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  #11  
Old 12-19-2016, 10:34 AM
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Bob Martin Bob Martin is offline
 
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Location: Charlottesville, Virginia
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Default Another Longeron

Quote:
Originally Posted by Mel View Post
I disagree that this is common. I've inspected a lot of RVs over the last 35 or so years and I find this rare. Yes, I've seen it, but not often.
Mel,
Doesn't the six have another longeron in this area and access on only one side, plus a smaller access panel as well?
Perhaps this is why the -6 is superior to the -7 ???
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  #12  
Old 12-19-2016, 11:07 AM
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Default OK, Here's my "guess"!

Quote:
Originally Posted by Bob Martin View Post
Mel,
Doesn't the six have another longeron in this area and access on only one side, plus a smaller access panel as well?
Perhaps this is why the -6 is superior to the -7 ???
On the -4 & -6, the center "J" stiffener continues all the way to the tail at the bottom of the inspection panel.
The -7 was designed after the -9. The -9 was not designed with a tailwheel version in mind.
Perhaps the designer didn't think that last bit of stiffener was needed on a tricycle. When the -7 came out, this was simply overlooked
My $.02!
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Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
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  #13  
Old 12-19-2016, 11:08 AM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Post

Quote:
Originally Posted by Bob Martin View Post
Mel,
Doesn't the six have another longeron in this area and access on only one side, plus a smaller access panel as well?
Perhaps this is why the -6 is superior to the -7 ???
Yes, it looks like the downside to the larger -7 access panel is the loss of the middle J-stringer in the aft most fuselage bay compared to the -6 models.
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  #14  
Old 12-19-2016, 11:19 AM
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Default Another suggestion:

Any time you add an "angle" stiffener to a skin, be sure to secure it to the bulkheads at each end, either by a joggle or a shim. Without this security the skin will eventually crack at the ends of the stiffener.
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Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
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  #15  
Old 12-19-2016, 12:03 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Default

Quote:
Originally Posted by Ironflight View Post
To me it looks like a classic case of side-loading the tailwheel - it falls off the pavement and gets caught on an edge, or the two bolts that hold the socket to teh spring shear as the tail is being swung around and it falls off an edge. Either way, the tailwheel itself comes to a sudden stop while the fuselage is still trying to swing, and you put a slight kink in the fuselage structure. I've seen it on a couple airplane's, and both have had a sudden tailwheel stop event.

Just one possibility.

Paul
Look at the bottom of the rudder fairing. If there is not indication of contact damage from the tail wheel, then the scenario Paul described above is likely the cause.

N477RV (the RV-7 owned by Van's and used by Mike Seager for transition training) has spent its entire life based on a grass runway airport. It is just a few hrs shy of 4800 hrs T.T. and has had nothing like this occur (not to mention all of the plopped in landings it has endured during training).

The inertia of the induced by the tail swinging can induce huge twisting loads on the tail spring mount if the tail wheel comes to a stop suddenly.
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  #16  
Old 12-19-2016, 12:07 PM
David Paule David Paule is offline
 
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Default

Quote:
Originally Posted by Mel View Post
Any time you add an "angle" stiffener to a skin, be sure to secure it to the bulkheads at each end, either by a joggle or a shim. Without this security the skin will eventually crack at the ends of the stiffener.
When you do this, you'll need at least 2 rivets per flange. Otherwise it won't carry any real load.



From one of my structural engineering texts, Bruhn's "Analysis and Design of Flight Vehicle Structures."

Dave
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  #17  
Old 12-19-2016, 12:59 PM
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High_Flyer High_Flyer is offline
 
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Default Sorry...

OK, looking at all the posts since this morning it seems that I gave incorrect informations.
I apologize if what I wrote was not good.
However it makes sense to me to put a reinforcing angle at that location, with all the precautions that others have stated.
Alain.
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  #18  
Old 12-19-2016, 02:12 PM
Ralph Inkster Ralph Inkster is offline
 
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Default

I agree with Paul's theory that the tail wheel was abruptly side loaded. Looking at that skin, I'd check further for possible internal damage.
The things I would check is; bolt holes in F711 & F712 bulkheads are not stretched, WD409 tail spring weldment wasn't cracked, F711 & F712 bulkhead rivet flanges were not stretched out, lower J strip not buckled.
The ripple in the skin has taken a lot of rigidity away from that section of the fuselage, stiffeners (more than one) might restore most but not all to that area.
First off- I'd be phoning the mothership for their suggested course of action.
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  #19  
Old 12-19-2016, 02:52 PM
cajunwings cajunwings is offline
 
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Location: new iberia la
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Default

Quote:
Originally Posted by Mel View Post
On the -4 & -6, the center "J" stiffener continues all the way to the tail at the bottom of the inspection panel.
The -7 was designed after the -9. The -9 was not designed with a tailwheel version in mind.
Perhaps the designer didn't think that last bit of stiffener was needed on a tricycle. When the -7 came out, this was simply overlooked
My $.02!
Can somebody post a photo of this area or the plans of a 4 or 6?

Don
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  #20  
Old 12-19-2016, 02:53 PM
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cdmiller cdmiller is offline
 
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Default Tailwheel side load

I have seen this exact deformation in the same location in an RV-8 that was ground looped. As the plane veered off the runway, the Tailwheel got caught in muddy grass while the fuselage continued to swing around. The rear part of the fuselage was buckled slightly where the Tailwheel spring attaches to the two rear fuselage bulkheads. Repair involved replacing both rear bulkheads (they both are double bulkheads), and the bottom rear fuselage skin. The top flat fuselage plate, under the horizontal stabilizer, may also be deformed and need to be replaced. It will still be difficult to remove the bump on the side fuselage skin. The bump can be minimized with an aluminum angle on the inside as suggested by others.

Dan Miller

Last edited by cdmiller : 12-19-2016 at 02:59 PM. Reason: Added info
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