I have a early 172, my mechanic and I were installing digital fuel gauges in the tanks and we took them out to clean the fuel bays.

He found intergranular along the angled support piece along the spar. Not the spar itself, the ipc denotes it as angle reinforcement.

He says it is probably from water soaking through it over the years from the rivnut on it that holds the fuel tank wing cover on, or was a manufacturing defect. Either way its been like that for decades, and we only saw it because I wanted to pull the tank to repaint it. What is the purpose of the cap, is it structural or does it just protect or reinforce the main spar?

He cut the bad section out, and the spar itself is fine no corrosion. He wants to splice a new section in from a scrap wing referencing an old ac.

I lost the section in the IPC that shows exact part number, but it looks like #5 on this pdf.

Here’s a picture before we cleaned it up.

We were prying on it with a screwdriver to see how deep it went. It was brittle like paper.

The spar underneath was fine

Airplane are full of surprises and a constant source of pleasure

aeronca_champ44 wrote:
the ipc denotes it as angle reinforcement.

What is the purpose of the cap, is it structural or does it just protect or reinforce the main spar?

spar splice.pdf

I'd say based on what it's called it is a reinforcement. There is a bunch of them on the top and bottom spar caps. Why replace a section of spar that is fine? Just replace the angle reinforcement.

AEROPOD wrote:

aeronca_champ44 wrote:
the ipc denotes it as angle reinforcement.

What is the purpose of the cap, is it structural or does it just protect or reinforce the main spar?

spar splice.pdf

I'd say based on what it's called it is a reinforcement. There is a bunch of them on the top and bottom spar caps. Why replace a section of spar that is fine? Just replace the angle reinforcement.

Not touching the spar, he just cut out the bad section of the angled piece and is splicing in a new one.

I was just curious what it's purpose was in relation to the spar.

There are standard repairs detailed in the 100 series maintenance manuals, have a look there first

aeronca_champ44 wrote:

AEROPOD wrote:

aeronca_champ44 wrote:
the ipc denotes it as angle reinforcement.

What is the purpose of the cap, is it structural or does it just protect or reinforce the main spar?

spar splice.pdf

I'd say based on what it's called it is a reinforcement. There is a bunch of them on the top and bottom spar caps. Why replace a section of spar that is fine? Just replace the angle reinforcement.

Not touching the spar, he just cut out the bad section of the angled piece and is splicing in a new one.

I was just curious what it's purpose was in relation to the spar.

The angle transfers the load to the spar through the structural bolts through the tank lid. Very important piece of the structure. Be sure it’s done correctly.

[quote="skyward II"

The angle transfers the load to the spar through the structural bolts through the tank lid. Very important piece of the structure. Be sure it’s done correctly.[/quote]

Yep, replace it carefully. Not sure how far outboard it goes. It may be doable on the fuselage or you may need to dig deeper.