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Cracked firewall flange

jrussl

BENEFACTOR
Madison, WI
I installed a new stainless firewall in 2013 during my rebuild but have already accumulated some 1300 hours on my plane, a PA-18. The firewall flange has cracked on both sides where the lower cowl rails attach. I am told that the flange is soft aluminum. While I can think of a number of ways to remedy this, I am looking for suggestions from the, been there, done that, part of our great community. It would be great if I could also beef it up a bit during the process.

Thanks in advance for your help

Jeff

IMG_2982.JPG


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You forgot the parts on back side of firewall going down side of boot cowl to spread the load to. Boot cowl


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You forgot the parts on back side of firewall going down side of boot cowl to spread the load to. Boot cowl


Sent from my iPhone using SuperCub.Org

Hmmmm.....

Thanks Mike. I will have to look at the parts diagram. The firewall and boot cowl I removed didn’t have any extra pieces in that area.

If anyone has any pictures of these parts, I would appreciate it if you would post them.

Jeff


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Hmmmm.....

Thanks Mike. I will have to look at the parts diagram. The firewall and boot cowl I removed didn’t have any extra pieces in that area.

If anyone has any pictures of these parts, I would appreciate it if you would post them.

Jeff


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There is an L shaped bracket similar to the one on the front side, but longer if i remember right, and 3 rivets or screws if you made it removable. There should be a doubler on the firewall too.boot cowl.png
 

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Those are steel angles behind the firewall and bootcowl in the picture Tom posted. Have seen this same problem on Crosswind STOL PA12 and a stock cowled PA12. Was able to be in from behind and add the angles and pull everything back together. Will find my pictures and post.
 
So this is the bracket from Univair. Should be 4 installed, one at each cowl rail attach bracket.
boot1.jpg
Here is how they are riveted on a Piper boot cowl.
boot4.jpg
I make a three piece boot cowl so I can remove the bottom and sides and use screws instead of rivets.
boot2.jpg
 

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Thanks guys! I really appreciate the help.

Luckily, when we rebuilt the plane we added rivnuts to the flange and the boot cowl is screwed on. Access is super easy and adding the brackets will be pretty straightforward. Forming some new sections of the flanges will be a bit more work.

One more question. When browsing through Christians drawing viewer, I noticed the following part. Might this actually be the one I want?

Piper 12840 Cowl reinforcement.jpg
Thanks Mike, Tom, and Steve.
 

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Yep, sorry. My picture was of the part in front of the firewall. Not enough coffee yet. ;) Use 3003 aluminum, it shrinks well and is what the original flange/boot cowl was made out of.
 
Yep, sorry. My picture was of the part in front of the firewall. Not enough coffee yet. ;) Use 3003 aluminum, it shrinks well and is what the original flange/boot cowl was made out of.


I am a little low on coffee this morning too.

For others that may stumble on this thread in the future.....here is another print I just found on Christian's site that shows the part numbers and more detail of the supports.

A3310164-page-001.jpg
 

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Thanks to Mike MCS and Steve Pierce for pointing me to the missing parts.

All is good again and all the parts are there this time.

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There is an L shaped bracket similar to the one on the front side, but longer if i remember right, and 3 rivets or screws if you made it removable. There should be a doubler on the firewall too.View attachment 45775

I have a Javron kit and they do not supply the doubler with the firewall, boot cowl and 3 hole L bracket that mounts on the backside of the firewall. I have seen a Piper print with that doubler and I have also seen a print without. I have built a few cubs now and I think I have done the doubler on one of them but not on the others. I know a lot of cubs are built without the doubler, I can't see where it would be required if you have the 3 hole L bracket attached to the boot cowl. Any thoughts, looking for feedback from the guys that see a lot of cubs like Steve Pierce
 
I have a Javron kit and they do not supply the doubler with the firewall, boot cowl and 3 hole L bracket that mounts on the backside of the firewall. I have seen a Piper print with that doubler and I have also seen a print without. I have built a few cubs now and I think I have done the doubler on one of them but not on the others. I know a lot of cubs are built without the doubler, I can't see where it would be required if you have the 3 hole L bracket attached to the boot cowl. Any thoughts, looking for feedback from the guys that see a lot of cubs like Steve Pierce


never seen the doubler, just the L bracket on new boot cowls, like Atlee's....
 
All the PA18s I have rebuilt were unmolested, never recovered or wrecked and had the doublers shown on drawing 12365. I have never seen the firewalls cracked unless the aircraft had been in a nose over. I use titanium for the firewalls and cut the doublers out of the scraps from the square sheet. I have a 1994 model Piper PA18 in here right now that was recovered and repaired by Cub Crafters with a Cub Crafters firewall and there are no doublers. Here is a link to pictures of the Cub Crafters firewall. https://photos.app.goo.gl/GbfJjqFQHjLSCURG6

You can see the two doublers on the upper firewall attachments in this picture. This is a firewall I fabricated from titanium with an aluminum flange for the boot cowl attachment that Clyde Smith made.
20190819_163531.jpg
 

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