Patching holes in a firewall

How to keep the Cessna 170 flying and airworthy.

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Vertical
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Joined: Mon Oct 08, 2018 12:41 am

Patching holes in a firewall

Post by Vertical »

Working on a PA-18 cub project. It has the galvanized steel firewall. What are the standard materials (not methods) for patching various holes? Some are just old screw holes that need a solid rivet. Some are 1"+ from old penetrations that will need a patch.

Do folks use aluminum rivets in a steel firewall? Is the dis-similar metal an issue? The mechanic wants to use solid steel rivets and steel patch sheet stock. My argument is that there are hundreds of aluminum rivets in the aluminum boot cowl that attaches to the firewall. We should just zinc chromate and use solid aluminum rivets. I can't even seem to find solid steel rivets in the standard aviation supply locations

I know this is not a 170, but the principle applies.

Thoughts?
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ghostflyer
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Re: Patching holes in a firewall

Post by ghostflyer »

The piper structural repair manual has all the info that you require for repairs . But saying that there is information in the manual regarding the number of repairs that can be done to fire walls due to it being a structural member . In my country it’s a requirement that fire wall replacements /repairs have to be sealed to the fuselage skin to stop the ingress of engine gases/oil . I used a PRC product plus the normal riveting of the firewall to the fuselage skin and components .
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cessna170bdriver
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Re: Patching holes in a firewall

Post by cessna170bdriver »

The aluminum-coated steel firewall on the B-model I share with a partner is cracked at the upper corners of the battery box attachment points. Our AI has approved a repair using 26-gauge 304 stainless steel doublers and AD rivets, the same rivets used in the original installation.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
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