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05-19-2011, 11:47 AM
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Join Date: Jul 2005
Posts: 1,347
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Quote:
Originally Posted by rocketbob
I disagree with the findings of the report (page 11).
1. Exact balance is not required of a control surface to prevent flutter.
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And the RV-3,4,6 don't even have rudder counterbalances.
I've often wondered about the torsional twist loads on those surfaces, usually when I'm slipping hard or doing coordination exercises, which I do below Va. For some reason the rudder always concerns me the most.
__________________
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N164WM
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
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05-19-2011, 11:48 AM
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Join Date: Aug 2007
Location: Wichita Falls, TX
Posts: 2,182
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Quote:
Originally Posted by Brantel
The later and larger RV7 rudder is built like the 9 rudder with two skins and a trailing edge wedge.
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The RV-10's rudder is also the same way.
It's got to take some truly violent action to split apart such a riveted seam as the trailing edge on those types of rudders.
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Neal Howard
Airplaneless once again...
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05-19-2011, 11:50 AM
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Join Date: Jan 2005
Location: Chandler, AZ
Posts: 2,904
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Hmmm....
After reading the entire report, I have to agree with RocketBob on this. There are some conclusions based on information but nothing conclusive. Since a video was running, what was shown at the moment of the first harmful event? I would think there would be some evidence on the video of a buzz, yawing etc...
Could this have been a fastener failure, metal failure, skin failure? Unfortunately, although eye opening, I think there are more questions than answers.
Regarding filler, I would think from an aerodynamic standpoint (beyond the weight added) that smoothing the trailing edge or skin would assist in preventing flutter by smoothing the air leaving the TE. I'm not an engineer so I'm just thinking out loud. The balancing is another issue.
Finally, with 1000's of these airframes flying, I believe this is the first confirmed problem with tail group. So, what happened?
Prevention- (not saying anything was done improperly here)
1) proper fasteners
2) proper thread clearance
3) proper torque
4) on going inspection
5) proper balance
6) current weight and balance data after painting
Just some thoughts guys. This is very sad and my thoughts are with the family. Lets keep this discussion going to the benefit of everyone.
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Darwin N. Barrie
Chandler AZ
www.JDair.com
RV-7 N717EE-Flying (Sold)
RV-7 N717AZ Flying, in paint
EMS Bell 407,
Eurocopter 350 A-Star Driver
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05-19-2011, 11:50 AM
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Join Date: Jun 2006
Location: 8I3
Posts: 3,564
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Quote:
Originally Posted by Pitts
Ok, at least you now admit that the rudder failed, for some reason. According to your investigation, why did the rudder fail?
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Well, the rudder WILL fail if the VS is torn off first. Judging by the pictures in the report, this is entirely possible. Pure speculation on my part.
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Please don't PM me! Email only!
Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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05-19-2011, 11:51 AM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by Pitts
Clearly, de nile isn't just a river in Egypt. Nothing is certain in this life, but from the wreckage, the rudder was torn to bits as if a stick of dynamite had gone off inside it.
True, but it was interesting to note that because of the excessive weight of paint and filler on the entire aircraft, he was almost certainly doing aerobatics outside the aerobatic W&B envelope.
Ok, at least you now admit that the rudder failed, for some reason. According to your investigation, why did the rudder fail?
Note that the TSB report contains several apparently orthogonal findings, such as the fact that they were doing aerobatics illegally at low altitude.
While you might argue that the altitude probably directly didn't cause the accident, the required maneuvering to avoid hitting the ground might have. Wasn't there a recorded descent rate of over 10,000 FPM shortly before the rudder and fin separated?
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The tsv report states
Quote:
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Therefore, the possibility exists that the vertical stabilizer and rudder separated as a result of overstress.
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and also is clear to say there are no proof of flutter in the damaged parts...
for me the conclusion is that the failure was the result of EITHER overstress OR flutter, or combination of the two, with no way to definitively say it was one or the other. That is the way i read the report, i believe that is the plain language conclusion...
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nothing special here...
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05-19-2011, 11:58 AM
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Join Date: Sep 2007
Location: pittsburgh pa
Posts: 533
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Indeed
a very informative, sobering, thought provoking.....and sad read.
I have some thoughts to add to the general discussion:
The early RV-6 rudder ("small tail") as previously mentioned is not balanced at all. To my knowledge, there are no reported cases of rudder flutter in these totally un-balanced rudders of similar (usually lighter) construction.
The investigators do not mention, and may have no knowledge of, the common practice of attaching rudder trim tabs to these rudders. Does anyone have knowledge of whether this -7 had a rudder trim tab?? What type it was, how mounted etc??
The area of the rudder failure in the photos coincides with the typical location for mounting these tabs.
Can any experienced aero engineer (Van or Kevin or other) address possible rudder structure effects and flutter effects that these tabs might have??
Might it be possible that a rudder trim tab was a factor in this incident?? If so, it would seem we need to look critically at these common installations.
__________________
Gary Reed
RV-6 IO-360
WW 200 RV now an Al Hartzell for improved CG
Last edited by gereed75 : 05-19-2011 at 12:00 PM.
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05-19-2011, 12:01 PM
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Join Date: Oct 2005
Posts: 706
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The NTSB is extremely good at getting data from the EFIS units, they have the tools to get the data from what we would have considered a destroyed memory IC.
Rob Hickman
Advanced Flight Systems Inc.
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05-19-2011, 12:04 PM
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Join Date: Jul 2005
Posts: 1,347
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Here?s my theory:
At way past Vne, the rudder counterbalance tore off, maybe due to a bit of flutter and the resulting aerodynamic load on the surface ahead of the hinge line when it got in the slipstream.
After that, things rapidly went from bad to worse.
As that happened, it overstressed the vertical stab, which broke off and ripped off the top half of the rudder, explaining the damage to the middle part of the rudder.
Otherwise, the damage to the top of the rudder makes no sense. It did not get damaged in the separation or ground impact. It had to be the initiating event.
discuss
__________________
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N164WM
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
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05-19-2011, 12:06 PM
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Join Date: Apr 2005
Location: KSLC
Posts: 4,021
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Quote:
Originally Posted by gereed75
Might it be possible that a rudder trim tab was a factor in this incident?? If so, it would seem we need to look critically at these common installations.
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As to trim tabs, the 7 has a built in offset in the vertical stab ( I believe), where the 6's original design were straight. This would make a difference, to having a tab at all.
L.Adamson --- RV6A
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05-19-2011, 12:09 PM
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Join Date: Jan 2005
Location: St. Paul, MN.
Posts: 4,792
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So I have this airplane project and the <strike>rudder</strike> elevator is not perfectly balanced. Why? Who knows why but it is aft heavy and when you add in the manual trim cable it is even more aft heavy. It's not painted, of course, but the tips are done.
Should I be cracking those emp tips open and starting over with adding more weight?
Last edited by LettersFromFlyoverCountry : 05-19-2011 at 12:28 PM.
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