipe rather than a solid leg? Wow.
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  #49  
Old 08-29-2017, 06:34 PM
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joedallas joedallas is offline
 
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Default direct replacement

I think you are missing the point?

If Michelin stopped making that exact tire ( after the blowout )and replaced it with a direct replacement , there may be a concern ( maybe they learned something ) ( this is where we are at )
My view

Joe Dallas




Quote:
Originally Posted by airguy View Post
At what level? Does Michelin revamp their entire tire lineup because one guy has a blowout? You know that doesn't happen - there has to be a certain level of field-failures that can be laid at the feet of the part unequivocally and not on the user before you start a recall/SB/AD procedure. Sticking with the tire example, the Firestone debacle some years ago on Ford vehicles was a good one - the number of failures in the field definitely exceeded "normal wear and tear" limits and we saw the result. Without hard numbers being presented about total units in service, time in service, and failure RATES per thousand hours, there is simply not enough data currently in evidence for anyone to rationally stand up and say there has to be a revision/SB/AD.
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  #50  
Old 08-29-2017, 06:41 PM
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Quote:
Originally Posted by Piper J3 View Post
Photos from Don below...
I'm just a nobody, but to me, the nose wheel assembly shown in that first photo appears really under-designed. I realize the the RV-12s only weigh...what?... 750 lbs. but even so.
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