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  #11  
Old 02-20-2018, 10:11 AM
337_Driver 337_Driver is offline
 
Join Date: Feb 2018
Location: Youngsville, NC
Posts: 23
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The damage is from a significant ground loop after a hard landing. The wings were replaced. It was 20+ years ago. If he and I can agree on a price I'm still strongly considering the airplane.
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  #12  
Old 02-20-2018, 10:32 AM
RV6_flyer's Avatar
RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,033
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Quote:
Originally Posted by Dayton Murdock View Post
What is flexing to cause this to happen. Until that is resolved this deformation will occur again.
There was a design change of the steel weldment in the four corners of the firewall longeron attachment located in the cockpit. (Wd-402L, Wd-402R, Wd-403L, and Wd-403R) It deals with early RV-4s. Later kits were shipped with an improved part. I thought there was a SB for it but cannot find it. The change was published in the early RVators. If you really want to know more, I will dig through my early paper copies of the RVator and email it to you.

Google search found this.


"Engine Mount Bracket Reinforcement"
"[1988]"
"Several RV-4 pilots have reported cracking failure of the engine mount brackets (WD-402 & 403) in the forward fuselage. Usually this has resulted from continued operation from rough airstrips or one or more extremely hard landings. Regardless, these brackets seem to be the structural Achilles Heel of the RV-4 airframe."
"Some time ago, we altered the bracket design by increasing the thickness of the attachment arms from .050 to .065". However, many RV-4s now flying have the .050 brackets. We have developed a couple of relatively simple mods which can be added during or after construction."
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NC25 RV-6
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Building RV-8 S/N: 80012

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Last edited by RV6_flyer : 02-20-2018 at 10:43 AM. Reason: add link and quoted text
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  #13  
Old 02-20-2018, 06:02 PM
designerX designerX is offline
 
Join Date: Sep 2005
Posts: 147
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Quote:
Originally Posted by RV6_flyer View Post
There was a design change of the steel weldment in the four corners of the firewall longeron attachment located in the cockpit. (Wd-402L, Wd-402R, Wd-403L, and Wd-403R) It deals with early RV-4s. Later kits were shipped with an improved part. I thought there was a SB for it but cannot find it. The change was published in the early RVators. If you really want to know more, I will dig through my early paper copies of the RVator and email it to you.

Google search found this.


"Engine Mount Bracket Reinforcement"
"[1988]"
"Several RV-4 pilots have reported cracking failure of the engine mount brackets (WD-402 & 403) in the forward fuselage. Usually this has resulted from continued operation from rough airstrips or one or more extremely hard landings. Regardless, these brackets seem to be the structural Achilles Heel of the RV-4 airframe."
"Some time ago, we altered the bracket design by increasing the thickness of the attachment arms from .050 to .065". However, many RV-4s now flying have the .050 brackets. We have developed a couple of relatively simple mods which can be added during or after construction."

As mentioned in the previous posts the original poster is asking about the footwell deformation which is NOT a weldment crack. This is a deformation of the stainless footwell due to a hard landing (or ground loop) which is a different issue. If the price and craftsmanship are right and there are no other signs of damage around the gear intersection, motor mount and no weldment cracks then buy it and fly it!
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RV-8 slow build fuselage w/showplanes fastback
RV-4 (bought flying)

Last edited by designerX : 02-20-2018 at 06:04 PM.
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  #14  
Old 02-21-2018, 11:54 AM
Sylvester Sylvester is offline
 
Join Date: Mar 2017
Location: Uk
Posts: 8
Default Footwell

See the other post on this page entitled Firewall wrinkle. I think it's important to squash the heavy landing/grounloop theory. It could cause the problem, but I had the cracks without either. It's a structural design problem, which can be cured, I hope, with gussets to brace the 3/4 x 3/4 verticals as per the RV7. Very complex loads in those front corners and not enough rigidity. Build accuracy helps too.
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  #15  
Old 11-05-2018, 05:06 PM
tcardenwebb tcardenwebb is offline
 
