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  #1  
Old 01-14-2012, 10:47 PM
flyingshocker's Avatar
flyingshocker flyingshocker is offline
 
Join Date: Jul 2011
Location: Omaha, NE
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Default LH Elevator LE Crack

Alright brain trust I figured I would throw a question at you before stooping to order a new skin. Don't ask how it happened but I ended up with a crack on the top surface of my left elevator skin. The crack is located on the outboard side, at the location where the leading edge flap will be rolled down to form the LE. The crack stopped just short of the dimple and did not make it into the hole for the spar. I figure I have two options, order a new skin or make a cut perpendicular to the spar, essentially trimming off the portion of the leading edge affected by the crack. Its been awhile since I've had my structures or aero classes in school but I dont see this posing an issue with either. That leaves the cosmetic issue. I realize I'll have to make the identical trim on the bottom tab, which, when the LE is formed, will leave a visible hole thru the skin (much like where the bearings attach the the horz stab). While not a perfectionist (I'm building in an apartment and let me tell you that apartment rash has got to be worse than hangar rash) I don't want to end up with something I'll be regretting later. Any input would be appreciated.
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  #2  
Old 01-15-2012, 05:09 AM
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Andy Hill Andy Hill is offline
 
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Hi Justin...

Quote:
or make a cut perpendicular to the spar, essentially trimming off the portion of the leading edge affected by the crack ... much like where the bearings attach the the horz stab
My instinct is uneasy about this on 2 counts:
  1. The Cutout will not be structurally as the "bearing" cutouts, since you have lost the element attaching to the spar (hole where you crack goes to).
  2. At the outboard end of the HS, you have an 8" arm going forward, with a Lead Weight on it. Whatever loads / damping / harmonic frequencies the counterweight deals with, these are now transferred to the spar significantly further inboard then designed.
Just think of those few lbs of Lead, at 200KIAS, at 6g, being buffeted around in the prop / wing slipstream - and ask if you are now happy with it being secured in an alternative, and clearly less desirable, manner? Were it to "let go" further, the flutter characteristics may also alter... and one read of the RV-7 flutter fatality with a (different) part of the empennage coming off might make you think again.

The 3rd option is of course to "replace" the lost strength with a patch or similar. Whether that can be done easily / aesthetically I do not know.

Clearly if Vans give you the go ahead, then do their view clearly overrides mine.
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  #3  
Old 01-15-2012, 10:25 AM
9erDriver 9erDriver is offline
 
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I would redo with new skin. Doesn't look like you are too far along beyond stiffeners, right? You wouldn't be the first one to order a replacement skin.
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  #4  
Old 01-15-2012, 10:29 AM
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N9331v N9331v is offline
 
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At this early stage I'd replace the skin.
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  #5  
Old 01-15-2012, 10:47 AM
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az_gila az_gila is offline
 
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Ask Vans... it could be that the rolled leading edge isn't too critical (but see Andy's comments) - it may be that an extra rivet into the spar flange on each side of the crack end will work...

It's an interesting crack since you probably haven't stressed that corner yet by rolling the LE.
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  #6  
Old 01-15-2012, 11:30 AM
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Andy Hill Andy Hill is offline
 
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Hi Gil...
Quote:
it could be that the rolled leading edge isn't too critical
To be clear, I agree / am fairly sure the rolled LE is not critical... but Justin's crack goes behind that into the skin / spar fasteners.

If you go OB 1 rivet hole (3rd from outside edge) this is the single spar / 2 x skin / counterbalance rib fastener, so there's a fair amount going on there.
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  #7  
Old 01-15-2012, 11:44 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by Andy Hill View Post
Hi Gil... To be clear, I agree / am fairly sure the rolled LE is not critical... but Justin's crack goes behind that into the skin / spar fasteners.

If you go OB 1 rivet hole (3rd from outside edge) this is the single spar / 2 x skin / counterbalance rib fastener, so there's a fair amount going on there.
Yes... but the spar and rib at that location are OK.

BUT - as I said - ask Vans first...

I still don't really see how the crack occured - shipping damage maybe?
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  #8  
Old 01-15-2012, 12:11 PM
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DanH DanH is offline
 
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Get a new skin.

The good airplanes often generate a pile of unacceptable parts under a workbench.
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  #9  
Old 01-15-2012, 12:33 PM
aerhed aerhed is offline
 
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Quote:
Get a new skin.
Use the old one for doo-dads...AHRS...switchplates...bondo palette.
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  #10  
Old 01-15-2012, 12:43 PM
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Just get a new skin. I rebuilt an entire elevator half when I found an unacceptable amount of twist in it when fitting and rigging it to the HS. As I recall, it wasn't that big of an expense or an excess amount of work. In the grand scheme of airplane building, it was barely a blip.

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