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09-26-2013, 02:32 PM
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Join Date: Dec 2005
Location: Sydney, Australia
Posts: 427
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This is a very helpful thread, inspection prior to my next flight..
I may be stateing the obvious but it seems to me that if one of the bearings is screwed out relative the the hinge line (ie a miss-aligned hinge as per the discussion), then this would result in a force on the elevator or rudder spar that in trail would be normal to the spar, but would vary in direction according to the control surface deflection. So moving the surface from full up to full down would correspond to one cycle of such a force. The least stiff part will 'give', this is probably the spar at exactly the point the cracking has occurred. It would be a large misalignment to be felt as binding.
I would expect cracking on the opposite side of the bearing as well if the bearings were misaligned only in the sense of one being screwed out beyond the hinge line.
Is there any evidence of the .063" doubler cracking?
What I am most concerned with would be the rudder bearing alignment. The lower bearing is tied to the fuselage and Tailwheel assembly and the lower part of the VS spar can be pulled out of alignment when mounted on the fuse. Also, any pressure on the VS forward spar when attached will also pull this alignment out. So it is mandatory to carefully realign these bearings after VS final attachment.
__________________
Doug Gray
RV-6 completed, flying since July 2010
Last edited by Doug : 10-05-2013 at 06:49 AM.
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09-26-2013, 04:25 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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In my sample size of (1), I found a 100% failure to properly align the empenage hinges. I don't know if it was built that way or moved into that condition, but I certainly found a significant problem upon disassembly.
All good now though. I'll check it in a few hundred hours, but I suspect that I'll find each bolt will still slip easily through each hinge point.
My vote is that "we" are creating our own problems.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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09-26-2013, 06:25 PM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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Checked my -6 elevator today, and thought I found a crack! Until I wiped my finger over the area and the hair that was stuck in the LPS residue came free. No cracks!
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Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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09-26-2013, 07:43 PM
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Join Date: Jan 2005
Location: Ruston, Louisiana
Posts: 879
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Not much news today
I checked the doubler with dye penetrant and it was not cracked.
Someone asked about it.
If anyone was ever concerned about epoxy resin bonding to the lead counterweight you can relax! Unbelievable bond. Tip had to be destroyed to get it off.
Elevator is apart now and I will start the re-assembly tomorrow.
I plan to put it back together per the plans.
Thanks for all the comments.
Mark
__________________
Mark Burns
Ruston, Louisiana
RV-7A N781CM 1,650+ hrs
FFI FL-24
A&P
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09-27-2013, 06:39 AM
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Join Date: Jan 2005
Location: Pakenham, Ontario, Canada
Posts: 586
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Quote:
Originally Posted by Ironflight
Stuff deleted....
Like most pilots, during preflight, I grab the elevator and give it a wag and a shake, then move on to the other one. Today, since I was doing a very THOROUGH job, I notice a little bit of a (tiny) clunk when I moved the left side. I moved to the right, and got the same feel. I then grabbed both of them - and they moved about 1 degree relative to each other !!
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This is EXACTLY what happened to me back in June. Scared the poop out of me. I was doing my walk around and gave the elevator my usual good shake and got a "thud" in return.
I have replaced the bolt and nut, but I think I'll take the advice I saw elsewhere in this thread and put another bolt through.
Now my walkaround includes reaching around the rudder, gripping both elevators, and then trying to move them in opposite directions.
__________________
Mark
RV-8 C-GURV (Flying since Nov 2004) - Sold 
Scratch building 4pl Bearhawk
Flying a '79 Maule M5-235C
President EAA Chapter 245
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09-27-2013, 07:45 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by Doug
I may be stateing the obvious but it seems to me that if one of the bearings is screwed out relative the the hinge line (snip)...It would be a large misalignment to be felt as binding.
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All true. However, Mark is sure his bearings were not misaligned, and reports no binding or odd feel. Right now I'm inclined to discount misalignment as a cause.
Quote:
Originally Posted by BillL
This may address why it happened there, through no apparent failure of the builder or maintenance, but not what developed a loading condition sufficient to fatigue this area. Warm days on the gulf coastal areas do present a lot of bumps in the warm months (many of them) at relatively low altitudes, but what other reasons could this bird be seeing more loading cycles than another? And, is it only on the lower edge and not showing much loading on the upper edge because this is the typical load direction for keeping the nose up and it is not precipitated by some overwhelming aerodynamic cyclic load?
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Bill, perhaps the cycles are vibratory, not aerodynamic. Explanation as we go along.
But first, here's a sketch with what I think is the bending mode when cycled:
In this illustration the tip of the elevator has been forced upward in relation to the fixed stabilizer pivot. The resulting load is as shown. The lower rivet is in tension. The spar material below the rivet is unsupported.
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Dan Horton
RV-8 SS
Barrett IO-390
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09-27-2013, 07:48 AM
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Join Date: Dec 2006
Location: Portland, OR
Posts: 827
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Loose jamb nuts
Yesterday I check my -9A and found the HS jamb nuts tight and no issues. BUT... all 3 of the VS/rudder jamb nuts were loose! I was stunned because the middle hinge nut was close to 2 turns loose!
The only mechanism I can picture is application of rudder loads causing the rudder spar to twist just enough to break the face to face friction of the nut to the spar. Then with induced vibration in the airframe, the nut continues to work it's way loose.
While I look at these nuts during inspections, I've never put a wrench to them since first flight. Not good. Locktite & an index mark goes on next!
Also, I wiggled the elevators against each other and found them to move separately by 1-2 deg! Re tightened the pushrod tube attachment bolt and all is as it should be now. I have to agree, I think a second bolt through these horns is a good idea.
__________________
Long-EZ built 1985 -> Sold 2007
RV-9A; N539RV First Flight: 7/2010
RV-8A N468DL 40 hr Flight Test Program
Building Log: www.mykitlog.com/n539rv
APRS Tracking: aprs.fi/n539rv
2017 Paid
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09-27-2013, 07:53 AM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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Dan, your sketch makes sense. Also looks like that's what would happen if the stick was locked and the elevator loaded upwards. Or, an up-slam against the stop. That's why I still like an external lock between the stab and the counterweight. Reduces the arm and supports the outboard area of the elevator.
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Actual repeat offender.
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09-27-2013, 08:50 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by aerhed
...That's why I still like an external lock between the stab and the counterweight. Reduces the arm and supports the outboard area of the elevator...
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Has Van signed off on this? Because Cessna doesn't. Throwing a big gust load at that little counterweight structure may do a lot of harm.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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09-27-2013, 09:14 AM
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Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,544
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Loose lock nuts on these bearings is very common. There is a bit of a settling in period that initially causes the nuts to loosen. As Dan's picture points out there is a load on this bearing. Back and forth, back and forth, with the "nut" supplying the main contact area. Imagine a slight gap between either the nut-plate and the backing plate, or the backing plate and the spar. It will take a bit of time, with pressure from the locking nut, to settle these parts together. Perhaps that is why some of the nuts never come loose and others do. For this reason I do not like witness marks, or lock tite, on these parts as it indicates that the parts were tight at the time but does not tell you if they are still under the proper torque. It does not take much flexing, and compression of the spar area for this nut to get loose. The next time you tighten that bolt it will stay tight much longer, the next time you snug it up it will likely never move as the parts have settled into place.
Bottom line is that these nuts need to be checked on a regular basis but the good news is that after time they will settle in.
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger
Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
Last edited by Tom Martin : 09-27-2013 at 09:20 AM.
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