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  #1  
Old 10-27-2017, 04:32 AM
Sylvester Sylvester is offline
 
Join Date: Mar 2017
Location: Uk
Posts: 4
Default Firewall wrinkle

Hi,
I've attached some pics of my firewall. The aircraft is a fairly early 4, and had issues here when I first started flying it. 9 years ago I rebuilt it after it suffered a landing accident, using new engine mount, long legs, firewall, side panels and new style corner weldments.
The aircraft operates from a grass strip, and has not had a heavy landing; I'm the only pilot. Within weeks of the rebuild I could hear the firewall flex as I taxied, and just new what was going to happen!
It's now back in the workshop for instrument and radio upgrade, and I'll be doing the firewall as well.
Vans have suggested incorporating the gusset in the lower corners, and I'll be taking great care with alignments.
Does anyone have any other suggestions. I don't really want to do it again!
Thanks
PS. I'm disabled from posting photos. Could do pm's perhaps ? [ed. Upper left corner look for 'Inserting Pics' link. That's how to do it. v/r,dr]

Last edited by DeltaRomeo : 10-27-2017 at 06:49 AM.
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  #2  
Old 10-27-2017, 04:57 AM
tgmillso tgmillso is offline
 
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 477
Default Pictures

Hi All,
Below are some pics of the RV-4 firewall in question.
Cheers,
Tom.

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  #3  
Old 10-27-2017, 10:51 AM
F1Boss's Avatar
F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 618
Default Hmmm

Had those same marks on my -4 way back when...~3000hrs later, it's still going with no signs of distress. If I can recall correctly, this sort of wrinkling is visible on more than a few -4's.

Yes - those showed up after a not-so-smooth landing on grass.

I wouldn't worry about the wrinkles, but I would have a look at the fwd corners to make sure all is well - seems like that area might benefit from some additional interior parts to spread the loads around better. Seems that corner area might be a wee bit too flexible.

I would also add a 1/8" 4130 gussets to the lower attach tubes..
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  #4  
Old 10-27-2017, 10:59 AM
Brian Vickers Brian Vickers is offline
 
Join Date: Mar 2005
Location: Bainbridge Island, WA
Posts: 318
Default gussets - see photo

I copied this from someone elses airplane.

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  #5  
Old 10-28-2017, 10:35 AM
1flyingyogi 1flyingyogi is offline
 
Join Date: Dec 2015
Location: Southern California
Posts: 163
Default

Very common. When I bought my plane, I saw that and the guy doing the pre-buy said not to worry. He's done many pre-buys and assured me they are present on almost half the RV4's he's seen. I had some gussets added to mine.
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  #6  
Old 10-28-2017, 11:08 AM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
Posts: 1,178
Default

I would have expected the vertical loads to be taken by the aluminum angles. Are these wrinkles from lateral loads? Is there a recommended beefup from Vans? I would prefer to do it now before I fly.
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  #7  
Old 10-28-2017, 11:15 AM
Sylvester Sylvester is offline
 
Join Date: Mar 2017
Location: Uk
Posts: 4
Default

The loading at that point is complex with the back and outwards sweep of the legs, the twisting moment that the brakes have, torque from the prop and the weight of the motor. I've sat and looked at it for ages and still can't see how it happens!
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  #8  
Old 10-28-2017, 11:49 AM
F1Boss's Avatar
F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 618
Default potential fix

Quote:
Originally Posted by Sylvester View Post
The loading at that point is complex with the back and outwards sweep of the legs, the twisting moment that the brakes have, torque from the prop and the weight of the motor. I've sat and looked at it for ages and still can't see how it happens!
The Harmon and F1 use the same sort of setup, but none of those have any firewall wrinkles. I would say that fwd fuselage side skin should be .040, as is done in the larger, heavier examples. Might add some skin stiffeners too, since the HR and F1 fwd side skins are curved, which changes the equation.
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"Not everyone needs a Rocket. Some folks, however, shouldn't live life without one.
You know who you are."
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  #9  
Old 10-28-2017, 12:03 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,321
Default

My early '90s era -4 has firewall wrinkles. But no evidence of skin, attach point weldments, or aluminum structure damage. No detectable distortion to the airframe. The motor mount still aligns when removed/reattached.

Perhaps it's worth pointing out that the firewall is non-structural. If it's wrinkled, it obviously indicates further inspection is needed, but it isn't structural damage in and of itself.
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  #10  
Old 11-06-2017, 09:56 AM
JimRice JimRice is offline
 
Join Date: Aug 2014
Location: Collierville, TN
Posts: 62
Default Same wrinkles

My 1994 RV-4 has same wrinkle. It has been this way for years and many hours. I didn't build it, but it was this way when I bought it. The A&P/IA maintaining it for almost ten years said if had been that way and unchanged it that time. I've had a couple of other RV builders look and no one seems to think it is an issue. Everything else is straight and solid. The plane has just over 1000 hours TTAFE.
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1994 RV-4 N4WJ (Purchased/Flying)
1946 J-3 Cub N7155H (Restored/Flying)
1946 Globe Swift N3368K (Purchased Restored/Flying SOLD)
1987 Starduster Too SA-300 (Purchased/Flying/SOLD)
1994 V6STOL (Built w/dad/SOLD)

US Army Retired (still working to pay for flying)

When my ship comes in, I'll probably be at the airport.

Last edited by JimRice : 11-06-2017 at 11:47 AM.
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