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09-22-2013, 09:39 PM
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Join Date: May 2009
Location: Colorado
Posts: 302
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Extra bolt
Quote:
Originally Posted by Ironflight
I flew both the RV-3 and V-8 today - but not before getting out a flashlight and inspection mirror and doing a thorough examination of hinge points and fasteners. The -3 passed with flying colors. The -8....well, that was a surprise. 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 !!
Obviously, the inspection covers came off, and I found that the bolt holding the two arms to the push rod was a little loose, allowing relative motion. Obviously, I replace things and tightened back to spec. Yes, this is one of those "Jesus Bolts" sprinkled throughout the airframe. The airplane is 3 months from the next condition inspection - but I took the time to inspect ALL of the visible control and hinge bolts today.
Remember, Condition Inspections are like medicals - they only prove that things were OK on the day they were signed off. I am shocked to find this on an airplane we fly numerous times a week. From now on, I'll be grabbing BOTH elevators at the same time during preflight - hope this gets a few other folks to inspect as well.
No cracks by the way...
Paul
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Paul,
This is why I install an extra AN3 bolt and spacer between the two elevator horns securing the two elevators together in addition to the rod end bolt.
Ryan
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09-22-2013, 09:42 PM
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Join Date: Feb 2011
Location: Brisbane, Australia
Posts: 37
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Gently push your elevators and rudder to the stops, and then GENTLY place some more load on the surface with your hand and watch what happens to the spar in the hinge areas. It was never designed to accept that load, especially repeatedly which happens if you park it out on gusty day and allow the wind to load the control against the stops.
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09-22-2013, 09:58 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by hayabusa
Gently push your elevators and rudder to the stops, and then GENTLY place some more load on the surface with your hand and watch what happens to the spar in the hinge areas. It was never designed to accept that load, especially repeatedly which happens if you park it out on gusty day and allow the wind to load the control against the stops.
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I don't think that is a valid statement.
A full rudder slip is definitely putting the same type of aerodynamic load on the rudder as you are describing (probably more), and full up elevator at 50 MPH during landing rollout is doing the same to the elevators.
Now if you are talking about an RV tied up outside during a hurricane your statement might be valid, but you said gently apply more load...
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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09-23-2013, 12:26 AM
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Join Date: Jul 2010
Location: Shorewood, Il.
Posts: 230
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Quote:
Originally Posted by rvbuilder2002
I don't think that is a valid statement.
A full rudder slip is definitely putting the same type of aerodynamic load on the rudder as you are describing (probably more), and full up elevator at 50 MPH during landing rollout is doing the same to the elevators.
Now if you are talking about an RV tied up outside during a hurricane your statement might be valid, but you said gently apply more load...
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I'm not so certain about your disagreement. In flight with a full deflection the wind load will be trying to move the surface AWAY from full deflection. In the previous description they were talking about forcing ( gently of course ) PAST full deflection as a wind gust would try to do. I would think that would do significant damage in gusty winds like Hyabusa was trying to describe. ( Think of a hyper extended knee, significant damage ) I also think this might allow you to see if there is flex on the spar. It might also allow you to see a minuscule crack open up that could not be seen without a load applied.
Mark
Last edited by RV Wannabe : 09-23-2013 at 12:32 AM.
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09-23-2013, 12:50 AM
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Join Date: Feb 2011
Location: Brisbane, Australia
Posts: 37
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I write this only as another angle to consider and mean no disrespect to the community here.
If you gently push your elevators and rudder to the stops, and then GENTLY place some more load on the surface with your hand and watch what happens to the spar in the hinge areas, you can see where the stress goes when the control surface tries to pivot against the stop but it can`t.
(In my opinion) It was never designed to accept that load - which happens if you park it out on gusty day and allow the strong buffeting winds to load the control against the stops repeatedly, or worse, bang away until the stop breaks off. In flight, aerodynamic load is developed across the surface and transferred through all the hinge points as intended, but not so when the stop comes into play and tries to act as a pivot point.
The aircraft in this thread, and the one that gave rise to it had something thing in common.
The one in this thread was left out in the wind as stated by the owner. This may, or may not have contributed to the crack.
