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  #31  
Old 09-23-2013, 08:40 AM
Wayne Gillispie Wayne Gillispie is offline
 
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Quote:
Originally Posted by 131RB View Post
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
Yes, why did I not think of that. Good idea. I always check for movement between my two elevator halves on pre-flight. Our trim tabs on the -10 do not move together at times which can induce a twisting moment. I think about that little -3 bolt on every preflight as I hope don't ever need to do a "trim" landing.
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  #32  
Old 09-23-2013, 08:51 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by RV Wannabe View Post
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
Quote:
Originally Posted by hayabusa View Post
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
It is all about where the restraint point is. Since the control activation point (cable on the horn, for the rudder; and push/pull rod on the elevators) is for all practical purposes, at the same location along the span of the control surface as the control stop, the loads in flight at full deflection will be similar to the load application you are describing. True, it will be in the opposite direction, but the same as if in your example you move the surface to the opposite stop and pushed the other way.

There is only one way that loads cause by wind gusts while tied down on the ground are different than would likely be induced in flight. That is the dynamic loads caused by the inertia of the counter balance weight(s) on an unrestrained control surface that is banging against the stops in the wind.
The reason that is different is because the inertia of the balance weight can cause a much higher torsional load than would likely ever be induced in flight. The loads caused by wind forces alone would be acting on the entire surface (along the full span)and not causing an appreciable torsional load.

So, if your concern was a surface banging against the control stops, then I agree with you. If it was just wind loads pushing on a restrained control surface, it is not an issue, and no different than the loads experienced in flight.
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  #33  
Old 09-23-2013, 08:51 AM
aerhed aerhed is offline
 
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I've inspected quite a few Cessna's that had looseness between the two elevators. On them (usually 182's) its usually loose rivets on the spar. Pulling the elevators in opposition is something I always do on preflight. That,s how you learn, one creak at a time.
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  #34  
Old 09-23-2013, 08:52 AM
Rupester Rupester is offline
 
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Quote:
Originally Posted by N941WR View Post
... remove[d] the empennage faring and inspect (Put a wrench) on all the bolts back there and look closely (using a magnifying glass) at the VS attach brace.
... look at the HS spar, as described in this thread.
Excellent precautionary move. I just did that as part of my first annual a couple weeks ago ... all was OK. (only 85hrs TT, but nice to see just the same)
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  #35  
Old 09-23-2013, 09:35 AM
Bavafa Bavafa is offline
 
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I went to the hanger to inspect mine and at first glance I saw what appeared to be a similar crack but upon closer inspection with a magnifying glass, it was a mark in the paint (perhaps as a result of the wrench on the nut)

Is there a good way to detect crack short of removing the part?
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  #36  
Old 09-23-2013, 11:27 AM
Barry_Barry Barry_Barry is offline
 
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Default Hoz Spar

Quote:
Originally Posted by Mark Burns View Post
Due to the recent loss of a VAF'er I decided to inspect my empennage very carefully.

I found a crack in the right elevator spar at the outboard attach point.
This is how it looked upon inspection. Just a black line.



I wiped the black off the left side but you can still see the crack below.



And here it is after the dye penetrant test.



It's an RV7A serial number 72183 with 908 hours.

Everyone please check your elevators carefully before your next flight!

Mark
================================
Mark thank you for an excellent post.

My knee-jerk response comes from looking at the pictures:
1 - In the first picture the crack looks like it is radiating from the rivet hole. This could be from:
a> None or incomplete de-burring of the rivet hole.
b> Too small a rivet hole as the rivet is stressing the hole from the inside.
c> Too big a rivet hole.
2 - Second picture: The dye penatrent is showing up around the nut and looks like it is even under the nut. This could be because:
a> Loss of chromate conversion protection in the area.
b> Movement of the nut - YET! It is only on one side so I doubt that is the issue.
c> Something in the order of Hard Dirt under the nut causing a stress point.
AHA! I also notice your 'witness mark' and that is looking good - So not a loose nut.
2 - In the second picture:
Notice the crescent shape of the dye. this indicates:
a> Uneven stresses across an area. It could be as unusual as the grain of the aluminum.
b> What is behind that area?
c> Sure looks like a Double is required in this area - Maybe an inner and an outer.

Please keep all of us posted with your findings and pictures.

Thank you very much for taking the time and effort.

Barry
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  #37  
Old 09-23-2013, 11:44 AM
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apkp777 apkp777 is offline
 
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I don't know if it was already addressed in the previous posts, but it is VERY important that the bolts slide in freely when you attach the rod-end to the the hinge bracket. Any "pre-load" could/will eventually lead to a crack. From what I see from the photo, I would suspect that as a possible cause.
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  #38  
Old 09-23-2013, 12:11 PM
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bobair43 bobair43 is offline
 
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Default stab spar cracks

First time user RV7A n838wt After the accident last week in NJ that looked like a structural failure of the rudder or elevator. The postings on stab cracks caused me to check my plane and I found a couple of lock nuts that need tightening . Thanks guys
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  #39  
Old 09-23-2013, 12:57 PM
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wjb wjb is offline
 
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Default This is why the jam nuts are there

Quote:
Originally Posted by Walt View Post
A loose jam nut could be the cause of such a crack, if the jam nut is loose the nutplate and nutplate rivets are carrying the full load of the fitting.

FYI - I find loose jam nuts on elevators and rudders routinely

PS: good find, everyone should inspect this area at the earliest opportunity.
Thanks for this post .. I wondered why the jam nut was there on the HS an VS rod end bearings. The darn thing's not gonna turn once the control surface is hung, and I had though that they were a bit superfluous.. Transferring the load to the spar is critical!
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Last edited by wjb : 09-27-2013 at 06:57 AM.
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  #40  
Old 09-23-2013, 01:23 PM
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Toobuilder Toobuilder is offline
 
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The rivets on the ears of the nutplates are there to keep the nutplate from turning - that's it. A rod end with loose or missing jamnuts is passing the entire load through those two #40 rivets... Much higher load than they are designed for. When they break, you have a control surface just flopping around back there. Bad news.
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