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06-16-2015, 05:39 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Well, the Probable Cause is released. Nothing that was not already said in the docket listing. Overspeed, 220 kts. Inflight breakup.
Reading and comparing the results back to the Canadian 7 ( http://www.vansairforce.net/safety/G-GNDY.pdf ) with the same results, the VS/Rudder failure appearance seems eerily the same. The same in terms of the physical separation. Flutter was not stated in the NTSB report, but I don't know why. Maybe it "is the meaning of is".
This being the second occurrence of the same root cause, and at a lower airspeed than 234 kts has me wondering what physical factors go to the direct cause of decreasing flutter from about 250 knots to 220 knots.
We can see how Tony rebuilt the rudder and had several layers of paint, but there is no information available that I can find that relates the rudder mass and CG to any change in flutter speed. Further, that aspect was not even mentioned in this report.
I thought that 15% margin for "any condition" was supposed to be provided (regs) for Vne to any analysis or testing for margin. Does this reduction to 10% due to unknown cause concern anyone?
Probable Cause Full Narrative
Docket -listing of all supporting information
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Last edited by BillL : 06-16-2015 at 05:52 AM.
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06-16-2015, 06:27 AM
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Join Date: Jan 2005
Location: Twin Cities, MN
Posts: 1,565
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Quote:
Originally Posted by BillL
I thought that 15% margin for "any condition" was supposed to be provided (regs) for Vne to any analysis or testing for margin. Does this reduction to 10% due to unknown cause concern anyone?
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No, because:
A) Vne is/was determined by multiplying Vd (design dive) by 0.9. See FAR 23.1505.
B) Full/abrupt control inputs anywhere near the speeds discussed are so far outside the aircraft's design envelope that it's essentially irrelevant. Such control inputs aren't appropriate above Va, let alone well past Vne.
If you are aware of another piece of reg that discusses 15% in relation to Vne, I'd be interested to learn more.
__________________
Brad Benson, Maplewood MN.
RV-6A N164BL, Flying since Nov 2012!
If you're not making mistakes, you're probably not making anything
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06-16-2015, 06:44 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by ChiefPilot
No, because:
A) Vne is/was determined by multiplying Vd (design dive) by 0.9. See FAR 23.1505.
B) Full/abrupt control inputs anywhere near the speeds discussed are so far outside the aircraft's design envelope that it's essentially irrelevant. Such control inputs aren't appropriate above Va, let alone well past Vne.
If you are aware of another piece of reg that discusses 15% in relation to Vne, I'd be interested to learn more.
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I am not a regs expert, not even close. My statement was related to what I read in FAR 23.629 - it may not apply and I am just flat wrong, but that is the reference.
edit: it also says "(1) Adequate tolerances must be established for quantities which affect flutter, including speed, damping, mass balance, and control system stiffness; and" Adequate tolerances, implies that the mass balance, torsional stiffness etc should have some known variation curves that show the envelope. This is what would be very helpful in not reducing the (flutter/Vne) margin
edit 1 -fat finger correction - the "reg" was actually an AC 23-629, not 23.269 as previously posted. I was looking at an older version. The new version does not mention any ratio with V dive. I stand corrected on the reference to V dive and Vne. Thanks
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Last edited by BillL : 06-17-2015 at 09:11 AM.
Reason: spellin'/ correction
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06-16-2015, 06:52 AM
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Join Date: Nov 2006
Location: Savannah, GA
Posts: 1,029
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Flutter may not have been an issue. A large control input, especially when exceeding Vne, could result in a static overload. See AA587.
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RV-7ER - finishing kit and systems installation
There are two kinds of fool in the world. The first says "this is old, and therefore good"; the second says "this is new, and therefore better".
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06-16-2015, 07:08 AM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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Quote:
Originally Posted by BillL
We can see how Tony rebuilt the rudder and had several layers of paint, but there is no information available that I can find that relates the rudder mass and CG to any change in flutter speed. Further, that aspect was not even mentioned in this report.
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My recollection is that it also had significant quantities of filler applied in spots to smooth it off before the paint was applied... So the imbalance was more significant than *just* extra layers of paint.
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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06-16-2015, 07:21 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by rmartingt
Flutter may not have been an issue. A large control input, especially when exceeding Vne, could result in a static overload. See AA587.
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Yes, but reading the details of the report, it doesn't seem consistent with the other actions. Is there something you saw in there that hints at this?
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Last edited by BillL : 06-16-2015 at 08:35 AM.
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06-17-2015, 04:12 AM
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Join Date: Feb 2011
Location: Brisbane, Australia
Posts: 37
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Is this what you are looking for?
All fractures exhibited characteristics consistent with static overload. No evidence of multiple dynamic loading fractures was found, nor evidence of fatigue characteristics or other preexisting damage.
I understand this to mean that the stabilisers were overloaded and basically each one snapped off, in one direction, with no cyclical loads leading to the break.
The whole situation is terrible.
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06-17-2015, 04:35 AM
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Join Date: Jan 2005
Location: Salem, OR
Posts: 296
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Where's the other prop blade? It was stated that it had an MT 3-blade prop, but the report only accounts for two blades?
__________________
Mitchell Lock
President Van's Aircraft
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06-17-2015, 05:49 AM
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Join Date: Dec 2009
Location: Montreal
Posts: 1,456
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Quote:
Originally Posted by hayabusa
Is this what you are looking for?
All fractures exhibited characteristics consistent with static overload. No evidence of multiple dynamic loading fractures was found, nor evidence of fatigue characteristics or other preexisting damage.
I understand this to mean that the stabilisers were overloaded and basically each one snapped off, in one direction, with no cyclical loads leading to the break.
The whole situation is terrible.
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Exactly. That sentence is saying that there was no evidence of flutter. The airplane was simply overloaded.
__________________
Scott Black
Old school simple VFR RV 4, O-320, wood prop, MGL iEfis Lite
VAF dues 2020
Instagram @sblack2154
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06-17-2015, 06:38 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by hayabusa
Is this what you are looking for?
All fractures exhibited characteristics consistent with static overload. No evidence of multiple dynamic loading fractures was found, nor evidence of fatigue characteristics or other preexisting damage.
I understand this to mean that the stabilisers were overloaded and basically each one snapped off, in one direction, with no cyclical loads leading to the break.
The whole situation is terrible.
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That is what i thought at first, then looking at the VS-rudder parts from C-GNDY, and looking where the rudder weight landed in respect to the other parts I got the impression that there was more than a single one time force that started the process.
Quote:
Originally Posted by sblack
Exactly. That sentence is saying that there was no evidence of flutter. The airplane was simply overloaded.
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At first, I thought that too. But . . . the separation results of the two incidents look exactly alike (VS/Rudder). Flutter discussed on one, not the other.
Flutter was, oddly, never mentioned in the NTSB report. They did not say it was, or it was not. From where the parts landed, it's almost like the rudder weight came off first, then the other parts.
220 knots for failure seems too close considering 190 knots, IAS, at 8500 is 220 TAS.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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