Join Date: Nov 2018
Location: Manchester, TN
Posts: 2
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Hey guys. New RV-4 owner. Just closed last week. Was trying to track down a nuisance oil leak last night and found slight deformation to the firewall in the bottom left and right corner. After further inspection I realized the firewall is actually cracked underneath the plane just infront of the rivet attachments. Is this an airworthiness concern, or just a blemish to an otherwise decent airframe? Don't want to pull the engine without serious need. Thanks
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  #16  
Old 11-05-2018, 06:33 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,203
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Are the aluminum angles around the firewall 'straight', and the steel weldments inside the fuselage + the motor mount crack free? If so, the only danger is CO entering the cockpit if the cracks allow exhaust gasses to come in.

I had a hard landing several years ago on my purchased (2002) 1991 -4, and when I pulled the engine to do the prop strike AD, I found some firewall wrinkles, and cracks that were obviously very old (they got extended slightly by my incident). The plane always flew fine before my incident, and flies fine now.

Charlie
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  #17  
Old 11-05-2018, 08:45 PM
tcardenwebb tcardenwebb is offline
 
Join Date: Nov 2018
Location: Manchester, TN
Posts: 2
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Thanks Charlie. Everything looks good... engine mount welds, attach points inside, etc, at least to my untrained eye. The crack is underneath where the firewall wraps under and is riveted to the fuselage. I was thinking about having someone more skilled than me bend and rivet in a doubler to cover the crack and reinforce it. I have a theory I havenít found online about the light bends in the firewall foot well... when I move the rudder pedals my heel can hit the firewall if Iím not paying attention. I wonder how many have bent their firewall taxiing or spinning at full deflection? Just a theory. Seems like a thin piece of metal.
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  #18  
Old 11-27-2018, 06:25 PM
designerX designerX is offline
 
Join Date: Sep 2005
Posts: 147
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Quote:
Originally Posted by tcardenwebb View Post
Thanks Charlie. Everything looks good... engine mount welds, attach points inside, etc, at least to my untrained eye. The crack is underneath where the firewall wraps under and is riveted to the fuselage. I was thinking about having someone more skilled than me bend and rivet in a doubler to cover the crack and reinforce it. I have a theory I havenít found online about the light bends in the firewall foot well... when I move the rudder pedals my heel can hit the firewall if Iím not paying attention. I wonder how many have bent their firewall taxiing or spinning at full deflection? Just a theory. Seems like a thin piece of metal.
When you say the crack is 'under' I'm picturing bottom skin aluminum rather than stainless steel firewall. Can you help with a picture?

Congrats on your new RV4 and grin!

Stan
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RV-8 slow build fuselage w/showplanes fastback
RV-4 (bought flying)
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  #19  
Old 11-28-2018, 06:48 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 358
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Firewall cracking in the lower corners is common in the RV-4. As Stan said, there are complex loads there during takeoff, landing and ground operations. The stainless is hardest material in a matrix that flexes during operation, especially in the event of hard landing. A wrinkle in the firewall may result in the event of a hard landing, but cracks in the lower corners may appear during general use as there is still flexing occurring, which causes the stainless to fatigue and crack.

My -4 had slight wrinkling and cracks when I purchased it. I replaced the lower firewall when the engine was removed for overhaul, and haven't had any subsequent wrinkling, but the lower corner has cracked. As a matter of fact, the new firewall cracked almost immediately, but stop drilled and sealed, it hasn't progressed in the subsequent 600 hours.

As I fly off a grass strip, I'm careful to also frequently check the weldments for cracking around the gear sockets and lower firewall attach points, and had to re-weld the gusset at the left socket at the 1200 hour point.

Enjoy the new airplane!

Cheers,

Vac
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RV-4 2112
Niceville, Florida
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