The other aircraft was also, and the details are in this thread.
http://www.vansairforce.com/communit...ad.php?t=97775
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09-23-2013, 06:46 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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Here's a good example of a crack, most appear as a very fine line eminating from a bolt hole, rivet hole or radius/bend line. It will generally appear as a VERY fine pencil line or small crack in the paint. As shown in this pic, it's easy to mistake or overlook a crack that is just starting out as there is no seperation of the material which is what most folks consider a "crack", in the begining it's just a very fine "line".
I WILL BE HAPPY TO DO FREE TAIL INSPECTIONS TO ANYONE THAT STOP BY MY HANGER
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
Last edited by Walt : 09-23-2013 at 07:48 AM.
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09-23-2013, 07:22 AM
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Join Date: Sep 2006
Location: Port Orange, FL
Posts: 1,020
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Just checked mine and no problems found. Took photo records for future reference.
__________________
Ted Chang, VAF #681
RV-9A #91048, flying since 8/2006. 2,050 hrs.
2018 Due paid
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09-23-2013, 08:12 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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This morning I removed the empennage fairing and inspected the elevator and rudder attach points, rod-end bearings, the HS and VS attach points.
No cracks, loose bolts, loose jam nuts, etc. were found. The torque seals were all unbroken. (Edit: My -9 is approaching 500TT.)
However, while inspecting my tail, I remembered something I did when building; rather than drilling those holes to final size, I drilled them undersize, reamed them to final size, and then deburred both sides of each hole.
Could the cracks be formed in those parts that were simply drilled to final size?
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
Last edited by N941WR : 09-23-2013 at 09:35 AM.
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09-23-2013, 08:26 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by rvbuilder2002
Mark,
A crack like yours doesn't typically occur from a single load event. It is classic of what would be caused by some type of load reversal / flexing across that point. One thing I would be looking for if I were inspecting the airplane, would be hinge axis alignment....If they are (ed; misaligned), the web of the spar would be forced to flex every time the elevator moved on its hinge axis
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Good call Scott.
Walt (and others who do a lot of RV condition inspections), are you seeing many cases of hinge misalignment? I recall you have written about poor center bearing shimming.
Quote:
Originally Posted by Ironflight
...I found that the bolt holding the two arms to the push rod was a little loose, allowing relative motion. Obviously, I replace things and tightened back to spec.
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Most readers are probably thinking about the possibility of a control disconnect here, but there are additional effects which are more subtle.
The pushrod bolt ties the two elevators together. In the context of flutter prevention, it is a link in a connecting torsional spring formed by the tubular weldments and arms. Torsionally (elevators moving in opposition) a loose bolt reduces the spring rate and/or introduces freeplay, with the potential to reduce the flutter margin in that mode. Is it critical, i.e. likely to actually allow flutter development? I don't know.
I will say this...I like all the margin I can get. Along those lines, I think elevators should be balanced separately, with the pushrod bolt removed, after painting. One elevator is often heavier than the other due to the trim tab and servo. Balancing as an assembly means the heavy elevator relies on the opposite lead weight for mass balance, acting through the torsional spring of the connecting members.
Set flutter aside and consider the ordinary effect of a single trim tab. When deflected it applies force to the attached elevator, which in turn applies force to the other elevator through an asymmetrical load on the pushrod bolt. RV-8's routinely require full up trim when landing solo.
Quote:
Originally Posted by 131RB
Paul,
This is why I install an extra AN3 bolt and spacer between the two elevator horns securing the two elevators together in addition to the rod end bolt.
Ryan
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A fine idea...positive effect, very low risk.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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09-23-2013, 08:32 AM
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Join Date: Apr 2009
Location: USA
Posts: 1,499
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Recheck torques on ALL critical fasteners often.
Most builders like to use a lot of paint to protect their aluminum. Many of our parts already come with a nice thick powder coating applied. When we torque a fastener approximately 55% of the torque applied is to overcome nutface friction, 30% thread friction and the remaining 15% to stretch or pre-load the bolt. Over time, our paint beneath the nut/washer/bolthead decreases in thickness which contributes to loose fasteners. I applied lock-tite to my rudder/elevator hinge rod-end jam nuts and to pushrod jam nuts to prevent any further loosening as they are not self locking. We still want to recheck all of these on every condition inspection or before.
__________________
Good judgment comes from experience, and a lot of that comes from bad judgment.
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